University of Nevada, Reno

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1 University of Nevada, Reno Using Coagulation to Enhance the Performance of Filtration at the South Truckee Meadows Water Reclamation Facility A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil and Environmental Engineering by Andres L. Urrego-Vallowe Dr. Keith E. Dennett/Thesis Advisor December, 2016

2 by Andres L. Urrego-Vallowe All Rights Reserved

3 THE GRADUATE SCHOOL We recommend that the thesis prepared under our supervision by ANDRES L. URREGO-VALLOWE Entitled Using Coagulation To Enhance The Performance Of Filtration At The South Truckee Meadows Water Reclamation Facility be accepted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Keith E. Dennett, Ph.D., P.E., Advisor Eric A. Marchand, Ph.D., P.E., Committee Member Glenn C. Miller, Ph.D., Graduate School Representative David W. Zeh, Ph.D., Dean, Graduate School December, 2016

4 i ABSTRACT During this research, enhanced coagulation was evaluated as part of the proposed treatment to improve the overall quality of the reuse water at the South Truckee Meadows Water Reclamation Facility (STMWRF) in Reno, Nevada. Extensive jar testing was conducted on the water returning from Huffaker Reservoir and the effluent from the secondary clarifiers to determine the coagulant dosages and the ph conditions for optimum coagulation to enhance the performance of the existing Parkson DynaSand upflow filters. Five different coagulants were tested including aluminum sulfate, ferric chloride, polyaluminum chloride, and two aluminum-based coagulants (CC2110 and CC2220). Results were compared with the U.S. EPA Guidelines for Water Reuse, the Nevada Administrative Code (NAC), and the California Department of Public Health Recycled Water Regulations. The optimum dosages of the coagulants used in jar testing effectively reduced the turbidity of filtered water below 2 NTU. Water quality testing at STMWRF was also performed during multiple 12-hour and 24-hour periods by monitoring ph, temperature, turbidity, total suspended solids, electrical conductivity, UV absorbance at 254 nm, and total organic carbon. Seasonal variations of ph, temperature, and turbidity of the water withdrawn from the reservoir were also assessed. From July through September 2016, in-situ water quality monitoring at different water depths at two locations within the reservoir was performed for ph, turbidity, temperature, and dissolved oxygen (DO). In general, the quality of the water within the reservoir deteriorated as the irrigation season progresses.

5 ii ACKNOWLEDGEMENTS I would like to acknowledge my thesis advisor Dr. Keith Dennett for his support during these two years of research. This research was made possible and founded by the Washoe County Department of Water Resources (DWR). I want to thank Viktoriya Weirauch and Veronica Edirveerasingam (Environmental Engineering Laboratories Managers) for their help during this project. Also, I want to thank John Hulett (senior environmental engineer at STMWRF) and the plant operators at STMWRF for their assistance, support and guidance. I want to recognize the support, dedication and hard work from all my fellow graduate and undergraduate students: Thomas Speer, Hailey Zimmerman, Justin Ellmaker, Nicole Furtaw, Aaron Mangione, Aaron Smith, Devon Eckberg, Daniela Maciel, Collin Sturge, Chris Carlson, and Roger Cox. Lastly, I want to thank Dr. Eric Marchand and Dr. Glenn Miller for being part of my graduate committee.

6 iii TABLE OF CONTENTS ABSTRACT... i ACKNOWLEDGEMENTS... ii LIST OF FIGURES... vi LIST OF TABLES... x CHAPTER 1 INTRODUCTION... 1 CHAPTER 2 LITERATURE REVIEW Importance of water reuse and characteristic of domestic wastewater Conventional wastewater treatment processes Coagulation/flocculation processes Mechanisms of coagulations Types of flocculation systems Coagulants used in water and wastewater treatment Aluminum Sulfate Ferric Chloride Jar Testing Optimization of alum-coagulation/flocculation for COD and TSS removal from municipal wastewater Natural organic matter in water Impact of ph on removal of natural organic matter from reservoir water by coagulation Coagulation for removal of natural organic matter Combined coagulation and flocculation pretreatment unit for municipal wastewater The effects of ph adjustment on removal of turbidity and NOM in conventional water treatment Dissolved oxygen stratification and response to thermal structure in a large and deep subtropical reservoir Regulations for recycled water for irrigation Physical water quality parameters Temperature Total suspended solids (TSS) Turbidity Chemical water quality parameters... 26

7 iv Fractions of total carbon Importance of total organic carbon in water ph Electrical conductivity (EC) UV 254 absorbance Alkalinity Dissolved oxygen (DO) CHAPTER 3 MATERIALS AND METHODS Water quality sampling Coagulants Aluminum sulfate (or alum) Ferric chloride Polyaluminum chloride (PACl) CC2110 and CC ph adjustment ph measurement ph calibration method setup Jar testing method Turbidity measurement Electrical conductivity measurement Electrical conductivity calibration method setup Preparation of glass bottles for TSS and TOC samples Total suspended solids analyses Materials Method Calculation Total organic carbon analyses CHAPTER 4 RESULTS AND DISCUSSION Results of jar testing for effluent from the secondary clarifiers from February through April Results of jar testing on water from Huffaker Reservoir from May through August Results of jar testing on water from Huffaker Reservoir in September and October

8 v 4.4 Results of jar testing on water from Huffaker Reservoir from June through August Cost estimate for full-scale coagulant addition Seasonal variations of water quality in Huffaker Reservoir hour water quality testing in July, August and September hour water quality tests in July 30 and August 6th, hour water quality test in September 24-25, hour water quality testing in July, August, and September hour water quality test on July 6-7, hour water quality test on July 18-19, hour water quality test on August 10-11, hour water quality test on August 24-25, hour water quality test on September 8-9, Reservoir water quality monitoring in July, August, and September CHAPTER 5 CONCLUSIONS REFERENCES

9 vi LIST OF FIGURES Figure 1. Solubility diagram for aluminum hydroxide (Reynolds, 1982) Figure 2. Solubility diagram for ferric hydroxide in water (Reynolds, 1982) Figure 3. Seasonal depth profiles of DO (a), water temperature (b) and CDOM (c) for Lake Qiandaohu from August 2011 to May 2012 (Zhang et al., 2015) Figure 4. Summary of the different forms of carbon in water (Shi et al., 2010) Figure 5. Effects of coagulant CC2110 dosage and raw water ph on filtered turbidity for secondary clarifier effluent (March through April 2015) Figure 6. Effects of final ph of the secondary clarifier effluent on filtered turbidity using coagulant CC2110 (March through April 2015) Figure 7. Effects of coagulant CC2220 dosage on filtered turbidity for effluent from secondary clarifiers (March through April 2015) Figure 8. Variation of filtered turbidity with final ph for secondary clarifier effluent using different coagulant dosages of CC2220 (March through April 2015) Figure 9. Effects of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (May 2015) Figure 10. Effects of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (June 2015) Figure 11. Effect of final ph of the water returning from the reservoir on filtered turbidity using the optimum coagulant dosage of CC2110 of 10 mg/l (May through June 2015). 58 Figure 12. Effects of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (May 2015) Figure 13. Effects of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (June 2015) Figure 14. Effect of final ph of the water returning from the reservoir on filtered turbidity using the optimum coagulant dosage of CC2220 of 20 mg/l (May through June 2015). 60 Figure 15. Effect of alum dosage on filtered turbidity for water returning from reservoir (July 2015) Figure 16. Effect of ph on filtered turbidity for various alum dosages (July 2015) Figure 17. Effect of ph on filtered turbidity for optimum dosage of alum of 10 mg/l (July 2015) Figure 18. Effect of ferric chloride dosage on filtered turbidity for reservoir water at different water ph (September through October 2015) Figure 19. Effect of ph on filtered turbidity (log scale) for various ferric chloride dosages (September through October 2015) Figure 20. Effect of PACl dosage on filtered turbidity for water returning from the reservoir (October 2015) Figure 21. Effect of filtered ph on turbidity removal for various PACl dosages (log scale) (October 2015) Figure 22. Effect of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (June 2016) Figure 23. Effects of final ph of water returning from the reservoir on filtered turbidity for various CC2220 dosages (June 2016)

10 Figure 24. Effect of aluminum sulfate dosage on filtered turbidity for water returning from the reservoir (June 2016) Figure 25. Effect of filtered ph on filtered turbidity with alum dosage of 8 mg/l Figure 26. Effect of ferric chloride dosage on filtered turbidity for water returning from the reservoir (July 2016). Coagulant dosages were initially varied from 10 to 50 mg/l (left) and later from 12 to 20 mg/l (right) Figure 27. Effect of filtered ph on filtered turbidity for various ferric chloride dosages (July 2016) Figure 28. Effect of polyaluminum chloride dosage on filtered turbidity for water returning from the reservoir (July 2016) Figure 29. Effect of filtered ph on filtered turbidity with PACl dosage of 6 mg/l Figure 30. Effect of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (August 2016) Figure 31. Effect of raw water ph on filtered turbidity for various CC2110 dosages (August 2016) Figure 32. Seasonal variations of ph in Huffaker Reservoir Figure 33. Seasonal variations of turbidity in Huffaker Reservoir Figure 34. Seasonal variations of temperature in Huffaker Reservoir Figure 35. Variation of water depth at the reservoir from May 2015 through September Figure 36. Sampling locations for 12-hour and 24-hour water quality tests in (A) filter influent for secondary clarifier effluent, (B) filter effluent for secondary clarifier effluent, (C) filter influent for reservoir water, (D) filter effluent of reservoir water, and (E) chlorine contact basin effluent Figure 37. Variation of turbidity of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right) Figure 38. Variation of ph of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right) Figure 39. Variation of EC of reservoir water and chlorine contact basin during July 30-31, 2015 (left) and August 6, 2015 (right) Figure 40. Variation of temperature of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right). Data for air temperature was also included Figure 41. Variation of TSS of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right) Figure 42. Relationship between turbidity and TSS for water returning from the reservoir and exiting the chlorine contact basin Figure 43. Variation of dissolved TOC (DOC) of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right) vii

11 Figure 44. Variation of UV absorbance at 254 nm of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right) Figure 45. Relationship between DOC and UV absorbance at 254 nm for water returning from the reservoir and exiting the chlorine contact basin during July 30-31, 2015 and August 6, Figure 46. Variation of turbidity of filter influent and filter effluent (for the effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, Figure 47. Variation of ph of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, Figure 48. Variation of electrical conductivity of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, Figure 49. Variation of temperature of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during September 24-25, Data for air temperature was also included Figure 50. Variations of TSS of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin, including filter loading rates during September 24-25, Figure 51. Variations in dissolved total organic carbon of filter influent and filter effluent (for effluent from secondary clarifiers and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, Figure 52. Variations in UV absorbance at 254 nm of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, Figure 53. Sampling locations for 24-hour water quality test in A) secondary clarifiers effluent, B) filter effluent of secondary clarifiers, C) water returning from the reservoir, and D) filter effluent of reservoir water Figure 54. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 6-7, 2016) Figure 55. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 18-19, 2016) Figure 56. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 18-19, 2016) Figure 57. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 10-11, 2016) Figure 58. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 10-11, 2016) Figure 59. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 24-25, 2016) Figure 60. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 24-25, 2016) viii

12 Figure 61. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (September 8-9, 2016) Figure 62. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (September 8-9, 2016) Figure 63. Sampling locations A and C in Huffaker Reservoir Figure 64. Variations in turbidity (NTU) with depth for location A (left) and location C (right) Figure 65. Variations in ph of the water with depth for location A (left) and location C (right) Figure 66. Variations in temperature (ºC) with depth (ft) from the bottom for location A (left) and location C (right) Figure 67. Variations in dissolved oxygen (mg/l) with depth (ft) for location A (left) and location C (right) Figure 68. Variations in temperature (ºC) with depth (ft) from the bottom for location A (left) and location C (right) from August 3, 2016 through September 29, ix

13 x LIST OF TABLES Table 1. Summary of U.S. EPA Guidelines for Water Reuse for irrigation (U.S. EPA, 2012) Table 2. Categories for reuse water established by NAC 445A pursuant to bacteriological quality Table 3. Typical UV absorbance and transmittance values at 254 nm for wastewater after various treatment processes (Metcalf & Eddy, 2013) Table 4. Volume of Al 2 O 3 for specific alum dosages Table 5. Volume of FeCl 3 for specific coagulant dosages Table 6. Volume of PACl as Al 3+ for specific coagulant dosages Table 7. Volume of CC2110 and CC2220 for specific coagulant dosages Table 8. Summary of recommendations based on the results of the jar test experiments performed during Table 9. Summary of recommendations based on the results of the jar test experiments performed during Table 10. Estimated costs for coagulant addition... 81

14 1 CHAPTER 1 INTRODUCTION This research project was sponsored by the Washoe County Department of Water Resources (WCDWR) in an effort to improve the quality of the reuse water at the South Truckee Meadows Water Reclamation Facility (STMWRF) in Reno, Nevada. The facility uses different processes to treat the raw wastewater, including screening, an activated sludge system in oxidation ditches, secondary clarifiers, upflow sand filtration, disinfection followed by pumping and storage of reuse water in Huffaker Reservoir. STMWRF has a hydraulic capacity of 4.1 million gallon per day (MGD) (30-day average) and provides chemical and biological treatment for domestic and commercial wastewater generated in the South Truckee Meadows area. The treated effluent or reuse water is then distributed via the reuse distribution system to reclaimed water customers for irrigation of golf courses, green areas, parks, schools, roadway medians, the South Valley Sports Complex, and other permitted areas located in south Reno (Mulligan, 2007). The treatment plant biologically degrades the organic matter through the activated sludge process in the oxidation ditch systems where the biochemical oxygen demand (BOD) and nitrogen are reduced. After the biological treatment, the wastewater goes to the secondary clarifiers, where settled sludge is separated and the clarified water then passes through Parkson DynaSand upflow sand filters to further reduce suspended solids. The filter effluent is delivered to the chlorine contact basin for disinfection. Then, it is either pumped into the reuse distribution system or pumped to Huffaker Reservoir for temporary storage (Mulligan, 2007).

15 2 Huffaker Reservoir is located next to STMWRF and stores treated effluent, especially during the winter and early spring before the irrigation season begins. The irrigation season generally runs from April through October. All treated effluent is stored within Huffaker Reservoir during the remainder of the year. When outdoor temperatures and water demands for outdoor irrigation increase, water is returned from the reservoir. It passes back through the upflow sand filters and the chlorine contact basin. Then it is pumped into the reuse distribution system. However, STMWRF has noticed the relatively poor quality of the water returning from the reservoir during the summer months (e.g., high turbidity and ph values, algae problems due to high concentrations of nitrogen, BOD and total organic carbon). This presents a challenge to the treatment plant in order to continue to provide a high quality effluent that can satisfy reuse water quality regulations for landscape irrigation. For this reason, WCDWR solicited this research project to determine if enhanced coagulation can be implemented to improve and maintain the overall quality of the reuse water. The objectives of this research were to investigate the effects of coagulant addition and the need for ph adjustment prior to coagulation to improve turbidity removal during filtration for water returning from Huffaker Reservoir and coming from the secondary clarifiers. Jar testing was performed between February and October 2015 and between June and September The objective of the jar testing was to determine the coagulant dosage and ph conditions for optimum coagulation. Different coagulants were tested including aluminum sulfate, ferric chloride, polyaluminum chloride, and two proprietary aluminum-based coagulants: CC2110 and CC2220. The performance of these coagulants were compared based on turbidity measurements before and after filtration in

16 3 order to identify those that performed best. A daily coagulant cost was estimated for each coagulant. This project also involved characterization of water quality during several 24-hour periods by collecting water samples every 15 to 60 minutes. The sources of the water samples included water returning from Huffaker Reservoir, effluent from the chlorine contact basin, effluent from the secondary clarifiers, and filter effluent. Various physicochemical parameters including ph, turbidity, electrical conductivity, total suspended solids, temperature, total organic carbon, and UV absorbance at 254 nanometers were monitored. In addition, from July through September 2016, samples were collected within Huffaker Reservoir at three water depths (i.e., 5 ft below surface, mid-depth and 5 ft above bottom) at two sampling locations in order to assess variations in water quality with depth and location within the reservoir as the irrigation season progresses through the summer. In-situ monitoring was conducted for ph, turbidity, temperature, and dissolved oxygen (DO). This work was performed on-site at STMWRF by personnel from the Department of Civil and Environmental Engineering (CEE) at the University of Nevada, Reno (UNR).

17 4 CHAPTER 2 LITERATURE REVIEW This chapter includes a review of previous studies that investigated coagulation and flocculation processes for the removal of typical water and wastewater pollutants such as organic matter, turbidity, suspended solids, chemical oxygen demand, and biochemical oxygen demand. Some of these studies also analyzed the effects of varying the ph of the water on the removal efficiency of targeted pollutants. Federal and state regulations for reuse of wastewater for irrigation purposes are included and serve as guidelines for assessing the effectiveness of treatment strategies. A description of important water quality parameters including temperature, ph, total suspended solids, turbidity, total organic carbon, electrical conductivity, UV absorbance, dissolved oxygen, and alkalinity are also discussed. 2.1 Importance of water reuse and characteristic of domestic wastewater Water scarcity is one of the most significant problems worldwide. Some of the reasons for water shortages include growing human population, climate change, contamination of surface water and groundwater resources, and lack of adequate or improper water resources management. As a result, reuse of treated wastewater is becoming one of the most important alternatives to mitigate the global water crisis. Water reuse projects which have replaced drinking water with treated wastewater for irrigation and industrial purposes are often economically feasible and have a good public acceptance (Asadollahfardi et al., 2015). Typical wastewater is often characterized by high concentrations of organic material, pathogenic microorganisms (e.g., bacteria, viruses, and protozoa), heavy metals, nutrients, and toxic compounds. Therefore, untreated wastewater represents a hazard for

18 5 public health and the environment, and must be treated appropriately before being discharged into waterbodies or being reused. The goal of wastewater treatment is the protection of the water supplies and public health (Ismail et al., 2012). 2.2 Conventional wastewater treatment processes Conventional wastewater treatment includes several physical, chemical, and biological processes to remove most of the suspended solids, and soluble organic and inorganic materials (Irfan et al., 2013) Coagulation/flocculation processes Coagulation is a process which results in the formation of micro-floc and flocculation is a process which develops macro-floc. The purpose of coagulation/flocculation processes is the destabilization of colloidal and suspended particles by neutralizing the surface charges of these particles. Cationic coagulants are used to decrease the negative charge of colloidal particles. Destabilized particles can then be brought together to form floc particles (Ashery et al., 2010; Irfan et al., 2013). Coagulation/flocculation processes can be used for treating different types of water and wastewater including drinking water supplies, domestic wastewaters, and industrial wastewaters (Cañizares et al., 2008). Coagulation and flocculation can be reduce biochemical oxygen demand (BOD) and suspended solids through the use of Al(III) and iron-based coagulants and polymers as flocculants (Guida et al., 2007). The conventional coagulation/flocculation processes involve a series of three stages: 1) rapid mixing; 2) flocculation; and 3) sedimentation. In the first stage, chemical reagents are added and completely dispersed throughout the water or wastewater by some type of intense mixing in order to distribute the coagulant and destabilize the surface

19 6 charges on particles. The aim of the flocculation stage is the formation of larger particles through slow mixing which promotes collisions between destabilized particles resulting in their aggregation. Finally, during the sedimentation stage, the aggregated particles are removed by gravitational sedimentation (Cañizares et al., 2008; Ismail et al., 2012) Mechanisms of coagulations There are two main mechanisms of coagulation: 1) charge neutralization; and 2) sweep coagulation. During charge neutralization, the metal coagulant (either iron or aluminum) must be dispersed very quickly (<0.1 sec) throughout the water. Within microseconds after coagulant addition, charged metal hydrolysis species are formed which interact with colloids and suspended particles. Charge neutralization is suitable for raw waters having relatively low turbidities and requires a rapid mixing device to achieve rapid dispersion of coagulant. Generally, charge neutralization forms small floc particles that may not settle well, but will likely filtered well as long as surface charges are sufficiently neutralized (Droste, 1997). The interaction between voluminous amounts of metal hydroxide precipitates and colloids present in the water is known as sweep coagulation. In conventional water treatment, the water is supersaturated with the metal coagulant resulting in the formation of solid metal hydroxide that precipitates, promoting the formation of large and settleable floc particles. In general, sweep coagulation is a slower process than charge neutralization; it is generally suitable for raw waters with high turbidities, typically requires higher coagulant dosages, and therefore produces more settled solids (Droste, 1997).

20 Types of flocculation systems Two common types of flocculator systems that can be used to provide mixing of the water after coagulant addition are: 1) hydraulic flocculators; and 2) mechanical flocculators. In a hydraulic flocculator, water flows through baffled channels which cause sudden directional changes which facilitate mixing. The baffle walls can be located either horizontally or vertically. Advantages of a hydraulic flocculator include minimal maintenance and low operational cost since no mechanical parts are involved. It also produces a minimal head loss along the flocculation basin. Some of the disadvantages are the higher velocity gradients at the bends around the baffles, and their lower degree of process control since the gradients depend on the flow rate through the basin (Ismail et al., 2012). On the other hand, mechanical flocculators are fitted with mechanical stirrers to promote slow mixing of water. Pani et al. (2007) reported that mechanical flocculators provide an average turbidity removal efficiency of approximately 70%. Mechanical flocculators depend upon the availability of electrical power to operate them and require routine maintenance. The problems associated with maintenance and running of the mechanical components can present severe limitations, especially in developing countries (Liu et al., 2004). 2.3 Coagulants used in water and wastewater treatment In water and wastewater treatment, chemical coagulants that are commonly used are Al(III) and Fe(II) or Fe(III) salts. These coagulants include aluminum sulfate or alum (Al 2 (SO 4 ) 3 14 H 2 O), ferric chloride (FeCl 3 6 H 2 O), ferric sulfate (Fe 2 (SO 4 ) 3 ), and ferrous sulfate (FeSO 4 7 H 2 O). The use of alum and ferrous sulfate as coagulants is a common

21 8 practice to reduce suspended solids in wastewater; these coagulants are affordable and safe to use and the sludge generated is relatively easy to process (Ismail et al., 2012). Aluminum sulfate (or alum) is more commonly used than iron salts because it is generally cheaper. The advantage of iron salts over alum is that it is typically effective over a wider range of ph conditions. Coagulant aids, which are usually organic polymers, are sometimes used to produce a rapid settling floc (Reynolds, 1982) Aluminum Sulfate Aluminum sulfate is available in either dry or liquid form [Al 2 (SO 4 ) 3 14 H 2 O]; however, the dry form is widely used. The dry form can be granular, powdered, or lump form, with granular being the most commonly used. The alum granules are 15 to 22 percent Al 2 O 3 with specific weights about 60 to 63 lb/ft 3. The liquid form is typically 50 percent alum. The dry form can be shipped in bags, barrels, or bulk, and the solution form in tank car or tank truck (Reynolds, 1982). When alum is added to a water containing alkalinity, it reacts according to the following equation, decreasing the alkalinity of the water (Guida et al., 2007): Al 2 (SO 4 ) 3 14 H 2 O + 6HCO 2 3 2Al(OH) 3 (sol) + 6CO H 2 O + 3SO 4 Based on the above reaction, each mole of alum added consumes six moles of alkalinity and produces six moles of carbon dioxide. Thus, the above reaction changes the carbonate equilibrium and decreases the ph. However, as long as sufficient alkalinity is present and CO 2 is allowed to evolve, the ph is not drastically reduced and is generally not an operational problem. Usually for the range of ph conditions involved, alkalinity is in the form of bicarbonate ion (Reynolds, 1982). Figure 1 illustrates the solubility of Al(OH) 3. The

22 9 shaded area corresponds to the typical coagulant dosages and ph conditions for water treatment. The most favorable operational ph range for alum is within ph 5 to ph 8; Al(OH) 3 is relatively insoluble within this range. Sufficient alkalinity must be present in the water to react with alum and produce the hydroxide precipitate (Reynolds, 1982). If natural alkalinity is not sufficient to react with alum, then alkalinity needs to be added. Alkalinity in the form of hydroxide ion can be supplied by adding calcium hydroxide (i.e., slaked or hydrated lime). The coagulation reaction for alum with calcium hydroxide is (Reynolds, 1982): Al 2 (SO 4 ) 3 14 H 2 O + 3Ca(OH) 2 2Al(OH) 3 (sol) + 3CaSO H 2 O Alkalinity can also be added in the form of carbonate ion by supplying sodium carbonate (i.e., soda ash). Since most waters contain sufficient alkalinity, no chemical addition is usually required other than the coagulant (Reynolds, 1982). Figure 1. Solubility diagram for aluminum hydroxide (Reynolds, 1982).

23 Ferric Chloride Ferric chloride reacts with alkalinity in the water (as bicarbonate) to form ferric hydroxide, according to the following reaction (Reynolds, 1982): 2FeCl 3 + 3Ca(HCO 3 ) 2 2Fe(OH) 3(sol) + 3CaSO 4 + 6CO 2 The ferric hydroxide precipitate forms a dense, rapid-settling floc. Based on the solubility diagram for ferric hydroxide (Figure 2), ferric hydroxide precipitate has a lower solubility over a broad ph range from ph 4 to ph 8 (Reynolds, 1982; Cañizares et al., 2008). Ferric chloride is available in liquid, powdered, or lump form. The lump form is most widely used for water and wastewater treatment; it is 59 to 61 percent FeCl 3 and has a specific weight in the range of 60 to 64 lb/ft 3. The powdered form is 98 percent FeCl 3 with specific weight in the range of 85 to 90 lb/ft 3. The liquid form is 37 to 47 percent FeCl 3 (Reynolds, 1982). Figure 2. Solubility diagram for ferric hydroxide in water (Reynolds, 1982).

24 11 When the natural alkalinity is insufficient, slaked lime may be added to form the hydroxide as indicated in the reaction (Reynolds, 1982): 2FeCl 3 + 3Ca(OH) 2 2Fe(OH) 3(sol) + 3CaCl Jar Testing In water and wastewater treatment, the effectiveness of a coagulant can be determined by performing a batch test or jar test, which is used to determine the proper coagulant and the optimum chemical dosage for a particular water (Weber, 1972; Reynolds, 1982). In a jar test experiment, a series of beakers are filled with a sample of water, and various coagulant dosages are added to the beakers, with one of them being the control (no coagulant addition). The samples are first stirred at a high velocity gradient to simulate rapid mixing and then gently stirred to simulate flocculation. Then, the mixing is stopped to allow for sedimentation. After an appropriate settling period, important characteristics about the settled floc (e.g., time for formation and size) can be monitored, and various water quality parameters (e.g., residual turbidity, color, and final ph) can be measured. The coagulant dosage determined during jar testing is an estimate of the dosage required for full-scale treatment (Reynolds, 1982). 2.5 Optimization of alum-coagulation/flocculation for COD and TSS removal from municipal wastewater Guida et al. (2007) studied the efficiency of alum coagulation in municipal wastewater treatment by statistically analyzing the effects of coagulation ph, alum dosage, and influent COD and TSS concentrations on the removal of COD and TSS. A series of jar test experiments were performed on samples taken from five wastewater treatment plants, each one with different influent COD and TSS concentrations. The

25 12 optimum ph conditions and alum dosages that provided the highest COD and TSS removal were determined. The results indicated that coagulation can achieve high COD and TSS removal efficiencies at relatively low alum dosages. However, COD removal was greatly affected by the chemical composition of the wastewater (e.g., surface active materials of wastewater), ph, alum dosage, and influent COD and TSS. TSS removal efficiency was affected by ph conditions, alum dosage, and influent TSS. 2.6 Natural organic matter in water Natural organic matter (NOM) refers to the organic material originating from natural sources (e.g., decomposition of vegetation) that are present in surface waters and groundwater. NOM concentrations in surface waters generally increase due to runoff after a precipitation event. NOM can be expressed as total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm, and specific UV absorbance (SUVA). In surface water, NOM concentrations may range from 1 to 75 mg/l as DOC (Ashery et al., 2010). Constituents of the NOM are generally hydrophilic, with a wide range of molecular weights, and compromised of humic and non-humic fractions. The humic fraction is categorized as humic acids and fulvic acids. The humic acids are organic compounds of high molecular weight and can exhibit colloidal properties (Ashery et al., 2010). Some studies (Ashery et al., 2010; Qin et al., 2005; Yan et al., 2008), have reported problems associated with NOM in the water. First, NOM may contribute to taste and odor issues in drinking water. NOM can act as substrate for bacteria, causing microbial regrowth within water distribution systems. In addition, it is possible that NOM interferes with oxidation and with the removal of iron and manganese. NOM can also

26 13 result in the formation of disinfection byproducts (DBPs) due to the chlorine demand, some of which are harmful to human health. The effects of different coagulants and ph conditions on the removal of NOM have been widely investigated (Dennett et al., 1996; Amirtharajah et al., 1993; Dennett and Dixon, 2003). Dissolved organic carbon (DOC) is often used as a quantitative indicator for concentrations of NOM in water. The removal efficiency of DOC is greatly dependent on the sources and characteristics of the raw water (Qin et al., 2005). 2.7 Impact of ph on removal of natural organic matter from reservoir water by coagulation Qin et al. (2005) examined the impact of coagulation ph and alum dosage on the removal of TOC and DOC from a reservoir water. Samples were collected from a local reservoir in Singapore containing a relatively high concentration of DOC. Typical water quality characteristics indicated that ph of reservoir water was nearly neutral (ph 6.7 to 6.9) while the turbidity and DOC fluctuated significantly. The turbidity of the raw water ranged from 5.0 to 17.2 NTU and the DOC ranged from 3.27 to 7.45 mg/l. Jar tests were conducted using an alum dosage of 6.5 mg/l as Al at different ph conditions. The optimum ph for the removal of TOC and DOC was found to be ph 5.2±0.1. Further experiments were performed at different alum dosages but at the optimal coagulation ph. The results indicated that the removal of TOC, DOC, and turbidity increased with increasing alum dosage. The research concluded that the optimum alum dosage for the removal of NOM was 5 mg/l as Al, which was found considering both DOC removal efficiency and the cost of alum. Under optimal conditions, coagulation and sedimentation

27 14 achieved 45% removal of NOM in terms of DOC and 97% removal of turbidity (Qin et al., 2005). 2.8 Coagulation for removal of natural organic matter Soluble natural organic matter can be effectively removed from water by coagulation and flocculation processes (Ashery et al., 2010). In this study, a linear correlation was observed between UV 254 absorbance and the concentration of organic matter. This enabled UV 254 absorbance data to be used as an indicator of the concentration of organic matter (as humic acid and fulvic acid). Therefore, UV 254 absorbance can often be a suitable parameter and a relatively simple method to study the removal efficiency of NOM. The ph is one parameter that affects the removal efficiency of NOM during coagulation and flocculation. Ashery et al. (2010) studied the relation between ph and NOM removal by conducting jar tests at different ph conditions and measuring UV 254 and DOC after coagulation. The alum dosage used was the average optimum dosage determined from jar tests performed at ph 5, 6, and 7. The results showed that the highest removal efficiency of NOM occurred when the ph of the water was reduced within the range of ph 5 to ph 6 prior to coagulant addition. This was thought to result in the formation of soluble NOM-aluminum complexes that reacted or bonded with each other, thus forming insoluble micro-flocs during coagulation and later formed larger macro-floc during flocculation. When ph increases, humic substances typically become more ionized as the carboxyl groups lose protons, and the positive species of coagulants are less prevalent. Since the difference between removal efficiency of NOM at neutral ph and at optimum ph conditions was

28 15 significant, adjustment of the raw water ph prior to coagulation should be evaluated (Ashery et al., 2010). 2.9 Combined coagulation and flocculation pretreatment unit for municipal wastewater Ismail et al. (2012) performed a series of jar tests using raw sewage at a wastewater treatment plant in Egypt. The objective of the jar testing was to select the optimum coagulant and the optimum coagulant dosages for the treatability of municipal wastewater. The coagulants which were tested included alum, ferrous sulfate, ferric sulfate, a mixture of ferric and ferrous sulfates, and mixture of lime and ferrous sulfate. The research evaluated the effects of varying the coagulant dosage on the removal efficiency of COD, BOD, TSS, and total phosphorus. According to the jar test results, as the alum dosage increased, the removal efficiencies for COD, BOD, TSS and PO 3-4 improved until they reached maximum values of 65%, 55%, 83%, and 76%, respectively. The results of this jar test study indicated that 60 mg/l of alum was the optimum dosage. The analysis also mentioned that alum addition increased the particle size of suspended solids, which enhanced the settling of suspended particles. This affected the removal of some biodegradable organics composing the suspended solids, so the BOD and COD concentrations were also reduced. ph adjustment was not necessary for coagulation with alum since the raw sewage had a ph in the range of ph 6.0 to 6.5, which is the optimum ph condition for alum coagulation. Ferrous sulfate was the second coagulant evaluated. It was observed that increasing the dosage of ferrous sulfate improved the removal efficiencies of COD, BOD,

29 16 TSS, and PO 3-4 until they reached maximum removals of 56%, 48%, 74%, and 69%, respectively. The use of 80 mg/l of ferrous sulfate was selected as the optimum dosage. Similar to the case of alum, the addition of ferrous sulfate increased the particle size of suspended material thus improving the settling of suspended particles. In the case of the coagulant ferric sulfate, the removal efficiencies of the target pollutants gradually increased with increasing dosage of ferric sulfate until they reached the maximums of 77% for TSS, 48% for BOD, 70% for PO 3-4, and 59% for COD at the optimum dosage of 60 mg/l of ferric sulfate. The removal efficiencies when using ferric sulfate were slightly higher than those obtained with ferrous sulfate, which was due to the greater charges of ferric ions (Ismail et al., 2012). Moreover, the performance of a combination of two coagulants together was also evaluated. In the first case, ferrous sulfate at its optimum dosage was combined with lime. The addition of lime slightly enhanced the removal efficiencies of organic matter and suspended solids in comparison with using only ferrous sulfate. This may have resulted from the higher ph conditions after adding lime. Adding lime also increased the alkalinity of the water, which could result in ph values higher than the typical recommended range of ph 6 to ph 9. In the other case, ferric sulfate at its optimum dosage was combined with ferrous sulfate. It was observed that increasing the dosage of ferrous sulfate improved the removal efficiencies of TSS, BOD, PO 3-4, and COD until they achieved maximum efficiencies of 86%, 50%, 76%, and 61%, respectively. The optimum dosage was 20 mg/l of ferrous sulfate (Ismail et al., 2012). Based on the results of the jar test experiments, the mixture of ferrous and ferric sulfate provided the highest removal efficiencies for the target parameters, which was

30 17 very similar to the removals obtained with alum. The study determined that alum was the optimum coagulant since the use of two chemicals implies an increase in the operational costs (e.g., storage tanks, pumping, and piping). It was also concluded that chemical pretreatment could be integrated within an existing wastewater treatment plant to reduce the organic matter present as particulate matter to the biological stage The effects of ph adjustment on removal of turbidity and NOM in conventional water treatment The alkalinity and ph of the water affects the interactions between the coagulant and NOM (Yan et al., 2008). Ashery et al. (2010) reported that coagulation ph is the most important parameter for proper coagulation as it affects the surface charge of colloids and the charge of NOM functional groups. Since metal coagulants are usually acidic, addition of coagulants typically consumes alkalinity, thus reducing the ph of the water. The addition of coagulants to waters with low alkalinity may drop the ph to levels too low for effective coagulation. On the other hand, high alkalinity waters may require higher coagulant dosages to lower the ph to optimum ph conditions for coagulation. Ashery et al. (2010) investigated the importance of varying the initial ph of the water before coagulation to achieve the maximum removal efficiencies of NOM and turbidity using the minimum coagulant dosage. Jar test experiments were performed using a synthetic raw water with desired turbidities and NOM concentrations. Aluminum sulfate, Al 2 (SO 4 ) 3 18 H 2 O, stock solution was used at various dosages for coagulation. The effects of ph adjustment were investigated using a synthetic water having a high initial turbidity of 130 NTU. Based on a series of jar tests conducted at ph conditions of ph 5, 6 and 7, the optimum coagulant dosage was determined to be 45

31 18 mg/l of alum. The effects of varying the ph of the water from ph 3 to ph 8 on turbidity removal using the optimum alum dosage was then analyzed. The results indicated that the optimum ph conditions for removal of turbidity were between ph 5 and ph 6. The difference between turbidity removal of neutral water and water at the optimum ph conditions was significant. Therefore, the study concluded that for waters with high turbidities, the ph of the raw water should be adjusted to the optimum ph conditions based on a reasonable number of jar tests (Ashery et al., 2010). The effects of ph adjustment on waters with low turbidity water was also studied. A series of jar tests were performed at ph 5, 6, and 7 on a synthetic water having an initial turbidity of 30 NTU. The source of turbidity material was kaolinite particles of sizes that varied from 10 to 0.1 μm. The optimum alum dosage was found to be 25 mg/l. Additional jar tests were conducted at ph conditions ranging from ph 3 to ph 8 and using the optimal coagulant dosage. The results indicated that the ph range for the best turbidity removal was between ph 5 and 6. However, the difference between turbidity removal at optimum ph and at neutral ph was not significant which suggested that, for waters with low turbidities, adjusting the ph of raw water prior to coagulation may not enhance the removal of turbidity (Ashery et al., 2010) Dissolved oxygen stratification and response to thermal structure in a large and deep subtropical reservoir Zhang et al. (2015) studied the depth profile of temperature, dissolved oxygen (DO), and chromophoric dissolved organic matter (CDOM) at three locations in Lake Qiandaohu in China. Lake Qiandaohu is a large deep-water artificial lake which serves as a reservoir for drinking water supply and recreational activities. Water quality problems

32 19 related to algal blooms in the reservoir have been documented since the 1990s due to increases in nitrogen and phosphorus loadings. The seasonal depth profiles for DO concentrations, water temperature, and concentrations of CDOM for Lake Qiandaohu are shown in Figure 3. The concentration of DO was never below 2 mg/l, the critical value for anoxia, indicating that no anoxic layer was found in Lake Qiandaohu. These results were similar to the concentrations of DO found in Lake Tahoe, where DO concentrations were greater than 6 mg/l within the water column. However, DO concentrations in other deep natural lakes were near zero, indicating the existence of benthic zones (Zhang et al., 2015). Figure 3. Seasonal depth profiles of DO (a), water temperature (b) and CDOM (c) for Lake Qiandaohu from August 2011 to May 2012 (Zhang et al., 2015) The results indicated that the DO depth profile and DO stratification were correlated with the water temperature depth profile and thermal stratification. However,

33 20 temperature of the water was not the only factor controlling the DO concentrations. A significant negative correlation was observed between DO concentration and CDOM concentration in the oxycline, which indicates that the increase concentrations of CDOM consumes and decreases the DO (Zhang et al., 2015) Regulations for recycled water for irrigation Although there are currently no federal regulations for reclaimed water use, the U.S. EPA has developed the Guidelines for Water Reuse (2012). The purpose of these guidelines is to provide reasonable guidance for water reuse and to represent a general standard for best practices in water reuse (U.S. EPA, 2012). Regulatory guidelines summarized in Table 1 were proposed as a general reference to compare the water quality parameters measured during this study. The U.S. EPA guidelines are enforced by the states through their own regulations for water reuse. For Nevada, the state regulations for water reuse are included in the Nevada Administrative Code (NAC), Chapter 445A Water Controls, Sections (Legislative Counsel State of Nevada, 2015). In particular, Section NAC 445A.275 General requirements and restrictions requires that reuse water has received at least secondary wastewater treatment. Secondary treatment is defined as the treatment of wastewater until the wastewater has, calculated as a 30-day average (Legislative Counsel State of Nevada, 2015): 1) A biochemical oxygen demand concentration (calculated as BOD 5 ) of 30 mg/l or less; 2) A total suspended solids concentration of 30 mg/l or less; and 3) A ph within the range of 6.0 to 9.0.

34 21 Table 1. Summary of U.S. EPA Guidelines for Water Reuse for irrigation (U.S. EPA, 2012). Reuse category description Urban Reuse Unrestricted The use of reclaimed water in nonpotable applications in municipal settings where public access is not restricted. Restricted The use of reclaimed water in nonpotable applications in municipal settings where public access is controlled or restricted by physical or institutional barriers, such as fencing, advisory signage, or temporal access restriction. Required treatment Secondary Filtration Disinfection Secondary Disinfection Reclaimed water quality ph = BOD 10 mg/l Turbidity 2 NTU No detectable fecal coliform/100 ml 1 mg/l Cl 2 residual (min.) ph = BOD 30 mg/l TSS 30 mg/l 200 fecal coliform/100 ml 1 mg/l Cl 2 residual (min.) Reclaimed water monitoring ph weekly BOD weekly Turbidity continuous Fecal coliform daily Cl 2 residual - continuous ph weekly BOD weekly TSS daily Fecal coliform daily Cl 2 residual - continuous Setback distances 50 ft to potable water supply wells; increased to 100 ft when located in porous media 300 ft to potable water supply wells 100 ft (30 m) to areas accessible to the public (if spray irrigation) In addition, NAC 445A has classified reuse waters into different categories based on bacteriological activity. This classification is defined in Section NAC 445A.276 Reuse categories: Requirements for bacteriological quality of effluent specific provisions include:

35 22 1) Treated effluent being used for an activity approved for a reuse category must meet the requirements for bacteriological quality for that category as indicated in Table 2. Table 2. Categories for reuse water established by NAC 445A pursuant to bacteriological quality. Total Coliform c.f.u. or mpn/100ml Fecal Coliform c.f.u. or mpn/100ml Reuse Category A B C D E 30-day geometric mean Maximum daily number No Limit No Limit 2) In Table 2, c.f.u. or mpn/100ml stands for colony forming units or most probable number per 100 milliliters of the treated effluent. STMWRF is currently producing water quality with reuse category A. However, Title 22 Code of Regulations from California was also used as reference for recycled water quality standards in this study. The current standards for the State of Nevada for reuse water are being revised and updated. The new standards for the State of Nevada will likely be similar to Title 22 Code of Regulations from California (SWRCB, 2014). In this project, experimental results were also compared with the California Department of Public Health - Recycled Water Regulations. These regulations are found in Title 22 Code of Regulations: Article 3 - Uses of Recycled Water (SWRCB, 2014). Section Uses of recycled water for irrigation states that recycled water to be used

36 23 for irrigation of the following should be disinfected tertiary recycled water, except for filtered wastewater defined in Section : food crops, parks and playgrounds, school yards, residential landscaping, unrestricted access golf courses, and other irrigation uses not specified but not prohibited by other sections of the California Code of Regulations (SWRCB, 2014). Coagulation is not required as long as the filter effluent turbidity does not exceed 2 NTU, the turbidity of the filter influent is continuously monitored, the turbidity of the influent does not exceed 5 NTU for more than 15 minutes and never exceeds 10 NTU, and chemical addition can be automatically activated or the course of the wastewater can be changed whenever the influent turbidity exceeds 5 NTU for more than 15 minutes (SWRCB, 2014). Section Filtered wastewater defines filtered wastewater as an oxidized wastewater which meets the criteria (a) or (b) (SWRCB, 2014): (a) Wastewater that has been coagulated and then passed through natural undisturbed soils or filter media such as sand and/or anthracite coal in accordance with the following: (1) At a flow rate no higher than 5 gallons per minute per square foot of surface area in a mono, dual or mixed media gravity, upflow or pressure filters, or not higher than 2 gallons per minute per square foot of surface area in traveling bridge filters; and (2) The turbidity of the filtered effluent must not exceed any of the following: a- An average value of 2 NTU during any 24-hour period; b- 5 NTU more than 5 percent of the time within a 24-hour period; and c- 10 NTU at any time.

37 24 (b) Has been passed through microfiltration or other membrane systems, so that the turbidity of the filtered wastewater does not exceed: (1) 0.2 NTU more than 5 percent of the time within a 24-hour period; and (2) 0.5 NTU at any time Physical water quality parameters For all raw waters, several parameters affect the effectiveness of coagulation including the concentration and type of particulate (colloidal) matter, the concentration of NOM, and the physical properties of the water such as temperature, total suspended solids (TSS) and turbidity. The common parameters used to characterize coagulation include coagulant type, dosage, and ph of the water before and after coagulation (Ashery et al., 2010) Temperature Wastewater temperature is typically higher than that of surface water sources due to the warm water discharges from customers. Since the specific heat of the water is higher than that of air, wastewater temperature is higher than the air temperature during most of the year and lower only during the hottest months (Metcalf & Eddy, 2013). Temperature is an important parameter because it affects chemical reactions and reaction rates, and aquatic life in the receiving water bodies. For example, significant changes in temperature can negatively affect the survival of biological species (Metcalf & Eddy, 2013). At high temperatures, dissolved oxygen (DO) concentrations can be reduced because the solubility of oxygen is lower in warm water than in cold water. Changes in biochemical reaction rates as a result of increased temperatures can cause a severe

38 25 reduction in the dissolved oxygen available during the summer months. Furthermore, high temperatures can stimulate the growth of undesirable plants such as algae and wastewater fungi (Metcalf & Eddy, 2013) Total suspended solids (TSS) TSS is the residue retained on a filter with a specified pore size, measured after being dried at a specified temperature (103 to 105 C). Because TSS depends on the pore size of the filter paper used in the analysis, the TSS test is somewhat arbitrary. It is important to note that the TSS test itself has no fundamental significance. The following reasons explain the lack of a fundamental basis (Metcalf & Eddy, 2013): a. The measured TSS value is dependent on the type and pore size of the filter, varying from 0.45µm to 2.0 µm. b. Auto filtration, where suspended solids retained by the filter also serve as a filter, can occur. Due to auto filtration, small particles can be intercepted, thus increasing the measured TSS over the actual value. c. Depending on the characteristics of the particulate matter, small particles may be removed by adsorption to material already retained by the filter. d. The test does not provide information about the number and size distribution of the particles. Despite these limitations, the TSS test is one of the universally used effluent standards (along with BOD) and its results are used to evaluate the performance of conventional wastewater treatment processes (Metcalf & Eddy, 2013).

39 Turbidity Turbidity is the measure of the scattering of light passing through a solution containing suspended solids and colloidal particles. A light source and a photodetector are required to measure the scattered light. The measured turbidity increases as the intensity of the scattered light increases. The intensity of the scattered light is dependent on the particle size distribution relative to the wavelength of the light source (Metcalf & Eddy, 2013). Turbidity is expressed in nephelometric turbidity units (NTU). Although suspended particles present in water contribute to turbidity, there is usually no direct correlation between turbidity and TSS concentrations in untreated wastewater Chemical water quality parameters Various chemical parameters that are used to characterize water quality include total carbon concentrations, ph, electrical conductivity, UV absorbance at 254 nm, alkalinity, and dissolved oxygen concentrations Fractions of total carbon According to Standard Methods of the American Public Health Association (APHA, 2012), the fractions of total carbon (TC) include: total inorganic carbon (TIC) carbonate, bicarbonate, and dissolved carbon dioxide; and total organic carbon (TOC) amount of all carbon bound in organic compounds (Figure 4 from Shi et al., 2010). Dissolved organic carbon (DOC) is the fraction of TOC remaining in the liquid after filtering a sample through a filter paper having a 0.45μm pore size (Metcalf & Eddy, 2013). Suspended organic carbon, also called particulate organic carbon, is the fraction of TOC retained on the 0.45μm filter paper. Purgeable organic carbon (POC), also referred

40 27 Figure 4. Summary of the different forms of carbon in water (Shi et al., 2010). to as volatile organic carbon (VOC), is the fraction of TOC removed from a sample by gas stripping. Non-purgeable organic carbon (NPOC) corresponds to the fraction of TOC not removed by gas stripping (APHA, 2012). A typical analysis for TOC measures both the total carbon (TC) and the total inorganic carbon (TIC). The TOC is determined by subtracting the TIC from the TC (Ashery et al., 2010) Importance of total organic carbon in water One method to estimate the amount of NOM present in water is by measuring the total organic carbon (TOC). Most groundwaters that are not directly influenced by surface waters have typically TOC concentrations of less than 2 mg/l. Surface waters usually have TOC concentrations within the range of 1 to 20 mg/l (Crittenden et al., 2005; Mackenzie, 2010). Measuring the TOC is of great importance for water and wastewater treatment. In wastewaters, organic matter may be present in very high levels (TOC>100 mg/l)

41 28 (APHA, 2012). Mackenzie (2010) resported that untreated domestic wastewater typically has TOC concentrations of 75 mg/l for weak wastewaters, 150 mg/l for medium, and 300 mg/l for strong. The organic matter in wastewater is also composed of diverse organic compounds with different oxidation states. A fraction of these organic compounds can be chemically or biologically oxidized, and BOD (biochemical oxygen demand) and COD (chemical oxygen demand) can be used to quantify and characterize them (APHA, 2012). The TOC of the wastewater can be used as a measure of waste strength and in some cases TOC can be related to BOD and COD concentrations (Metcalf & Eddy, 2013). TOC is a more direct and convenient measurement of organic content than either BOD or COD; however, it does not replace BOD and COD testing. In contrast with BOD and COD, TOC is independent of the oxidation state of the organic compounds and does not include elements bound to carbon, such as nitrogen or hydrogen, which can contribute to oxygen demand (APHA, 2012). An important reason to remove organic material before disinfection is the formation of disinfection byproducts (DBPs). The reaction of disinfectants commonly used to eliminate pathogenic microorganisms in water with NOM is a public health concern in particular for drinking water. When chlorine is added to water containing TOC, the chlorine and TOC may react to form DBPs. One class of DBPs is known as trihalomethanes (THMs), which are known carcinogens (Mackenzie, 2010). Optimum coagulation can help reduce the potential for the formation of DBPs by enhancing the removal of TOC during filtration (Ashery et al., 2010; Mackenzie, 2010).

42 ph The ph of a water sample is a measure of the hydrogen-ion concentration. It is an important water quality parameter because it affects the chemical dosages added during coagulation process. ph is defined as the negative logarithm to the base 10 of the hydrogen-ion concentration: ph = -log 10 [H + ] The concentration of hydrogen ions can be calculated when water molecules dissociate into hydroxide ions and hydrogen ions as follows: H 2 O H + + OH - The thermodynamic equilibrium constant is defined as: K = [H+ ][OH ] H 2 O where the brackets indicate the concentration of the species in moles per liter. In a dilute aqueous solution, the concentration of water is constant and, therefore, it can be included into the equilibrium constant K to yield: K w = [H + ][OH ] where K w represents the ionization constant and has a value of approximately 1x10-14 at a temperature of 25 C. Since poh is defined as the negative logarithm of the hydroxideion concentration, the relationship between ph and poh is established as: ph + poh =14 The ph of an aqueous solution is commonly measured with a ph electrode, also known as ph meter. ph is used to specify the acidity or basicity of a solution. Solutions with a ph lower than 7.0 are acidic and solutions with ph greater than 7.0 are basic.

43 30 In wastewater treatment, ph is an important water quality parameter as the range suitable for most biological aquatic life is within the range of ph 6 to ph 9. The biological treatment of a wastewater with very high ph is difficult, and if the ph is not adjusted before discharge, the effluent may have a negative impact on the receiving waters. For treated effluents discharged to the environment, the desirable ph usually varies within the range of ph 6.5 to ph 8.5 (Metcalf & Eddy, 2013) Electrical conductivity (EC) The EC of water quantifies its ability to conduct an electric current. The electrical current is transported by the ions present in the water. Thus, the conductivity increases as the concentration of ions increases. In this way, the EC is an indirect measure of the concentration of total dissolved solids (TDS). In wastewater treatment, the salinity of a treated wastewater used for irrigation is estimated by measuring its electrical conductivity. Therefore, EC is an important water quality parameter to determine the suitability of reuse water for irrigation (Metcalf & Eddy, 2013). The electrical conductivity is expressed in SI units as millisiemens per meter (ms/m) and in micromhos per centimeter (µmho/cm) in US customary units. An empirical relationship between TDS concentration of a water and electrical conductivity is given as (Metcalf & Eddy, 2013; Walton, 1989): TDS (mg/l) = EC (µs/cm or µmho/cm)x K where the K factor is typically 0.7 for natural waters. The above relationship does not apply for raw wastewaters or high-strength industrial wastewaters. In addition, it can also be used to verify if the chemical analysis are acceptable (APHA, 2012).

44 UV 254 absorbance The constituents of wastewaters have an effect on the average UV absorbance. Absorbance is a measure of the amount of light, of a specific wavelength, absorbed by the constituents in a solution. It is measured using a spectrophotometer typically with a fixed simple path length of 1.0 cm at a wavelength of 254 nm (Metcalf & Eddy, 2013). Although absorbance is dimensionless, it is often reported in units of cm -1, which corresponds to absorptivity. If the length of the path is 1 cm, then absorbance and absorptivity are equal (Metcalf & Eddy, 2013). Transmittance is defined as Transmittance, T, % = ( I I 0 ) x100 where I is the light intensity at a specified distance from the light source and I 0 is the light intensity at light source. Table 3 presents typical UV absorbance and transmittance values for different wastewater treatment processes (Metcalf & Eddy, 2013). Table 3. Typical UV absorbance and transmittance values at 254 nm for wastewater after various treatment processes (Metcalf & Eddy, 2013). Treatment process UV absorbance (cm -1 ) Transmittance (%) Primary Secondary Nitrified secondary Filtered secondary Microfiltration Reverse osmosis Since several organic compounds present in wastewater strongly absorb ultraviolet (UV) radiation, UV absorbance can often be used as a surrogate measure of organic compounds including humic substances, lignin, fulvic acids, tannin, and some aromatic compounds. The UV wavelength at which adsorption is commonly reported is

45 nm. Therefore, this method may be used to assess the presence of UV absorbing compounds in wastewater. Measurements of UV absorption at 254 nm can often be correlated to the amount of dissolved organic carbon (DOC) in a sample of water that has been filtered through a 0.45 µm filter (Metcalf & Eddy, 2013). This correlation is reported as specific UV absorbance (SUVA). SUVA is defined as the UV absorbance at 254 nm in cm -1 divided by the DOC concentration in mg/l (Weishaar et al., 2003). SUVA is the measure of the nature of the carbon present in the sample, in terms of the aromatic character of the carbon (Metcalf & Eddy, 2013) Alkalinity Alkalinity is defined as the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. In this way, alkalinity in wastewater helps to resist changes in ph caused by the addition of acids (Metcalf & Eddy, 2013). Alkalinity serves as measure of the buffering capacity of a water. The greater the alkalinity, the greater the buffering capacity (Mackenzie, 2010). Alkalinity in water results from the concentration of hydroxides [OH ], carbonates [CO 2 3 ], and bicarbonates [HCO 3 ] of calcium, magnesium, sodium, potassium, and ammonia. Wastewater is usually alkaline, and its alkalinity is dependent on the characteristics of the drinking water supply and the constituents added during domestic use (Metcalf & Eddy, 2013). Alkalinity is determined by titrating with a standard acid. For practical purposes, alkalinity is be defined as (Mackenzie, 2010): Alkalinity, meq/l = [HCO 3 ] + 2[CO 2 3 ] + [OH ] - [H + ]

46 33 where [ ] refers to the constituent concentration in moles/l. In practice, the results are expressed in terms of the concentration of calcium carbonate (i.e., mg/l as CaCO 3 ). In order to convert from meq/l to mg/l as CaCO 3, the following relationship can be used: Miliequivalent mass of CaCO 3 = (100 mg/mmole) (2 meq/mmole) = 50 mg/meq Dissolved oxygen (DO) Dissolved oxygen (DO), commonly measured in mg/l, is the amount of oxygen present in the water (Chapra, 1997). The concentration of DO is important for a healthy ecosystem since sufficient oxygen is required to support the aquatic life and the oxygen demand due to natural decomposition of organic matter. It was reported that hypoxia, a condition in which the DO levels are below 6.5 mg/l, affects the physiological functions of fish in the benthic region which is at the lowest level of a body of water (Zhang et al., 2015). Harmful effects can occur when DO levels are lower than 4 or 5 mg/l, depending on the aquatic species (Naik et al., 2010). The saturation concentration of oxygen in surface waters is typically around 10 mg/l. However, this saturation concentration varies depending on several environmental factors including temperature, salinity and partial pressure variations (Chapra, 1997).

47 34 CHAPTER 3 MATERIALS AND METHODS In this chapter, information about the five different coagulants (i.e., alum, ferric chloride, polyaluminum chloride, CC2220 and CC2110) evaluated during jar testing experiments is included with calculations of the coagulant dosages. This chapter also contains a detailed description of the experimental methodologies that were followed for the analyses of water quality parameters including turbidity, ph, electrical conductivity, total suspended solids, TOC analyses, and UV absorbance at 254 nm. These methodologies were in accordance with Standard Methods of the American Public Health Association (APHA, 2012). Procedures which were followed for the jar testing experiments and for the preparation of bottles required to collect samples for TOC and TSS are also included. 3.1 Water quality sampling Water samples were collected from the effluent of the secondary clarifiers, the flow returning from Huffaker Reservoir (when available), the filter effluent, and the effluent of the chlorine contact basin. Samples were stored in coolers and delivered to the laboratory, where they were refrigerated at 4 C. These samples were then analyzed for TSS, TOC and UV absorbance at 254 nm. 3.2 Coagulants The coagulants evaluated during jar testing included aluminum sulfate, ferric chloride, polyaluminum chloride, and CC2110 and CC2220 two proprietary aluminumbased coagulants manufactured by Cal-Chem (California Aluminum Chemicals).

48 35 Stock solutions of each coagulant were prepared. The required volume of stock solution needed to achieve the desired coagulant dosage in each beaker during jar testing was recorded Aluminum sulfate (or alum) The Thatcher Company (Downey, CA) reported the concentration of the stock alum solution as 8.25% as Al 2 O 3 with a specific gravity of (at 15 C). The following procedure was employed to determine the required volume of alum to achieve a coagulant dosage of 10 mg/l: a. Calculation of density of the stock chemical: The specific gravity (SG) of a material is defined by the expression: SG = ρ material ρ water The density of water at 20 C is 1 g/cm3 or 1000 kg/m 3 (USGS, 2015). ρ material = 1000 kg kg (1.333) = 1333 m3 m 3 (or kg L ) b. Calculation of the concentration (C) of alum in the stock chemical as g/l of Al 2 O 3 : g alum C = 8.25 ( 100 g solution ) (1.333 kg L ) 103 g 1 kg = g L Al 2O 3 c. Calculation of coagulant volume (V) required to provide a specific coagulant dosage (initially 10 mg/l of Al 2 O 3 ) and for the volume of the jar test beaker of 2 liters. 10 mg V = L Al 2O 3 (2L) g L Al 2O 3 ( mg = 1.82x10 4 L = μl 10 3 g ) d. Step c. was repeated for the other coagulant dosages. Since the 1000 μl auto pipette was employed to measure the volumes, the calculated

49 Ferric chloride volumes were rounded to the closest whole number and the pipettes were carefully checked to verify that calculated volumes were actually achieving the specific dosages. The weight (W) of the coagulant volume (V) was obtained using an analytical balance and used to determine the concentration for alum as mg/l of Al 2 O 3. Then, the corresponding coagulant dosage for jar testing was calculated by multiplying the concentration of alum by V and dividing by the volume of water in the jar test beaker of 2 liters. The calculated volumes for different aluminum sulfate dosages that were evaluated during this project are given in Table 4. Table 4. Volume of Al 2 O 3 for specific alum dosages Alum Dosage Volume (mg/l) (μl) Kemira Water Solutions (Mojave, CA) reported the concentration of the stock solution as 42.10% as FeCl 3 with a specific gravity of (at 60 F). Following the same procedure as presented above for alum, the following quantities were determined for ferric chloride.

50 37 ρ material = 1441 kg m 3 (or kg L ) C = g L FeCl 3 V = μl (for a dosageof 10 mg L FeCl 3 ) The calculated volumes for different dosages of ferric chloride that were evaluated during this project are given in Table 5. Table 5. Volume of FeCl 3 for specific coagulant dosages Polyaluminum chloride (PACl) Ferric Chloride Dosage (mg/l) Volume (μl) Kemira Water Solutions (Spokane Valley, WA) reported the concentration of the stock solution as 10.41% as Al 3+ with a specific gravity of (at 60 F). Following the same procedure as presented above for alum and ferric chloride, the following quantities were determined for polyaluminum chloride. ρ material = 1258 kg m 3 (or kg L ) C = g L Al3+ V = μl (for a dosage of 10 mg L as Al3+ )

51 38 The calculated volumes for different dosages of PACl that were evaluated during this project are given in Table 6. Table 6. Volume of PACl as Al 3+ for specific coagulant dosages CC2110 and CC2220 Polyaluminum chloride Dosage Volume (mg/l) (μl) Cal-Chem (California Aluminum Chemicals) is the chemical company that provided the coagulants CC2110 and CC2220 (blended aluminum coagulant solutions). Coagulant CC2110 is a PACl, organic coagulant, and a polymer. Coagulant CC2220 is also a blend of PACl and organic coagulant. They both have a specific gravity of Following the same procedure as presented above for the other coagulants, the following quantities were determined for CC2110 and CC2220: ρ material = 1270 kg m 3 (or 1.27 kg L ) C = 1270 g L V = μl (for dosage = 10 mg/l) The calculated volumes for different dosages of CC2110 and CC2220 that were evaluated during this project are given in Table 7.

52 39 Table 7. Volume of CC2110 and CC2220 for specific coagulant dosages 3.3 ph adjustment CC2110 and CC2220 Dosage (mg/l) Volume (μl) To adjust the ph of the raw water before coagulant addition, a stock solution of (37% concentrated, or 12M) hydrochloric acid (HCl) was used. Acid was added in small increments using a 1 ml Fisherbrand serological pipette and a Bel-Art 2 ml pipette pump. After acid was added, the water was stirred and thoroughly mixed. After mixing, the ph of the water was monitored using a ph meter. 3.4 ph measurement The ph of the water was measured using a Beckman Coulter 510 ph meter with a Beckman Coulter probe. The following procedure was used to measure the ph of the water: a. Rinse the electrode with deionized water to remove any potential contaminants and dry it using a Kimwipe. b. Insert the electrode into the sample and wait until the ph meter displays ready.

53 40 c. Record the ph reading of the sample and rinse the electrode with deionized water. d. Repeat steps a through c for the next sample. e. Place electrode in the ph storage solution after all samples have been analyzed. 3.5 ph calibration method setup The Beckman Coulter 510 ph meter allows the user to define which ph buffers are used for calibration. By default, the ph meter is calibrated with two points: ph 7.0 for the first point and ph 4.0 for the second point (BeckmanCoulter, 2008). The following procedure was used to calibrate the ph meter: a. Press CAL. b. Rinse the electrode with deionized water to remove any contamination and dry it using a Kimwipe. c. Place the electrode in the first solution of ph 7.0. d. Press ENTER to set the first calibration buffer and wait until the wait icon stops flashing. e. The display will show the ph buffer for the next calibration point. f. Repeat steps b through d for the second buffer of ph 4.0. g. The display will show a slope value. Slope should be a reasonable value (>95%). If not, change the buffers for fresh solutions. h. Press ph and the instrument is ready to use.

54 Jar testing method Jar tests were performed using a Phipps & Bird PB-900 six-paddle jar tester with square 2-liter beakers. Each jar test was performed using the following procedure: a. Calibrate the ph meter by using the ph standards of ph 7.0 and ph 4.0. b. Wash the 5-liter buckets used for collecting raw water and the 2-liter square jar test beakers with tap water. c. Collect a water sample using a bucket and identify the source of the sample. d. Measure typical parameters of the sample such as initial ph, turbidity, electrical conductivity, and temperature. e. If the initial ph was higher than desired, adjust the ph by adding hydrochloric acid in small quantities. Record the amount of acid added. For effective coagulation, the target ph conditions were typically between ph 6.5 and ph 7.0. f. Stir and thoroughly mix the acid into the water by transferring the water, back and forth, between two buckets, for about seven times. g. Monitor the ph of the water to check if it is within the desired range. If not, repeat steps e and f. h. Stir the stock solution of the coagulant and dispense the desired volume of coagulant into test tubes by using Eppendorf reference series adjustablevolume pipettes of volumes 10 to 100 μl and 100 to 1000 μl, and one of the μl natural beveled tips.

55 42 i. Place the six 2-liter square beakers on the jar test apparatus and fill each beaker with 2 liters of the water sample. j. Turn on the jar test apparatus select the mode sequential. Add the coagulant dosages simultaneously into individual 2-liter beakers and immediately push the START button to start the rapid mixing. k. The jar test apparatus was operated at the following mixing conditions: Coagulation rapid mixing: 300 rpm for 1 minute. Flocculation slow mixing: 100 rpm for 5 minutes and then 30 rpm for 5 minutes. l. Allow a settling time of 10 minutes, with the stopwatch being started when slow mixing stops. m. After settling, collect the samples of the settled water in 50 ml beakers from the sampling port. When sampling, it is important not to disturb the settled floc, and to avoid re-suspending particles. n. Connect each beaker to the conventional gravity sand filter columns and filter the settled water. Collect samples at the outlet of each filter in 50 ml beakers. o. Monitor water quality parameters (i.e., turbidity, ph, electrical conductivity, and final temperature) for the samples taken before and after filtration. p. The filter columns were backwashed after each set of jar tests. For filter backwashing, change the inlet and the outlet of one filter column to mode backwash. Fill a clean 5-liter bucket with tap water and connect a

56 43 centrifugal pump set to the filtration apparatus. Pump the water to the filter columns and the water flows in the upflow direction. Avoid the loss of media by agitating the columns and regulating the flow with a valve. Backwash each filter for about one minute or until the water flowing through the column is clear. 3.7 Turbidity measurement Turbidity was measured using a 2100N Laboratory Turbidimeter (Hach, 1999). The following procedure was used to measure the turbidity of each sample: a. Rinse the inside of the empty sample cell with deionized water and drain to remove any impurities. b. Fill the cell with the sample to the line (about 30 ml) and immediately close the cell with the cap. c. Clean the exterior of the sample cell by rinsing with deionized water and gently rubbing the glass with a Kimwipe to remove any fingerprints or water spots. d. If there are scratches present on the glass, apply a few drops of silicone oil from top to the bottom of the cell. Use the Kimwipes to equally distribute the oil through the cell surface in order to polish the scratches present on the glass. Remove any excess oil on the sample cell. e. Gently and slowly invert the sample cell to make sure there are no bubbles and that the sample is homogeneous throughout. f. Place the sample cell in the cell holder, aligning the triangle mark on the cell with the mark on the sample cell holder. Close the cover.

57 44 g. Wait until the reading on the display stabilizes and record the turbidity. 3.8 Electrical conductivity measurement The electrical conductivity of the water was measured using a YSI model 556 Multi-Probe System (MPS) handheld multi-parameter instrument. The following procedure was used to measure the electrical conductivity of the water: a. Before measuring the electrical conductivity of a sample, make sure the probe module is attached to the instrument and calibrate the sensors. b. Press the On/off key to display the main menu. c. Use the arrow keys to highlight the Run selection. d. Press the Enter key to display the run screen. e. Rinse the probe module with deionized water to remove any potential contaminants. f. Place the probe module in the sample and completely immerse all the sensors. g. Move the probe module through the sample to provide fresh sample to the sensor. h. Once the reading on the display stabilizes, record the electrical conductivity of the sample. 3.9 Electrical conductivity calibration method setup The following procedure from the YSI 556 MPS Operations Manual (YSI Inc., 2009) was used to calibrate the multi-probe instrument: a. Use the arrow keys to highlight the Conductivity option and press Enter to display the conductivity calibration selection screen.

58 45 b. Use the arrow keys to highlight the Specific Conductance option and press Enter. c. Rinse the probe meter and the transport/calibration cup with deionized water to remove any potential contamination and dry it using Kimwipes. d. Place the conductivity standard solution into the transport/calibration cup. e. Use the keypad to enter the calibration value of the standard that is being used, making sure to enter the value in units of ms/cm. In this research, a calibration standard solution of ms/cm was used. f. Press Enter and wait about one minute for instrument to stabilize. The current values of the sensors will appear on the screen and will change with time as they stabilize. g. When the reading for specific conductance stabilizes, press the Enter to accept the calibration. h. Then press Enter again to return to the Conductivity Calibrate Selection Screen. i. Press Escape to return to the calibration menu and Escape again to display the main menu screen Preparation of glass bottles for TSS and TOC samples Glassware used to collect water samples for analyses of TOC and TSS were prepared using the following procedure: a. Rinse glass bottles and lids with methanol to remove any residual carbon. b. Leave plastic lids on a tray and cover with aluminum foil.

59 46 c. Place glass bottles in the oven at 400 C for one hour to remove any traces of carbon. d. Turn oven off, open the oven door and let bottles cool down for at least 30 minutes. e. Remove the bottles from the oven using heat resistant tongs and immediately cover them with aluminum foil. f. Rinse glass bottles with methanol again. g. Place glass bottles in the oven at 115 C for 35 minutes to evaporate methanol. h. Take bottles out and screw on the lids. i. Do not open bottles until the moment of collecting samples to avoid carbon contamination in the bottles. j. Collect the samples by filling the bottles completely, making sure no air bubbles remained inside and screw on the lids. k. Store glass bottles in a cooler with ice to keep them dark and at 4 C Total suspended solids analyses Total suspended solids (TSS) were analyzed following the standard method established by the American Public Health Association (APHA), American Water Works Association (AWWA) and Water Environment Federation (WEF) (APHA, 2012). The materials and method used for TSS analyses are summarized as follows: Materials a. Aluminum weighing dishes. b. Dressing forcep tweezers.

60 47 c. Mettler Toledo AB204 S analytical balance, capable of weighing to 0.1 mg. d. Glass-microfiber filter disks: 4.7cm diameter, 1.2µm binder free glass microfiber. Grainger, model # 12K886. e. Filtration apparatus with cylinder funnel and coarse (40 to 60 µm) fritted disk as filter support. f. Suction flask and vacuum. g. Graduated cylinder. h. Drying oven, for operation at 103 to 105 C. i. Desiccator, containing a desiccant with a color indicator of moisture content. j. Deionized water (DIW). k. Metal tray Method a. Preparation of glass-fiber filter disk: Place the filter with wrinkled side up on filtration apparatus. Apply vacuum and wash filter with three successive 20-mL portions of deionized water (DIW). Continue suction to remove all traces of water, turn vacuum off and discard water. Remove the filter from the filtration apparatus and place it on an aluminum dish. Label each aluminum dish with the sample name. Dry in the oven at 103 C for one hour. Place aluminum dishes in desiccator to let filters cool. Zero the analytical balance by pressing the zero button. Using tweezers, place the filter on the scale to weigh. Repeat the process of drying, cooling,

61 48 desiccating, and weighing until weight change is less than 4% of the previous weighing or within 0.5 mg. Store filters in desiccator to avoid absorption of moisture from the air. b. Selection of filter and sample sizes: Choose sample volume to yield between 2.5 and 200 mg dried residue. If volume of water filtered does not meet the minimum yield of dried residue, increase sample volume. c. Sample analysis: Assemble filtering apparatus. Using tweezers, place the filter on the filter support and turn the vacuum on. Wet filter with small volume of DIW to seat it. Agitate the water sample to obtain a more uniform (homogeneous) distribution of particle sizes. Then, measure the desired volume (determined in step b) using the graduated cylinder and filter the sample. Wash the filter with three successive 10-mL volumes of DIW, let all washings drain, and continue suction for about 3 minutes until all the liquid has drained through the filter. Samples with high dissolved solids may require additional washings. Turn off vacuum, carefully remove the filter from filtration apparatus using tweezers and transfer to an aluminum weighing dish. Place all the filters on a tray and place the tray in the oven. Dry for at least 1 hour at 103 C. Remove the samples from the oven using tweezers. Cool in desiccator to balance temperature and weight. Remove dish from the desiccator. First, zero the balance with the door closed, then open the door and place the filter on the scale using tweezers. Close the door, allow the reading to stabilize and record the weight.

62 Calculation where: mg total suspended solids/l = A = weight of filter + dried residue, mg B = weight of filter, mg 3.12 Total organic carbon analyses (A B)x1000 sample volume, ml A Shimadzu TOC-V CPH carbon analyzer with a ASI-V autosampler was used to measure total organic carbon. The high-temperature combustion method was used since it is suitable for samples containing high concentrations of organic carbon, which may not be efficiently oxidized by the persulfate or the ultraviolet methods. The materials and method provided by the Standard Methods (APHA, 2012) are summarized as follows: 1. Materials a. Total organic carbon analyzer. b. Sampling, injection, and sample preparation instruments. c. Sample blender or homogenizer. d. Magnetic stirrer and TFE-coated stirring bars. e. Filtering apparatus. f. HPLC syringe filter, pore size 0.45 µm. g. 2 liter glass bottles. 2. Procedure (APHA, 2012) a. Sample injection: Withdraw a portion of the sample by using the 10 ml sterile syringe with blunt tip needle.

63 50 b. The solution goes into the combustion chamber which is supplied with purified air. In the combustion chamber total combustion of a sample is achieved by oxidation of the carbon through heating and combustion at 680 C under a high oxygen condition. The TC from the sample is oxidized to carbon dioxide. The carbon dioxide generated is cooled and dehumidified, and then transferred to the non-dispersive infra-red (NDIR) detector. The NDIR detects the carbon dioxide and outputs a peak area that is proportional to the TC concentration in the sample. The concentration of TC in the sample is obtained through comparison with a calibration curve. c. Two carbon standards for TOC analysis were used: the calibration curve using potassium hydrogen phthalate (C 8 H 5 KO 4 ) was used for the TC analyses, and a calibration using sodium bicarbonate (NaHCO 3 ) and sodium carbonate (Na 2 CO 3 ) for the IC analyses. d. To determine the concentration of inorganic carbon (IC), the oxidized sample was further subjected to the sparging process. Under acidic conditions, the inorganic carbon of the sample was converted to carbon dioxide, which was then transferred to the NDIR detector where the IC concentration was obtained. 3. Calculations TOC = TC IC where TOC is total organic carbon, TC is total carbon, and IC is inorganic carbon.

64 51 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Results of jar testing for effluent from the secondary clarifiers from February through April 2015 Jar tests were conducted on a weekly basis on water samples of the effluent from the secondary clarifiers. The performance of the two proprietary aluminum-based coagulants (i.e., CC2110 and CC2220) was evaluated. A total of 17 jar tests were performed at the treatment plant, nine using CC2110 and eight using CC2220. The water quality parameters that were monitored during jar testing included the initial and final phs and turbidities as well as water temperature. In order to evaluate the effects of ph during jar testing, the ph of the water was adjusted by adding hydrochloric acid as described in the ph adjustment procedure in Section 3.4. The results of jar testing conducted using CC2110 at various dosages and different ph conditions are summarized in Figures 5 and 6. The optimum coagulant dosage was around 30 mg/l resulting in a filtered water turbidity of less than 1 NTU, which is in compliance with the maximum turbidity of 2 NTU established by the federal guidelines for water reuse (U.S. EPA, 2012) and Title 22 California Code of Regulations (SWRCB, 2014). In some jar tests, the turbidity was not very high initially so coagulation and filtration did not provide any further improvement in the water quality.

65 Filtered turbidity (NTU) Adjusted raw water ph ph=7.40 ph=7.23 ph=7.21 ph=6.92 ph=6.87 ph=6.75 ph=6.74 ph= Coagulant dosage (mg/l) Figure 5. Effects of coagulant CC2110 dosage and raw water ph on filtered turbidity for secondary clarifier effluent (March through April 2015). The effects of adjusting the ph of the effluent from the secondary clarifiers on filtered turbidity when using CC2110 as the coagulant is illustrated in Figure 6. In general, coagulant CC2110 works well over a wide range of ph conditions. According to the results, lower final ph conditions resulted in lower filtered turbidity when the coagulant dosage was 30 mg/l or greater. Based on filtered turbidity, the results indicated that reducing the ph of the raw water to a range between ph 6.5 and ph 6.9 provided somewhat more effective coagulation for coagulant dosages of 30 mg/l and higher. For the optimum CC2110 dosage identified as 30 mg/l, reducing the ph from about ph 7.4 to ph 6.6 decreased the filtered turbidity from 0.76 NTU to 0.24 NTU.

66 Filtered turbidity (NTU) Coagulant dosage 0 mg/l 10 mg/l 20 mg/l 30 mg/l 50 mg/l 60 mg/l Filtered ph Figure 6. Effects of final ph of the secondary clarifier effluent on filtered turbidity using coagulant CC2110 (March through April 2015). Therefore, the optimum ph condition when using coagulant CC2110 for the secondary clarifiers effluent is around ph 6.6. This value also meets the federal and state ph discharge permit requirements for water reuse, which ranges from ph 6.0 to ph 9.0 (U.S. EPA, 2012; Legislative Counsel State of Nevada, 2015). The performance of coagulant CC2220 was also investigated in March and April Jar tests using the effluent from the secondary clarifiers were conducted to determine the ph and coagulant conditions that enhanced both coagulation and filter performance. The results for filtered water turbidity and coagulant dosage are presented

67 Filtered turbidity (NTU) 54 in Figure 7. The turbidity of the filtered water decreased as the coagulant dosage increased until about 30 mg/l. Coagulant dosages above 30 mg/l did not provide any further noticeable reduction in the turbidity of the filtered water. Furthermore, with a coagulant dosage of 20 mg/l, filtered turbidity was still lower than 2 NTU. However, in some of the jar tests the filtered turbidity with no coagulant addition was below 2 NTU, which is in compliance with the guidelines for water reuse developed by the U.S. EPA (U.S. EPA, 2012) and the regulations for filtered turbidity from Title 22 California Code of Regulations (SWRCB, 2014). Thus, coagulation of the water returning from the secondary clarifiers is not required since the turbidity of the raw water was relatively low Adjusted raw water ph ph=7.10 ph=7.09 ph=6.95 ph=6.93 ph=6.92 ph=6.90 ph=6.87 ph= Coagulant dosage (mg/l) Figure 7. Effects of coagulant CC2220 dosage on filtered turbidity for effluent from secondary clarifiers (March through April 2015).

68 Filtered turbidity (NTU) 55 The results of the jar tests to determine the ph conditions that enhanced coagulation when using CC2220 are shown in Figure 8. Ingeneral, coagulant CC2220 works well over a wide range of ph conditions. According to the results, the optimum ph was found to be around ph 6.8 to ph 7.0 since filtered turbidity was minimized under this condition when using the optimum CC2220 dosage of 20 mg/l. This ph range is in compliance with the permit limit of ph 6.0 stated in the federal guidelines for water reuse (U.S. EPA, 2012) and the Nevada Administrative Code (NAC 445A.275) (Legislative Counsel State of Nevada, 2015). Adjusting the ph of the water prior to the coagulation and filtration processes is recommended in order to improve the quality of the filtered water Coagulant dosage 0 mg/l 10 mg/l 20 mg/l 30 mg/l 50 mg/l 60 mg/l Filtered ph Figure 8. Variation of filtered turbidity with final ph for secondary clarifier effluent using different coagulant dosages of CC2220 (March through April 2015).

69 Results of jar testing on water from Huffaker Reservoir from May through August 2015 From the end of May 2015 to the end of August 2015, jar tests were performed on water withdrawn from Huffaker Reservoir. A total of 23 jar tests were conducted with CC2110 as the coagulant, 22 tests using CC2220, and 15 tests using aluminum sulfate. The water quality parameters that were monitored during the testing included turbidity, ph, electrical conductivity, and temperature for the raw water at the beginning of each jar test and the filtered water at the end of each jar test. Since the water samples were collected at different times of the month, the quality of the raw water may vary between jar tests. The effect of coagulant dosages on filtered turbidity were investigated during May 2015 (Figure 9) and June 2015 (Figure 10). The results indicated that a coagulant dosage of CC2110 of 10 mg/l provided effective coagulation and reduced the turbidity of the filtered water below 2 NTU which meets the state and federal regulations for filter effluent turbidity for reuse water. This optimum dosage of 10 mg/l was also effective for the higher raw water turbidities observed during June. In most cases, coagulant dosages of more than 20 mg/l provided minimal reductions in the turbidity of the filtered water. In two cases, a slight increase in filtered water turbidity was observed at the highest coagulant dosage of 60 mg/l likely because of charge reversal or restabilization of particles in the water as a result of overdosing. The effects of adjusting the ph of the water returning from the reservoir on filtered turbidity for the optimum coagulant dosage of CC2110 of 10 mg/l is depicted in Figure 11. In general, coagulant CC2110 works well over a wide range of ph conditions.

70 Filtered turbidity (NTU) Filtered turbidity (NTU) Adjusted raw water ph ph=6.91 ph=6.84 ph=6.82 ph=6.66 ph=6.56 ph= Coagulant dosage (mg/l) Figure 9. Effects of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (May 2015) Coagulant dosage (mg/l) Adjusted raw water ph ph=7.26 ph=7.16 ph=7.10 ph=6.89 ph=6.84 ph=6.80 ph=6.75 ph=6.72 ph=6.71 ph=6.66 ph=6.61 Figure 10. Effects of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (June 2015).

71 Filtered turbidity (NTU) Filtered ph Figure 11. Effect of final ph of the water returning from the reservoir on filtered turbidity using the optimum coagulant dosage of CC2110 of 10 mg/l (May through June 2015). No relationship was found between filtered ph and filtered turbidity of the reservoir water. Therefore, adjusting the ph of the raw water prior to coagulation using coagulant CC2110 does not enhance turbidity removal. Jar tests were also performed using different dosages of CC2220 and at different initial ph conditions by adjusting the ph of the raw water. The effects of coagulant dosage at different initial ph conditions on filtered turbidity is shown in Figures 12 and 13. The optimum coagulant dosage was observed to be 20 mg/l for both May and June, which generally reduced the turbidity of the filtered water to around 0.5 NTU. The slight increase in filtered water turbidity at the highest coagulant dosage of 60 mg/l was probably due to overdosing which causes charge reversal resulting in restabilization of particles in the water.

72 Filtered turbidity (NTU) Filtered turbidity (NTU) Adjusted raw water ph ph=7.00 ph=6.94 ph=6.90 ph= Coagulant dosage (mg/l) Figure 12. Effects of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (May 2015) Coagulant dosage (mg/l) Adjusted water ph ph=7.25 ph=7.14 ph=7.10 ph=7.05 ph=7.01 ph=7.00 ph=6.97 ph=6.95 ph=6.91 ph=6.91 ph=6.90 ph=6.89 ph=6.79 ph=6.62 Figure 13. Effects of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (June 2015).

73 Filtered turbidity (NTU) 60 The effects of ph on filtered turbidity for the optimum coagulant dosage of CC2220 of 20 mg/l is given in Figure 14. The results indicated that adjusting the ph of the water provided no noticeable effect on turbidity removal. Hence, ph adjustment of the water returning from the reservoir prior to coagulation is not recommended when using CC2220 as the coagulant. It was observed that both coagulants CC2110 and CC2220 performed equally well overall for reducing the filtered turbidity when treating water withdrawn from the reservoir Filtered ph Figure 14. Effect of final ph of the water returning from the reservoir on filtered turbidity using the optimum coagulant dosage of CC2220 of 20 mg/l (May through June 2015). The effect of coagulant dosage and ph on filtered turbidity was also investigated using aluminum sulfate (i.e., alum) as the coagulant. A total of 15 jar tests were performed in July 2015 using water returning from Huffaker Reservoir. The results for filtered water turbidity and initial raw water ph for each jar test are presented in Figure 15. The initial ph of the raw water was only adjusted in two tests (ph = 6.57 and 6.51)

74 Filtered turbidity (NTU) Initial raw water ph ph=8.54 ph=8.53 ph=8.10 ph=8.04 ph=7.90 ph=7.89 ph=7.87 ph=7.85 ph=7.85 ph=7.79 ph=7.66 ph=7.65 ph=7.59 ph=7.33 ph=6.57 ph= Coagulant dosage (mg/l) Figure 15. Effect of alum dosage on filtered turbidity for water returning from reservoir (July 2015). because adding alum to the water consumed the alkalinity (in form of bicarbonate ion) and, therefore, reduced the filtered ph to levels below the minimum permit of ph 6.0. Hence, no ph adjustment was implemented in the other jar tests. This observation is consistent with the theory of coagulation using alum (Guida et al., 2007) as well as previous studies (Ismail et al., 2012; Ashery et al., 2010).

75 62 The results were compared with Title 22 California Code of Regulations which requires 2 NTU for filtered water turbidity in order to determine conditions for enhanced coagulation. According to Figure 15, the most effective alum dosage was 10 mg/l, which satisfies the regulation of a filtered turbidity of 2 NTU. It was also observed that when the initial ph of water ph was reduced to ph 6.57 and ph 6.51, the filtered water turbidity began to increase slightly when the alum dosage exceeded 20 mg/l, likely because of charge reversal or restabilization of particles in the water. The effects of ph on filtered turbidity for various alum dosages are depicted in Figure 16. It was observed that the water quality was clearly improved with coagulant addition. The results indicate that the turbidity of the filtered water generally decreased as the ph decreased. However, ph conditions lower than 6.0 are not recommended since is not in compliance with the minimum permit limit for effluent ph of 6.0 (U.S. EPA, 2012; Legislative Counsel State of Nevada, 2015; SWRCB, 2014). Furthermore, an increase in filtered turbidity was observed for ph below 5.0 for alum dosages above 20 mg/l, corresponding to the two jar tests in which the raw water ph was adjusted to ph 6.57 and ph This indicates that ph adjustment is not recommended when using alum as coagulant, which was consistent with the research presented by Ismail et al. (2012). The effect of ph on filtered turbidity when using the optimum alum dosage of 10 mg/l is shown in Figure 17. The optimum range for filtered ph which enhances coagulation and meets the regulations was found to be between ph 6.2 and ph 7.0.

76 Filtered turbidity (NTU) Filtered turbidity (NTU) Coagulant dosage 0 mg/l 10 mg/l 20 mg/l 30 mg/l 40 mg/l 50 mg/l Filtered ph Figure 16. Effect of ph on filtered turbidity for various alum dosages (July 2015) y = x R² = Filtered ph Figure 17. Effect of ph on filtered turbidity for optimum dosage of alum of 10 mg/l (July 2015).

77 Results of jar testing on water from Huffaker Reservoir in September and October 2015 During September and October 2015, jar tests were performed on water returning from Huffaker Reservoir. The performance of the coagulants ferric chloride and polyaluminum chloride was evaluated. The water quality parameters that were monitored during the jar testing included turbidity, ph, and temperature for the raw water at the beginning of each jar test and the filtered water at the end of each jar test. Since the water samples were collected at different times of the month, the quality of the raw water may be different between jar tests. A total of 10 jar tests were conducted with ferric chloride as the coagulant. The effect of coagulant dosage on filtered water turbidity is presented in Figure 18. Filtered turbidity consistently decreased as the dosage of ferric chloride increased. The coagulant dosage that reduced the filtered turbidity below 2 NTU was 40 mg/l. Perhaps the required dosage was higher than during jar testing performed in earlier months using other coagulants because the turbidity of the raw water from the reservoir was noticeably higher, ranging from 13 to 23 NTU. The results of jar testing performed in 2016 and presented in Section 4.4 examined this further. Increasing the coagulant concentration up to 50 mg/l did not noticeably improve turbidity removal. As was observed when aluminum sulfate (alum) was used as the coagulant, the ph of the water dropped noticeably with the addition of ferric chloride.

78 Filtered turbidity (NTU) Adjusted raw water ph ph=7.19 ph=7.14 ph=7.13 ph=7.10 ph=7.08 ph=7.00 ph=6.97 ph=6.90 ph=6.71 ph= Coagulant dosage (mg/l) Figure 18. Effect of ferric chloride dosage on filtered turbidity for reservoir water at different water ph (September through October 2015). The effects of ph on filtered turbidity for various ferric chloride dosages are presented in Figure 19. Filtered turbidity is presented on log scale with base 10. The results demonstrated that the coagulant dosage of 40 mg/l of ferric chloride provided effective coagulation over the entire range of ph conditions that were evaluated. However, adjusting the ph of the raw water had no noticeable effect on turbidity removal. Figure 19 also suggests that turbidity removal generally increased as the dosage of ferric chloride increased.

79 Filtered turbidity (NTU) Coagulant dosage 0 mg/l 10 mg/l 20 mg/l 30 mg/l 40 mg/l 50 mg/l Filtered ph Figure 19. Effect of ph on filtered turbidity (log scale) for various ferric chloride dosages (September through October 2015). A total of 12 jar tests on water returning from Huffaker Reservoir were performed during October 2015 using polyaluminum chloride (PACl) as the coagulant. The effect of coagulant dosage on filtered turbidity is presented on Figure 20. The first jar test (redline, initial ph 8.87) was performed without adjusting the ph of the raw water in order to compare with the conditions when acid was added to reduce the initial ph. Reducing the

80 Filtered turbidity (NTU) Adjusted raw water ph ph=8.87 ph=7.58 ph=7.21 ph=7.04 ph=7.00 ph=6.83 ph=6.83 ph=6.67 ph=6.62 ph=6.60 ph=6.60 ph= Coagulant dosage (mg/l) Figure 20. Effect of PACl dosage on filtered turbidity for water returning from the reservoir (October 2015). initial ph of the raw water had a noticeable influence on the results for coagulant dosages in the range of 10 mg/l to 40 mg/l. A coagulant dosage of 10 mg/l was sufficient to provide effective coagulation since all but two filtered turbidities were below 2 NTU. Furthermore, PACl seems to work better when adjusting the initial water ph because lower ph values were generally associated with lower filtered turbidities.

81 Filtered turbidity (NTU) 68 In order to find the optimum ph conditions for PACl, the relationship between filtered ph and filtered turbidity using different coagulant dosages is presented in Figure 21. In Figure 21, filtered turbidity is shown on log scale with base 10. In general, lower filtered ph conditions were associated with lower filtered turbidity. For the optimum PACl dosage of 10 mg/l, filtered ph conditions in the range of ph 6.3 to ph 6.7 resulted in the lowest filtered turbidities Coagulant dosage 0 mg/l 10 mg/l 20 mg/l 30 mg/l 40 mg/l 50 mg/l Filtered ph Figure 21. Effect of filtered ph on turbidity removal for various PACl dosages (log scale) (October 2015).

82 Results of jar testing on water from Huffaker Reservoir from June through August 2016 From June through August 2016, additional jar tests were performed on water returning from Huffaker Reservoir in order to confirm and optimize the coagulant dosages which were determined during jar testing in A total of eight jar tests were conducted with CC2220 as the coagulant, 13 tests using aluminum sulfate, 18 tests using ferric chloride, 15 tests using polyaluminum chloride, and 13 tests using CC2110. The water quality parameters that were monitored during the testing included turbidity, ph, and temperature for the raw water at the beginning of each jar test and the filtered water at the end of each jar test. The quality of the raw water may be different between jar tests since samples were collected at different times of the month. Figure 22 illustrates the effect of CC2220 on filtered turbidity. Coagulant dosages were varied from 10 to 14 mg/l. The initial ph of the water was adjusted in some tests to compare turbidity removal at different ph conditions. According to the results, a coagulant dosage of CC2220 of 14 mg/l provided effective coagulation and reduced filtered turbidities to values that meet the limit of 2 NTU for filtered turbidity over the entire range of ph conditions that were evaluated.

83 Filtered turbidity (NTU) Filtered turbidity (NTU) Adjusted raw water ph ph=7.90 ph=7.88 ph=7.84 ph=7.08 ph=6.85 ph=6.67 ph=6.60 ph= Coagulant dosage (mg/l) Figure 22. Effect of coagulant CC2220 dosage on filtered turbidity for water returning from the reservoir (June 2016) Coagulant dosage 0 mg/l 10 mg/l 11 mg/l 12 mg/l 13 mg/l 14 mg/l Filtered ph Figure 23. Effects of final ph of water returning from the reservoir on filtered turbidity for various CC2220 dosages (June 2016).

84 71 The effects of ph on filtered turbidity for various CC2220 dosages are depicted in Figure 23. The results demonstrated that adjusting the ph of the water withdrawn from Huffaker Reservoir had no noticeable effect on turbidity removal for the various dosages of CC2220 evaluated. The same observation was found from the jar tests performed using CC2220 during 2015 and previously discussed in Section 4.2. During late June 2016, 13 jar tests on water returning from Huffaker Reservoir were performed using aluminum sulfate as the coagulant. In order to further assess the best alum dosage of 10 mg/l found in 2015, coagulant dosages were varied from 2 to 10 mg/l. The effect of coagulant dosage on filtered water turbidity is presented in Figure 24. Filtered turbidity was further reduced as the dosage of alum increased. The optimum dosage that reduced the filtered turbidity below 2 NTU in all but one test was 8 mg/l.

85 Filtered turbidity (NTU) Adjusted raw water ph ph=7.92 ph=7.84 ph=7.64 ph=7.51 ph=7.45 ph=7.29 ph=6.93 ph=6.75 ph=6.70 ph=6.60 ph=6.48 ph=6.45 ph= Coagulant dosage (mg/l) Figure 24. Effect of aluminum sulfate dosage on filtered turbidity for water returning from the reservoir (June 2016). The effect of adjusting the ph of the reservoir water prior to coagulation on filtered turbidity when using alum as the coagulant is illustrated in Figure 25. Lower final ph conditions consistently resulted in lower filtered turbidity when the coagulant dosage was 8 mg/l. Based on filtered turbidity, the results indicated that a target final ph of the filtered reservoir water in the range of ph 6.2 and ph 7.0 enhanced coagulation. This ph range is still in compliance with the federal and state requirements for a lower limit of ph 6.0 for water reuse (Legislative Counsel State of Nevada, 2015; SWRCB, 2014; U.S. EPA, 2012).

86 Filtered turbidity (NTU) Filtered ph Figure 25. Effect of filtered ph on filtered turbidity with alum dosage of 8 mg/l. The recommendation of implementing ph adjustment prior to coagulation during 2016 was in contradiction with the recommendation found during 2015 of no ph adjustment. To clarify this observation, adjusting the ph of the reservoir water prior to coagulation was beneficial only when using alum dosages lower than 10 mg/l. Since the coagulant dosages employed during the jar test experiments performed during 2015 varied from 10 to 50 mg/l, adjusting the ph was not recommended under these conditions. Performance of ferric chloride as a coagulant was investigated further in July A total of 18 jar tests were conducted on water returning from Huffaker Reservoir. The effect of coagulant dosages on filtered turbidity for water returning from the reservoir when using ferric chloride as the coagulant is presented in Figure 26. Coagulant dosages were initially varied from 10 to 50 mg/l. According to Figure 26 (left), a coagulant dosage of 20 mg/l of ferric chloride generally reduced the turbidity of the

87 74 filtered water below 2 NTU. In order to optimize this ferric chloride dosage, nine additional jar tests were then performed using coagulant dosages ranging from 12 to 20 mg/l. The results are depicted in Figure 26 (right). The optimum coagulant dosage of ferric chloride was observed to be around 14 mg/l. In most cases, coagulant dosages of more than 14 mg/l provided no further noticeable reduction of the turbidity of the filtered water. It was observed that the required coagulant dosage of 40 mg/l during jar testing performed in September and October 2015 was higher than during jar testing performed in July 2016, most probably because the turbidity of the raw water from the reservoir was noticeably higher during Therefore, the turbidity of the raw reservoir water influences the required coagulant dosage. The effect of final ph on the filtered turbidity when using ferric chloride as a coagulant is illustrated in Figure 27. The coagulant dosage of 14 mg/l of ferric chloride effectively reduced the filtered water turbidity over the entire range of ph conditions that were evaluated. However, the results indicated that reducing the ph of the raw water had no noticeable effect on the removal of turbidity for all the coagulant dosages of ferric chloride evaluated. This observation was consistent with the results from the jar tests performed during 2015 using ferric chloride as the coagulant.

88 Filtered turbidity (NTU) Filtered turbidity (NTU) Adjusted raw water ph 4 Adjusted raw water ph 5 4 ph=7.54 ph=7.46 ph=7.34 ph= ph=7.63 ph=7.52 ph=7.51 ph= ph=6.86 ph=6.76 ph= ph=6.74 ph=6.66 ph= ph=6.65 ph= ph=6.64 ph= Coagulant dosage (mg/l) Coagulant dosage (mg/l) Figure 26. Effect of ferric chloride dosage on filtered turbidity for water returning from the reservoir (July 2016). Coagulant dosages were initially varied from 10 to 50 mg/l (left) and later from 12 to 20 mg/l (right).

89 Filtered turbidity (NTU) Coagulant dosage 12 mg/l 14 mg/l 16 mg/l 18 mg/l 20 mg/l Filtered ph Figure 27. Effect of filtered ph on filtered turbidity for various ferric chloride dosages (July 2016). A total of 15 jar tests were performed using polyaluminum chloride (PACl) as the coagulant for the water returning from Huffaker Reservoir during July The results of jar testing using polyaluminum chloride (PACl) at various dosages and at different ph conditions are depicted in Figure 28. Coagulant dosages were varied from 2 to 10 mg/l in an effort to verify and reduce the recommended dosage of 10 mg/l determined in October A coagulant dosage of 6 mg/l was sufficient to provide effective coagulation since filtered turbidities were below 2 NTU. Coagulant dosages above 6 mg/l did not provide any further reductions of the turbidity of the filtered water. Figure 29 presents the effect of reducing the ph of the water returning from the reservoir on the filtered turbidity for the optimum PACl dosage of 6 mg/l. The results indicate that reducing the ph of the raw reservoir water prior to coagulation improved the filtered turbidity when using the optimum dosage. Since the average initial ph of the water

90 Filtered turbidity (NTU) 77 returning from the reservoir was ph 7.7±0.2, adjusting the ph of the reservoir water to target a filtered water ph within the range of ph 6.2 to ph 7.0 is recommended. The optimum ph conditions determined from the jar test experiments during 2016 were consistent with the ph conditions recommended from the jar tests conducted in This recommended ph range is also in compliance with the federal and state permit discharge lower limit of ph 6.0 for water reuse (Legislative Counsel State of Nevada, 2015; SWRCB, 2014; U.S. EPA, 2012) Coagulant dosage (mg/l) Adjusted raw water ph ph=7.96 ph=7.86 ph=7.79 ph=7.74 ph=7.73 ph=7.49 ph=7.28 ph=6.96 ph=6.91 ph=6.67 ph=6.61 ph=6.60 ph=6.54 ph=6.50 ph=6.28 Figure 28. Effect of polyaluminum chloride dosage on filtered turbidity for water returning from the reservoir (July 2016).

91 Filtered turbidity (NTU) Filtered ph Figure 29. Effect of filtered ph on filtered turbidity with PACl dosage of 6 mg/l. The performance of coagulant CC2110 was also evaluated for the water returning from Huffaker Reservoir. A series of jar tests using CC2110 as the coagulant were performed during August 2016 in an effort to verify the optimum coagulant dosage of 10 mg/l determined during Coagulant dosages were varied from 8 to 16 mg/l. The results of jar testing performed using CC2110 at various dosages and different ph conditions are illustrated in Figures 30 and 31. The optimum coagulant dosage was 16 mg/l resulting in a filtered water turbidity below 2 NTU. However, the required dosage of 16 mg/l was higher than during jar testing conducted in May through June 2015 using CC2110 because the initial ph of the raw water from the reservoir has higher, ranging from ph 7.5 to ph 8.9. Although coagulant CC2110 provided effective coagulation over the range of ph evaluated, adjusting the ph of the raw water prior to coagulation had no

92 Filtered turbidity (NTU) Filtered turbidity (NTU) Coagulant dosage (mg/l) Adjusted raw water ph ph=8.89 ph=8.47 ph=8.41 ph=8.35 ph=8.26 ph=8.25 ph=7.02 ph=6.80 ph=6.66 ph=6.61 ph=6.60 ph=6.48 ph=6.40 Figure 30. Effect of coagulant CC2110 dosage on filtered turbidity for water returning from the reservoir (August 2016) Filtered ph Coagulant dosage 8 mg/l 10 mg/l 12 mg/l 14 mg/l 16 mg/l Figure 31. Effect of raw water ph on filtered turbidity for various CC2110 dosages (August 2016).

93 80 apparent effect on turbidity removal. This observation was consistent with the jar testing results using coagulant CC2110 in The recommendations based on the results for all the jar testing experiments performed during 2015 and during 2016 are summarized in Tables 8 and 9, respectively. Aluminum sulfate and polyaluminum chloride performed remarkably well by reducing the filtered turbidity of the water returning from Huffaker Reservoir with relatively lower Table 8. Summary of recommendations based on the results of the jar test experiments performed during February through April 2015 Coagulant Optimum Optimum filtered ph dosage (mg/l) conditions Water sample CC Clarifier effluent CC Clarifier effluent May through August 2015 Coagulant Optimum Optimum filtered ph dosage (mg/l) conditions Water sample CC No correlation Reservoir CC No correlation Reservoir Alum Reservoir September and October 2015 Coagulant Optimum Optimum filtered ph dosage (mg/l) conditions Water sample Ferric chloride 40 No correlation Reservoir PACl Reservoir Table 9. Summary of recommendations based on the results of the jar test experiments performed during June through August 2016 Coagulant Optimum Optimum filtered ph dosage (mg/l) conditions Water sample CC No correlation Reservoir Alum Reservoir Ferric chloride 14 No correlation Reservoir PACl Reservoir CC No correlation Reservoir

94 81 dosages than the other coagulants evaluated, as long as the ph adjustment prior to coagulation is implemented. Coagulants CC2110, CC2220 and ferric chloride required higher dosages. Furthermore, implementing coagulation on the water from the secondary clarifiers is not recommended since it did not noticeably reduce filtered effluent turbidity. 4.5 Cost estimate for full-scale coagulant addition The daily cost of coagulant dosing was estimated for coagulants CC2110, CC2220, aluminum sulfate, ferric chloride and polyaluminum chloride. The following equation was employed in order to calculate the daily coagulant cost: Coagulant required (lb/day) = Coagulant dosage(mg/l) xflow plant (MGD)x8.34 Daily coagulant cost (USD/day) = coagulant required ( lb ) x cost of coagulant day Table 10. Estimated costs for coagulant addition Ferric CC2110 CC2220 PACl Alum chloride Units Optimum dosage mg/l Flow plant MGD (30-day average) Coagulant required lb/day Coagulant cost USD/lb Daily coagulant cost $312 $326 $94 $52 $177 USD/day According to Table 10, alum was found to have the lowest cost. Coagulants CC2110, CC2220 and ferric chloride are not recommended due to their relatively higher dosages and their higher costs to implement.

95 ph Seasonal variations of water quality in Huffaker Reservoir STMWRF has reported water quality problems associated with the water stored in Huffaker Reservoir during the irrigation season. The quality of the water generally deteriorates as the irrigation season progresses from mid-april through late-october. Some of these problems include algae growth, ph fluctuations, and elevated turbidities. Figures 32, 33 and 34 provide information regarding the variation of water quality parameters (i.e., ph, temperature, and turbidity) during the period from May 2015 through October 2015 and June 2016 through August The data correspond to the water samples collected in early daylight hours, usually between 7:30 a.m. and 11:00 a.m. prior to jar test experiments / / / / / / / /2016 Figure 32. Seasonal variations of ph in Huffaker Reservoir.

96 Temperature ( C) Turbidity (NTU) / / / / / / / /2016 Figure 33. Seasonal variations of turbidity in Huffaker Reservoir / / / / / / / /2016 Figure 34. Seasonal variations of temperature in Huffaker Reservoir.

97 84 As indicated in Figure 32, the ph of the reservoir water was higher during the fall 2015 than during the summer. During the summer 2015 and 2016, the ph usually fluctuated between ph 7.0 and ph 8.0. However, ph conditions ranging from ph 7.4 to ph 8.9 were observed in August During the fall 2015, the ph increased above ph 8.5. A maximum of ph 9.24 was observed on September 14, The increase in the ph of the reservoir water at STMWRF was previously reported and was linked to the photosynthesis of algae present in the reservoir (CH2M HILL, 2012). During photosynthesis, plants remove the carbon dioxide from the water to form glucose, thus increasing the ph of the water. The observation of higher ph values is consistent with the violation reports issued by the Nevada Division of Environmental Protection which state that STMWRF exceeded the permit limitation of ph 9.0 for effluent during September Based on the information presented, adjusting the ph of the reservoir water before coagulation and filtration is recommended since the ph was usually higher than the optimum ph for enhanced coagulation determined from the jar testing experiments. However, the amount of acid solution or carbon dioxide required to reduce the ph of the reservoir water varies each day and throughout the day. Therefore, a continuous ph monitoring device should be provided in conjunction with an acid/carbon dioxide feed device to dose the proper amount of solution required to regulate the ph at the optimum ph conditions. The results indicated a pronounced increase in turbidity of the reservoir water over time during 2015 (Figure 33). In particular, turbidity gradually increased from an average of 3.5±0.5 NTU in May up to 8.8±2.6 NTU in July. Moreover, water quality

98 85 continued to deteriorate during the fall as turbidity exceeded 13 NTU in September 2015 and reached a maximum of 23.7 NTU in October 8, It was observed that the water quality of the reservoir was better during Turbidity readings from June through August were usually within the range of 2.5 to 5.5 NTU. No dramatic increases in turbidity were observed during A high-density polyethylene (HDPE) liner was installed in the reservoir during the last half of 2015 which is thought to have contributed to the improved water quality. The elevated turbidity during 2015 could be attributed to lower reservoir water level as the irrigation season progressed. The variation of the water depth within the reservoir from May 2015 through September 2016 is presented in Figure 35. The high turbidity values observed in Figure 33 during September and October 2015 corresponded to the lower water depth of only around 3 feet (Figure 35). In addition, the construction associated with the installation of the HDPE liner in the reservoir during this period may have also affected the water quality of the reservoir water by contributing suspended particles from dust to the water, thus increasing the turbidity. Variation of water temperature with time is depicted in Figure 34. Water temperatures were above 20 C during the months of July 2015 and August Water temperatures were lower during October 2015 and June 2016 with temperatures ranging from 15 to 18 C. Water temperature is an important parameter that needs to be monitored since it has biological implications on the aquatic life. As previously mentioned, high temperatures can stimulate the growth of undesired aquatic plants like algae (Metcalf & Eddy, 2013; CH2M HILL, 2012).

99 Water depth at the reservoir (ft) /14/2015 8/22/ /30/2015 3/9/2016 6/17/2016 9/25/2016 Figure 35. Variation of water depth at the reservoir from May 2015 through September hour water quality testing in July, August and September 2015 The influent and effluent water quality of the existing Parkson DynaSand filters was monitored over extended periods of 12 and 24 hours. The following physicochemical water quality parameters were tested every 15 minutes: temperature, turbidity, ph and electrical conductivity. Additional samples were collected every hour for UV absorbance at 254 nm, total organic carbon (TOC), total carbon (TC), inorganic carbon (IC), and total suspended solids (TSS) analyses; these samples were stored in a cooler with ice to keep them dark and cool at 4 C. Water samples were collected from different sources including: filter influent and filter effluent for water returning from Huffaker Reservoir, the effluent from the chlorine contact basin, and filter influent and filter effluent for water from the secondary clarifiers

100 87 (Figure 36). Two 12-hour water quality tests were performed on July 30 and 31, 2015 and August 6, 2015 and a 24-hour test was performed on September 24 and 25, E A B D C Figure 36. Sampling locations for 12-hour and 24-hour water quality tests in (A) filter influent for secondary clarifier effluent, (B) filter effluent for secondary clarifier effluent, (C) filter influent for reservoir water, (D) filter effluent of reservoir water, and (E) chlorine contact basin effluent hour water quality tests in July 30 and August 6th, 2015 Two 12-hour tests were conducted. The first 12-hour test was performed from 9:00 p.m. on July 30, 2015 until 9:00 a.m. on July 31, The second 12-hour test was conducted on August 6, 2015 from 9:00 a.m. until 9:00 p.m. When the water reuse pumps are running, the treatment plant uses water returning from the reservoir and the effluent from the secondary clarifiers. Water returning from the reservoir was pumped into the reuse distribution system between 9:00 p.m. until 4:00 p.m. on the following day. In the late afternoon, when the water reuse pumps were turned

101 88 off, the filter effluent was disinfected in the chlorine contact basin, and was then pumped into Huffaker Reservoir. Water being pumped into the reservoir was tested on August 6, On that day, the water reuse pumps were turned off at 4:00 p.m. Water samples were collected every 15 minutes from the outlet of the chlorine contact basin, between 4:15 p.m. and 9:00 p.m. Figure 37 displays the results for turbidity before and after filtration for water returning from Huffaker Reservoir. The upflow filters did not effectively reduce turbidity. In general, the turbidity of water returning from the reservoir during this period was relatively high. The highest filter influent turbidity corresponded to 25.4 NTU at 10:00 p.m. and the lowest was 7.25 NTU. The turbidity of the filter effluent was also relatively high, exceeding 6 NTU during most of the time, indicating that the filters were not working efficiently. These results were compared with the California Department of Public Health Recycled Water Regulations. According to the Title 22, Section 60304, the filter influent turbidity was found to exceed the permit limitation of 5 NTU for more than 15 minutes and it also exceeded the maximum of 10 NTU during most of the time. Furthermore, the filter effluent turbidity was never in compliance with the regulation of 2 NTU. Water being pumped into Huffaker Reservoir after disinfection was also monitored. Turbidity was typically within the range of 3 to 5 NTU. Typically, the turbidity of the filter effluent slightly decreased as the flow passed through the chlorine contact basin due to the possible sedimentation of suspended particles. The results of this research suggest that a coagulation process for the water returning from the reservoir should be implemented as part of the treatment in order to

102 89 enhance the performance of the filters and meet the water quality standards for effluent turbidity. Proper coagulation is essential for effective filtration. The variation of ph with time for water returning from Huffaker Reservoir and for the effluent from the chlorine contact basin are illustrated in Figure 38. In general, the ph of the filtered water was slightly lower than the filter influent ph most of the time. ph values were higher during the late morning hours than during the night. A maximum of ph 8.95 for filter influent was observed at 12:45 p.m. on August 6, The ph almost exceeded the maximum permit limit of ph 9.0 for effluent established by the U.S. EPA Guidelines for Water Reuse for irrigation (U.S. EPA, 2012) and by the Nevada Administrative Code 445A.275 (Legislative Counsel State of Nevada, 2015). This observation of high ph values was consistent with the Nevada Division of Environmental Protection, which reported that STMWRF has exceeded the permit limit of ph 9.0 for effluent. The problem of higher ph values could be due to algae growth in the reservoir. As indicated in Figure 38, a rapid increase in ph was observed between 9:15 p.m. and 10:30 p.m. The reason for this was that while the water reuse pumps were off, all the filters were receiving water only from the secondary clarifiers. When the water reuse pumps begin operating at 9:00 p.m., water begins returning from Huffaker Reservoir. The reservoir water gradually displaces the secondary clarifier effluent within the filters at location D in Figure 36. Eventually, all of the water exiting this filter was water returning from the reservoir.

103 Turbidity (NTU) Turbidity (NTU) Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent 0 0 9:00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Pumps to reservoir on Water reuse pumps on Water reuse pumps on Water reuse pumps off Figure 37. Variation of turbidity of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right).

104 ph ph Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent 7.0 9:00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM 7.0 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Water reuse pumps on Water reuse pumps on Pumps to reservoir on Water reuse pumps off Figure 38. Variation of ph of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right).

105 92 The results also indicate that the ph of the effluent from the chlorine contact basin effluent decreased as time progresses. The reason for this was that while the water reuse pumps were on, the chlorine contact basin was receiving water from both the secondary clarifiers and the reservoir. When the water reuse pumps were turned off at 4:00 p.m., water stops returning from Huffaker Reservoir. The effluent from the secondary clarifiers gradually displaces the reservoir water within the entire basin. Hence, the chlorine contact basin eventually receives only the water from the secondary clarifiers. According to these results, implementing ph adjustment and coagulation of the water returning from the reservoir prior to filtration is recommended. The optimum ph conditions were determined based on jar testing and vary somewhat depending on the coagulant. ph adjustment can be accomplished by adding acid or by introducing carbon dioxide. Variations in electrical conductivity (EC) before and after filtration for reservoir water and effluent from chlorine contact basin are depicted in Figure 39. As previously discussed, EC measures the concentration of ions present and is an indirect estimate of the total amount of solids dissolved in water (TDS). EC was observed to be within the range of 1.75 and 2.40 ms/cm. Using a relationship between EC and TDS proposed by Walton (1989), the corresponding TDS values ranged from approximately 1,200 to 1,700 mg/l. Results were compared with water quality guidelines for reuse water for irrigation purposes reported by Tchobanoglous et al. (1998). Based on the TDS values, the water retuning from the reservoir had slight to moderate salinity which is an acceptable reuse water for irrigation.

106 Conductivity (ms/cm) Conductivity (ms/cm) Reservoir water before filtration Reservoir water after filtration Chlorine contact basin effluent :00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM 9:00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM Water reuse pumps on Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Figure 39. Variation of EC of reservoir water and chlorine contact basin during July 30-31, 2015 (left) and August 6, 2015 (right).

107 Temperature ( C) Temperature ( C) Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent Air temperature :00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Water reuse pumps on Water reuse Pumping system to reservoir on pumps on Water reuse pumps off Figure 40. Variation of temperature of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during July 30-31, 2015 (left) and August 6, 2015 (right). Data for air temperature was also included.

108 95 Figure 40 shows the variation in water temperature for water returning from Huffaker Reservoir and for the effluent from the chlorine contact basin. The temperature of reservoir water was observed to be as high as 27 C at 9:00 p.m. and gradually decreased with time until it reached 20 C in the early morning. These values are typical of wastewater in the United States during the months of July through August (Metcalf & Eddy, 2013). Hourly air temperatures were collected from the National Weather Service. The temperature of the effluent from the chlorine contact basin was within the range of 21 to 24 C. Samples for total suspended solids (TSS) were collected every hour and TSS analyses were performed within 24 hours after collecting the samples. TSS was monitored for both the water returning from Huffaker Reservoir and the water being pumped into the reservoir after disinfection. Variations of TSS with time are presented in Figure 41. According to the results, the highest TSS for filtered water returning from the reservoir corresponded to 20.6 mg/l at 2:00 a.m. on July 31, The highest TSS concentration for filter influent was 35.6 mg/l at 10:00 p.m. on July 30, The Parkson DynaSand upflow filters marginally reduced the TSS of the water returning from the reservoir. However, filtered effluent TSS was in compliance with the federal and state requirements for a maximum TSS of 30 mg/l for water reuse established by the U.S. EPA (2012) and the Nevada Administrative Code 445A.275 (Legislative Counsel State of Nevada, 2015). However, for the water samples collected at 2:00 and 3:00 a.m. on July 31, 2015, the TSS of the filter effluent for water returning from the reservoir were higher than the

109 96 TSS of the filter influent indicating that the existing upflow filters were not effectively removing TSS. The TSS in water being pumped into the reservoir after disinfection gradually decreased from 5.1 mg/l at 5:00 p.m. to 2.5 mg/l at 9:00 p.m. on August 6, This suggests that the chlorine contact basin allowed for some settling of particles within the basin. This observation was consistent with the results for turbidity in the effluent from chlorine contact basin which were discussed earlier. Operators at STMWRF have reported solids accumulation at the bottom of the chlorine contact basin which requires regular cleaning and proper maintenance. Implementing a coagulation/flocculation process, followed by sedimentation for the water returning from the reservoir is recommended to enhance the performance of the existing Parkson DynaSand filters and prevent solids accumulation in the chlorine contact basin. A linear correlation between TSS and turbidity was found with R 2 =0.87, as shown in Figure 42. This relationship was based on all samples collected of filter influent and effluent for water returning from the reservoir and for water being pumped into the reservoir after chlorination.

110 TSS (mg/l) TSS (mg/l) Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent :00 PM 1:00 AM 4:00 AM 7:00 AM Water reuse pumps on 0 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Figure 41. Variation of TSS of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right).

111 TSS (mg/l) y = 1.474x R² = Turbidity (NTU) Figure 42. Relationship between turbidity and TSS for water returning from the reservoir and exiting the chlorine contact basin.

112 99 Total organic carbon (TOC), total carbon (TC), inorganic carbon (IC) and UV absorbance at 254 nm were monitored every hour during the first two 12-hour water quality tests. The results are expressed as dissolved TOC (DOC) since each sample was filtered through a filter with a 0.45 μm pore size prior to the TOC analyses. Figure 43 depicts variations in DOC concentrations with time. No noticeable differences were observed between the filter influent and filter effluent samples since the filters would not be expected to remove dissolved organic matter. Figure 44 illustrates the variations in UV absorbance at a wavelength of 254 nm during the two 12-hour tests. UV absorbance for the filter effluent was generally lower than the filter influent, indicating that upflow filters were able to remove some fraction of matter in the water returning from the reservoir that absorbs at UV 254. DOC and UV absorbance at 254 nm were then compared in an effort to determine any possible relationship (Figure 45). No correlation was observed between UV absorbance and organic carbon.

113 Dissolved total organic carbon (mg/l) Dissolved total organic carbon (mg/l) Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent 0 0 9:00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Water reuse pumps on Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Figure 43. Variation of dissolved TOC (DOC) of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right).

114 UV absorbance (cm -1 ) UV absorbance (cm -1 ) Filter influent reservoir water Filter effluent reservoir water Chlorine contact basin effluent :00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM Pumping system to reservoir on Water reuse pumps on Water reuse pumps on Water reuse pumps off Figure 44. Variation of UV absorbance at 254 nm of filter influent and filter effluent for water from the reservoir and water entering into the reservoir after chlorination during July 30-31, 2015 (left) and August 6, 2015 (right).

115 Dissolved total organic carbon (mg/l) UV absorbance at 254 nm Figure 45. Relationship between DOC and UV absorbance at 254 nm for water returning from the reservoir and exiting the chlorine contact basin during July 30-31, 2015 and August 6, hour water quality test in September 24-25, 2015 During the fall, demand for reuse water for irrigation was lower than during the summer months. It was also noticed that lower water level in the reservoir greatly impacted the water quality. The second 24-hour water quality test was conducted at the end of September Water samples were collected every 15 to 30 minutes starting at 8:00 a.m. on September 24, 2015 and finishing at 8:00 a.m. on September 25, Water quality was characterized by monitoring typical water quality parameters including ph, turbidity, electrical conductivity, and temperature. Water samples for UV absorbance, TSS, TC, IC and TOC analyses were collected on an hourly basis.

116 103 On September 24, 2015, reuse water was being pumped into the reuse distribution system between 8:00 a.m. and 4:00 p.m. During this period, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir. Samples were collected from the filter influent and filter effluent in order to evaluate the performance of the filters. Depending on their location, some of the filters were mainly receiving reservoir water, while others were mainly filtering the effluent from the secondary clarifiers, and some received a mix of water from the reservoir and the secondary clarifiers (Figure 36). Reuse system pumps were turned off at 4:00 p.m. Between 4:00 and 11:00 p.m., the filters only received water from the secondary clarifiers, which was disinfected after filtration and then pumped into Huffaker Reservoir. During this period of time, sampling locations included the filter influent, the filter effluent, and the effluent from the chlorine contact basin. The treatment plant began withdrawing water from the reservoir again at 11:00 p.m. and the treated effluent was pumped to the distribution system overnight. Samples of water returning from the reservoir were collected from the filter influent and filter effluent between 11:00 p.m. and 8:00 a.m. Variations in turbidity for each sample location during the 24-hour period are illustrated in Figure 46. The results indicated that the quality of the water from the secondary clarifiers is considerably better (2 to 3 NTU) than the quality of the water returning from the reservoir (12 to 17 NTU). The Parkson DynaSand filters marginally reduced the turbidity of the water returning from the reservoir and the effluent from the secondary clarifiers. However, in the case of water returning from the reservoir, the filter

117 104 effluent turbidity exceeded 10 NTU during a majority of the time, which is not in compliance with the Recycled Water Regulations established by the California Department of Public Health (Title 22 Code of Regulations, Article 3 Uses of Recycled Water). Since the effluent turbidity exceeded 2 NTU, and the influent turbidity exceeded 5 NTU for more than 15 minutes and always exceeded 10 NTU, it is strongly recommended that coagulation before filtration is implemented as part of the treatment process for water returning from the reservoir. The desired ph conditions and the optimum coagulant dosage to reduce filtered turbidity were determined during jar testing. Proper coagulation can dramatically improve filter performance. The filtered turbidity of the reservoir water was observed to increase from about 3 NTU at 11:00 p.m. up to about 10 NTU at 3:00 a.m. This increase in filter effluent turbidity was because all of the filters were still filtering water from the secondary clarifiers at 11:00 p.m. and it took some time for reservoir water to pass through the filters. The same situation was observed during the previous 12-hour tests. Variations in the ph for the filter influent, the filter effluent, and the effluent from the chlorine contact basin are shown in Figure 47. The results indicated that the ph of the water returning from the reservoir varied within the range of ph 8.8 and ph 9.3. The high ph of the water in the reservoir was associated with the photosynthesis of algae present in the reservoir. The filter effluent did not meet the federal and state permit discharge limit for reuse water whenever it exceeded ph 9.0 (Legislative Counsel State of Nevada, 2015; SWRCB, 2014; U.S. EPA, 2012). The ph of the effluent from the secondary clarifiers and the effluent from the chlorine contact basin was within the acceptable

118 Turbidity (NTU) Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifier Filter effluent secondary clarifier Chlorine contact basin effluent 0 8:00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Water reuse pumps on Figure 46. Variation of turbidity of filter influent and filter effluent (for the effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, 2015.

119 ph Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers Chlorine contact basin effluent 6.8 8:00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Water reuse pumps on Figure 47. Variation of ph of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, 2015.

120 Conductivity (ms/cm) Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers 2.0 8:00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps on Water reuse pumps off Figure 48. Variation of electrical conductivity of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, 2015.

121 Temperature ( C) :00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Water reuse pumps on Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers Air temperature Figure 49. Variation of temperature of reservoir water for filter influent, filter effluent, and chlorine contact basin effluent during September 24-25, Data for air temperature was also included.

122 109 range. No significant differences were found between the ph of the water before filtration (Mean=9.21, SD=0.095) and after filtration (Mean=9.18, SD=0.083), p-value= A rapid increase in ph from ph 7.2 to ph 8.8 was observed between midnight and 2:00 a.m. after the water reuse pumping system was turned on, and the treatment plant started to receive water returning from the reservoir. The increase of water ph was due to the filters receiving mostly water from the secondary clarifiers at 11:00 p.m. The transition from effluent from the secondary clarifiers to water returning from the reservoir occurred between 12:00 a.m. and 2:00 a.m. After 2:00 a.m. the filters were receiving mostly water from the reservoir. Electrical conductivity (EC) was another parameter monitored during the 24-hour test. The variation of EC during the 24-hour testing are shown in Figure 48. No significant difference was observed between the conductivity of the reservoir water before filtration (Mean=2.29, SD=0.11) and after filtration (Mean=2.32, SD=0.13), p- value=0.38. In addition, the difference in conductivity between the filter influent (Mean=2.44, SD=0.047) and the filter effluent (Mean=2.43, SD=0.052) for the water from the secondary clarifiers was not significant, p-value= In general, the EC was observed within the range of 2.1 and 2.6 ms/cm. Using the relationship between EC and TDS proposed by Walton (1989), the corresponding TDS values ranged from approximately 1500 to 1800 mg/l. Results were slightly higher than the previous two 12- hour tests. The results for TDS were compared with the guidelines for interpretation of water quality for irrigation purposes reported by Tchobanoglous et al. (1998). According to the results, the water retuning from the reservoir presents a slight to moderate salinity which is an acceptable reuse water for irrigation.

123 110 Variations in water temperature for water returning from Huffaker Reservoir, the effluent from the secondary clarifiers, and the effluent from the chlorine contact basin during September 24-25, 2015 are presented in Figure 49. Hourly air temperatures were obtained from the National Weather Service. The temperature of the water returning from the reservoir ranged from 16 to 21 C, which was slightly lower than the range of temperature (20 to 27 C) observed during the two 12-hour tests conducted on July and August 6, Temperature of the effluent from the secondary clarifiers was typically higher than the temperature of the water returning from the reservoir. The highest temperature of the secondary clarifier effluent was observed to be 24 C at 4:30 p.m. which corresponded to at the highest air temperature of the day which was 32 C. In general, temperature of the secondary clarifier was within the range of 21 to 24 C. This range is consistent with the mean temperature of wastewater in the United States during the month of September (Metcalf & Eddy, 2013). During the day, temperature of the water was lower than temperature of the air because water has a higher specific heat capacity than air. Specific heat capacity is defined as the ability of a medium to store (or absorb) heat (J) per unit change in temperature ( C) of the medium and per unit mass (kg). In fact, one gram of water has to absorb Joules of heat for its temperature to increase 1 degree celsius ( C). In contrast, the specific heat capacity of the air is Joules per gram per C (Kaviany, 2001). During early morning and during the night, the temperature of the water returning from the reservoir was within the range of 17 to 19 C. Water samples for total suspended solids (TSS), total organic carbon (TOC) and UV absorbance were collected every hour, stored in coolers, and analyzed within 24

124 111 hours after collection. Sample locations included the filter influent and the filter effluent for both the effluent from the secondary clarifiers and the water returning from Huffaker Reservoir (when the water reuse pumping system was on), and the effluent from the chlorine contact basin. Variations of TSS over the 24-hour sampling period is depicted in Figure 50. According to the results, the filtered effluent was in compliance with both the federal (U.S. EPA, 2012) and state (Legislative Counsel State of Nevada, 2015) regulations for total suspended solids of a maximum of 30 mg/l. The upflow filters reduced the TSS for both the water returning from reservoir and the clarifiers effluent. However, for the samples collected from the reservoir at 9:00, 11:00 and 12:00 a.m., the TSS of the filtered effluent was higher than the TSS of the filters influent. Hence, the results indicate that the performance of the Parkson DynaSand filters was inconsistent for TSS removal. Similar trends were observed when analyzing TSS during the previous 12-hour water quality tests. The treated effluent that was disinfected and then pumped into Huffaker Reservoir was also monitored for TSS. The results indicated that the TSS of the filtered water dropped from 5.1 mg/l at 5:00 p.m. to 2.5 mg/l at 9:00 p.m. as the flow passed through the chlorine contact basin. This suggested that the chlorine contact basin allows for some settling of solids within the basin. This observation was consistent with the results for turbidity in the effluent from chlorine contact basin which were discussed earlier and also with the TSS and turbidity analyses during the previous 12-hour water quality tests. The filter loading rate was around 1.7 gpm/ft 2 when the reuse pumps were off and

125 TSS (mg/l) Filter loading rate (gpm/ft 2 ) Filter influent reservoir water :00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Water reuse pumps on Figure 50. Variations of TSS of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin, including filter loading rates during September 24-25, Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers Chlorine contact basin effluent Filter loading rate

126 113 about 3.2 gpm/ft 2 when the reuse pumps were on. The results indicate that the higher filter loading rate may be associated with higher turbidities. Implementing a coagulation/flocculation process, followed by sedimentation for the water returning from the reservoir may improve removal of TSS in the existing Parkson DynaSand filters and reduce the accumulation of solids within the chlorine contact basin. Variations in dissolved organic carbon (DOC) with time for the different sampling locations is presented in Figure 51. The difference between the DOC of the filter influent (Mean=23.2, SD=9.17) and the DOC of the filter effluent (Mean=23.5, SD=12.05) for the water returning from the reservoir was not significant, p- value=0.9476; therefore, the upflow filters did not remove dissolved organic carbon. The DOC of the water returning from the reservoir ranged from 6 to 45 mg/l. As previously explained, TOC is an indicator of NOM concentration. In this case, the organic matter found in the reservoir likely consists of natural organic substances resulting from the decay of algae and other aquatic organisms (Mackenzie, 2010). High DOC concentrations (above 15 mg/l) were also observed at the effluent of the chlorine contact basin. As a result, it is likely that trihalomethane (THM) concentrations are elevated as well. THMs are formed when a water containing an organic precursor is chlorinated. In this case, the precursor is any organic compound capable of reacting to produce a THM. However, the plant effluent is for irrigation purposes and not for drinking water, so THMs are not currently regulated. Variations in UV absorbance at 254 nm with time are presented in Figure 52. Results were compared with typical UV absorbance values at 254 nm reported by

127 114 Metcalf & Eddy (2013), which were given in Table 3 in Section The UV absorbance of the effluent from the secondary clarifiers ranged from to cm -1, which was within the typical absorbance range of 0.15 to 0.35 cm -1 for effluent from secondary wastewater treatment processes. UV absorbance readings of filtered secondary clarifiers varied from to cm -1, which was also consistent with the typical range of 0.10 to 0.25 cm -1 for filtered effluent from secondary wastewater treatment processes.

128 Dissolved total organic carbon (mg/l) Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers Chlorine contact basin effluent 0 8:00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps on Water reuse pumps off Figure 51. Variations in dissolved total organic carbon of filter influent and filter effluent (for effluent from secondary clarifiers and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, 2015.

129 UV absorbance (cm -1 ) Filter influent reservoir water Filter effluent reservoir water Filter influent secondary clarifiers Filter effluent secondary clarifiers Chlorine contact basin effluent :00 AM 11:00 AM 2:00 PM 5:00 PM 8:00 PM 11:00 PM 2:00 AM 5:00 AM 8:00 AM Water reuse pumps on Pumping system to reservoir on Water reuse pumps off Water reuse pumps on Figure 52. Variations in UV absorbance at 254 nm of filter influent and filter effluent (for effluent from secondary clarifiers, and water returning from the reservoir), and the effluent from the chlorine contact basin during September 24-25, 2015.

130 hour water quality testing in July, August, and September 2016 The influent and effluent water quality of the Parkson DynaSand filters were monitored over a 24-hour period. ISCO Portable Auto Samplers (model 913 High Capacity Power Pack 120-volt) were set up to collect samples every hour. Samples were collected from four different locations: the filter influent and filter effluent for water returning from Huffaker Reservoir as well as the filter influent and filter effluent for effluent from the secondary clarifiers (Figure 53). Water samples were analyzed for turbidity and UV absorbance at 254 nm. These results were compared with the California Department of Public Health Recycled Water Regulations (Title 22 Code of Regulations, Section Filtered wastewater). A B D C Figure 53. Sampling locations for 24-hour water quality test in A) secondary clarifiers effluent, B) filter effluent of secondary clarifiers, C) water returning from the reservoir, and D) filter effluent of reservoir water.

131 Turbidity (NTU) Filter loading rate (gpm/sq ft) hour water quality test on July 6-7, 2016 The results for the 24-hour testing performed on July 6-7, 2016 are presented in Figure 54. Water samples were collected every hour starting at 9:00 a.m. on July 6, 2016 and finishing at 8:00 a.m. on July 7, Water returning from the reservoir was pumped into the reuse distribution system between 10:00 p.m. until 2:00 p.m. on the following day. During this period, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir. Reuse system pumps were turned off at 2:00 p.m. Between 2:00 p.m. and 10:00 p.m., the filters only received water from the secondary clarifiers :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on Clarifier Effluent Turbidity Filtered Clarifier Effluent Turbidity Filter Loading Rate Figure 54. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 6-7, 2016). 0.0 Raw Reservoir Turbidity Filtered Reservoir Water Turbidity

132 119 The results showed that the quality of the water from the secondary clarifiers was generally better than the water returning from the reservoir. The Parkson DynaSand filters noticeably reduced the turbidity of the effluent from the secondary clarifiers with an average turbidity of 1.4 ± 0.4 NTU. Since the average effluent turbidity was below the 2 NTU within the 24-hour period, coagulation would not be required for the water coming from the secondary clarifiers. However, in the case of water returning from the reservoir, the filter influent turbidity exceeded the permit limitation of 5 NTU during more than 15 minutes and the average effluent turbidity of 3.9 ± 0.8 NTU exceeded 2 NTU within the 24-hour period. Hence, the quality of the water returning from the reservoir is not in compliance with the Recycled Water Regulations established by the California Department of Public Health (Title 22 Code of Regulations, Section ). Thus, coagulation should be implemented as part of the treatment process to enhance the performance of the upflow filters. Furthermore, the increases in the effluent turbidities from the filters generally corresponded with higher filter loading rates, especially from midnight until 6:00 a.m hour water quality test on July 18-19, 2016 The results for the 24-hour testing performed on July 18-19, 2016 are presented in Figure 55. Water samples were collected every hour starting at 9:00 a.m. on July 18, 2016 and finishing at 8:00 a.m. on July 19, Water returning from the reservoir was pumped into the reuse distribution system between 9:00 p.m. until 2:00 p.m. on the following day. During this period, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir. Reuse system

133 Turbidity (NTU) Filter loading rate (gpm/sq ft) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Figure 55. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 18-19, 2016). pumps were turned off at 2:00 p.m. Between 2:00 p.m. and 9:00 p.m., the filters only received water from the secondary clarifiers. The variations in turbidity indicate that the quality of the water from the secondary clarifiers is noticeably better than the quality of the water returning from the reservoir. In the case of the water from the secondary clarifiers, the filter effluent turbidity was typically below 2 NTU, and reached a maximum of 2.9 NTU at 6:00 a.m. and a minimum of 0.9 NTU at 2:00 a.m. The average filter effluent turbidity was 1.7 ± 0.6 NTU. Clarifier Effluent Turbidity Filtered Clarifier Effluent Turbidity Filter Loading Rate Water reuse pumps on 0.0 Raw Reservoir Turbidity Filtered Reservoir Return Turbidity

134 121 The existing Parkson DynaSand filters did not effectively reduce the turbidity of the water returning from the reservoir. The results indicated that the filter influent turbidity exceeded the allowable maximum of 5 NTU for more than 15 minutes. The turbidity of the filter effluent varied within the range of 2.1 and 4.1 NTU with an average of 2.9 ± 0.6 NTU suggesting that the filter effluent turbidity did not meet the regulation of an average of 2 NTU within the 24-hour period. Hence, coagulation should be implemented as part of the treatment process to improve the water quality of the water returning from the reservoir. The filter loading rate was about 4 gpm/ft 2 when the water reuse pumps were on and about 1.6 gpm/ft 2 when the reuse pumps were off. The rapid increase in filter loading rate may influence effluent turbidities. It could be beneficial to minimize rapid changes in filter loading rates, for example, by adding more filters. Variations in UV absorbance at 254 nm with time are presented in Figure 56. Results were compared with typical UV absorbance values at 254 nm reported by Metcalf & Eddy (2013), which were given in Table 3 in Section The UV 254 readings of filtered secondary clarifiers varied from 0.10 to 0.15 cm -1, which was consistent with the typical range of 0.10 to 0.25 cm -1 for filtered effluent from secondary wastewater treatment processes. The UV absorbance of the water from the secondary clarifiers ranged from 0.13 to 0.16 cm -1, which was mostly within the typical absorbance range of 0.15 to 0.35 cm -1 for effluent from secondary wastewater treatment processes.

135 UV absorbance (cm -1 ) Raw reservoir water Filtered reservoir Clarifier effluent Filtered clarifier :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on Figure 56. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (July 18-19, 2016) hour water quality test on August 10-11, 2016 The results for the 24-hour testing performed on August 10 11, 2016 are presented in Figure 57. Water samples were collected every hour starting at 9:00 a.m. on August 10, 2016 and finishing at 8:00 a.m. on August 11, Reuse water was being pumped into the reuse distribution system from 10:00 p.m. until 1:00 p.m. During this period, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir. Reuse system pumps were turned off at 1:00 p.m. Between 1:00 p.m. and 10:00 p.m., the filters only received water from the secondary clarifiers.

136 123 There were no noticeable differences between the water quality of the filter effluent of secondary clarifiers and the filter effluent of water returning from the reservoir. The turbidity of the filter effluent for the secondary clarifiers varied within the range of 1.9 to 9.7 NTU with an average of 2.8 ± 1.5 NTU. In the case of the water returning from the reservoir, the turbidity of the filter effluent varied within the range of 1.8 to 3.4 NTU with an average of 2.6 ± 0.4 NTU. According to the Title 22, Section , the turbidities of the filter effluent for the secondary clarifiers and the water returning from the reservoir did not meet the regulation of an average of 2 NTU within the 24-hour period. The results from the 24-hour testing performed on August 10 11, 2016 differed from the results of the 24-hour water quality tests conducted in July 6-7, 2016 and July 18-19, 2016 which concluded that the quality of the water from the secondary clarifiers was noticeably better than the quality of the water returning from the reservoir. The filter loading rate was observed around 1.8 gpm/ft 2 when the reuse system pumps were off and then increased to 4.0 gpm/ft 2 after the water reuse pumps were turned on. The rapid increase in filter loading rate may influence the filtered turbidities of the water from the secondary clarifiers and the water returning from the reservoir. Figure 58 illustrates the variations in UV absorbance at a wavelength of 254 nm during the 24-hour water quality test in August 10-11, The UV absorbance of the effluent from the secondary clarifiers ranged from 0.13 to 0.16 cm -1, which was mostly within the typical absorbance range of 0.15 to 0.35 cm -1 for effluent from secondary wastewater treatment processes (Metcalf & Eddy, 2013). UV absorbance readings of

137 Turbidity (NTU) Filter loading rate (gpm/sq ft) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on 0.0 Clarifier Effluent Turbidity Raw Reservoir Turbidity Filtered Clarifier Effluent Turbidity Filtered Reservoir Water Turbidity Filter Loading Rate Figure 57. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 10-11, 2016). filter effluent from the secondary clarifiers varied from 0.10 to 0.14 cm -1, which was also consistent with the typical range of 0.10 to 0.25 cm -1 for filtered effluent from secondary wastewater treatment processes (Metcalf & Eddy, 2013). The UV absorbance for the filter effluent was generally lower than the filter influent, indicating that upflow filters were able to remove some fraction of matter in the water from the secondary clarifiers that absorbs at UV 254.

138 UV absorbance (cm -1 ) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Raw reservoir water Clarifier effluent Water reuse pumps on Filtered reservoir Filtered clarifier Figure 58. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 10-11, 2016) hour water quality test on August 24-25, 2016 The results for the 24-hour testing performed on August 24 25, 2016 are presented in Figure 59. Water samples were collected every hour starting at 9:00 a.m. on August 24, 2016 and finishing at 8:00 a.m. on August 25, Water returning from the reservoir was pumped into the reuse distribution system between 11:00 p.m. until 2:00 p.m. on the following day. During this period, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir. Reuse system pumps were turned off at 2:00 p.m. Between 2:00 p.m. and 11:00 p.m., the filters only received water from the secondary clarifiers.

139 126 The results showed that the quality of the water from the secondary clarifiers was generally better than the water returning from the reservoir. The Parkson DynaSand filters reduced the turbidity of the effluent from the secondary clarifiers to an average of 2.3 ± 0.8 NTU. However, since the filter effluent turbidity exceeded the regulation of an average of 2 NTU within the 24-hour period, coagulation process could be implemented as part of the treatment in order to enhance the performance of the filters. No significant differences were found between the turbidity of the water before filtration (Mean=2.5, SD=0.4) and after filtration (Mean=2.3, SD=0.8), p-value= The water returning from the reservoir was also monitored. The turbidity of the filter effluent was typically within the range of 2.9 to 4.1 NTU with an average of 3.4 ± 0.3 NTU. The water returning from the reservoir was above 5 NTU from 12:00 p.m. until 2:00 p.m. Hence, the quality of the water returning from the reservoir was not in compliance with the Recycled Water Regulations established by the California Department of Public Health (Title 22 Code of Regulations, Section ). Since the effluent turbidity exceeded an average of 2 NTU within the 24-hour period, and the influent turbidity exceeded 5 NTU for more than 15 minutes, coagulation should be implemented as part of the treatment process to enhance the performance of the upflow filters. The increase in filtered turbidity of the secondary clarifiers above 2 NTU that was observed between 3:00 a.m. and 8:00 a.m. may be related with the rapid increase in filter loading rate from around 1.9 gpm/ft 2 when the reuse system pumps were off to 3.3 gpm/ft 2 once the water reuse pumps were turned on. Figure 60 illustrates the variations in UV absorbance at a wavelength of 254 nm for filter influent and effluent of water from the secondary clarifiers and water returning

140 Turbidity (NTU) Filter loading rate (gpm/sq ft) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on Clarifier Effluent Turbidity Filtered Clarifier Effluent Turbidity Filter Loading Rate Raw Reservoir Turbidity Filtered Reservoir Water Turbidity Figure 59. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 24-25, 2016). from the reservoir. Results were compared with typical UV absorbance values at 254 nm reported by Metcalf & Eddy (2013), which were given in Table 3 in Section The UV 254 absorbance of the effluent from the secondary clarifiers ranged from to cm -1, which was within the typical absorbance range of 0.15 to 0.35 cm -1 for effluent from secondary wastewater treatment processes. UV absorbance readings of filtered secondary clarifiers varied from 0.12 to 0.16 cm -1, which was also consistent with the typical range of 0.10 to 0.25 cm -1 for filtered effluent from secondary wastewater treatment processes. No seasonal variations of UV absorbance were observed for the water returning from the reservoir and the effluent from the secondary clarifiers.

141 UV absorbance (cm -1 ) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on Raw reservoir water Clarifier effluent Filtered reservoir water Filtered clarifier Figure 60. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (August 24-25, 2016) hour water quality test on September 8-9, 2016 The results for the 24-hour testing performed on September 8 9, 2016 are presented in Figure 61. Water samples were collected every hour starting at 9:00 a.m. on September 8, 2016 and finishing at 8:00 a.m. on September 9, Reuse system pumps were turned off at 2:00 p.m. Between 2:00 p.m. and 11:00 p.m., the filters only received water from the secondary clarifiers. When the water reuse pumps were on, the upflow Parkson DynaSand filters were receiving water from secondary clarifiers and water returning from the reservoir.

142 129 The results indicated that the upflow filters did not effectively reduce turbidity. In general, the turbidity of water returning from the reservoir during this period was relatively high. The highest filter influent turbidity corresponded to 5.2 NTU and the lowest was 3.7 NTU. The turbidity of the filter effluent varied from 2.4 to 6.6 NTU. Since the average turbidity of the filer effluent was 3.5 ± 1.0 NTU, the filter effluent turbidity did not meet the regulation of an average of 2 NTU within a 24-hour period. Hence, implementing coagulation of the water returning from Huffaker Reservoir prior to filtration is recommended to improve the water quality of the filter effluent. The water from the secondary clarifiers was also monitored. The turbidity of the filter effluent was typically within the range of 2.0 to 2.6 NTU with an average of 2.3 ± 0.2 NTU. Since the effluent turbidity exceeded an average of 2 NTU within the 24-hour period, the quality of the filtered water was not in compliance with the Recycled Water Regulations established by the California Department of Public Health (Title 22 Code of Regulations, Section ). Therefore, implementing coagulation of the water from the secondary clarifiers is recommended. No definitive relationships between the higher filter loading rates and the turbidities of the filter effluent were observed. Variations in UV absorbance at 254 nm during the 24-hour water quality test are presented in Figure 62. Results were compared with typical UV absorbance values at 254 nm reported by Metcalf & Eddy (2013), which were given in Table 3 in Section The UV absorbance of the effluent from the secondary clarifiers ranged from 0.14 to 0.17 cm -1, which was within the typical absorbance range of 0.15 to 0.35 cm -1 for effluent from secondary wastewater treatment processes. UV absorbance readings of filtered water from the secondary clarifiers varied from 0.13 to 0.16 cm -1, which was also

143 Turbidity (NTU) Filter loading rate (gpm/sq ft) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Water reuse pumps on Clarifier Effluent Turbidity Filtered Clarifier Effluent Turbidity Filter Loading Rate Figure 61. Variations in turbidity for filter influent and effluent of secondary clarifiers and water returning from the reservoir (September 8-9, 2016). consistent with the typical range of 0.10 to 0.25 cm -1 for filtered effluent from secondary wastewater treatment processes. A decrease in absorbance of the filter effluent for water returning from the reservoir was observed from 0.15 cm -1 at 11:00 p.m. to 0.08 cm -1 at 2:00 a.m. The decrease of UV absorbance was due to the filters receiving mostly water from the secondary clarifiers at 11:00 p.m. After the water reuse pumping system was turned on at 11:00 p.m., the treatment plant started to receive water returning from the reservoir. The reservoir water gradually displaces the secondary clarifier effluent within the filters at Raw Reservoir Turbidity Filtered Reservoir Return Turbidity

144 UV absorbance (cm -1 ) :00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 Water reuse pumps on Water reuse pumps off Raw reservoir water Clarifier effluent Figure 62. Variations in UV absorbance at 254 nm for filter influent and effluent of secondary clarifiers and water returning from the reservoir (September 8-9, 2016). location D in Figure 53. The transition from effluent from the secondary clarifiers to water returning from the reservoir occurred between 11:00 p.m. and 2:00 a.m. After 2:00 a.m., the filters were receiving mostly water from the reservoir. Water reuse pumps on Filtered reservoir Filtered clarifier 4.9 Reservoir water quality monitoring in July, August, and September 2016 Routine in-situ monitoring of water quality in Huffaker Reservoir was performed for ph, turbidity, temperature, and dissolved oxygen (DO). Water samples were collected every two weeks from July 7, 2016 through September 29, 2016, within the time period between 8:00 a.m. and 10:00 a.m. Samples were collected from three water depths (i.e., 5 ft below surface, mid-depth, and 5 ft above bottom) using a Wildco vertical water

145 132 sampler (Wildlife Supply Company, model 1120-G45). The two sampling locations are shown in Figure 63. Location A was the deepest section of the reservoir. Location C was located at a shallower area of the reservoir near the dam. Samples from locations A and C were compared to determine if the water quality in the reservoir varies with water depth and location. Figure 63. Sampling locations A and C in Huffaker Reservoir. The water depth in the reservoir gradually decreased over time as the irrigation season progressed through the summer and into the fall. Location C was the first to get too shallow and eventually dried up by the end of September. Analyses of the water quality data were done using Excel in combination with D- Plot to create the isopleths (or contour lines) depicting the various water quality parameters. The vertical axis represents the water depth in feet measured from the bottom of the reservoir.

146 133 The vertical distribution of turbidity with water depth at locations A and C is given in Figure 64. In general, the water quality in the reservoir decreased as the water depth in the reservoir decreased as the irrigation season progressed. At location C, turbidity values indicated some stratification from mid-july until mid-august. Lower turbidities were observed in the range of 0.8 to 1.7 NTU within the first 19 feet below the water surface. The turbidity of the water at the bottom ranged between 1.7 and 6.5 NTU. Sedimentation of particles near the bottom of the reservoir could contribute to higher turbidity. The water in location A was vertically mixed because it was too shallow to sustain stratification as suggested in previous studies by Zhang et al. (2015) and CH2M HILL (2012). The ph of the water in the reservoir varied from ph 7.0 to around ph 10.0 as indicated in Figure 65. The results indicated that the ph of the water increased as the irrigation season progressed. As previously discussed in Section 4.6, the increase in the ph of the water is consistent with photosynthesis of algae present in the reservoir and the presence of ammonia (CH2M HILL, 2012).

147 134 Figure 64. Variations in turbidity (NTU) with depth for location A (left) and location C (right). Figure 65. Variations in ph of the water with depth for location A (left) and location C (right). Variation of temperature with depth is depicted in Figure 66. During July and August, thermal stratification was observed in the reservoir. The highest water temperature at location A was around 24ºC at a water depth 5 ft below surface in the mid- August. In September, the reservoir was more vertically mixed because water depth became too shallow to sustain thermal stratification (CH2M HILL, 2012).

148 135 Figure 66. Variations in temperature (ºC) with depth (ft) from the bottom for location A (left) and location C (right). The concentrations of dissolved oxygen were monitored over the period of August 3, 2016 through September 29, Figure 67 presents the vertical distribution of DO concentrations at locations A and C. Over the two-month sampling period, the average DO concentration at locations A and C at a depth of 5 ft below the water surface were 12.7±3.2 mg/l and 12.9±3.6 mg/l, respectively. Anoxic conditions were found near the bottom of the reservoir where the DO was observed to be lower than 2 mg/l (the critical value for anoxia) by the beginning of August at location A and the middle of August at location C. These results are similar to those observed in other natural deep water lakes (e.g., Lake Valkea-Kotinen, Finland and Lake Kinneret, Israel) where DO concentrations were near zero in the benthic zones (Zhang et al., 2015). Initially, the DO concentrations appeared to be stratified at both locations A and C. The DO concentration at 5 feet below the water surface at location C remained at approximately 12.1±1.7 mg/l and then decreased to an average of 2.7±1.1 mg/l near the

149 136 bottom of the reservoir. Thermal stratification was also observed at locations A and C during August as indicated in Figure 68. Toward the beginning of September, the water was less stratified and DO concentrations did not vary with water depth at location A. Minor variations with depth were observed at location C. As previously discussed, by the beginning of September the water depth at the reservoir was too shallow to sustain thermal stratification at locations A and C (Figure 68). Therefore, the DO stratification was correlated with the thermal stratification, which was consistent with previous studies by CH2M HILL (2012), and Zhang et al. (2015) as described in Section Figure 67. Variations in dissolved oxygen (mg/l) with depth (ft) for location A (left) and location C (right).

150 Figure 68. Variations in temperature (ºC) with depth (ft) from the bottom for location A (left) and location C (right) from August 3, 2016 through September 29,