NITRIFICATION PERFORMANCE OF A MODIFIED AERATED LAGOON. A Thesis presented to the faculty of the Graduate School at the

Transcription

1 NITRIFICATION PERFORMANCE OF A MODIFIED AERATED LAGOON A Thesis presented to the faculty of the Graduate School at the University of Missouri Columbia In Partial Fulfillment of the Requirements for the Degree Master of Science By KANCHANA MAGULURI Dr. Thomas E. Clevenger, Thesis Supervisor MAY 2007

2 The undersigned, appointed by the dean of the Graduate School, have examined the thesis entitled NITRIFICATION PERFORMANCE OF A MODIFIED AERATED LAGOON presented by Kanchana Maguluri, a candidate for the degree of master of science, and hereby certify that, in their opinion, it is worthy of acceptance. Professor Thomas E. Clevenger Associate Professor Kathleen Trauth Professor Ron Belyea

3 ACKNOWLEDGEMENTS I would like to thank the faculty of Civil and Environmental Engineering for their support throughout this project. I would like to extend my special thanks to Dr. Clevenger for his timely encouragement and valuable guidance as advisor, Dr. Reed for providing insights of the sewage treatment processes, Dr.Vikram Pattarkine and Mr. Randy Chann, Environmental Dynamics Inc., for funding and giving me an opportunity to work on this project, and Mr. Kevin D. Wilkerson of the Village of Kingdom City for providing information about the Kingdom City lagoon. I am thankful to Dr. Kathleen Trauth and Dr. Ron Belyea for serving on my committee. Mr. Dan Crosby provided much help in the lab and field. Lastly I would like to thank my parents, sister and brother for being on my side all the times and giving me moral support, and my friends, especially Alex and Shri, for their technical comments and discussions which helped me accomplish this project. ii

4 TABLE OF CONTENTS ACKNOWLEDGEMENTS... ii LIST OF ILLUSTRATIONS...v LIST OF TABLES... vii ABSTRACT... viii CHAPTER 1. INTRODUCTION OVERVIEW: AERATED LAGOONS, FIXED FILMS OBJECTIVES LITERATURE REVIEW AMMONIA BIOCHEMICAL OXYGEN DEMAND FIXED FILMS EXPERIMENTAL METHODS MATERIALS METHODS AMMONIA NITRITE NITRATE TSS AND VSS BIOLOGICAL OXYGEN DEMAND CHEMICAL OXYGEN DEMAND ALKALINITY...27 iii

5 4. RESULTS AND DISCUSSIONS AMMONIA NITRATE TOTAL SUSPENDED SOLIDS BIOCHEMCIAL OXYGEN DEMAND CONCLUSIONS AMMONIA BOICHEMICAL OXYGEN DEMAND TOTAL SUSPENDED SOLIDS NITRATE...44 REFERENCES...46 APPENDICES APPENDIX 1: RAW DATA...49 APPENDIX 2: CHARTS...53 iv

6 LIST OF ILLUSTRATIONS Figure Page 1. Biochemical oxygen demand curves Overview of the Kingdom City wastewater lagoon A view of the fixed films installed at Kingdom City Sample collection from influent Partial mix zone Sample collection from partial mix zone Quiescent zone in Kingdom City lagoon Effluent outlet at Kingdom City lagoon ph and alkalinity values in the effluent zone of the lagoon Ammonia concentration in all the zones % Removal rates of Ammonia across the lagoon Temperature and ammonia relationship in effluent Removal rates of ammonia and SBOD values in effluent Nitrate levels across the lagoon Plot displaying the concentrations of ammonia and nitrate in effluent Total suspended solids across the lagoon Effluent TSS vs VSS TSS vs TBOD in the effluent zone...38 v

7 19. % removal rates of BOD in the lagoon Influent TBOD, effluent TBOD, and effluent SBOD Effluent temperature and BOD of the lagoon Effluent SBOD 5 and SCOD in the lagoon COD/BOD 5 in effluent zone of the lagoon...43 vi

8 LIST OF TABLES Tables Page 1. Nitrogen concentrations of different types of domestic sewage Flow data for Kingdom City lagoon Percentage removal rates of ammonia Percentage removal of BOD 5 in the lagoon...40 vii

9 NITRIFICATION PERFORMANCE OF A MODIFIED AERATED LAGOON Kanchana Maguluri Thomas E. Clevenger, Academic Advisor ABSTRACT The performance of a modified wastewater lagoon and the factors affecting the treatment process are discussed. This study was conducted over a period of twelve months at the Kingdom City, Missouri lagoon. A polyethylene fixed film media was incorporated in the lagoon to modify its waste treating ability. However, further study of the performance of the lagoon would be required to assess the effectiveness of the media in treating the wastes. The study recognizes the affect of seasonal changes on the treatment process. Analysis of various characteristics of wastewater such as ammonia, biochemical oxygen demand (BOD 5 ), nitrites, nitrates, total suspended solids (TSS), volatile suspended solids, chemical oxygen demand, and alkalinity were performed during the study period. The parameters of ph, dissolved oxygen concentration, and temperature were monitored at the time of sample collection in the field. Results indicate that the average ammonia removal rate was 87% and 98% removal rates were achieved during the summer. It was observed that nitrification is greatly influenced by temperature. Eighty four percent of BOD 5 was removed on an average and the lagoon was able to maintain low BOD 5 values during The concentration of nitrate was consistent with nitrification levels. An average of 86% of TSS was removed from the lagoon during the study period. The study provides good preliminary data for evaluating the performance of a lagoon. The advancement of wastewater treatment technology in lagoons with the help of fixed films can be achieved by further studies and monitoring of the lagoon based upon the current observations. viii

10 CHAPTER 1 INTRODUCTION (a) Overview: Aerated lagoons, fixed films Aerated lagoons are common wastewater treatment facilities in small communities. Traditionally, lagoons are designed to stabilize organic wastes by biochemical oxidation and therefore have been focused on biochemical oxygen demand (BOD 5 ) and total suspended solids (TSS) removal. Most facilities are not designed for ammonia removal. As a result, the effluent waters have elevated amounts of ammonia which create a toxic environment for aquatic life, regulatory non-compliance and other environmental problems. Lately, stringent limits on effluent ammonia levels have required the upgrading of old lagoon systems and lagoon technology has given way to the innovation of more costly technologies for the removal of ammonia. Incorporation of fixed films in a lagoon is one of the technologies being developed to improve the efficiency of facilities. They require minimal costs compared to upgrading the lagoons to a secondary treatment process unit. Aerated lagoons are cost effective and simple in operation. Wastewater treatment is achieved in these facilities by either natural processes or through mechanical sources. Different lagoon processes designed for treating wastewater are oxidation (or facultative) lagoons, aerated flow through lagoons with partial mixing, aerated completely mixed lagoons with solids recycle and aerated complete mixed lagoons. They are characterized by distinctive hydraulic flow patterns, hydraulic loading rates, flow rates, and by the way 1

11 solids are handled. Oxidation lagoons are designed for shallow depths to permit light to penetrate for the photosynthetic activity of algae. The sources of oxygen are algae activity and wind action at the liquid surface. Facultative lagoons are aerobic near the surface with an oxygen gradient to anaerobic conditions near the bottom. Partial mix lagoons use mechanical aerators to supply sufficient oxygen for the biological degradation of organic waste. The aeration equipment does not keep all the solids in suspension and results in the accumulation of sludge at the bottom of the lagoon. The hydraulic and solids retention times are the same in these lagoons. Solids are removed prior to the discharge in a sedimentation zone. Unlike the activated sludge process, recirculation of the solids is not required, as most of the active biomass would be retained within the lagoon. Aerated lagoons with solids recycle are similar to an activated sludge process. Higher energy is provided when compared to partial mix lagoons to keep all of the solids in suspension. Turbulent conditions and a lack of light penetration reduce the growth of algae in the basin. To increase the efficiency of aerated lagoons without adopting costly treatment processes the concept of fixed films can be considered to get better results. The nitrifying bacteria attach and colonize any suitable surfaces where the nutrients are abundant. This principle is used in the fixed films systems where the bacteria is present as a film on an inert and solid medium. This technology is considered cost effective than the secondary treatment process. Aerated lagoons with integrated fixed films are being developed to be effective in accelerating nitrification, removal of other nutrients and increasing effluent quality. 2

12 The microbial biomass grows as a layer on the surface of the inert and solid fixed film. The wastewater is allowed to flow past the film and come in contact with the film to achieve the required stabilization of the nitrogenous wastes. The fixed film should provide an extensive surface to support the biological film for the purification of wastewater. Fixed films could have either mineral or plastic as their media. Plastic fixed films have many advantages over the mineral media. They possess a high specific surface area, are light weight, and are immune to blockages due to accumulated microbial film. Mineral media because of its less voidage allows less oxygen to penetrate through the media and gets clogged after a period of time. It needs to be replaced from time to time. Mineral media is heavier than plastic media. Plastic media is about 10% of the weight of mineral media whereby it significantly cuts the capital cost of building the media. Plastic fixed films have the ability to treat high hydraulic and organic loads and allow thorough aeration. They should be chemically inert, durable, possess high physical strength to support sufficient biomass and light bulk density to reduce structural costs, uniform configuration and must be cost effective. The Kingdom City, Missouri lagoon is a partial mix aerated lagoon which started its operations in The town is mainly residential with 100 houses, a few restaurants, and a couple of gas stations. Water consumption of the town is 85, ,000 gpd. On average, the lagoon discharges nearly 80,000 gallons/day of wastewater. Mechanical aeration is provided by an Environmental Dynamics Inc. FlexAir system. The lagoon is 620 feet in length and 250 feet in width. It is divided into three zones: partial mix zone 1, partial mix zone 2, and a quiescent zone. Flex-air diffusers are provided in the two partial 3

13 mix zones. Retention time in the lagoon is 60 days. As in the regular lagoons, the Kingdom City lagoon experiences low nitrification rates during winter. In order to overcome this problem, Environmental Dynamics Inc. has installed polyethylene fixed film media in the lagoon. (b) Objective The objectives of this project are to : 1. Provide background and preliminary data. 2. Evaluate the performance of the Kingdom City lagoon for the removal of biochemical oxygen demand (BOD 5 ), chemical oxygen demand (COD), ammonia, nitrate (nitrite), and total suspended solids (TSS), and 3. Monitor ph, alkalinity, VSS, and temperature in order to explain removal rates. 4

14 Chapter 2 Literature Review 2.1 Ammonia The greatest contaminant concentrations in domestic wastes are typically organic carbon followed by organic nitrogen. The organic nitrogen is readily converted into ammonium in the wastewater. Urea present in the wastewaters is hydrolyzed by urease enzyme to release ammonia in the form of ammonium carbonate. Total nitrogen removal takes place due to nitrification, denitrification, assimilation, and probably due to ammonia stripping (Al-Nozaily and Alaerts, 2000). Ammonia poses a serious threat to fish as it depletes oxygen in the receiving waters. The availability of nitrogen in the lagoons can contribute to eutrophication and nitrate is a potential health hazard in water consumed by infants (Sedlak). Nitrogen concentrations in different types of wastes can be seen in Table 1. It is biologically removed in the lagoons through nitrification in which ammonia is first oxidized to nitrite under aerobic conditions and then nitrite is oxidized to nitrate. This biological oxidation of ammonia to nitrate is carried out by autotrophic bacteria (nitrosomonas and nitrobacter) which oxidize inorganic compounds (ammonia or nitrite) for energy, use oxygen as a terminal electron acceptor, use ammonia as source of nitrogen and utilize carbon dioxide or carbonate as a carbon source (Campbell and Lees). 5

15 Table 1. Nitrogen concentrations of different types of domestic sewage (Sedlak) Type of Sewage Nitrogen form Strong Medium Weak Organic, mg N/l Ammonia, mg N/l Total, mg N/l Nitrosomonas bacteria are responsible for the oxidation of ammonia to nitrite and the nitrobacter bacteria carry out the oxidation of nitrite to nitrate. The reactions are shown below. + Nitrosomonas + 2 NH 4 + 3O2 2NO2 + 4H + 2H 2O Nitrobacter 2NO + O2 2NO3 2 + New cells Heterotrophic bacteria, which utilize organic matter and release carbon dioxide and water after stabilizing wastes, remove lesser amounts of ammonia. A high BOD loading rate inhibits nitrification due to excess numbers of heterotrophic bacteria in comparison to autotrophic bacteria (Hamoda et al, 1996). Nitrifying bacteria multiply very slowly the doubling time being 2-6 days. The oxidation of one gram of ammonia requires 7.14 g of alkalinity in the form of CaCO 3. Nitrification produces free acid (H + ) thereby reducing the alkalinity. Mild alkaline conditions are required for nitrification of waste in a wastewater treatment plant. A ph ranging from 7.2 to 9.0 would be ideal for nitrification, with an lying optimum value in the range of

16 At ph>9, inhibition of microbial activity occurs and for ph<6, growth of fungi dominates the growth of bacteria. Nitrification is completely inhibited at ph<5. Ammonia is mostly lost due to volatilization at ph>8.5 due to photosynthetic activity (Reed, Crites, Middlebrooks). Unionized ammonia volatilizes at high ph and high temperatures (Kadlec, Knight). Ammonia stripping at ph levels of 7.5 to 8.2 is considerably insignificant (Metcalf and Eddy, 2003) Davies-Colley et al, showed that at ph>9, NH 3 -N exceeds by 40% of the actual value and concentrations exceeding 10 mg/l inhibit algal photosynthesis. Further algal photosynthesis increases the ph and creates a toxic environment for algae. The resulting lower photosynthetic oxygen diminishes the microbial oxidation of soluble organics. The presence of high algal concentrations promotes nitrification and overpowers heterotrophic bacteria which try to retard nitrification (Hurse and Connor, 1999). Rich (1996) observed that algal growth is suppressed by sufficient turbidity levels due to aeration supplied to keep solids in suspension in aerated lagoons. It is observed that attached growth systems can withstand lower temperatures (less than 15 0 C) than suspended growth systems. This is due to the increase in the slime thickness attached to the media. In the range of 5-35 C, biological activity almost doubles for every 10 0 C rise in temperature (Hurse and Connor, 1999). Benefield and Randall (1980) and Barnes et al, (1983) found that above 35 C there would be rapid decrease in the growth rate of nitrifiers which almost falls to zero at 45 C. 7

17 In a study conducted by Surampalli, Ninaroon, and Banerji (1999) it was found that concentrations of all nitrogen forms present in the lagoon decreased with an increase in temperature. Ammonia removal efficiency varied from -67% in April 1991 to 98% in November 1991, with an average of 59%. The settled sludge could have released ammonia-n to the aqueous phase during the spring turnover which could be the reason for the negative percent removal rate in April The increase in temperature was from 9.5 C to 27 C. It was also found that during the spring and fall seasons, the nitrifying bacteria need to adjust to the temperature changes. In the spring, they still might not act as efficiently as expected with rising temperatures and in later fall the removal efficiency will be high. Nitrification is greatly retarded at dissolved oxygen levels of 1 to 2 mg/l. It was found in the studies of Hurse and Connor (1996) that the ammonia removal rates were around 5mg/l at DO concentrations below 1 mg/l. In a pilot study conducted in New Hampshire (Ripple, 2002) using fixed film media, it was found that the fixed film technology may help in enhancing nitrification. It was also found that complete ammonia removal can be achieved at temperatures as low as 3 C. The lagoon system with fixed films achieved summer limits much earlier at the end of spring. For an organic loading of 50g COD m -2 day -1, a maximum ammonia removal rate of 4.5g Nm -2 day -1 was observed in a study conducted in a fixed film reactor. This was very high in comparison to the values reported by Surampalli et al, (1999) for rotating biological contactors (1.5g Nm -2 day -1 ). 8

18 Also, it was reported that nitrification wasn t completely inhibited at high organic loadings (Hamoda et al, 1996). The ammonia removal rate was increased by 54% in a ringlace fixed film reactor compared to a no-media reactor (Sen et al, 1994) Denitrification is a process in which nitrate is converted to gaseous nitrogen via nitrite under low dissolved oxygen conditions. A wide range of facultative anaerobes, unlike nitrification, including pseudomonas and alcaligenes, are responsible for denitrification. Nitrate acts as an electron acceptor and a carbon source acts as an electron donor in the denitrification process (Metcalf and Eddy, 2003) NO 3 NO2 NO N 2O N 2 In the quiescent zone of the lagoon, there is enough organic carbon remaining which aids the process. The quiescent zone is not equipped with air blowers. This zone also acts as the specific denitrification zone in the lagoon. The ph and alkalinity increase in denitrification. For every 1mg of nitrate reduced to nitrogen gas, 3.6 mg of alkalinity as CaCO 3 is produced. This can be seen in the equation below where C 10 H 19 O 3 N represents the biodegradable matter in wastewater (Metcalf and Eddy, 2003) C H O N NO3 5N CO2 + 3H 2O + NH 3 + OH The optimum ph for proper denitrification is in the range of and temperature is C. According to United States Environmental Protection Agency (USEPA), denitrification occurs in a wide range of temperatures ranging from C. The process also releases oxygen into the water, helping the heterotrophic bacteria to reduce organic 9

19 matter in the absence of supplied dissolved oxygen. Sen et al, (1994) found that denitrification rates were high in the aerobic zone of fixed film media reactors when compared to no-media reactors with zero aerobic denitrification. This occurred at DO concentrations above 6 mg/l. It was observed by Goreau et al, (1980) that nitrification occurred at DO as low as 0.18 mg/l but with increased production of nitrous oxide (N 2 O). At low temperatures production of nitrous oxide (N 2 O) was found to be enhanced from to 0.1 mol of N in nitrous oxide compared to the production of nitrite. It was also found that at a DO concentration of 0.15 mg/l, the growth of nitrosomonas bacteria was reduced to one half of its high oxygen value. 2.2 Biochemical Oxygen Demand (BOD 5 ) Carbon that is essential for the growth and biological activity of microorganisms is measured in terms of biochemical oxygen demand (BOD 5 ). The degradable organic form of carbon is the major constituent of wastewater and is calculated by its consumption of dissolved oxygen. BOD 5 represents the amount of dissolved oxygen required by the organisms, mainly bacteria, to biologically oxidize the biodegradable organic matter in the wastewaters in five days. The organic matter is broken down into carbon dioxide and some of it is converted into new cells, while other is oxidized for energy. Waters with high BOD 5 values deplete dissolved oxygen levels in receiving waters. The factors which effect BOD 5 are temperature, low initial bacterial content, soluble and particulate 10

20 organics, solids, presence of nitrifying bacteria, toxic compounds and algae (Standard Methods for the Examination of Water and Wastewater, 2000) Treatability of the wastewaters is ensured by the availability of nutrients (nitrogen and phosphorous) for the growth of bacteria. For carbon: nitrogen: phosphorous weight ratio (C: N: P) of 100:17:5, abundant nutrients would be available for the microorganisms for their survival and growth. Less phosphorous is required by the bacteria than nitrogen. The range of C: P ratio of :1 would be sufficient for the biological treatment of the wastewaters. It was observed that the efficiency of the microorganisms in treating the wastes decreases above 150:1 C: P ratio (Gray, 2004) Nitrogen serves as the second important nutrient to the bacteria. A carbon to nitrogen ratio equal to or less than 18:1 is effective in biological treatment of the wastes. If the C: N: P ratio is not met by the wastes, the addition of nutrients should be carried out to ensure biological oxidation. Jackson and Lives (1972) found that BOD 5 removal in a cider effluent treatment plant was increased from 92 to 99% after the addition of an inorganic supplement to balance the nitrogen and phosphorous proportions. The oxidation of ammonia to nitrate exerts a nitrogenous demand and interferes with BOD 5 determination. The concentration of nitrifying bacteria capable of oxidizing ammonia affects the nitrogenous demand in the BOD 5 test. Usually, raw wastewaters do not contain sufficient numbers of such bacteria to carry nitrification during the 5-day incubation period (Standard Methods for Examination of Water and Wastewater, 2005). 11

21 In raw wastewaters, nitrification becomes significant and exerts oxygen demand after 8-10 days, while in treated effluents, it dominates the oxygen demand after few days (less than 5 days and reduces the oxidation of BOD 5 ). Figure 1 shows the biochemical oxygen demand curve and how it varies over a period of 30 days (Delzer and Mckenzie, 2003). The conversion of ammonia to nitrate requires more than four times oxygen than required for an equal amount of conversion of sugar to carbon dioxide and water (Gray, 2004) Figure 1. Biochemical oxygen demand curves: (A) typical carbonaceous demand curve showing the oxidation of organic matter, and (B) typical carbonaceous and nitrogenous demand curve showing the oxidation of ammonia and nitrite According to the current National Pollution Discharge Elimination System (NPDES) regulatory permits, BOD 5 in an effluent shall not exceed 30 mg/l for a 30 day period. Surampalli, Ninaroon, and Banerji (1999) evaluated the performance of an aerated lagoon in different seasons in the Midwest and observed that there was an average of 75% 12

22 reduction in BOD 5 with a maximum of 97% removal. High BOD removal rates are achieved in summer owing to high reproduction rates of bacteria. Over 90% BOD 5 removal can be observed in summer months which would diminish to 60% in winters (Wright, 1966) in aerated lagoons. In a study conducted by Rich (1996) on modified aerated lagoons, the average effluent BOD 5 value in four years of observation was 11 mg/l and had met the 30 mg/l limit. It was found in the observation studies of 11 domestic sewage lagoons in New Zealand by Davis-Colley et al, (1995) that filtered BOD 5 removal increased 3-fold in summer over winter. It was observed by Surampally, Ninaroon, and Banerji (1999) that the TSS removal was paralleled with the BOD 5 removal during the period of study. It was found that infiltration due to rainfall has an influence on TSS removal. The system under study recorded a TSS value of 28mg/l in May 1991 due to rainfall event. It also recorded higher values in April, May and November 1991, due to presence of chlorophyll a, indicating algae in the effluent samples. The average TSS removal for the lagoon was 73% TSS values increase due to the presence of algae. The presence of algae also increases the turbidity in lagoons. It was observed that every µg of chlorophyll a is equivalent to mg/l of TSS (Hurse and Connor, 1999). Also in the studies conducted by Surampally et al. (1999) high TSS values were recorded in April, May, and November due to the presence of algae. Algal concentrations in lagoons are proportional to hydraulic retention times (Rich, 1996) 13

23 2.3 Fixed films A number of factors influence the growth of microbial films on the surface of fixed films. Microorganisms tend to attach to the surfaces where nutrients are always available. A variety of microbes like bacteria, protozoa, fungi, other mesofauna, macroinvertibrates (such as enchytraeids and lumbricid worms), dipteran fly larve, etc, graze the film. Adsorption is the first step in the purification of wastewater using a fixed film. Wastewater is allowed to flow over the surface of the film and some of it also passes through it. Wastewater passing through the film is dependent on the film thickness and hydraulic loading (Metcalf and Eddy, 2003). Flow through the film is inversely proportional to the hydraulic loading. In low-rate lagoons, a large proportion of the wastewater flows through the film at any one time and the physical straining action of the film gives higher microorganism-wastewater contact in other words, a high hydraulic retention time (HRT) resulting in clean effluents. On the other hand the higher the hydraulic loading the greater the proportion of water passing over the films which results in lower HRT and a lower quality effluent. Heterotrophic micro-organisms stabilize the organic matter aerobically in the wastewater and they constitute the majority of the microbes attached to the films (Hamoda et al, 1996). They secrete extracellular polymers which flocculate the fine particles in the wastewater. Organic nutrients, trapped by the film and the flock of fine particles, are adsorbed onto the surface of the film. They are broken down by the enzymes secreted by heterotrophic bacteria and fungi. The soluble nutrients produced from the enzymatic 14

24 activity and those available in the wastewater are readily absorbed by the microbes and synthesized (Metcalf and Eddy, 2003). The thickness of the film influences the oxygen profile in the film. Oxygen diffuses first into the water and then into the film. It diffuses to only certain thickness of the film leaving the deeper areas anaerobic. The first layer of biomass receives maximum oxygen and greater exposure to the wastewater. The cells developing on top of the first layer make it difficult for oxygen to penetrate through and reach the first layer of biomass. The greater the thickness of the film, the less oxygen that is available for the deeper layers. Therefore, the surface layer is efficient in terms of oxidation. The depth of oxygen penetration depends on composition, density of the film and the rate of respiration within the film. The surface area is more important than the biomass for oxidation via the film. The optimum thickness of the film for efficient purification is 0.15 mm. Temperature plays a vital role in the development of a film. The accumulation of cells on the film is lower in the summer due to high metabolic and grazing rates and higher in the winter when the growth rate of micro-organisms is reduced. Usually it takes 2-3 weeks for the film to establish on the medium during summer for maximum purification and up to 2 months during winter. The thickness of the film is controlled by various factors like ambient temperature, organic load, distribution system, microbial characteristics of the film, and the activity of grazers (Wheatley and Williams, 1976). It is found that the rate of film accumulation increases rapidly below 10 C (Hawkes and Shephard, 1971). 15

25 Film accumulation is mainly due to an increase in microbial biomass and due to physical entrainment of particulate matter. Growth on media increases with soluble COD however, nitrification rates are inhibited at very high COD levels due to the presence of heterotrophic bacteria in excess of autotrophic bacteria which reduce the availability of ammonia and DO to nitrifiers (Sen et al, 1994). As the film grows and exceeds critical thickness an anoxic environment develops below the aerobic zone. Most of the soluble nutrients will be utilized by the aerobic zone before they reach the lower microorganisms, forcing them into the endogenous phase of growth. Under such conditions, lower micro-organisms lose their ability to hold on to the surface of the medium and will be subjected to stress. The stress increases as the thickness continues to increase and destabilizes the lower layer first. The cells which cannot withstand the stress spread the stress to the adjacent cells and detach themselves from the medium. Likewise most of the cells in the anaerobic zone lose strength due to high stress and result in detachment and washing away of the film. This process is known as sloughing. Sloughing may occur due to excessive biomass growth on the film and due to high velocities of the wastewater. Excessive growth of the film reduces the volume of the interstices, reducing ventilation, until they are completely blocked. This clogging of the film decreases wastewater movement and increases anoxic zones. Such phenomenon is known as ponding and occurs on the surface of the film. At higher temperatures, a greater portion of the BOD 5 adsorbed onto the film is oxidized and results in the accumulation of fewer solids, 16

26 whereas at lower temperatures, the rate of oxidation decreases although the adsorption rate of BOD 5 remains unaltered due to decrease in the growth of micro-organisms. Thus, at lower temperatures, more solids will be accumulated resulting in clogging. The literature review on the performance of aerated lagoons and the advantages of incorporating fixed films in an aerated lagoon has given scope to implement the technology in a low cost aerated lagoon and evaluate the performance of the lagoon. 17

27 CHAPTER 3 EXPERIMENTAL METHODS 3.1 Materials Samples were collected in clean plastic bottles from the influent inlet, partial mix zone 1 (PM1), partial mix zone 2 (PM2), and the effluent outlet of the Kingdom City lagoon. Pictures of the different locations of sampling are provided below. Overview of the Kingdom City lagoon can be seen in Figure 2. Figure 3 shows the partial mix zone 1 with mechanical aerators. Table 1 lists the flow data in the lagoon. After sampling, the samples were brought to the University of Missouri Columbia and refrigerated at less than 4 C. Analysis was performed as soon as possible. Fisherbrand 5.5 cm diameter glass fiber filter circles were used for filtering the raw samples. Ammonia salicylate, ammonia cyanurate, nitriver 3 nitrite, nitraver 5 nitrate reagents, and bromcresol green-methyl red indicator powder were obtained from Hach. A Hach spectrophotometer DR/2500 was used for the spectrophotometeric analysis of ammonia, nitrate, and nitrite. A digestion solution for COD for the range ppm was purchased from Hach for COD analysis. The BOD 5 standard solution, nutrient buffer pillows and seed for the BOD 5 test were obtained from Hach. A sulfuric acid standard solution of N was also obtained from Hach for the alkalinity test. 18

28 Fig 2. Overview of the Kingdom City wastewater lagoon Fig 3. A view of the fixed films installed at Kingdom City 19

29 Fig 4. Sample collection from influent Fig 5. Partial mix zone 1 20

30 Fig 6. Sample collection from partial mix zone 2 Fig 7. Quiescent zone in Kingdom City lagoon 21

31 Fig 8. Effluent outlet at Kingdom City lagoon. 22

32 Table 1. Flow data for Kingdom City lagoon Date Flow, mgd 1/12/ /8/ /2/ /6/ /4/ /1/ /6/ /4/ /20/ /17/ /9/ /15/ /12/ /16/ /7/ /17/ /11/ /5/ /5/ /10/ /14/ /9/

33 3.2 Methods Ammonia A 0.1 ml filtered sample from each zone was placed in a 10ml glass vials and was diluted to 10 ml with deionized water. Ammonia was analyzed colorimetrically using Hach DR 2500 with the method The obtained values were multiplied by a dilution factor of 100. The ammonia standard was prepared according to Standard Method 4500-NH3 D. 3d. Standards were run for the test and the results were in the range of ± 20%. (Standard Methods for the Examination of Water and Wastewater, 2000) Nitrite A 2 ml filtered sample from each zone was placed in a 10 ml glass vial and diluted to 10 ml. Hach method 8507, diazotization method; LR (0.002 to mg/l NO 2 -N) was used to determine the nitrite content in the samples. Ammonium nitrite standards were run and the results were in the range of ± 4%. Final values were multiplied by a dilution factor of five. (Standard Methods for the Examination of Water and Wastewater, 2000) Nitrate A 4 ml filtered sample from influent, PM1, PM2, and the effluent was placed in a 10 ml glass vial. The nitrate standard was prepared following 4500-NO B. 3.b method from standard handbook (Standard Methods for the Examination of Water and Wastewater, 2000). Nitrate content in the samples was determined using Cadmium reduction method, HR (0.3 to 30.0 mg/l NO3-N, Hach). Results obtained were multiplied by a dilution factor 3 24

34 of 2.5. The standard values were in the range of ± 5%. ( Standard Methods for the Examination of Water and Wastewater, 2000) TSS and VSS Fisherbrand 5.5 cm diameter glass filters were used to filter the raw samples. Dry filters were rinsed with deionized water to clear the pores of the filters. Wet filters were put in aluminum boats and dried in the oven at a temperature of 105 C for one hour. After one hour they are taken out of the oven and put into a desiccator to cool. The filters were taken out of the desiccator after half an hour and the filters were weighed and initial weights recorded. Weighed filters were used to filter the raw wastewater samples. 50ml of influent and 100 ml each of PM1, PM2, and effluent samples were filtered through the oven dried filters D and 2540 E (Standard Methods for the Examination of Water and Wastewater, 2000) method were used to determine total suspended solids and volatile suspended solids Biochemical Oxygen Demand Method 5210 B (Standard Methods for the Examination of Water and Wastewater, 2000) was used to determine BOD 5. BOD 5 nutrient and seed were purchased from Hach. BOD 5 nutrient was prepared by placing one nutrient packet in 6 liters of deionised water. Nutrient water was aerated for one hour until the dissolved oxygen concentration was in the 8-9 mg/l range. The seed solution was prepared by putting one seed capsule in 500 ml of dilution water and aerating it for one hour. Both total and soluble BOD 5 for the samples were determined. A 9 ml raw influent sample was placed into a 300 ml BOD 5 25

35 bottle with 2 ml of seed solution and filled with dilution water. For PM1, PM2 and the effluent, 60 ml samples were placed into BOD 5 bottles for the determination of total BOD 5. The bottles were then filled with 2 ml of seed solution and dilution water. The same procedure was repeated with filtered samples for soluble BOD 5. A blank was prepared with 2 ml of seed solution and dilution water in the 300 ml BOD 5 bottle. Dissolved oxygen readings were taken for all the samples and were recorded as D 1. After five days, final readings of dissolved oxygen were measured and recorded as D 2. BOD 5 in each sample is calculated as under where: BOD 5 = (D 1 - D 2 ) - (B P 1 - B 2 ) D 1 = DO of diluted sample immediately after preparation, mg/l, D 2 = DO of diluted sample after 5 d incubation at 20 o C, mg/l, P = decimal volumetric fraction of sample used, B 1 = DO of seed control before incubation, mg/l, B 2 = DO of seed control after incubation mg/l Chemical Oxygen Demand Hach Method 8000, reaction digestion, was used to determine the chemical oxygen demand in the filtered samples from influent, PM1, PM2, and effluent. 2 ml each of the samples were transferred to digestion solution vials. One blank was run with 2 ml of deionized water. DR 2000 was used to determine the COD values of the samples. 26

36 3.2.7 Alkalinity 2320 B method (Standard Methods for the Examination of Water and Wastewater, 2000) was used to determine the alkalinity of the filtered influent and effluent samples. A 25 ml sample was placed into a conical beaker N sulfuric acid was used as titrant and bromcresol green-methyl red was used as the indicator powder. The end point was determined when the green color of the solution turned red. Duplicates were run and the average value was determined as the alkalinity of the respective sample. 27

37 CHAPTER 4 RESULTS AND DISCUSSIONS 4.1 Ammonia Figure 9 shows ph and alkalinity values in the effluent zone. ph values were well within the ideal values ( ) for nitrification to take place. The average ph value was 8.2 which was in the range of optimum values ( ) for nitrification (Gray N. F and Metcalf & Eddy). 5 th May to 30 th June 2006 marked the period of ph>8.5. At such values ammonia is lost due to volatilization (Reed, Crites, Middlebrooks). Increased nitrification and almost zero ammonia concentrations in the effluent support this point. Changes in the concentration of ammonia across the lagoon can be seen in Figure 10. No significant difference was observed among PM1, PM2, and effluent ammonia values across the lagoon. Most of the nitrification occurred in PM1. Ammonia concentration was reduced on an average by 87.7% in PM1. Figure 11 shows the percentage removal of ammonia in the lagoon in the effluent zone. The temperatures falling from 20 C to 10 C had little affect on the nitrification process. It is reported that as the temperatures decrease there is a decrease in the growth of the nitrifiers and less microbial activity (Surampally et at, 1999, Gray, 2004, Sedlak, 1991).However, temperatures below 10 C from October 2005 to March 2006, as shown in Figure 12, had a significant influence on the growth of nitrifying bacteria and their role in reducing ammonia. There was a significant drop in removal rates from December 2005 to March It is reported that temperature has a major effect on nitrification (Gray, 28

38 2004). The nitrification rate in January 2006 was 77.5% and 41.4% in early March (3/10/2006) at such temperatures, the growth of bacteria is greatly reduced and results in lower nitrification rates. This can be observed in Figure 11 and Figure 12. At relatively high temperatures, from April to November 2006, higher nitrification rates can be observed. Ammonia removal rates increased from 73.2% in April 2006 to 100% in May 2006 which can be observed in Figure 11. This is due to higher microbial growth rates and the higher oxidation of ammonia to nitrite at higher temperatures. Temperatures slowly started increasing from 10.7 C in March 2006 to 19 C in April During this period, the bacteria needed time to adjust to the changing temperatures and little increase in nitrification removal was observed. Form late August 2006 through November 2006, when the bacteria adjusted to the new temperature, slightly increased ammonia concentrations were observed in the effluent. Also the death of algae reduces the ammonia removal rates due to reduced assimilation. Table 2 displays the ammonia removal rates. The influence of oxidation of organic matter in the wastes on nitrification can be seen in Figure 13. It has been reported (Hamoda, Zeidan, & Al-Haddad, 1996) that high BOD 5 can influence nitrification. Figure 13 does not show any such trend. This may be due to the fact that the BOD 5 was very low throughout the study. No obvious relationship was observed between ammonia and PM1 soluble BOD 5 (SBOD 5 ) concentrations. The period from mid February 2006 to April 2006 had low ammonia removal rates. This can be 29

39 attributed to the temperature adjustment period of the nitrifiers when the rate of nitrification is still low with high ammonia values in the effluent. In summary, 86.5% was the average ammonia removal rate in PM1. In PM2, an ammonia removal rate of 8% was observed. The average effluent ammonia removal rate between PM2 and the effluent was 0.80%. 9.5 ph 475 Alkalinity ph Alkalinity, mg/ /28/05 9/5/05 12/14/05 3/24/06 7/2/06 10/10/06 1/18/07 Date 225 9/5/05 12/14/05 3/24/06 7/2/06 10/10/06 1/18/07 Date Fig 9. ph and alkalinity values in the effluent zone of the lagoon 30

40 Inf PM1 PM2 Eff Fixed Films installed NH 3 -N (mg/l) /11/2005 9/5/2005 9/30/ /25/ /19/ /14/2005 1/8/2006 2/2/2006 2/27/2006 3/24/2006 4/18/2006 5/13/2006 6/7/2006 7/2/2006 7/27/2006 8/21/2006 9/15/ /10/ /4/2006 Date Fig 10. Ammonia concentration in all the zones. 120 Fixed films installed % NH3 Removal 100 % NH3 removed /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 11. % Removal rates of Ammonia across the lagoon. 31

41 Fixed films installed Temp NH Temp, C NH3, mg/l 0 0 7/17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 12. Temperature and ammonia relationship in the effluent Fixed films installed % NH3 Removal % SBOD Removal % NH3 removed /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 13. Removal rates of ammonia and SBOD values in effluent. 32

42 Table 2. Percentage removal rates of ammonia Date Inf NH3 (mg/l) Eff NH3 (mg/l) % NH3 removal 9/6/ /10/ /3/ /17/ /8/ /5/ /3/ /15/ /23/ /10/ /17/ /24/ /13/ /20/ /5/ /19/ /2/ /15/ /30/ /14/ /27/ /17/ /31/ /14/ /28/ /13/ /4/ Nitrate Nitrate concentrations were similar for PM1, PM2, and the effluent (Figure 14). Only on June 2, 2006 was the effluent nitrate concentration higher (effluent =16 mg/l while PM1= 6.5 mg/l). This was probably due to a lag time in the PM1 reaching the effluent. The increase in nitrate concentrations in PM1, PM2, and the effluent from mid April 2006 to June 2006 indicates an increase in nitrification rates owing to higher temperatures in the wastewater. NH 3 and NO 3 across the lagoon are in good agreement. The consistency of nitrate with ammonia data is shown in Figure

43 As the nitrification rates went down in January 2006, low concentrations of nitrates were observed. This phenomenon continues until mid April 2006 when the temperatures started to rise, increasing the nitrification rates. An increase in the NO 3 levels can be observed from April 20, 2006 to mid June NO 3 values started dropping in the later part of June 2006 and remained fairly low until November This could be due to the assimilation of nitrate by algae, the accumulation of biomass at the bottom of the quiescent zone, the absence of supplied DO, and/or an increased growth of duckweed and algae at the surface which might have resulted in anoxic conditions below the surface favoring denitrification in the quiescent zone Fixed films installed Inf NO3 PM1 PM2 Eff NO3-N (mg/l /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 14. Nitrate levels across the lagoon 34

44 18 16 Eff NH3 Eff NO NH3, NO /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 15. Plot displaying the concentrations of ammonia and nitrate in effluent 4.3 Total Suspended Solids (TSS) Most of the spikes in the TSS in Figure 16 coincide with rain events, however, the lagoon is effective in removing the increased TSS. No significant difference was observed in the TSS values in PM1, PM2, and the effluent and for this reason only the effluent data is considered further. An increase in effluent TSS values can be observed from April 2006 to July 2006 (Figure 17). High values of TSS in this period are due to the presence of algae. The color of the effluent sample collected in April was greener than the previous samples indicating the presence of algae. The overall average removal rate of TSS from September 2005 to November 2006 was 86.3%. The performance of the lagoon in eliminating TSS is shown in Figure 18. There was 87% removal in PM1 and 19% of the remaining TSS is removed in PM2. 35

45 In later March 2006, it rained and the lagoon received high total suspended solids. This can be observed in the plot of TSS and VSS in Figure 17. High TSS values and relatively low VSS reduces indicate the presence of inorganic matter entering the lagoon through the rain water and since the retention time is 60 days, the high values of TSS are carried further until mid July. Also, this period saw algae growth in the lagoon. In July, it rained a couple of times and duckweed was present in the quiescent zone. This could have been the reason for the increase in TSS values from September 2006 to November It was observed that most of the duckweed died during this period increasing the TSS values. It can be observed from Figure 17 that VSS values are similar to the TSS values confirming the presence of high organic matter in the effluent samples. This is due to dead duckweed and algae leaving the lagoon. November 2006 marked the start of cold weather resulting in low metabolism rates and slow growth of the bacteria. All the green algae and duckweed present in the lagoon was washed out by November 2006 increasing TSS & VSS values. Figure 18 shows fairly constant TBOD in 2006 when compared to TSS in the effluent. 36

46 Inf PM1 PM2 Eff 450 TSS, mg/l /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 16. Total suspended solids across the lagoon Eff TSS Eff VSS TSS, VSS /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 17. Effluent TSS vs VSS 37

47 Fixed films installed TSS TBOD TSS, SBOD mg/ /17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 5/13/06 7/2/06 8/21/06 10/10/06 11/29/06 Date Fig 18. TSS vs TBOD in the effluent zone 4.4 Biochemical Oxygen Demand (BOD 5 ) The influent BOD 5 values varied from 80 mg/l in November 2005 to as high as 258 mg/l in The effluent BOD 5 ranged from 0 to 50.7 mg/l; both values being observed in the winter of BOD 5 removal rates are plotted in Figure 19. The average BOD 5 removal rate was 86% which is slightly higher than the required 85% removal rate. November 2005 observed 100% BOD 5 removal and the lagoon achieved as high as 98% BOD 5 removal during The percentage removal rates can be seen in Table 3. In 2006, the effluent values ranged from 4.3 mg/l (August) to 43.1 mg/l (April) (Figure 20). 38

48 The winter of 2005 (until February 2006) saw lower removal rates due to low temperatures inhibiting the growth of heterotrophic bacteria responsible for the reduction of BOD 5 than during warmer periods. In addition, the algae dying in the lagoon diminished the BOD 5 reduction rates and added biomass contributing to the high effluent BOD 5. This can be observed in Figure 21. November 2005 had unusually low flows and influent BOD 5 values. This particular sampling period had complete removal of BOD 5. The lagoon had low BOD 5 removal rates from March 2006 to June This could be due to the presence of algae and possibly nitrification in the effluent. Again there was an increase in the BOD 5 reduction rates from mid July 2006 to mid September. From October 2006, a decrease in the removal rates was observed owing to a decrease in the temperatures and also because of dying algae and duckweed contributing to the dead biomass. It can be observed in Figure 23 that the COD of the effluent was correlated with the BOD 5. The average ratio of COD to BOD 5 in the effluent was 2.7, as shown in Figure 24. The ratio decreased from March 2006 to June 2006, indicating the presence of comparatively more biodegradable matter than non-biodegradable matter in the effluent. The growth of algae during this season could be the reason for the increased BOD 5 and corresponding low COD to BOD 5 ratio. The period from mid July 2006 to November 2006 produced reduced levels of BOD 5 removal whereby the COD to BOD 5 ratio was increased indicating good BOD 5 removal rates in the lagoon. 39

49 Table 3. Percentage removal of BOD 5 in the lagoon Date Inf BOD 5 Eff BOD 5 % removal 9/6/ /10/ /3/ /17/ /8/ /5/ /3/ /15/ /23/ /10/ /17/ /24/ /13/ /20/ /5/ /19/ /2/ /15/ /30/ /14/ /27/ /17/ /31/ /14/ /28/ /13/ /4/