HEATHER L. FITZPATRICK

Transcription

1 COVERING CHLORINE CONTACT BASINS AT THE KANAPAHA WATER RECLAMATION FACILITY: EFFECTS ON CHLORINE RESIDUAL, DISINFECTION EFFECTIVENESS, AND DISINFECTION BY-PRODUCT FORMATION By HEATHER L. FITZPATRICK A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2005

2 Copyright 2005 by Heather L Fitzpatrick

3 ACKNOWLEDGMENTS I would like to thank my supervisory committee members (Dr. Paul Chadik, Dr. David Mazyck, and Dr. Benjamin Koopman) for their input and assistance during this investigation. Special thanks go to my supervisory committee chair (Dr. Chadik) for his technical support and guidance during this study; they were of immeasurable significance to this research and to me. Also, I would like to thank the Gainesville Regional Utilities staff for their support throughout the course of this research. The help of Christina Akly in the field and at the University of Florida was of great importance and greatly appreciated. I would also like to thank my family, friends, and especially my husband for their continuous support during my graduate career. iii

4 TABLE OF CONTENTS page ACKNOWLEDGMENTS... iii LIST OF TABLES... vii LIST OF FIGURES...x ABSTRACT... xvi CHAPTER 1 INTRODUCTION...1 Pilot Study...5 Full-Scale Study...7 Clarifier Chlorine Addition REVIEW OF LITERATURE...9 Nitrification/Denitrification...9 Chlorine Disinfection...10 Free Chlorine...11 Combined Chlorine...12 Break-Point Chlorination...13 Contact Time...14 Disinfection By-Product Formation...15 Sunlight/UV Irradiation MATERIALS AND METHODS...27 Measured Parameters...27 Global Solar Radiation...27 Ultraviolet Radiation...27 Total and Free Chlorine Residual...28 Total Suspended Solids...29 Total Coliform...29 Trihalomethane (THM)...30 Haloacetic Acid (HAA)...30 ph...31 iv

5 Conductivity...31 Dissolved Oxygen...32 Sampling...32 Pilot Scale System...32 Wastewater Feed System Materials...34 Chlorine Dosing...37 Pump Test...37 Full Scale...38 Calculations...40 Disinfection By-Product Data Normalization...40 Trihalomethane normalization...40 Haloacetic acid normalization...42 Average Radiation...43 Standard Deviation...44 Paired T-Test...44 Linear Correlation DISCUSSION: PILOT-SCALE BASIN...47 Solar Radiation/Temperature...47 Chlorine Residual...50 Free Chlorine...51 Total Chlorine...57 Disinfection By-Products...60 Trihalomethane...61 Haloacetic Acid DISCUSSION: FULL-SCALE STUDY...86 Chlorine Residual...86 Free Chlorine...86 Total Chlorine...89 Disinfection By-Products...91 Trihalomethane...91 Haloacetic Acid DISCUSSION: MEASURED PARAMETERS Temperature Total Coliform Total Suspended Solids ph Conductivity Dissolved Oxygen CONCLUSIONS v

6 APPENDIX A PILOT-SCALE BASIN DESIGN B FLUOROSCEIN TRACER ANALYSIS C CHLORINE DOSING CALCULATIONS D E COMPILED DATA PILOT-SCALE DATA F FULL-SCALE DATA G H GAS CHROMATOGRAPHY INFORMATION T-TEST AND PEARSON COEFFICIENT TABLES LIST OF REFERENCES BIOGRAPHICAL SKETCH vi

7 LIST OF TABLES Table page 3-1 Chlorine contact basin dimension ratios Pilot chlorine contact basin dimension Normalization factors used to normalize OPAQ TTHM effluent concentrations to TRANS TTHM effluent concentrations Normalization factors used to normalize OPAQ HAA(5) effluent concentrations to TRANS HAA(5) effluent concentrations Normalization factors used to normalize COV TTHM effluent concentrations to UNCOV TTHM effluent concentrations Normalization factors used to normalize COV HAA(5) effluent concentrations to UNCOV HAA(5) effluent concentrations A-1 South chlorine contact basin A-2 North chlorine contact basin A-3 Pilot basin B-1 Fluoroscein tracer at KWRF pilot basin, clear top B-2 Conditions during tracer analysis B-3 Flouroscein F curve calculation B-4 The F curve values C-1 Chlorine dosing during pilot-scale study C-2 Acid and base addition during pilot-scale study D-1 Pilot-scale study compiled and calculated parameter data D-2 Pilot-scale study compiled chlorine data and differences D-3 Pilot-scale study compiled TTHM data and differences vii

8 D-4 Pilot-scale study compiled TTHM and normalization factors D-5 Pilot-scale study compiled normalized TTHM data and differences D-6 Pilot-scale study compiled HAA(5) data D-7 Pilot-scale study compiled normalized HAA(5) data D-8 Pilot-scale study compiled differences in HAA(5) and HAA(5) data D-9 Full-scale study compiled and calculated parameter data D-10 Full-scale study compiled chlorine data and differences D-11 Full-scale study compiled TTHM data and differences D-12 Full-scale study compiled TTHM and normalization factors D-13 Full-scale study compiled normalized TTHM data and differences D-14 Full-scale study compiled HAA(5) data D-15 Pilot-scale study compiled normalized HAA(5) data D-16 Full-scale study compiled differences in HAA(5) and HAA(5) data E-1 Trihalomethane mass concentrations in the pilot-scale study E-2 Trihalomethane molar concentrations in the pilot-scale study E-3 Haloacetic acid mass concentrations in the pilot-scale study E-4 Haloacetic acid molar concentrations in the pilot-scale study E-5 Pilot-scale study chlorine effluent concentrations E-6 Pilot-scale probe parameter data E-7 Pilot-scale data provided by GRU laboratory F-1 Trihalomethane mass concentrations in the full-scale study F-2 Trihalomethane molar concentrations in the full-scale study F-3 Haloacetic acid mass concentrations in the full-scale study F-4 Haloacetic acid molar concentrations in the full-scale study F-5 Full-scale study chlorine effluent concentrations viii

9 F-6 Full-scale probe parameter data F-7 Full-scale data provided by GRU H-1 Pilot-scale t-test values H-2 Full-scale t-test values H-3 Pilot-scale Pearson coefficient and linear correlation value H-4 Full-scale Pearson coefficient and linear correlation values ix

10 LIST OF FIGURES Figure page 1-1 Kanapaha Water Reclamation Facility flow diagram Overhead layout of the KWRF Wastewater process from filtration through chlorination Chlorine addition at the clarifiers Percent of free chlorine compound (HOCl and OCl - ) versus ph Breakpoint chlorination: Species of chlorine residuals present during chlorination when ammonia is present The THM species The HAA(5) species Predicted versus the observed concentration of CHCl 3 for the entire model development database from the 1993 AWWA report Predicted versus the observed concentration of DCAA for the entire model development database from the 1993 AWWA report Radiometer, pyranometer, and datalogger setup Pilot basin system setup Pilot scale setup; chlorine and acid/base solution containers, solution pumps, influent water spigot, static mixers, t-split, TRANS and OPAQ basins Full-scale setup. (a) Uncovered side of the basin. (b) Covered side of the basin during the full-scale study Sampling points in the post-aeration basin and North chlorine contact basin for the full-scale study Average global horizontal radiation versus the average UV radiation The effluent temperature of the TRANS and OPAQ basins plotted versus the average UV radiation exposure of the TRANS basin over the HRT x

11 4-3 Difference in effluent temperature of the basins (TRANS-OPAQ) plotted versus the average UV radiation over the HRT Free chlorine residual sampling sets in particular residual ranges for the TRANS and OPAQ basins Free chlorine residual difference of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus average UV Radiation over the HRT of the wastewater in the basin for all pilot studies Free chlorine residual difference of the OPAQ and TRANS basins (TRANS-OPAQ) plotted versus average UV radiation over the HRT of the wastewater in the basin for baseline parameters Free chlorine difference of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the difference in temperature for all of the pilot studies Free chlorine difference of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the difference in temperature for baseline parameters Total chlorine residual sampling sets in particular residual ranges for the TRANS and OPAQ basins Total chlorine residual difference of the OPAQ and TRANS basins (TRANS- OPAQ) plotted versus average UV Radiation over the HDT of the wastewater in the basin for all pilot studies Total chlorine residual difference of the TRANS and OPAQ basins (TRANS- OPAQ) plotted versus the difference in temperature between the basins The TTHM effluent mass concentrations for the TRANS and OPAQ basins are shown in range increments The TTHM effluent molar concentrations for the TRANS and OPAQ basins are shown in range increments Difference in TTHM concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into mass concentration ranges Difference in TTHM concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into molar concentration ranges Difference in TTHM effluent mass concentration of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the difference in free chlorine residual of the TRANS and OPAQ basins xi

12 4-17 Difference in TTHM effluent molar concentration of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the difference in free chlorine residual of the TRANS and OPAQ basins Difference in TTHM mass effluent concentration between the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the difference in free chlorine residual between the TRANS and OPAQ basins for baseline runs Speciation of the THM formation in the TRANS effluent on a mass basis sampled at 9 am on August 23, Normalized TTHM effluent mass concentrations for the TRANS and OPAQ basins are shown in range increments Normalized TTHM effluent molar concentrations for the TRANS and OPAQ basins are shown in range increments Difference in TTHM concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into mass concentration ranges Difference in TTHM concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into molar concentration ranges Difference in normalized TTHM mass concentration of the TRANS and the OPAQ basins (TRANS-OPAQ) plotted versus the average UV radiation. exposure over the HRT Difference in normalized TTHM molar concentration of the TRANS and the OPAQ basins (TRANS-OPAQ) plotted versus the average UV radiation exposure over the HRT The HAA(5) effluent mass concentrations for the TRANS and OPAQ basins are shown in range increments The HAA(5) effluent molar concentrations for the TRANS and OPAQ basins are shown in range increments Difference in HAA(5) concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into mass concentration ranges Difference in HAA(5) concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into molar concentration ranges Difference in HAA(5) mass concentration of the TRANS and the OPAQ basins (TRANS-OPAQ) plotted versus the difference in free chlorine residual of the TRANS and OPAQ basins (TRANS-OPAQ) xii

13 4-31 Difference in HAA(5) molar concentration of the TRANS and the OPAQ basins (TRANS-OPAQ) plotted versus the difference in free chlorine residual of the TRANS and OPAQ basins (TRANS-OPAQ) Speciation of the HAA(5) formation in the OPAQ effluent on a mass basis sampled at 12 pm on August 30, The HAA(5) effluent mass concentrations for the TRANS and OPAQ basins are shown in range increments The HAA(5) effluent molar concentrations for the TRANS and OPAQ basins are shown in range increments Difference in HAA(5) concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into mass concentration ranges Difference in HAA(5) concentration between the TRANS and OPAQ sides (TRANS-OPAQ) separated into molar concentration ranges Difference in HAA(5) effluent mass concentration of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the average UV radiation exposure over the HRT Difference in HAA(5) effluent molar concentration of the TRANS and OPAQ basins (TRANS-OPAQ) plotted versus the average UV radiation exposure over the HRT Free chlorine residual of the UNCOV and COV side effluents separated into concentration ranges Difference in free chlorine residual between the UNCOV and COV sides (UNCOV-COV) separated into concentration ranges Free chlorine difference of the UNCOV and COV basin sides plotted versus the difference in temperature Total chlorine residual of the UNCOV and COV side effluents separated into concentration ranges Total chlorine difference of the UNCOV and COV basin sides plotted versus the difference in temperature The TTHM effluent mass concentrations for the UNCOV and COV sides are shown in range increments The TTHM effluent molar concentrations for the UNCOV and COV sides are shown in range increments...93 xiii

14 5-8 Difference in TTHM concentration between the UNCOV and COV sides (UNCOV-COV) separated into mass concentration ranges Difference in TTHM concentration between the UNCOV and COV sides (UNCOV-COV) separated into molar concentration ranges Difference in the TTHM effluent mass concentration between the UNCOV and COV sides (UCOV-COV) plotted versus the difference in free chlorine residual of the UNCOV and COV sides (UCOV-COV) Difference in the TTHM effluent molar concentration between the UNCOV and COV sides (UCOV-COV) plotted versus the difference in free chlorine residual of the UNCOV and COV sides (UCOV-COV) Speciation of the TTHM formed in the UNCOV side sampled at 9 am on August 25, The TTHM mass concentration instances separated into concentration ranges for the UNCOV and COV side The TTHM molar concentration instances separated into concentration ranges for the UNCOV and COV side Difference in TTHM concentration between the UNCOV and COV sides (UNCOV-COV) separated into mass concentration ranges Difference in TTHM concentration between the UNCOV and COV sides (UNCOV-COV) separated into molar concentration ranges The HAA(5) effluent mass concentrations for the UNCOV and COV sides are shown in range increments The HAA(5) effluent molar concentrations for the UNCOV and COV sides are shown in range increments Difference in HAA(5) concentration between the UNCOV and COV sides (UNCOV-COV) separated into mass concentration ranges Difference in HAA(5) concentration between the UNCOV and COV sides (UNCOV-COV) separated into molar concentration ranges Difference in HAA(5) effluent mass concentration of the UNCOV and COV sides versus the difference in free chlorine residual of the UNCOV and COV sides Difference in HAA(5) effluent molar concentration of the UNCOV and COV sides versus the difference in free chlorine residual of the UNCOV and COV sides xiv

15 5-23 Speciation of the HAA(5) formation in the COV effluent on a mass basis sampled at 12 pm on August 25, The HAA(5) effluent mass concentrations for the UNCOV and COV basin sides are shown in range increments The HAA(5) effluent molar concentrations for the UNCOV and COV basin sides are shown in range increments Difference in HAA(5) concentration between the UNCOV and COV sides (UNCOV-COV) separated into mass concentration ranges Difference in HAA(5) concentration between the UNCOV and COV sides (UNCOV-COV) separated into molar concentration ranges Total coliform and temperature plotted against sampling time on July 14, Total suspended solids and temperature plotted against sampling time on July 14, ph and temperature plotted against sampling time on July 14, Conductivity and temperature plotted against sampling time on July 14, The D.O. and temperature plotted against sampling time on July 14, B-1 Fluoroscein versus sampling time B-2 The F curve G-1 Trihalomethane GC for spiked sample G-2 Trihalomethane GC for blank sample G-3 Trihalomethane GC for field sample G-4 Haloacetic acid GC for spiked sample G-5 Haloacetic acid GC for blank sample G-6 Haloacetic acid GC for field sample xv

16 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering COVERING CHLORINE CONTACT BASINS AT THE KANAPAHA WATER RECLAMATION FACILITY: EFFECTS ON CHLORINE RESIDUAL, DISNIFECTION EFFECTIVENESS, AND DISINFECTION BY-PRODUCT FORMATION By Heather L. Fitzpatrick May 2005 Chair: Paul A. Chadik Major Department: Environmental Engineering Sciences It is commonly understood that sunlight, specifically ultraviolet (UV) radiation, degrades chlorine and thus reduces chlorine residual in uncovered chlorine contact basins. Its effect on disinfection by-product (DBP) formation, however, has not been significantly studied. A pilot and full-scale study were performed at the Kanapaha Water Reclamation Facility (KWRF) to investigate the effect of UV radiation on chlorine residual, disinfection-by-product formation, and inactivation of bacteria. For both the pilot and full-scale studies, two chlorine disinfection processes were setup in parallel, for effluent parameter comparisons. One process allowed for the exposure of the wastewater to UV radiation. In the other process an opaque cover was used to prevent solar radiation exposure of the wastewater during chlorine disinfection. Preventing UV radiation exposure of wastewater provided higher chlorine residuals (on average 0.4 and 0.7 mg/l free chlorine higher) for pilot and full-scale averages xvi

17 respectively. Extent of chlorine loss from UV radiation exposure was directly proportional to the UV exposure intensity during chlorine disinfection. Both processes, with and without UV radiation exposure, provided adequate total coliform inactivation. To compensate for the difference in effluent conditions (such as chlorine residual and temperature), the effluent DBP concentrations were normalized. In the normalization process, non-exposed effluent DBP concentrations were normalized to UV-exposed effluent DBP concentrations using normalization factors. Normalization factors were calculated from parameter data collected during each sampling run. By preventing UV radiation exposure during chlorine disinfection, free chlorine residual was found to be significantly higher, and also the total trihalomethane effluent concentration was found to be significantly less (on average 17.1 and 7.5 µg/l less for normalized concentrations) than for pilot and full-scale averages, respectively. In the full-scale study haloacetic acid (HAA(5)) concentration was significantly less in the process that prevented UV radiation exposure (on average, 39.0 µg/l less). However, the pilot-scale did not show the same degree of HAA(5) concentration difference; thus, no significant difference was found between the UV radiation exposed and non-exposed processes. Preventing UV radiation, if it does not lessen HAA(5) formation, does not increase formation. Our studies provide evidence contrary to common theory that an increase in free chlorine during chlorination will result in higher DBP formation. The significance lies in using chlorine disinfection processes where wastewater is covered to prevent UVradiation exposure. When used it could lower the amount of chlorine loss, and help to lower DBP formation. xvii

18 CHAPTER 1 INTRODUCTION The Kanapaha Water Reclamation Facility (KWRF), owned and operated by Gainesville Regional Utilities (GRU), treats wastewater from the west side of Gainesville, Florida, and its outlying areas. The plant uses a modified Ludzak-Ettinger process to treat the wastewater. 1 The plant operation promotes biological removal of nitrogen and carbonaceous biological oxygen demand (CBOD). After the aeration basins, the wastewater moves to the clarifiers (where solids are removed). Then the wastewater flows through filters (which remove the fine particles that did not settle out in the clarifiers). The wastewater is then collected in a clearwell, sent to the post-aeration basin, and then disinfected in the chlorine contact basins (Figure 1-1). Figure 1-1. Kanapaha Water Reclamation Facility flow diagram. 1

19 2 The plant (Figure 1-2) was recently expanded from a 10 million gallon per day (MGD) to a 14 MGD capacity. A schematic of the wastewater process from filtration through the chlorine contact basins is shown in (Figure 1-3). Figure 1-2. Overhead layout of the KWRF. 6 - Filters Post-Aeration Basins North Chlorination Basin South Chlorination Basin Figure 1-3. Wastewater process from filtration through chlorination.

20 3 From the clarifiers, the wastewater is sent to six filters setup in parallel. The filter effluents combine into a single 100,000-gallon clearwell. Chlorine gas is injected into the pipe as the wastewater flows from the post-aeration basin to the first of two chlorine contact basins, to begin the disinfection stage of the treatment process. The two chlorine contact basins are setup in series (the North and the South chlorine contact basins). The first chlorine contact basin (the North basin), with a volume of 0.16 MG, is part of the original plant. The wastewater then flows to a second chlorine contact basin (the South basin) with a volume of 0.57 MG. The South basin was added after the original plant was built, to increase treatment capacity. A previous study at the KWRF determined that the North and South basins together model as 60 tanks-in-series while the North basin models as 100 tanks-in-series separately. 2 As stated, the KWRF relies on chlorine to disinfect the wastewater. Enough chlorine gas is injected to create sufficient free chlorine to meet the chlorine demand of the wastewater and leave enough effluent residual to meet the standards set by the Environmental Protection Agency (EPA) and upheld by the Florida Department of Environmental Protection (FDEP). According to the KWRF permit, the effluent must have at least a 1 mg/l Cl 2 free chlorine residual. In the chlorination process at the KWRF, the contact basins are open to the environment; allowing the wastewater to be exposed to UV radiation from sunlight. The UV radiation acts as a catalyst to reduce the free chlorine (Equation 1-1). This reduction leads to an appreciable amount of chlorine loss due to UV radiation exposure. UV + 2HOCl 2H + 2Cl + O 2 (1-1)

21 4 Since the KWRF injects treated wastewater into deep wells in the Floridan aquifer (a drinking water source), and is used in reuse applications, the finished wastewater must meet EPA and DEP permit requirements. Disinfection by-product formation is of increasing concern, since these by-products are linked to harmful health effects. Pregeant 1 using wastewater from the KWRF showed a positive correlation between free chlorine residual and THM formation. As the chlorine residual was increased the THM concentration formed also increased, given that there were THM precursors left in the wastewater to react. 1 In a previous study performed by the Integrated Product and Process Design (IPPD) team sponsored by Gainesville Regional Utilities (GRU) in the chlorine loss at the KWRF was investigated. 2 Most chlorine loss was assumed to result from chlorine decay by ultraviolet (UV) irradiation (Equation 1-1). Thus it was suggested that covering the basin would decrease chlorine loss caused by this mechanism. The IPPD study provided good insight into the hydrodynamic behavior of the treated wastewater as to flows through the chlorine contact basins and the disinfection process at the KWRF. The study comprises two days worth of data compilation, March 19 th and January 24 th, for chlorine concentration, total trihalomethane (TTHM) concentration, and the volume of water irradiated by sunlight. In the study one side of the chlorine contact basin was covered with a polypropylene tarp while the other side was left open. The covered side of the basin had a higher chlorine residual than the uncovered basin verifying a definite correlation between sunlight exposure and chlorine degradation. 2 The study also showed that as the sunlight intensity increased from winter

22 5 to summer months, the chlorine loss within the uncovered basin increases also. The study provided some unexpected results: the total trihalomethane (TTHM) concentrations were actually lower in the covered basin than the control, or uncovered basin. 2 This phenomenon is opposite of that found in the Pregeant 1 study and is contrary to common theory, where a higher residual produced a higher trihalomethane (THM) concentration. One aspect of this study was to further investigate the phenomenon found by the IPPD team. In order to further ascertain the impact of solar radiation, ultraviolet (UV) and visible radiation, on the chlorination process in the wastewater treatment plant, a research plan was proposed to and accepted by the Gainesville Regional Utilities. One focus of this study is the UV radiation catalysis of the oxidation reaction of water by chlorine to form oxygen and the chloride ion, Equation 1-1. Also, this study reviews the impact of UV radiation and global horizontal radiation on bacterial inactivation and disinfection byproduct (DBP) formation. This study involves both a pilot and full-scale investigation of the chlorination process at the KWRF to determine to what extent solar radiation affects chlorine residual, disinfection effectiveness, and disinfection by-product formation. Pilot Study The pilot basin study involved two pilot basins scaled after the KWRF chlorine contact basins. One basin was equipped with an opaque acrylic cover to block solar radiation from entering and coming in contact with the water during chlorination. The second basin was equipped with an UV transmitting clear acrylic, or UV-TRANS, cover that allowed solar radiation, both UV and visible radiation, to come in contact with the water during chlorination.

23 6 The feed water for the pilot basins had gone through the plant filters but was not chlorinated by the plant chlorination system. The feed water to the pilot basins was first dosed with a known concentration of chlorine (NaOCl), and then split into two equal streams before entering the pilot basins. The pilot basin study makes it possible to keep flow rate and chlorine dosage constant which was not possible in the full-scale study. It also enabled the control and variation of flow rates, ph levels, and chlorine dose to determine the extent of their involvement in the effects of solar radiation on the chlorination process and water quality parameters. KWRF average, minimum, and maximum chlorine dosage, ph, and flow rates were used in this phase of the study. The KWRF s effluent wastewater had a total chlorine residual minimum of 1.4 mg/l as Cl 2, an average of 2.8 mg/l as Cl 2, and a maximum of 4.8 mg/l as Cl 2 according to data provided by GRU for In the pilot study the average plant value was used as the pilot baseline value while chlorine dosing that produces water with minimum and maximum residual values was also tested. The influent ph, or raw ph, experienced at the KWRF does not vary much from a neutral ph, around 7. Thus, for this experiment a ph of 7 was used as the baseline value while ph values of 6 and 8 were also tested to determine the influence of ph on the pilot system. In the pilot study a baseline hydraulic retention time (HRT) of 2.75 h was used. A longer HRT of 3.81 hrs was also tested to amplify the effect of radiation on water quality parameters in this study. The KWRF average and maximum HRT in the chlorine contact basins is approximately 1.8 and 4.4 h, respectively.

24 7 Full-Scale Study A full-scale study was also implemented to further investigate the effect of solar radiation on the disinfection chlorination stage of the wastewater treatment under normal operating conditions. The full-scale study was performed on the North basin and did not include the south basin. In the North basin the flow is split immediately into two parallel streams after it enters the basin. Chlorine gas is injected into the pipe that transfers the wastewater from the post-aeration basin to the North chlorine contact basin. In the full-scale study one half of the basin was covered with polypropylene tarps and the other half was left uncovered. As in the pilot-scale study the effect of UV radiation on the chlorine residual, disinfection effectiveness, and disinfection by-product formation was investigated. The full-scale study was performed to determine the effect of covering the basin under standard plant chlorination procedures so no special adjustments were made. Just as in the pilot study, the UV radiation impact on chlorine residual, disinfection effectiveness, and DBP formation was examined. Clarifier Chlorine Addition The KWRF has recently installed chlorine injection pipes in the clarifiers (Figure 1-4). The chlorine addition was implemented to reduce algae growth in the weirs of the clarifiers. The chlorine addition at the clarifiers, however, would also result in the formation of DBP and could have a lingering effect on chlorine residual and demand. This would lead to inaccuracies in data collected during the pilot and full-scale studies. In order to prevent the interference caused by the chlorine dosing of the clarifiers the chlorine dosing of the clarifiers was ceased at 4 pm the day prior to sampling and remained turned off until 4 pm the day of the testing. Sampling and analysis of the pilot

25 8 basin feed wastewater indicated that ceasing the addition of chlorine in the clarifiers at 4:00 pm ensured that the chlorine residual and TTHM concentrations were below detection at 9:00 am the next morning. Figure 1-4. Chlorine addition at the clarifiers.

26 CHAPTER 2 REVIEW OF LITERATURE Nitrification/Denitrification Nitrogen is incorporated into all living things, and is also present in the atmosphere. Nitrogen is taken from the atmosphere by nitrogen-fixing bacteria and through the action of electrical discharge during storms. 3,4 Although nitrogen is necessary for life, if too much nitrogen is fed into a receiving body of water an over production of algae and other aquatic life can occur, or eutrophication. 4,5 Also, organic nitrogen compounds and ammonia exert a chlorine demand. A higher chlorine dose would be required to achieve adequate disinfection if organic nitrogen and ammonia were not removed prior to disinfection. 6 Domestic raw wastewater contains mostly organic and ammonia nitrogen, or Kjeldahl nitrogen. 5 One of the major treatment processes at the KWRF is the use of biological nitrification and denitrification to remove nitrogen from the wastewater. The autotrophic nitrifying bacteria group, Nitrosomonas, under aerobic conditions oxidizes ammonia and ammonium to form nitrite (Equation 2-1). 3,4,5,7 Nitrite can then be oxidized further by the bacteria group Nitrobacter to form nitrate (Equation 2-2). 3,4,5,7 The aerobic oxidation of organic nitrogen to inorganic nitrogen, nitrification, is carried out in the aeration basins and also in the newly installed carousel at the KWRF. Nitrosomonas + 2NH 3 + 3O2 2NO2 + 2H 2O + 4H (2-1) 2NO NO Nitrobacter 2 + O2 2 3 (2-2) 9

27 10 After the ammonia and ammonium are converted to nitrite and nitrate it can be reduced to nitrogen gas by facultative anaerobic bacteria, such as Pseudmonas. 3,5,7 It is presumed that any nitrate present is reduced to nitrite and then to nitrogen gas. The overall denitrification is shown in (Equation 2-3). At the KWRF the reduction of nitrite and nitrate to nitrogen gas, denitrification, takes place in the anoxic basins and in the newly installed carousel. bacteria 6NO 5CH 3OH 3 N 2 + 5CO2 + 7H O + 6( OH ) (2-3) Chlorine Disinfection Disinfection of wastewater can be dated back to the late 1800s with the use of chlorinated lime for odor control and the treatment of fecal material from hospitals. 8 Because of the known health problems inflicted on humans by microbial organisms, disinfection of wastewater has become a mainstream procedure. The disinfection of wastewater helps prevent bacterial contamination of drinking water sources, thus, aiding in the control of waterborne diseases. Chlorine is one of the most widely used disinfectants for both potable and wastewater treatment because of its relatively low cost and effectiveness as a disinfectant when compared to other alternatives. 6,8 At atmospheric pressure and room temperature chlorine exists as a poisonous yellow gas. 8 For the purpose of water and wastewater treatment chlorine gas is pressurized as a dry, liquefied gas and is stored in steel cylinders to make it easier to store and apply. During chlorine disinfection three types of reactions can occur: oxidation, addition, and substitution. 9

28 11 Free Chlorine In wastewater the chlorine gas is added to water and hydrolyzes to hypochlorus acid (HOCl) and the hypochlorite ion (OCl - ) (Equations 2-4 and 2-5). 4,6,7 Together, HOCl and OCl - are called free chlorine. Cl H O HOCl + H + Cl (2-4) + HOCl OCl + H (2-5) Studies show HOCl to be a more efficient disinfectant and a stronger oxidant than OCl - hence HOCl is the desired species when disinfecting. 8,10 The pk a for HOCl is 7.5at 25 C, thus, at a ph of 7.5 HOCl and OCl - exist in equal concentrations. If the ph is below 7.5 the predominant species is HOCl while at a ph above 7.5 OCl - predominates. 4 The percentage of free chlorine as HOCl and OCl - is dependent on the ph and temperature conditions (Figure 2-1). 4 Most wastewater treatment facilities operate in a range where the HOCl species is prevalent thus increasing their disinfection efficiency and lowering the chlorine dose required to achieve disinfection. 6 Figure 2-1. Percent of free chlorine compound (HOCl and OCl - ) versus ph.

29 12 Chlorine can react with many chemicals, inorganic and organic, present in the wastewater stream. The amount of chlorine dissipated during these reactions is referred to as the chlorine demand the wastewater possesses and dictate the amount of chlorine that must be added to achieve a specific chlorine residual and good disinfection. Combined Chlorine In the presence of ammonia (NH 3 ) the free chlorine species HOCl will react to form chloramines that consist of monochlroamine (NH 2 Cl), dichloriamine (NHCl 2 ), and nitrogen trichloride (NCl 3 ). 4,6,10 (Equations 2-6, 2-7, and 2-8). NH 3 + HOCl NH 2Cl + H 2O (2-6) NH 2 Cl + HOCl NHCl2 + H 2O (2-7) NHCl2 + HOCl NCl3 + H 2O (2-8) Chloramines have the capacity to disinfect wastewater but are not as effective as free chlorine. All domestic wastewaters contain organic nitrogen compounds, including amino acids and proteins. 6,8 Chlorine reacts with these organic nitrogen compounds to form organic chloramines. Though these organic chloramines contribute to the combined chlorine concentration they have no known disinfecting capability. 6,8 Organic chloramines show up as combined chlorine in the iodometric and DPD chlorine residual methods. 8 The speciation of inorganic chloramines is more related to the ph of the wastewater and the chlorine to ammonia molar ratio and not as much on the contact time of ammonia and HOCl. 6,8 Under normal operating conditions monochloramine predominates. As the ph decreases below neutral (ph=7) and as the Cl 2 :N mass ratio

30 13 value increases from 3:1 up to 7:1 the formation of dichloramine is favored. As the ph continues to decrease nitrogen trichloride will form. 6 The chloramine hydrolysis reactions will result in the release of ammonia, which could play a role in nitrification (i.e. formation of NO - 3 ). The decomposition of dichloramine increases as the ph and alkalinity increase. 6,8 This makes dichloramine less stable than monochloramine under normal wastewater conditions. The decomposition of monochloramine occurs in essentially two reactions the first being hydrolysis and the following being the acid catalyzed reaction with the generated free chlorine and results in the formation of dichloramine and ammonia in the wastewater. 6,8 Break-Point Chlorination In order to form HOCl in the presence of ammonia or other organic nitrogen enough Cl 2 gas must be added to reach and pass what is called the breakpoint (Figure 2-2). 4 The process is therefore termed breakpoint chlorination. Beyond the breakpoint free chlorine is dominant and makes up a large percentage of the total chlorine. However, also present beyond the breakpoint are what are termed irreducible or nuisance chlorine residuals that show up in total chlorine residual measurements but do not have the disinfecting capabilities that free chlorine possesses. 6 The organic chloramines and, if present, nitrogen trichloride contribute to the irreducible chlorine residual.

31 14 Figure 2-2. Breakpoint chlorination: Species of chlorine residuals present during chlorination when ammonia is present. Compounds other than ammonia and organic nitrogen compounds can exert a chlorine demand; the demand exerted is related to their concentration in the wastewater. For example, inorganic substances such as the sulfide, sulfite, nitrite, iron (II), and manganese (II) ions all can exert a chlorine demand. 8 If ammonia is present in the wastewater stream the demand these species exert is reduced and sometimes even eliminated. 8 Contact Time One of the most important parameters in chlorine disinfection is contact time. Inactivation of pathogens increases with an increase in contact time. The disinfection effectiveness is expressed as Ct; where C is the disinfectant concentration, and t is the contact time necessary to inactivate the desirable amount of the pathogenic organism. 3,7 In essence, the longer the provided contact time, the subsequently less chlorine is

32 15 necessary to achieve sufficient disinfection. Based on a comprehensive pilot plant study Collins et al. developed an equation to determine bacterial inactivation at wastewater treatment plants (Equation 2-9). 6 The equation fits best where good initial mixing followed by plug flow conditions occur. The wastewater at the KWRF is first filtered prior to chlorine disinfection. Accordingly, the initial bacterial concentration would probably range from 3,000 to 10,000 coliforms per 100 ml. 6 3 y = yo [ ct] (2-9) y o = initial bacterial concentration prior to chlorination y = bacterial concentration at end of contact chamber or at time T in minutes c = initial chlorine concentration t = contact time in minutes The model can be used to predict bacterial inactivation in wastewater given the HRT provided in the disinfection chamber. As the model demonstrates, the disinfection of wastewater with chlorine depends greatly on chlorine concentration addition as well as contact time. The KWRF uses chlorine contact basins, described earlier, to provide the contact time necessary to inactivate the indicator organisms, total and fecal coliforms. As wastewater chlorine demand changes the chlorine addition is altered to provide adequate disinfection. Disinfection By-Product Formation Though the chlorination of wastewater is beneficial in inactivating disease-causing organisms it can also cause the formation of potentially harmful and carcinogenic compounds. According to epidemiological studies there is a correlation between water chlorination and rectal and bladder cancer cases. 11 When organic compounds or precursors such as natural organic matter (NOM), humic and fulvic acids, are present

33 16 during chlorination they may react with the free chlorine to form what are collectively called disinfection-by-products (DBPs). 4 The main concern for public health surrounds the formation of DBPs known as trihalomethanes (THMs) and haloacetic acids (HAAs). Because of the public health concern surrounding these compounds, the federal Environmental Protection Agency (EPA) has imposed a maximum concentration allowed in drinking water. As of 2004 the regulatory drinking water MCL standards for TTHM and HAA(5) are 80 µg/l and 60 µg/l, respectively. 12 THM species include chloroform (CHCl 3 ), a known human carcinogen, bromoform (CHBr 3 ), bromodichlormethane (CHBrCl 2 ), and dibromochlormethane (CHBr 2 Cl) (Figure 2-3). The five HAA species that are currently under regulation include monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), dibromoacetic acid (DBAA), and trichloroacetic acid (TCAA) (Figure 2-4). 8,13 There are several factors that can affect the formation of these DBPs, such as, temperature, ph, precursor concentration, chlorine dose, contact time, and bromide concentration. Cl Br H C Cl H C Br Cl Br Chloroform Bromoform Cl Cl H C Cl H C Br Br Br Bromodichloromethane Dibromochloromethane Figure 2-3. The THM species.

34 17 Cl O Br O H C C OH H C C OH H H Monochloroacetic acid (MCAA) Monobromoacetic acid (MBAA) Cl O Br O Cl C C OH Br C C OH H H Dichloroacetic acid (DCAA) Dibromoacetic acid (DBAA) Cl O Cl C C OH Cl Trichloroacetic acid (TCAA) Figure 2-4. The HAA(5) species. The natural organic matter (NOM) present in wastewater is a precursor for DBPs during chlorination. 11 The NOM is measured as dissolved organic carbon (DOC) or total organic carbon (TOC). NOM consists largely of aromatic compounds, thus, studies have found that aromaticity was a good surrogate for the prediction of DBP formation. 14,15 In general, as the NOM concentration increases the DBP formation during chlorination also increases. This increase in DBP formation is the result of an increase in these DBP precursors but also is due to the increase in chlorine demand exerted by the NOM. 11 With the increase in chlorine demand a higher chlorine dose is necessary to maintain the required chlorine residual. The increase in chlorine dose will result in an increase in DBP formation. In one study, lower molecular weight NOM compounds resulted in a higher

35 18 total trihalomethane (TTHM) yield. 16 In general, as the molecular weight of the NOM present in the water or wastewater decreased the TTHM yield increased. 16 In one study, findings showed that when chlorine is applied to water containing NOM the hydrophobic NOM fraction resulted in a higher DBP formation than the equivalent hydrophilic fraction. 17 Through the oxidation of NOM with chlorine intermediate compounds may form. 11 These intermediates are further oxidized by chlorine, or bromine, to form DBPs. Generally, as precursor concentration, NOM, increases so does the DBP production, but it will tend to plateau and even decline after the residual chlorine is exhausted. 1 The apparent decrease in THM production shown in the study done by Pregeant et al. which was carried out at high precursor concentrations was hypothesized to result from the predominance of THM intermediates when excess precursors existed. 1 The reactions that result in the direct formation of DBP tend to occur more quickly and form earlier during the chlorination process than those that have an intermediate step. 11 Environmental factors such as bromide concentration and the amount of natural organic matter affect the amount of DBPs formed during chlorination. Chlorine oxidizes the bromide ion forming hypobromous acid (HOBr) and hyprobromite (OBr - ) ion, depending on the ph. 18 The hypobromous acid and, to a lesser extent, the hypobromite ion react with DBP precursors by oxidation and substitution reactions to form brominated DBPs. 11,18 As the bromide concentration increases the chlorinated HAA concentration decreases. 18 Given the same chlorine dosing, the addition of the bromide ion results in an increase in the HAA concentration. Studies have also shown that the hypobromous acid oxidizes NOM more readily than hypochlorous acid. 11,18,19 In one study it was determined that bromine reacted ten times faster with NOM isolates than chlorine. 19 The

36 19 presence of the bromide ion (Br - ) in the wastewater stream can greatly alter the speciation and formation of THM and HAA during chlorination. 18 The free chlorine oxidizes the Br - to hypobromous acid (HOBr) (Equation 2-10); HOBr will ionize as the ph increases to OBr -. HOCl + Br HOBr + Cl (2-10) The bromide ion can have a substantial effect on the mass concentration of DBP as bromine has a greater molecular weight, 80, than chlorine, The DBPs formed when HOBr reacts with organic precursors have a higher molecular weight than those with chlorine. This is a concern as the EPA MCLs for DBP are on a mass basis, µg/l, and not a molar basis. As the temperature of the wastewater increases so does the HAA and THM concentrations. The ph has a variable effect on the DBP concentration. Studies have found that as the ph is increased from 6 to 8, the THM formation also increased but resulted in a lower HAA formation. 11,17,20 When the ph is lowered from a neutral ph to 6 the HAA formation increased. 11,17 A longer chlorine contact time will result in a higher DBP formation because more time is allowed for chlorine to react with NOM. An increase in contact time will allow those reactions that require intermediate steps more time to react to completion. The formation of THM increases as time allowed for reaction with free chlorine increases, or the contact time, though the rate of formation is not constant. The chlorine dose has a similar effect on DBP formation as the dose increases so does the DBP concentration

37 20 sometimes reaching a plateau. 1 The chlorine dose can also affect the speciation of DBP as the dose increases the ratio of THM to total halogenated DBP ratio also increases. Modeling of DBP formation. Disinfection by-product formation modeling helps to predict the amount of DBP formed during the chlorination of a feed water if the necessary parameters are known. The EPA has developed disinfection/disinfection byproduct rule models to predict THM and HAA formation to determine operational and economic impacts of setting new MCLs. 13 The models used to predict THMs were developed by Malcome Pirnie and models used to predict HAAs were developed by Dr. Charles Haas, contracted by the AWWA D/DBP Technical Advisory Workgroup (TAW). 13 Since the KWRF provides tertiary wastewater treatment where additional solids are removed by the six media filters the EPA models developed for drinking water are applicable.. AWWA contracted Montgomery Watson to develop new model equations for individual THM and HAA species and published the findings in a March 1993 report. 13 Environmental parameters used in the formation of the model equations include bromide concentration, TOC, ultraviolet light absorbance at 254 nm, temperature, chlorine dose, ph, and reaction time. Using the basic equation (Equation 2-11) 13, as a guideline the coefficients for each environmental variable were determined through a step-wise regression model procedure for individual THM and HAA species. DBP a b c d e f g = k ( TOC) ( ph) ( TEMP) ( CL2DOSE) ( BR) ( UV 254) ( TIME) (2-11) k, a, b, c, d, e, f, and g are empirical constants

38 21 The program STATVIEW was used in the step-wise regression procedure to determine the coefficients. Another study showed that if the data is available nitrate, calcium, and alkalinity could be used in the prediction of THM formation. 21 Chloroform made up the majority of the TTHM concentrations in this study and thus the AWWA model equation for chloroform (Equation 2-12) 13 was used to normalize the sampling sets; an explanation of the normalization method used is in the Materials and Methods section. CHCl 0 + UV t =.064[ TOC ] ph T [ Cl 2 Dose] [ Br 0.01] (2-12) CHCl = µg / L T = Temperature( C) t = Time( hrs) TOC = mg / L Cl Dose = mg / L Cl Br UV = mg / L = cm 1 2 The model predicted chloroform concentration is plotted versus the observed chloroform concentration for the whole model development database from the March 1993 AWWA report (Figure 2-5). 13 A perfect prediction would result in a slope of 1, the farther from the perfect prediction line the less accurate the prediction. 13 The prediction versus the actual chloroform coincides better from 0 to 200 µg/l than concentrations greater than 200 µg/l. Typical wastewater TTHM concentrations do not exceed 200 µg/l. 13

39 22 Figure 2-5. Predicted versus the observed concentration of CHCl 3 for the entire model development database from the 1993 AWWA report. The AWWA model equation for dichloroacetic acid (DCAA) was used to normalize HAA(5) concentrations of the sampling sets, an explanation of the normalization method is in the Materials and Methods section. The relationship of the variable environmental parameters in the formation of the HAA(5) species DCAA is shown in (Equation 2-13) DCAA = 0.605[ TOC ] [ Temp ] [ Cl 2 Dose] [ Br ] t [ UV 254] (2-13) DCAA = µ g / L t = Time( hrs) TOC = mg / L Cl Dose = mg / L Cl Br 2 1 = mg / L o Temp= C 2

40 23 The model predicted DCAA concentration was plotted versus the observed DCAA concentration for the whole model development database from the March 1993 AWWA report (Figure 2-6). 13 The predicted concentrations do not correlate perfectly with the observed values, however, the points lie close to the perfect prediction line, slope =1, and is sufficiently accurate. 13 Figure 2-6. Predicted versus the observed concentration of DCAA for the entire model development database from the 1993 AWWA report. Sunlight/UV Irradiation At the KWRF, chlorine disinfection of wastewater occurs in an open flow-through basin. This allows sunlight to come in contact with the chlorinated water. Aqueous chlorine is unstable when exposed to sunlight, which results in the degradation of free chlorine within the wastewater stream (Equation 2-14). 7 UV + 2HOCl 2H + 2Cl + O 2 (2-14)