Control of Trihalomethanes in Wastewater Treatment

Guanghui Hua and Steven Yeats

ontrolling trihalomethanes (THMs) cause health and regulatory concerns. DBPs discharged with wastewater treatment have been linked to an increased risk of cer - Guanghui Hua, Ph.D., and Steven Yeats, plant final effluent has become an im - tain cancers and adverse reproductive effects. P.E., are with the water and wastewater Cportant issue across the United States. Chlori - THMs) and haloacetic acids (HAAs) are the process engineering group in the nation is by far the most widely used method two most abundant groups of known DBPs. Gainesville office of the engineering firm for disinfecting treated wastewater. The reac - The U.S. Environmental Protection Jones Edmunds & Associates. This article tion of free chlorine with certain organic com - Agency (EPA) Stage 2 D/DBP rule sets the max - was presented at the Florida Water Re - pounds in the wastewater leads to the imum contaminant level for four THMs and sources Conference in April 2009. formation of disinfection byproducts, includ - five HAAs at 80 g/L and 60 g/L, respectively, ing THMs. Limited knowledge is available on a basis of a locational running annual aver - about the formation and control of THMs age for drinking water. The four regulated formation during chlorine disinfection is crit - during wastewater disinfection. THMs are chloroform, bromodichloromethane ical for wastewater utilities to meet the FDEP’s Many utilities in Florida discharging to sur - (BDCM), dibromochloromethane (DBCM), THM surface water discharge standards. face waters are having difficulty complying with and bromoform. Figure 1 shows the chemical limits for bromodichloromethane and dibro - structures of the THMs. Trihalomethane Formation mochloromethane, the two regulated THMs. To protect surface water quality, the During Chlorination This article presents a comprehensive evaluation Florida Department of Environmental Protec - of factors affecting THM formation during tion (FDEP) sets regulatory limits for THMs When chlorine is introduced into water, chlorination and details available technologies for treated wastewater effluents discharged to it reacts with DBP precursors to form byprod - for controlling THMs in wastewater. The article surface waters. Unlike the Stage 2 D/DBP rule ucts. Natural organic matter (NOM) present also recommends ways for wastewater utilities for drinking water, the FDEP sets a regulatory in source water is the primary precursor for to meet the effluent THM limitations. limit for each THM species. The annual aver - the formation of DBPs in drinking water Disinfection is a vital process to inactivate age limits for chloroform, BDCM, DBCM, and (Reckhow et al, 1990). NOM is a complex mix - pathogenic microorganisms in drinking water bromoform are 470.8, 22, 34, and 360 g/L, re - ture of organic compounds derived from the and wastewater, but since the 1970s it has been spectively, for a Class II or Class IIIµsurface decay of vegetation and animal material. recognized that disinfection can produce harm - water discharge (Table 1). The organic matter found in municipal ful byproducts and cause health concerns. Because the limits for chloroform and wastewater is significantly different from drink - Chorine is by far the most widely used chemical bromoform are relatively high, it is not diffi - ing water supplies. The organic matter in waste - disinfectant in water and wastewater treatment. cult for wastewater utilities to meet the chlo - water typically consists of proteins, carbohydrates, Chlorine readily reacts with certain or - roform and bromoform standards under and oils and fats (Metcalf & Eddy, 2002). ganic compounds in water and wastewater to typical wastewater chlorination conditions. In addition to organic matter, bromide form disinfection byproducts (DBPs) that Consequently, controlling BDCM and DBCM ions are important inorganic DBP precursors. Bromide ions are ubiquitous in water and wastewater and are quickly oxidized by chlo - Cl Br Br Br rine to bromine during chlorination. Subse - quent reactions between bromine and organic H C Cl H C Cl H C Br H C Br matter result in the formation of brominated THMs and HAAs. These reactions are sum - marized in Equations 1-3. Cl Cl Cl Br

Chloroform Bromodichloromethane Dibromochloromethane Bromoform HOCl + Organics DBPs (Equation 1) HOCl + Br - HOBr + Cl - (Equation 2) Figure 1: The THM Species HOBr + Organics DBPs (Equation 3)

When ammonia is present in treated efflu - Class III : Rec rea ti on , Prop agati on and ents, it reacts with chlorine to form chloramines. Class I: Class II : Maintenance of a Hea lt hy , We ll- The formation of chloramines can be summa - Potable Shell fish Balance d Popu lati on of Fish and THMs rized in its simplest form by Equations 4-6. Wa ter Prop agati on or Wil dli fe Supp ly Harvesti ng Predo minantl y Predo mi nantl y NH 3 + HOCl NH 2Cl + H 2O (Equation 4) Fresh Wa ter Marine Wa ter NH 2Cl + HOCl NHCl 2 + H 2O(Equation 5) CHCl3 5.67 μg/L 470 .8 μg/L 470 .8 μg/L 470 .8 μg/L NHCl 2 + HOCl NCl 3 + H 2O (Equation 6) CHBrCl2 0.27 μg/L 22 μg/L 22 μg/L 22 μg/L CHBr2Cl 0.41 μg/L 34 μg/L 34 μg/L 34 μg/L The distribution of mono-, di-, and CHBr3 4.3 μg/L 360 μg/L 360 μg/L 360 μg/L trichloramines primarily depends on the chlo - rine-to-ammonia ratio and the pH. Mono - Table 1: Criteria for Surface Water Quality Classifications (FDEP, FAC 62-302.530) Continued on page 8 6 • APRIL 2010 • FLORIDA WATER RESOURCES JOURNAL Continued from page 6 pH, chlorine dose, and temperature. As shown in Figure 5, Chloroform yield chloramine is predominant at low Cl 2 –N ra - Several mechanistic and empirical mod - gradually decreased while bromoform yield tios (e.g. < 5 mg Cl 2/mg N). Free chlorine els have been developed to describe the forma - gradually increased as bromide was increased. residual appears when the chlorine-to- tion of THMs. For example, Equation 7 shows CHCl 2Br and CHClBr 2 yields passed through ammonia ratio exceeds a certain point (theo - an empirical model to predict the formation of the maximum at 2-10 mol/L (160-800 g/L) retical value at 7.6). This is often referred to as the four regulated THMs (Westerhoff, 2006). bromide concentratioµn and decreased µwhen break-point chlorination (Figure 2). bromide ions were increased. Bromoform was 1.098 0.152 - 0.068 In general, chloramines form fewer THMs = 0.0412[TOC] [Cl 2] [Br ] dominant when the bromide concentration THMs and HAAs than free chlorine. Dihalo - [Temp] 1.069 [pH] 0.263 (Equation 7) was increased to 30 mol/L (2400 g/L). genated HAAs are the predominant known Figure 6 showsµthat THM conµcentration DBPs identified in chloraminated waters (Hua This model predicts that the concentra - increased as reaction time and pH value in - and Reckhow, 2008). tion of THM increases with increasing total creased. The formation of THMs exhibited an Figure 3 shows a conceptual model of the organic carbon (TOC), chlorine dose, bro - initial rapid phase within a few hours, followed formation pathways of THMs and HAAs dur - mide, temperature, pH, and reaction time. by a more steadily increasing phase. ing chlorination and chloramination. Based Bromide ions affect the yield of THMs and Varying pH also strongly influenced the on this model, formation of THMs, greatly influence the speciation of THMs. formation of THMs. THM concentration in - trichloroacetic acid (TCAA), and Consequently, the presence of bromide is crit - creased by a factor of 2.8 and 1.6, respectively, dichloroacetic acid (DCAA) proceeds through ical for controlling individual THM species. when increasing pH from 5 to 7 and 10 for a common dihalogenated intermediates. The distribution of THM species depends 24-h contact time. Further halogenation of dihalogenated primarily on the bromide-to-chlorine ratio. The chlorine dose and reaction tempera - intermediates by chlorine leads to the forma - Figure 4 shows a qualitative profile of THM ture also have a significant impact on THM tion of THMs and TCAA. THMs form speciation as a function of the Br/Cl 2 ratio. formation. The concentrations of THM in - through base-catalyzed hydrolysis, and the for - Chloroform predominates at low Br/Cl 2 ratios. creased nearly linearly with an increasing chlo - mation of THMs is favored at high pH values. More brominated THM species are formed rine dose (Figure 7). A more than 100-percent Certain chemical factors prohibit chloramines with increasing bromide concentrations. The increase in THMs was observed when increas - from adding a third halogen to dihalogentaed maximum levels of BDCM and DBCM appear ing the reaction temperature from 5 oC to 30 oC intermediates; therefore, chloramines are not at a medium range of bromide to chlorine ra - (Figure 8); therefore, wastewater utilities may active in the formation of THMs. tios. Thus, the formation of BDCM and DBCM experience increased THMs in the chlorine Numerous water quality and treatment can be reduced or minimized either by reduc - contact basin during warm-weather operation factors affect THM formation. The formation ing the bromide concentration to low levels or compared to cold-weather operation. and speciation of THMs primarily depends on by increasing bromide concentration to high Figure 9 shows the influence of ammonia source water characteristics and specific disin - levels to shift the speciation toward the forma - on the formation of DBPs during chlorination. fection conditions. The type and abundance of tion of chloroform or bromoform. The ratio of chlorine to ammonia had a great organic precursors and bromide and iodide Figures 5-8 present examples of the effect impact on the THM yield. THM concentra - concentrations have been shown to signifi - of bromide concentration, pH, reaction time, tions decreased rapidly as the ammonia-to- cantly influence the concentration and specia - dose, and temperature on THM formation. chlorine ratio increased. THM concentrations tion of THMs. Important disinfection variables These results were obtained from laboratory were below 8 g/L when the Cl 2/N (mg/mg) affecting THM formation include contact time, bench-scale tests using natural waters. µ Continued on page 10

8 NOM l a N - u 4 d

H 6 i Oxidation & Substitution s N (chlorine & chloramines) e NHCl2 g R

m 4 e / 2 n l i - r C HOCl + OCl o l g 2 O O O O h m C NH2Cl NCl 3 R'' C CCl C R' R'' C CCl2C OH 0 2

0 2 4 6 8 10 12 14 16 Hydrolysis Hydrolysis

Chlorine Dose, mg Cl2/mg NH4-N O Hydrolysis & Oxidation O

R'' C CHCl2 Slow Figure 2: Theoretical Break-point Chlorination Curve Cl2HC COHDCAA

Substitution (free chlorine only) O

R'' C CCl Figure 3: Conceptual model of the formation pathways 3 Hydrolysis Oxidative Hydrolysis of THMs and HAAs from chlorine and chloramines O TCAA (Adapted from Hua and Reckhow 2008) THM CHCl3 Cl3C COH

8 • APRIL 2010 • FLORIDA WATER RESOURCES JOURNAL Continued from page 8 For example, enhanced coagulation has likely present a significant financial burden for 140 mass ratio was lower than 5. Adjusting the ad - been shown to be effective in removing high many wastewater utilities. 350 THM dition of ammonia is a practical way to con - molecular weight and highly humic organic 120 trol effluent THM levels for wastewater matter, such as humic acid and fulvic acid Optimizing the Chlorination Process 300 ) L utilities using chloramines for disinfection. from drinking water (Chadik and Amy, 1985), (1) Optimizing chlorine contact time and / 100 g 250 μ μ μ μ

but the occurrence of humic substances in chlorine dose ( (

n / n L o 80 treated wastewater may not be significant. Wastewater utilities in Florida with surface o i ) i Control of Trihalomethanes t 200 t a a r

One study showed that coagulation is not water discharge are required to meet the mini - r t t

in Wastewater Treatment n n

e 60 effective in removing dissolved organic carbon mum microorganism disinfection standards e c

150 c n n

THM Precursor Control (DOC) from a treated wastewater (Silva and and then dechlorinate the effluent before dis - o o C

As part of the EPA’s D/DBP rule, removal Milligan, 2006). For this study, the DOC re - charge. A typical chlorine contact basin design C 40 M 100 H

of NOM was defined as the best available tech - moval rate was only 20 percent at the highest requires a minimum 15-minute contact time at T 20 nology to lower the concentration of DBPs in alum coagulant dose (150 mg/L). design peak hour flow. The actual chlorine con - 50 finished drinking water. Typical methods of Other precursor-control technologies, tact time could be much longer when the plant controlling DBP precursors during drinking such as GAC adsorption, ion exchange, and flow rate is well below the peak flow. Wastewater 0 0 0.00.5 1.0 1.5 2.0 water treatment include enhanced coagula - membrane filtration, usually have very high treatment plants can use multiple chlorine in - 5 15 30 operation and maintenance (O&M) costs jection points based on plant flow to reduce the N:Cl2 (M:M) tion, granular activated carbon (GAC) ad - o sorption, ion exchange, and membrane when applied to treated wastewater for DOC contact time and chlorine consumption. Temp ( C) filtration, but these precursor-control tech - removal due to wastewater characteristics (e.g., (2) Reducing Sunlight Irradiation 10 5 3.4 2.5 Cl2:N (mg/mg) nologies may not be effective or practical for high total organic carbon and total dissolved Wastewater treatment plants typically use Figure 8: Effect of Temperature on THM Formation wastewater DBP control because of the signif - solids); therefore, the application of these tech - uncovered chlorine contact basins for disin - (Reaction Conditions: TOC=5.0 mg/L, time=48h, Figure 9: Effect of Chlorine-to-Ammonia Ratio icant difference in water quality. nologies for THM precursor control would fection, allowing the wastewater to be exposed pH=7, Cl2=6.0 mg/L) on THM Formation (Reaction Conditions: TOC=2.6 mg/L, pH=7, time=48h, temp =20 oC) 1.8 CHCl3 CHCl3 CHBrCl2 1.6 CHBrCl2 to UV irradiation from sunlight. Sunlight ir - chlorine contact basins is an effective way to moamines from ammonia and bromine. 1 CHBr2Cl CHBr Cl ) 1.4 2 radiation can cause dissociation of chlorine lower the THM levels during chlorination. Au - L

CHBr / 3 l CHBr3 (Equation 8) and lead to chlorine loss in con - tomated acid injection/mixing at the begin - NH 3 + HOBr NH 2Br + H 2O (Equation 10) o n 1.2 o m i 2 2 2

t tact basins. Consequently, higher chlorine ning of the basin and base injection/mixing at NH Br + HOBr NHBr + H O (Equation 11) μ μ ( c

a n 1.0 2 3 2 r doses are needed to maintain chlorine residu - the end of the basin may be necessary for ef - NHBr + HOBr NBr + H O (Equation 12)

o i F

t - r

a als at the end of the contact basin. fective THM control and pH compliance. NH 2Cl + Br NH 2Br + H 2O (Equation 13) r a 0.8 l t o n At the same time, UV irradiation may act (4) Adding Ammonia e M

c 0.6 n

M as a catalyst for THM formation, which results Chloramine has been an increasingly pop - The most critical parameter for the ap - o H C T 0.4 in increased THM concentrations. This hy - ular secondary disinfectant for drinking water plication of chloramination in wastewater is pothesis is shown in Equation 9. Fitzpatrick because of the stricter regulations on DBPs, but the chlorine-to-ammonia ratio. The dosage of 0.2 (2005) investigated the effect of sunlight irra - there has been some controversy over the appli - chlorine and ammonia must meet the re - 0.0 diation on THM formation during wastewater cation of chloramines in drinking water. Nitri - quirements of disinfection, chlorine residual disinfection. The results showed that free chlo - fication in the distribution system, degradation compliance, and THM compliance. The opti - 0 5 10 15 20 25 30 rine residual was significantly higher and the of elastomers in piping and plumber systems, mum chlorine-to-ammonia ratio is site spe - Br/Cl Ratio 2 Bromide Added (μmol/L) THM concentration was significantly lower in increased lead concentrations, and formation of cific and can vary depending on the water Figure 4: Qualitative profile of THM Speciation as a function of Figure 5: Effect of Bromide Concentration on THM Speciation the covered chlorine contact basins compared nitrogenous DBPs (e.g, N-Nitrosodimethy - quality and environmental conditions. with those in uncovered basins. lamine (NDMA)) and iodinated DBPs have Although chloramination is an easy-to- 2 (Reaction conditions: TOC=8.5 mg/L, pH=7, time=48h, Br/Cl Ratio This study suggests that covered chlorine caused significant concern (Singer, 2006). practice and effective method of controlling o temp=20 C, Cl 2=5.0 mg/L) contact basins effectively reduced chlorine loss Nonetheless, chloramination has been THMs in wastewater, it has some significant and THM formation. Wastewater utilities shown to be a practical, highly effective method disadvantages. Adding ammonia to treated 400 200 should take measures to reduce the sunlight ir - of controlling DBPs in drinking water. Chlo - wastewater increases the effluent total nitro - pH 5 THM pH 7 175 radiation to the chlorine contact basin to lower ramination also has been used in wastewater gen (TN) concentration. Many wastewater

) pH 10 chlorine consumption and THM formation. disinfection for THM control (Erdal et al, 2008). treatment plants are required to reduce the ni - L ) / 300 L g / 150 In general, chloramines are weaker disin - trogen and phosphorus loads to receiving wa - μ μ g

( UV

+ - n ( 2HOCl 2H + 2Cl + O 2 (Equation 8) fectants than free chlorine, but chloramines ters to control eutrophication and protect o

i 125 UV n t o

a HOCl + TOC Enhanced THMs (Equation 9) are more stable and last longer than free chlo - surface water quality. i r t t a n 200 r rine because of their lower oxidation poten - Adding ammonia for THM control may t 100 e n c e

n (3) Controlling chlorination pH tial. Adding ammonia can help maintain a not be feasible for those plants with a stringent c o n 75 C o Many wastewater utilities have converted lasting residual during wastewater disinfec - effluent TN limit. Also, chloramination can C M

H 100 their chlorine gas disinfection system to the tion, so adding ammonia to wastewater does form several highly toxic emerging DBPs, such T 50 use of a sodium hypochlorite solution for not necessarily deteriorate the efficacy of the as NDMA and iodo-acids, so using chlorami - 25 chlorination primarily for safety and regula - disinfection in the chlorine contact basin. nation for wastewater THM control must be tory concerns. Unlike chlorine gas, the addi - Another potential benefit of adding am - carefully studied. 0 0 tion of sodium hypochlorite increases the monia in THM control is the formation of (5) Bromide addition 0 4 8 12 16 20 24 0123456 wastewater pH due to the hydrolysis of bromoamines from the reaction of ammonia Similar to chlorine, bromine is a highly Time (hour) Chlorine dose (mg/L) hypochlorite solution. and bromine. Bromoamines are not active in effective disinfectant. The application of Figure 6: Effect of Reaction Time and pH on THM Formation Figure 7: Effect of Chlorine Dose on THM Formation (Reaction As shown in Figure 6, THM formation is the formation of brominated THMs. Equa - bromine in wastewater can be achieved by o o (Reaction conditions: TOC=5.0 mg/L, temp=20 C, Cl 2=8.1 mg/L) conditions: TOC=5.0 mg/L, temp=20 C, time=48h, pH=7) favored at high pH values. Controlling pH in tions 10-13 summarize the formation of bro - Continued on page 12

10 • APRIL 2010 • FLORIDA WATER RESOURCES JOURNAL FLORIDA WATER RESOURCES JOURNAL • APRIL 2010 • 11 Continued from page 11 using either commercial bromine solution or THMs CHCl3 CHBrCl2 CHBr2Cl CHBr3 by in-situ generation by adding chlorine and MW (g/m ol) 119 .4 163 .8 208 .3 252 .7 bromide ions simultaneously to the contact Boili ng Point (oC) 62 90 117 149 basin. The latter may be a more robust method Henry’s Law Con stant KH @ -3 -3 -3 -3 o 3 2.95 10 1.24 10 0.642 10 0.385 10 for wastewater disinfection and CHBrCl 2 and 20 C (Atm-m /mol) CHBr 2Cl control. As shown in Figures 4-5, the formation of Table 2: Chemical Characteristics of THMs THM shifts to more brominated species as bro - mide concentration increases. The addition of water disinfection has been studied extensively treated wastewater, and factors affecting THM bromide does not control the formation total and evaluated. These alternative disinfectants formation during wastewater disinfection THMs; in fact, it can actually increase total do not form THMs to any significant levels. should be investigated. Optimizing chlorination THM concentrations due to the higher mass Each has advantages and disadvantages. conditions and post-treatment can reduce weight of bromide than chloride. Because of Ozone and chlorine dioxide are less popu - THM concentrations in the treated effluent. By concerns over the formation of other bromi - lar in the U.S. for wastewater disinfection. employing multiple control strategies and treat - nated DBPs, the bromide dose should be lim - Ozone can oxidize bromide to form bromate, ment technologies, utilities will improve per - ited to the level that can effectively control and chlorine dioxide degrades to chlorite. Bro - formance and meet effluent THM limitations. effluent CHBrCl 2 and CHBr 2Cl concentrations. mate and chlorite both present health concerns. Although the use of UV applications has in - References Post Treatment creased significantly, this method of disinfec - Surface water discharge usually requires tion typically has high capital and O&M costs. 1. Chadik, P. A.; Amy,G. L. 1987, Molecular the wastewater effluent dissolved oxygen (DO) weight effects on THM control by coagulation concentration to be elevated prior to dis - Summary and adsorption. Journal of Environmental En - charge. A re-aeration tank is often used to in - gineering , 113, 1234-1248. crease the DO levels in the effluent. The Control of THMs in wastewater can be 2. Erdal, U.G.; Chaney, K.; Ganesan, S.; re-aeration tank can be used for THM reduc - achieved by removing precursors, optimizing Daigger, G.T., 2008. Full-scale evaluation of tion because of the volatility of THMs. chlorination conditions, implementing post- THMs formation and minimization of THMs THM removal by aeration is a function of treatment, and using alternative disinfectants. via chloramination. WEFTECH, Chicago, IL. initial THM concentration, water flow rate, Typical precursor removal methods for drink - 3. Fitzpatrick, H.L., 2005. Covering chlorine and air flow rate (Tarquin, 2005). The removal ing water, such as enhanced coagulation, GAC contact basins at Kanapaha Water Reclamation of the individual species varies depending on adsorption, ion exchange, and membrane fil - Facility: Effect on chlorine residual, disinfec - the chemical properties of the THMs. Table 2 tration, may not be effective and have high tion effectiveness, and disinfection by-product presents some chemical characteristics of the capital and O&M costs for wastewater utilities. formation. Thesis, University of Florida. four THMs. Alternative disinfectants, such as ozone, 4. Hua, G.; Reckhow, D.A., 2008. DBP for - Henry’s law constant ( KH) is an indicator chlorine dioxide, and UV, do not form THMs mation during chlorination and chloramina - of the solubility of a gas at a certain pressure. to significant levels, but the use of alternative tion: Effect of reaction time, pH, dosage, and The higher the KH, the lower the solubility of a disinfectants for THM control should be care - temperature. Journal American Water Works gas. The order of the solubility of the four fully evaluated for cost and for their formation Association , 100, 8, 82-95. THMs is CHBr 3>CHBr 2Cl>CHBrCl 2>CHCl 3. of other byproducts. 5. Metcalf and Eddy. Wastewater Engineer - The reverse order is true for the volatility of Wastewater utilities using chlorine for ing : Treatment and Reuse, 2002. the THMs; therefore, the removal efficiency of disinfection should focus on optimizing chlo - 6. Reckhow, D. A.; Singer, P. C.; Malcolm, R. THMs by aeration is expected to be in the rination conditions and post-treatment for L. 1990, Chlorination of humic materials: order of CHCl 3>CHBrCl 2>CHBr 2Cl>CHBr 3. controlling THMs. It is critical for utilities to Byproduct formation and chemical interpre - Aerated chlorine contact basins have been improve chlorine contact tank efficiencies, op - tations. Environmental Science & Technology , used for disinfection and increasing effluent timize chlorine dose and contact time, prevent 24, 1655-1664. DO levels, but aeration may reduce disinfec - direct sunlight irradiation, and adjust pH in 7. Silva, V.D.; Milligan, J. 2006. Operational tion efficiency by altering the basin from a order to reduce THM formation. challenges to meeting new copper & THM ef - plug flow reactor to segments of completely In some cases, adding ammonia to form fluent limits at Clearwater APCFS. Florida mixed reactor basins, which may promote chloramines is a practical method of control - Water Resources Journal , 4, 49-57. short-circuiting. ling THM formation, but this method may in - 8. Singer, P.C., 2006. DBPs in drinking water: Also, an aerated chlorine contact basin crease effluent total nitrogen concentrations additional scientific and policy considerations may not be effective in THM removal because and produce some toxic nitrogenous and iod - for public health protection. Journal American THM removal by aeration is a function of the inated DBPs in the effluent. Water Works Association , 98, 10, 73-80. initial THM concentration. Aeration does not Adding bromide can shift the formation 9. Tarquin, A.J., 2005. Removal of THMs remove THM efficiently when the THM con - of THM toward bromoform and reduce from drinking water using an induced draft centration is low. The re-aeration step can be BDCM and DBCM concentrations. Post-treat - strip tower. AWWA Water Quality Technology placed after the chlorination and dechlorina - ment, such as aeration, is a viable method of Conference, Quebec City, Quebec. tion process to optimize THM removal by aer - further reducing THM concentrations in the 10. Westerhoff, P., 2006. Chemistry and treat - ation and maintain disinfection efficiency. effluent because of the volatility of THMs. ment of disinfection byproducts in drinking Overall, controlling THMs in wastewater water. Southwest Hydrology , 12, 20-21. Alternative Disinfectants treatment is a challenging task. More study is The use of alternative disinfectants such needed to determine THM precursors in as ozone, chlorine dioxide, and UV for waste -

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