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1 Manuscript for AWWA ACE26 (/2.ffk Awvv A A"'m'rd t',.,,ju'""<< 4' ZX(osiltf>, /"rvcudi{js ) Sa.. /lnle>nib 1 T.rH Greater Boston Drinking Water Quality Comparison of Full Scale and Pilot Study I: Monochloramine and ph change Xin (Cindy) Huang, Graduate Student, Civil and Environmental Engineering Department, Northeastern University, Boston, MA Irvine W. Wei, Ph.D., M.AWWA, Associate Professor, Civil and Environmental Engineering Department, Northeastern University, Boston, MA Windsor Sung, Ph.D., PE, M.ASCE, Program Manager, Chemistry Quality Assurance Department of MWRA, Southborough, MA ABSTRACT Massachusetts Water Resources Authority (MWRA) has been providing drinking water for Greater Boston area since The new John J. Carroll Treatment Plant came online on July 2i h, 25. Ozone instead of chlorine is now used for primary disinfection. MWRA has been monitoring the water quality before and after the new treatment plant was online. In this paper, quantitative comparison is presented between full scale data and data from a pilot study, which was carried out two years ago to study the impact on water quality from this change in treatment. BACKGROUND MWRA water system. Categorized as a very large water system, MWRA provides water to 2.2 million people and 5,5 industrial users. The source water comes from the Wachusett and Quabbin reservoirs, which are located approximately 6 and 9 miles west of Boston respectively. The raw water has a low alkalinity (less than 1 mg/l CaC3), and a hardness of 8 to 18 mg/l as CaC3. Prior to July 2ih, 25, the treatment processes were chlorination for primary disinfection, alkalinity and ph adjustment, and chloramination for residual disinfectant. After the new John J. Carroll Treatment Plant became operational on July 2ih, 25, ozone is now used for primary disinfection. Other treatment processes remained the same but are now consolidated under one roof in the new treatment facility. MWRA has a 3mile pipeline network. Approximately 45 percent of it and nearly 5% of the 5,5mile network of community pipes are old unlined cast iron pipes. These pipes experience corrosion problems as well as biofilm accumulation, which can cause water quality to deteriorate (Sarin et al, 23; AWWA, 1996; Geldreich, 1996).. ;ltr6 1/19

2 Manuscript for A WW A ACE26 During the construction of the new treatment plant, bench and pilot scale studies were carried out to study the impact of this treatment change on water quality. The results from the studies suggested that in transmission lines, ozonation may cause faster monochloramine decay and larger decrease of ph, while in the distribution system, where corrosion and biological activity are present, water quality deteriorated rapidly (ChinLeung, 23; Huang, 25), and the effect from ozonation was usually overwhelmed by that of the pipe wall. Monochloramine chemistry. Chloramines have long been used to provide residual disinfectant in distribution systems where it is difficult to maintain free chlorine residual. Chloramines also have been used to replace free chlorine because they produce less Disinfection by Product (DBP). It has been used for over 5 years in MWRA's system (Sung, 24). Chloramines are produced by combining ammonia with free chlorine. At different chlorine to ammonia nitrogen ratios, different species of chloramines, monochloramine, dichloramine, and trichloramine, may be produced. Monochloramine is the most desirable one for disinfection purpose. Therefore the chlorine to ammonian ratio is crucial to any disinfection facilities. Theoretically the optimum CI2:N weight ratio for monochloramine formation is 5 or less. The ratio used in MWRA is targeted at 4.7, at which ammonia is slightly in excess to obtain the stability of monochloramine. After monochloramine is formed, there are several reactions which could consume monochloramine, autodecomposition (Wilczak et al., 23; Woolschlager, 21 ), reaction with Natural Organic Matter (NOM) (Wilczak et al, 23), and inorganic reducing species such as nitrite or ferrous ion. In the water distribution system, other than the reactions stated above, the corrosion process and the existence of the biofilm on the pipe wall also consume monochloramine (Woolschlager et al., 21). In his study, Woolschlager suggested that a novel acid catalysis reaction that was known to occur on concrete surfaces might cause faster monochloramine decay. It was shown that this mechanism accounted for up to 6 percent of the loss of monochloramine in a distribution system with concrete and concretelined pipes (Woolschlager, 2). Monochloramine decay model. Monochloramine experiences a significant initial drop shortly after its formation, followed by a slower decay afterwards (Valentine et al., 1998; Woolschlager et al., 21; Wei et al., 24). The initial drop within a certain time, after monochloramine is introduced to the treated water, is defined as the Initial Demand (ID). ID is mostly due to the reaction of chloramines with NOM and was found to have a linear relationship with organic matter in the source water (Valentine et al., 1998). For this study, the time period was defined as one hour. The slower decay is described kinetically by kmo. which was suggested by Valentine et al (1998) in a secondorder kinetic model. 2/19

3 Manuscript for A WW A ACE [NH 2Cl], [NH /] hm t (1) where [NH2CI]1 = monochloramine concentration at time t [NH2CI]o = monochloramine concentration at time kmo =the monochloramine decay coefficient, in M" 1 hr" 1. Dominated by monochloramine autodecomposition, the value of kmo is expected to increase with decreasing ph, increasing temperature, and increasing chlorine to ammonia nitrogen ratio (Valentine et al, 1998). Natural organic matter (NOM) is expected to accelerate monochloramine decay (Valentine et al, 1998). Ozonation. When ozone is used for primary disinfection, different source waters may yield different oxidation products. If the source water contains larger organic molecules, ozonation process tends to yield more precursors to the formation of Disinfection ByProduct (DBP) as well as the initial monochloramine demand (Wilczak et al, 23, Singer et al, 1999). It was found that a higher ozone dose for primary disinfection was associated with faster monochloramine decay (ChinLeung, 23). In the distribution system, ozonation was reported to cause a significant increase in the assailable organic carbon concentration as well as in the bacterial counts (Escobar, 21) The ph change. The ph change in the treated water has not been thoroughly studied, despite the fact that it is an important factor for corrosion control. Chin Leung (23) found a ph decrease up to.7 units during 1 days in a bench. scale simulation of the new John J. Carroll Treatment Plant. In the bench study, water from the reservoir was treated with ozone and stored in clean BOD bottles at room temperature, after carbonate has been added for ph adjustment and monochloramine was introduced. It simulated the case of a clean distribution system. In the pilot study, same trend was observed from the homogenous samples, yet the heterogeneous samples experienced an increase in ph (Huang et al, 25). Ozonation seemed to expedite these changes in ph. EXPERIMENTATION The Pilot Study. A Pipe Loop Pilot Plant (PLPP) was constructed at the Wachusett Reservoir. It included ozonation for primary disinfection, followed by ph and alkalinity adjustment, chlorination, and ammonia addition for monochloramine production. The treated water then passed through a series of pipes, which were excavated by Boston Water and Sewer Commission (BWSC) from its distribution system, and used to simulate the actual corroded system conditions. The total estimated detention time of all the pipes was 5.88 hours, based on a flow rate of.16 m 3 /hour (.6 gpm). A recirculation pump was installed to enable the system to simulate the circulation time in the MWRA system, which can have a maximum of up to 1 days. 3/19

4 Manuscript for A WW A ACE26 Ten experiments were carried out over a two year period. For details please refer to Huang (23). After ammonia addition, sample was drawn for bottle study, which was to simulate a very clean distribution system condition. These samples were defined as homogeneous samples, which were free from contact with the pipes. Meanwhile the heterogeneous samples, taken after water contacted with or even recirculated inside the pipes, simulated the conditions such as dead ends far from the water main. Parameters analyzed were temperature, ph, alkalinity, turbidity, dissolved oxygen (DO), total chlorine, monochloramine, total ammonia, total organic carbon (TOC), UV254, nitrate, nitrite, DBP, and total iron. Full scale sampling scheme and sample analyses. Full scale data were collected from both online sensors and field sampling. Distribution system samples were usually collected on Mondays. Field measurements included total chlorine and free ammonia (Standard Methods 45CI G DPD Method), ph (Standard Methods 45H+B Electrometric method), and temperature (APHA 1998). Laboratory measurements included alkalinity (EPA 31.1); nitrate and nitrite (EPA methods and ); and iron, phosphorus, sulfur and zinc (EPA method 2.7). Disinfection byproduct (DBP) measurements follow EPA method 524 for total trihalomethanes (TTHM) and EPA method for haloacetic acids (HAA) are now measured monthly at selected sites, as well as aldehydes, predominantly an ozone byproduct. Bottle study was conducted in the full scale John J. Carroll Treatment Plant. Two experiments were carried out in March 26. Sample was drawn right after ammonia was added in the full scale plant, and stored in 6 amber glass bottles. At subsequent times, one of the bottles was opened and the sample was tested for temperature, ph, total chlorine, and monochloramine and free ammonia. Limitations of the study. The variability inherent in a pilot study did not allow precise control of some of the parameters, e.g. chlorine dose, sodium carbonate and bicarbonate dose, chlorine to ammonia nitrogen weight ratio. The actual water temperature within the pipes was impacted by room temperature, which was not well controlled. Although the new full scale plant was in operation since July 25, there were startup issues and it did not stabilize until the end of the year. Therefore only those data in early 26 were used. Due to the abundance of online and field data, and the variation of the full scale system, monthly average values were used for analyses. RESULTS The pilot study. Within the 1 experiments, four were designed to study the impact of ozonation. The experimental conditions are listed in Table 1. 4/19

5 Manuscript for A WW A ACE26 Table 1 Pilot Study Experimental Conditions Group Group 1 Group 2 Exp# Exp6 Exp7 ExpA ExpB Ozone Cl2 Mono Initial CI2/N dose contact Cone. weight TOC UV254 mg/l min mg/l ratio mg/l Abs/cm Temp oc I { :: C:::==*. ::: == ""'il'"!". =.=:. =*.;"'=.=.=:;; 3 x x..... >< x,.._ :::! 2 +".,._= 1 C)... E _ 1.5 +:===========e u c 1 +1 (.) I. Exp6 Exp 7. ExpA x ExpB I Figure 1 Pilot Study Monochloramine Change in Homogeneous Samples Figure 1 showed the monochloramine decrease over time in homogenous samples. An initial drop of monochloramine concentration was found in most of the homogeneous samples subjected to ozonation. Thus in this study, the difference of the initial monochloramine concentration and the concentration at about one hour after its addition was defined as initial demand (I D). Then starting from one hour and beyond, the second order decay kinetics from Valentine was adopted by plotting 1/[NH2CI]1 1/[NH2CI]1 h r versus time t. The slope of the straight line, after unit conversion, is kmo in (Mhf 1. ID and kmo of the four experiments are summarized in Table 2. Only the experiments subjected to ozonation (Experiment 7 and A) had ID within an hour after the ammonia addition. The other two had no ID at all. This was suspected to be due to ozonation. And the 3 minutes chlorination before ammonia addition may weaken this effect. As shown in Table 1, Experiment 7 had a lower initial monochloramine concentration and higher chlorine to ammonia ratio, which resulted in much less 5/19

6 Manuscdpt for A WW A ACE26 excess free ammonia than Experiment 6. This, rather than ozonation, may be the major contributor to a much faster kmo in Experiment 7 than Experiment 6..3., aJ :. =::! y7=.14x Exp6 Exp7 ExpA X ExpB I Figure 2 Pilot Study Monochloramine Decay in Homogeneous Samples With a lower initial chlor<?mine concentration, and less chlorine to ammonia ratio, Experiment A was expected to have a slower decay than Experiment B. Yet the kmo of Experiment A was slightly greater than that of Experiment B. This is likely to be due to ozonation. Table 2 Pilot Study Monochloramine ID and kmo in Homogeneous Samples Exp# kmo, kmo. R2 ID (mgd/l) 1 (Mhr 1 mg/l Exp Exp ExpA ExpB When ozonation is not used, the complex organic molecules in raw water may have less potential to react with monochloramine and result in a less or no ID. When ozonation is used, it breaks the complex molecules down into simpler ones (Singer et al, 1999), which may be easier to react with monochloramine. In homogenous samples, ozonation expedite monochloramine decay as well as ID. The bench scale study showed a faster monochloramine decay with higher ozone dose (ChinLeung, 23), which is consistent with the finding in this study. Wilczak et al (23) also found an increased chloramines demand contributed by ozonation. As shown in Figure 3, in heterogeneous samples, monochloramine plummeted within one day and was almost depleted after three days in the simulated distribution system. The ID was overwhelmed by the fast decay and thus was not 6/19

7 Manuscript for A WW A ACE26 evaluated for heterogeneous samples. 1/[NH2CI]t 1/[NH2CI] versus time t were plotted only over a 1 day period for heterogeneous samples before the complete depletion of monochloramine. The regression lines in Figure 4 were forced to go through the origin u 1/) 2.5 (Q ::::! 2 C) E 1.5 d c: 1 u.5 \ \\\_ \ I. +. Exp6 Exp 7.._ ExpA. ExpB I Figure 3 Pilot Study Monochloramine Change in Heterogeneous Samples As shown in Table 3 and Figure 4, the kmo of the heterogeneous samples of all the four experiments were two orders of magnitude larger than those of the homogeneous samples, indicating much faster decay in the heterogeneous samples. The impact from ozonation was not able to be delineated from the data '...J 3 6=.1272x C) y7=.139x E u x u Exp6 Exp7 ExpA xexpb I Figure 4 Pilot Study Monochloramine Decay in Heterogeneous Samples 7/19

8 Manuscript for A WWA ACE26 Table 3 Pilot Study kmo in Heterogeneous Samples Exp # kmo. (mgd/l) 1 kmo, (Mh)" 1 Exp Exp ExpA ExpB The change of ph was also studied during the pilot study. After chloramination, ph in the homogeneous samples showed a decrease during the 1 days. As shown in Table 4, with ozonation, Experiment 7 had more ph drop compared to Experiment 6. Same trend can be concluded when comparing Experiment A and B. The overall ph decrease for all the experiments are within.5 ph units in 8 days. The ph increases in the heterogeneous samples are also listed in Table 4. The experiments with ozonation, i.e. Experiment 7 and A, both had a larger ph increase within the 1 days. And the total increase of ph in 1 days was within.9 units. Ozonation seemed to expedite the ph change. Table 4 Pilot Study ph Change in 1 Days Exp# Exp6 Exp7 ExpA ExpB Homogeneous ph Change, unit Heterogeneous The FullScale New System. As stated in the Experimental section, the monthly averages of the monitoring data in the first three months of 26 are used. The raw water quality is presented in Table 5. Table 5 Raw Water Quality of the New System Month Alkali nit Conductivit H Tern TOC UV254 m!ij/l as CaC3 fls!cm c mg/l abs/1\cm Jan Feb Mar The bottle study Bottle study was conducted to evaluate the chloramine decay when isolated from the pipe wall effect. As plotted in Figure 5, monochloramine did not decay more than.7 mg/l over 7 days. Right after ammonia addition was the designated time zero. Since there was no data available at this point, it was impossible to 8/19

9 .. : Manuscript for A WW A ACE26 evaluate 1. The first data point in Figure 5 is at one hour after the ammonia addition. 3.Si 2.5 lq == ; c.) 1 c Exp1 & Exp2 I Figure 5 Bottle Test of the Fullscale New System Monochloramine Change 1/[NH2CI]1 1/[NH2CI]1hr versus time t are plotted in Figure 6. The values of kmo are listed in Table 6. The ph decreases through 7 days are also calculated and listed in Table r,.16 t :7"'l ,... y 2=. :: ::: 1, x,...c ; c,.12 +'7""""=!.s.1 t"7""'::::i.8 t,,l,..l.i y 1 =.8x 'f"'.6 +"""7""=:::r""'t :...4 1't 'f"'.2 t::>? 4 o.,...,...:ri Exp1 Exp2 I Figure 6 Bottle Test of the Fullscale New System Monochloramlne Decay 9/19

10 Manuscript for A WW A ACE26 Table 6 Bottle Test of the Fullscale New System kmo and ph Change Exp 1 2 k kmo ph change (mg/l)1 hr1 M1 hr1 unit The fullscale monitoring data The monthly averages of the monitoring data from the full scale plant are plotted in Figure 7. Time zero was defined as right after ammonia addition, and no data was available, thus no 1 can be calculated. The first data point in Figure 7 is at 5 hours after ammonia addition. The detention times of the other data points are 41 hours, 53 hours, and 7 days (assumed value for end of the distribution system) respectively. 3.!::l 2.5 (.) 1/) 2 co 1.5 c.) 1 c (.) Jan6 Feb6..._ Mar6l Figure 7 Fullscale Monitoring New System Monochloramine Change Due to the distinctive nature of the transmission line and distribution system, the data were separated into two groups according to the location of the sampling points. The first two data points were used to calculate kmo in the transmission line, shown in Figure 8. The other two data points were used for analyzing the distribution system, as in Figure 9. The kmo values are summarized in Table 7. In distribution system, chloramine decays an order of magnitude faster than in transmission line. The ph in the transmission line did not change significantly, considering the slight differences among the ph probes. The ph changes in the distribution system were calculated as the difference of ph at the last two data points in Figure 7 and are listed in Table 8. 1/19

11 .. Manuscript for A WW A ACE26 Table 7 Fullscale Monitoring New System kmo Month Jan6 Feb6 Mar6 Transmission line Distribution System k, (mg/l)1 hr1 kmo, M1 hr1 k, (mg/l)1 hr1 kmo, M1 hr ":'.J C'l E... (,) "" I... (,) "" Jan6 Feb6 A Mar6 J 4 Figure 8 Fullscale Monitoring New System Monochloramine Decay in Transmission Line 14 I.J C'l E... (,) "" I... "" I Jan6 Feb6 A Mar6 j Figure 9 Fullscale Monitoring New System Monochloramine Decay in Distribution System 11/19

12 Manuscript for AWWA ACE26 Table 8 Fullscale Monitoring New System ph changes Month Jan6 Feb6 Mar6 ph change, unit The FullScale Old System. For comparison purpose, the monitoring data from January to March 25 of the old treatment system were also analyzed. The raw water qualities during these months are shown in Table 9. The monthly average data from the old full scale system are plotted in Figure 1. Due to the unavailability of the data at time zero, no 1 can be delineated. The detention times of the data points are respectively 3 hours, 15 hours, 27 hours, and 7 days (an estimation for the end of the distribution system) after the ammonia addition. Month Table 9 Full Scale Old System Raw Water Quality Alkalinit Conductivit H Tem TOC UV254 mg/l as CaC3 Jlslcm c mg/l abs/cm Jan Feb Mar (.) (/) 1.4 ns.j 1.2 C) 1 E.8 <.) c.6.4 (.) 1: I... I a. ';:;. "'.....,.. ''... _ Jan5... Feb5 Mar5l Figure 1 Full Scale Old System Monochloramine Change The first three data points are used for analysis of the transmission line, shown in Figure 11. And the last two points are used for the distribution system in Figure 12. The values of kmo are summarized in Table 1. 12/19

13 Manuscript for A WW A ACE26 Table 1 Full Scale Old System kmo Month Jan5 Feb5 Mar5 Transmission line Distribution system k, (mg/l)1 hr1 kmo. M1 hr1 R2 k, (mg/l)1 hr1 kmo. M1 hr ,,.3 ;:T.x.. 1 ";' y 1=.14x.25 t/'1 ) r1 i u.15 +/=.1 c3.1 t7'"="""t,...5 +,L====...,=1 y 2 =.2x o ======,.r=1 1 Jan5 2 Feb5 "' Mar5 3 Figure 11 Full Scale Old System Monochloramine Decay in Transmission Line 6...,.. :......I 5 t :1>l y1 =.416x 4t=j S y 3=.413x 3 t7 2 +,.. 1 += 2 4 I Jan Feb5 "' Mar5 Figure 12 Full Scale Old System Monochloramine Decay in Distribution System 13/19

14 Manuscript for A WW A ACE26 In the distribution system, kmo is in the order of thousands, which is two orders of magnitude larger than that in the transmission line. No ph change was observed along the transmission line. The ph changes through the distribution system are listed in Table 11. Table 11 Full Scale Old System ph Changes Month Jan5 Feb5 Mar5 ph change, unit DISCUSSION The values of all kmo are grouped and presented in the following three tables and plotted in Figure 13. kmo M1 hr1 Table 12 kmo of Samples Isolated from Pipe Wall Effect Pilot Study Pilot Study Full Scale New System Homogenous Homogenous Bottle Study, Sample, w/o 3 Sample, w/ 3 w/ Average Table 13 kmo of Transmission Line Samples kmo M1 hr1 Average Full Scale Old System Transmission line, w/o Full Scale New System Transmission line, w/ Table 14 kmo of Distribution System Samples kmo M1 hr1 Average Full Scale Old System Full Scale New System Pilot Study Distribution System Distribution System wlo 3 w/ Heterogeneous Sample, Extreme Condition

15 Manuscript for A WW A ACE26 Impact of ozonation on monochloramine ID and kmo As discussed before, ozonation seems to lead to higher ID and kmo, No ID data can be generated from the fullscale monitoring due to the lack of data at time zero. Online monitoring chloramine concentration right after ammonia addition in the new treatment plant would be helpful in collecting data at time zero and delineating ID in future work. Table 12 includes kmo of the bottle studies in both pilot study and full scale new system. They are all in the same order of magnitude, with the ones with ozonation larger than the one without ozonation. The kmo of the new system transmission line is one order of magnitude larger than the bottle test of the full scale new system. Since there is no significant biological activity observed in the transmission lines, this difference might be due to the acidcatalysis reactions from the concrete pipe surface (Woolschlager, 2). In the transmission line, chloramine experienced a faster decay in the new system than in the old one. Ozonation as well as the lack of chlorination process before ammonia addition in the new treatment scheme may contribute to this outcome. 1, T" 1, I.c I 1 c :::1: CJ 1. Pilot study homogeneous sample, w/o ozonation o 2. Pilot study homogeneous sample, w/ ozonation o 3. New system full scale bottle test, w/ ozonation 4. Old system full scale transmission line, w/o ozonation 5. New system full scale transmission line, w/ ozonation o 6. Old system full scale distribution system, w/o ozonation 7. New sytem full scale distribution system, w/ ozonation o 8. Pilot study heterogeneous samples, extreme condition Figure 13 Average kmo of All Sample Groups Impact of distribution system on monochloramine kmo The kmo of both new and old system are in the order of thousands M1 hr1, and are much larger than those of the transmission line. The organic, inorganic, and mostly biological reducing species in the pipe probably caused this faster decay. After the new treatment plant is online, chloramine experienced a faster decay in the distribution system. It seemed that ozone broke down NOM into more readily biodegradable organic matters, which caused thriving of the microorganisms 15/19

16 Manuscript for A WW A ACE26 inside the distribution pipes. Therefore the disinfectant was consumed faster. The TOC changes in the distribution systems support the above hypothesis. As listed in Table 15, the TOC removal, after the new treatment plant was online, is at least three time of that in the old system. Table 15 TOC Change in the Distribution System Month Old system New System mg/l as C mg/l as C Jan Feb Mar Although the kmo of the heterogeneous sample in the pilot study are also in the order of thousands, some of them are almost twice as much as the full scale kmo in distribution system. The pilot heterogeneous samples appear to simulate some extreme conditions in a corroded distribution system, such as dead end. ;t:: c.6.5 ::s Cl).4 (/) <V.3 Q) ".2 :::r: c c 1. Pilot study homogeneous sample, w/o ozonation o 2. Pilot study homogeneous sample, w/ ozonation o 3. New system full scale bottle test, w/ ozonation 4. Old system full scale distribution system, w/o ozonation 5. New system full scale distribution system, w/ ozonation Figure 14 Average ph Decreases One site, during full scale monitoring, was found to have phenomena of denitrification, such as ph and alkalinity increase, low chloramine residual, low free ammonia, high nitrate etc. These are consistent with the findings from the heterogeneous samples of the pilot study

17 Manuscript for A WW A ACE26 Impact of ozonation on ph. During a water treatment process utilizing oxidation, such as ozonation or chlorination, complex organic molecules are broken down into smaller molecules, which may include smallmolecular organic acids. These acids may be responsible for the decrease of ph in homogeneous samples. Since ozone has a higher oxidation potential than chlorine, ozonation may result in the production of more of these acids and expedite ph decrease as compared to chlorination alone. As shown in Figure 14, the ph decreases in the ozonated water (Experiments 7 and A from the pilot study or bar 2, the bottle test, or bar 3 and the fullscale monitoring of the new treatment plant, or bar 5), are always larger as compared to those of chlorinated water (Experiments 6 and B from the pilot study, or bar 1, the fullscale old system, or bar 4). Without ozonation, the ph drop does not exceed.1 ph unit throughout 7 days, whereas ozonated water may have a drop up to.6 ph units. When compare the ph decrease of the new system in the bottle study and in the distribution system, pipe wall seemed to contribute to this decrease. No ph increase was observed in full scale operation except one site where denitrification was detected. CONCLUSIONS The full scale data confirmed the conclusions drawn from the pilot study: ozonation expedites monochloramine decay as well as ph decrease. The values of kmo are in the same order of magnitude as those in pilot study. As summarized in Table 12, 13, 14, and Figure 13, 14, in transmission lines, chloramine experienced a faster decay than in the old system; there is no significant ph change. In the distribution system, TOC was removed as the water flew through the pipes; both chloramine decay and ph decrease are more than those in the old system. MWRA is continuously monitoring the water quality. More data will be available for future studies, e.g. seasonal impact. ACKNOWLEDGEMENT The authors acknowledge the assistance of James Muri, Mary Bezek, and Lisa Wong from MWRA for their assistance during the pilot study, as well as Michael Sheu and Dianne Rossi for running the bottle tests. The authors also appreciate the support of Civil and Environmental Engineering Department of Northeastern University. This paper represents personal opinions of the authors and not those of the MWRA

18 Manuscript for A WW A ACE26 REFERENCES American Water Works Association Research Foundation (AWWARF), Internal Corrosion of Water Distribution Systems, (2n d Ed.), DVGM Technologiezentrum Wasser, AWWARF Report No APHA, AWWA, & WEF, Standard Methods for the Examination of Water and Wastewater, 2 th Edition, Washington, DC. ChinLeung, Dirk, 23. "Bench Simulation of MWRA's Walnut Hill Treatment Plant Operation: Impact of Ozonation on Monochloramine Decay & ph and a Kinetic Study of DBP formation", Master Thesis, Northeastern University, Boston, MA. Escobar, Isabel C.; and Randall, Andrew A., 21, Ozonation and Distribution System Biostability, J. of AWWA, 93:1, Geldreich, Edwin. E., Microbial Quality of Water Supply in Distribution Systems, Lewis Publishers. Huang, Xin (Cindy).; Wei, Irvine. W.; and Sung, Windsor. (25). "Pilot study of Greater Boston drinking water quality changes Monochloramine and ph change", Proc. of the 25 AWWA annual conference, San Francisco, CA. Huang, Xin (Cindy), 23. "Pilot Study of MWRA's Walnut Hill Water Treatment Plant and Distribution System Operation: Impact of Ozonation and Distribution System on Monochloramine Decay & ph', Master Thesis, Northeastern University, Boston, MA. Sarin, Pankaj; Clement, A. J.; Soneyink, Vernon L., and Kriven, Waltraud M., 23. Iron Release from Corroded, Unlined Castiron Pipe, J. of A WWA, 95:11, Singer, Philip C.; Harrington, Gregory W.; Cowman, Gretchen A.; Smith, Marla E.; Schechter, Daniel S., and Harrington, Lori J., Impacts of Ozonation on the Formation of Chlorination and Chloramination Byproducts, AWWA Research Foundation and American Water Works Association, AWWARF Report No Sung, Windsor, 24. Corrosion Control and Chloramine: Discolored Water and Nitrification, Proc. (jh Annual Symposium on Water Distribution Systems Analysis, Salt Lake City, UT. Valentine, Richard L.; Ozekin, Kenan, and Vikesland, Peter J., Chloramine Decomposition in Distribution System and Model Waters, AWWA Research Fondation and American Water Works Association, AWWARF Report No Wei, I. and Morris, J., Dynamics of break point chlorination. Chemistry of Water Supply, Treatment and Distribution. A. Rubin (ed.). Ann Arbor Science Publishers, Ann Arbor, Michigan, /19

19 Manusctipt for A WW A ACE26 Wilczak, Andrzej; Hoover, Linnea L., and Lai, H. Hubert, 23. Effects of Treatment Changes on Chloramines Demand and Decay, J. of AWWA, 95:7, Woolschlager, J.; Rittmann, B.; Piriou, P.; Kiene, L. and Schw,artz, B., 21. Using a comprehensive model to identify the major mechanisms of chloramines decay in distribution systems. Water Science of Technology: Water Supply, 1 (4), Woolschlager, J., 2. "A Comprehensive Disinfection and Water Quality Model for Drinking Water Distribution Systems", Ph.D dissertation, Northwestern University, Evanston, Illinois, USA. Footnotes: 1 MWRA, Charlestown Navy Yard, 1 First Ave, Boston, MA /19