Modeling Cyanogen Chloride Kinetics in Distribution Systems: a Semi-Batch C

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OZONE SCIENCE & ENGINEERING 0191-9512101 $3.00 + .M) International Ozone Association Vol. 23. pp. 15-33 Copyright 8 200! Printed in the U.S.A. Modeling Cyanogen Chloride Kinetics in Distribution Systems: A Semi-Batch C . t Protocol for Natural Waters

Darren E. ~omain',*Robert C. ~ndrews~,Bryan W. ICamey2,and Riccardo ~i~ci~io~

1. Hankin Atlas Ozone Systems Limited, Scarborough, Ontario, Canada. 2. University of Toronto, Department of Civil and Environmental Engineering, Toronto, Ontario, Canada. 3. Enviromega Ltd., Flamborough, Ontario, Canada. * Author to whom correspondence should be addressed Received for Review: 2 February 2000 Accepted for Publication: 24 February 2000

Abstract Experiments were undertaken with the primary objective of developing kinetic relationships for the formation of cyanogen chloride (CNCl), which could then be integrated into a multi-constituent water quality model. The use of ozone in combination with monochloramine has been reported in the literature to enhance CNCI formation. A procedure to determine C t, a surrogate used to estimate the level of microbial inactivation achieved, was also developed using a semi-batch methodology. Water collected from the Mannheirn Water Treatment Plant (WTP) (Waterloo, Ontario, Canada) at 7OC and 20°C was ozonated using a semi-batch procedure to achieve a desired level of inactivation. A series of specific steps were then followed to simulate treatment at the Mannheim WTP as closely as possible at bench-scale. Three different levels of microbial inactivation were selected to simulate 0.5-log Giardia inactivation, and both 1.0-log and 3.0-log Cryptosporidiurn inactivation. Kinetic relationships were developed which described CNCl formation as a function of log Cryptosporidium inactivation, monochlorarnine concentration, and time. It was concluded that CNCI formation followed an exponential function of time that depended on both monochlorarnine concentration and microbial inactivation level.

Key Words

Ozone; Cyanogen Chloride Kinetics; Mannheirn Water Treatment Plant; Cyptosporidium Inactivation; C-t Protocol; Monochloramine Addition;

Introduction regarding the implications of full-scale application. A methodology for performing bench-scale ozone Ozone use in drinking water treatment has been disinfection experiments has been developed to increasing due to proposed regulations that would address this concern. Bench-scale experiments are lower current regulatory limits on disinfection by- often used in preliminary assessments prior to ozone products (DBP) in drinking waters (USEPA, 1994). implementation at pilot- or full-scale. Since the One of the potential barriers to the widespread Surface Water Treatment RuIe (SWTR; USEPA, implementation of ozone is a lack of understanding 1991) is based on the C . t (residual concentration x 15 16 D. Romain el al.

contact time) concept for the inactivation of Giardia directly, as opposed to a batch mode procedure and viruses, the development of a protocol for where "pure" water (e.g., ~illi-~~water) is first conducting experiments at bench-scale utilizing real ozonated and then added to the sample. The term water matrices is required to evaluate disinfection "semi-batch" is used because the reactor is batch practices in these terms. with respect to the water phase but incorporates a continuous ozone gas flow. Batch-type experiments A semi-batch bench-scale C . t protocol using could not be conducted due to the dilution factors natural waters was applied in the evaluation of associated with the high ozone doses required to cyanogen chloride (CNCI) formation kinetics. This overcome the ozone demand. The C . t-inactivation research examined the effect of disinfecting to three relationship for Giardia is given by: levels of inactivation (0.5-log Giardia, 1-log Ctyptosporidium, and 3-log Cryptosporidium) in terms of C . t, on CNCl formation. As well, the subsequent application of 3 levels of chloramination kiardia= 1.04 exp 0.0714(7) [21 was also investigated. The concentration of CNCl N was then measured as a function of time, and kinetic where log ~p is the log inactivation of viable parameters were determined. Experiments such as microorganisms, [O,] is the ozone residual these could be used by utilities to estimate potential concentration in water (mg/L), t is the contact time DBP concentrations and evaluate compliance with (min), kiardiais the pseudo first-order reaction rate DBP regulations prior to either the implementation constant, and T is the temperature ("C). C . t values of ozone or increasing its dosage to achieve higher related to inactivation of Cryptosporidium were microbial inactivation levels. This research obtained by applying two relationships developed by incorporated the results of bench-scale ozonation Finch et al. (1994), which were based on a batch experiments in the development of CNCl formation protocol in pure water. The C . t-inactivation equations that may be used to predict the relationships for Ctypfosporidium are presented in concentration of CNCl reaching a consumer through Eq. [3 ]for 7°C and Eq. [4]for 22°C (Finch et al., a water distribution system. 1994): Background

Disinfection

Inactivation of viruses and microorganisms such as Giardia and Cryptosporidium is a primary objective Using the relationships shown above one can of drinking water treatment. To this end, the determine the ozone residual concentrations required USEPA has promoted the use of a surrogate to for a given contact time to achieve a desired level of estimate the level of microbial inactivation achieved Giardia or Cryptosporidium inactivation. in a given treatment process: the C - t product (USEPA, 1991). The C . t product can be defined Disinfection By-Products knowing only the residual disinfectant concentration C, and the contact time t. Several methods are In general, the use of ozone in combination with available for the determination of both C and t in post-chloramination has been reported to produce full-scale ozone contactors; these are discussed the lowest DBP concentrations when compared to elsewhere (USEPA, 1991). In this study the other combinations of ozone, free chlorine, or relationships between C . t and ozone inactivation of chloramines (Clark et al., 1994,. Lykins et al., 1994, Giardia were obtained from the SWTR (USEPA, Jacangelo et al., 1989). Ozone treatment usually 1991). C t values shown in the SWTR were produces lower levels of halogenated by-products, developed using a batch ozonation protocol. such as trihalomethanes (THMs) and haloacetic acids (HAAs), with the notable exception of For the purpose of the experiments described herein, cyanogen chloride (CNCI) and the brominated ozone was applied to water samples in a semi-batch species such as brornoform, and mono- and di- mode, i.e., ozone was applied to the water sample bromoacetic acid (Shukairy et al., 1994). Ozone Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 17

also results in an increased production of oxygenated DBPs). By contrast, the advection-dispersion by-products such as aldehydes and carboxylic acids equation is a general differential equation that is (Schechter and Singer, 1994, and Weinberg et al., applied to analyze water quality propagation in pipes 1993), as well as bromate (CrouC et al., 1996, Najm and accounts for all common one-dimensional mass and Krasner, 1995, and Shukairy et al., 1994). transport phenomena which occur in pipeline systems. It has been applied by Axworthy and The use of ozone in a treatment train which includes Karney (1996), Lu et al. (1995), and Elshorbagy and monochloramine addition to provide a distribution Lansey (1994) for the purpose of modeling chlorine system residual has been reported to enhance CNCl propagation in pipes. The advection-dispersion formation (Smith and Singer, 1994, Singer et al., equation with a reaction term is: 1994, and Jacangelo et.al., 1989). Smith and Singer (1994) have suggested that formaldehyde, an ozonation by-product, serves as an intermediate in the CNCl formation pathway by way of a reaction where C(x,t) is the constituent (e.g., chlorine) with monochloramine. Although the epidemiology concentration (pg/L), x is the longitudinal axis of CNCl is not well understood at the present time, it distance (m), t is the time (hrs), u is the mean warrants attention due to the unique synergistic velocity of flow (rnh), D is the coefficient of effect of an ozonation by-product (formaldehyde) longitudinal diffusion (m2/hr), and 8 (C(x.t)) is the and monochlorarnine. rate of reaction of constituent (pg L" w'). The first term in Eq. [5] accounts for the change in Distribution System Water Quality Modeling concentration at a point in the system with respect to time. The second term'accounts for the advection of Distribution systems and their associated physical, the bulk water. The third term accounts for chemical, and biological components can influence diffusion. Finally, the fourth term accounts for the DBP concentrations reaching consumers. THM reaction (formation/decay) of the constituent. When concentrations can increase, especially in the first-order kinetics are used to model constituent presence of a free chlorine residual (Baribeau et al., decay, the reaction term can be replaced by 8 1994, Clark et al., 1994a, and Lyn and Taylor, (C(x,i)) = kC(x,t), where k is the. first-order decay 1993). Formaldehyde concentrations have been constant (hr-I). The reaction term for the buIk water observed to decrease due to biological interactions can be determined experimentally as described in (Baribeau et al., 1994, and Levi et al., 1993), this study. More complex reaction terms as however the authors know no research investigating developed by Vasconceles et a/. (1997) to describe CNCl propagation and reaction in distribution pipe wall effects can also be used. ' systems. A series of mass-transport equations (similar to Eq. The simulated distribution system (SDS) [5]) can be set up and solved simultaneously to methodology described by Koch et al. (199 I) as well model the transport of several constituents. The as the uniform formation condition (UFC)procedure reaction term in each equation may be a function of (Summers et al., 1996) yield timeidependent DBP another constituent's concentration. A water quality concentration data. The SDS and the UFC do not on model that incorporates multi-constituent transport their own provide the information required for as well as inter-constituent reactions is capable of incorporation into a numerical water quality more accurately predicting distribution system Framework. However, the data can be manipulated dynamics and hnetics than one which ignores these to provide the desired kinetic relationships. A model terms. This paper describes the methodology used that incorporates DBP propagation and the factors that affect the propagation (e.g., chlorine residual in the development of the inter-constituent reaction concentration) is required to accurately model and terms. predict DBP concentrations reaching consumers. Analytical Methods Numerical water quality models, such as EPANET (USEPA, 1993), are generally capable of describing Ozone advective transport and reaction of both water and constituents (e.g., disinfectants, microorganisms, and Ozone was produced using a 1.2 lblday (0.54 18 D. Romain et al. kglday) ozone generator'. All connecting tubing and Darby (1 992) was used to account for suspended was of either 316 stainless steel or ~eflon~~.All material in the ozonated real water. This method appurtenances were 3 16 stainless steel or ~eflon~- involves taking an absorbance reading of an indigo lined. A custom-made 2.9-L glass reactor2 was used blank (indigo in ~illi-Q~),an ozonated water for all semi-batch ozonation experiments. Two 500- sample, and an ozonated water sample with indigo. mL pyrexTM gas-washing bottles served as The difference in absorbance AA represents the potassium iodide (KI) traps, which were required for difference between the indigo blank plus the the determination of both applied ozone dose and ozonated water sample, and the water sample with off-gas concentrations. A constant ozone gas flow indigo. That is: rate of 0.3 Llmin was used for all experiments; applied doses were achieved by varying the length of AA = Indigo blank + Ozonated water sample - ozonation application time. Ozonated water with indigo PI

The ozone concentration in the supply gas was determined using the ozone demand requirement-semi batch method (Standard Method where b is the path length of cell (cm), V is the 2350 E, APHA, AWWA, and WEF, 1995). Three volume of sample (mL), and f = 0.42. potassium iodide (KT) trap tests were conducted to determine the applied ozone dose prior to Prior to use, the 2.9-L reactor was made ozone- commencing an experiment. An acceptable error demand-free by contacting the glassware with water between the three tests was set at a standard containing a measurable ozone residual. deviation of 2% (maximum error was 1.9%). Ozone off-gas concentration was determined by routing the Cyanogen Chloride ozone through a KI trap following the reactor. , Cyanogen chloride (CNCI) concentrations were Residual ozone concentration in the water was determined using a liquid-liquid extraction measured using the indigo colorimetric method procedure as described by the Metropolitan Water (Sfandard Method 4500-O3 B, APHA, AWA,and District of Southern California (1994). Ascorbic WEF, ' 1995). The spectrophotometric procedure acid (20 mg) was added (to provide dechlorination) employed a Hewlett-Packard Diode Array to each 40-mL sample vial prior to sampling. A 25- Spectrophotometer, Model 8 452~',equipped with a rnL aliquot of sample water was added to each flow through cell utilizing a 1-cm path length and a sample vial. Approximately 10 g of sodium sulfate peristaltic pump Model 89052~'. Ozonated water (Na2S04)and 4 mL of the extraction solvent, methyl was added to a 100-mL volumetric flask containing tert-butyl ether (MtBE), containing an internal indigo until the color was almost completely standard 1,2-dibromopropane (1,2-DBP), was then dissipated. A modification to the indigo added to the sample vial. The sample vials were colorimetric method conducted in this research is sealed, shaken for 7 minutes, and allowed to stand described as follows. The volume of sample V for 10 minutes prior to transferring the MtBE layer added to the 100-rnL flask was determined by to 1.5-rnL autosampler vials. Analysis was always adding known amounts of ~illi-Q~water conducted within 48 hours of sample collection following the ozonated water sample addition. The (typically within 6 hours). A Hewlett Packard 5890 volume of sample V is : Series I1 plusTMGas ~hromatogra~h',fitted with an V = 100-Volume of Indigo-Volume of ~illi-~~[6] HP-5 capillary column3 (30m length, 0.250mm inside diameter) and an electron capture detector This method was preferred over that described in (ECD) was used for all analyses. The minimum S~andardMethods due to its shorter sampling time. reporting level (MRL) for CNCl was determined to A modified indigo method as described by Williams be 0.25 pgL. The temperature program was as follows: 35OC for 1 minute, followed by 10"Clmin to I OzotecTMType S Model 3, Hankin Atlas Ozone Ltd., 120°C. The injector and detector temperatures were Scarborough, Canada, M 1 H 3A6 157°C and 300°C, respectively. ' Dept. of Chemistry, Univ. of Toronto ' Hewlett-Packard (Canada) Ltd., Kirkland, PQ, Canada, H9J 2x8 Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 19

Chlorine Residual t-inactivation equations (Eqs. [I] to [4]). A range of typical inactivation requirements was selected based Free chlorine, monochloramine, and total chlorine on a review of the SWTR Rule (USEPA, 1991) and measurements were conducted with amperimeiric the proposed Enhanced SWTR (ESWTR) Rule titration (Standard Method 4500-C1 D, APHA, (USEPA, 1994b). The desired levels of inactivation AWWA, and WEF, 1995) using a Wallace & for each microorganism are listed in Table I for ~iernan~~Series A-790 amperimetric titrator4. disinfection conducted at 7OC and 20°C. Experiments were conducted at 7OC since C . t- Monochloramine was formed by adding an ammonia inactivation relationships have been reported for this chloride (NE-14C1) solution to chlorine in a ratio of temperature (Finch et al., 1994). The ambient 5:l total chlorine (mg C12/L): ammonia (NH3 as mg temperature of the laboratory in which the NIL). experiments were performed was 20f l°C and as such was selected to perfom the higher temperature All glassware that came into contact with either a experiments. C t-inactivation relationships free chlorine or a monochloramine residual was developed by Finch et al. (1994) at 22OC were made chlorine demand free. This was achieved by directly applied since a 2OC difference'would not contacting the glassware with a 10 mg C12/L chlorine result in significant error. solution prepared in distilled water for at least 3 hours. To evaluate the C t product, the residual ozone concentration was measured over time following the Experimental Protocol termination of ozone gas flow into a semi-batch reactor. Information gained from decay tests include A protocol which allows the generation of bench- the order of decay (typically first order), and the 'scale operational curves that relate applied dose to a decay coefficient, ko3. The equation describing first- desired level of Giardia and Cryptosporidium inactivation was developed first. The resulting order decay is shown below: curves allow an experimenter to apply ozone to achieve a desired level of microbial inactivation. Separate curves must be developed for waters which have different water quality characteristics (i.e., ozone demand). Curve characteristics may also be dependent on reactor configuration and ozone flow where [03], is the ozone residual concentration (mg rates into the reactor. The second part of this section OJL) at time t, [0310is the initial ozone residual describes the protocol that was used to develop the concentration (mg OJL), ko3 is the ozone decay DBP kinetic relationships. coefficient (min-'), and t is the contact time (min). In cases where ozone follows a first order decay, Eq. Applied Dose-Inactivation Relationships [9] can be solved for ko3to determine the decay coefficient, as shown below: Ozone was initially applied at a dose which was anticipated to be near to that required to provide a desired level of Giardia or Cryptosporidium inactivation. h appropriate starting point was an applied ozone dose to organic carbon ratio of 1: 1. Ozone decay was measured over time by taking a series of ozone residual measurements using the Concentration C indigo colorimetric method. The C - t product was then calculated for 6 applied doses (as described in Two methods were investigated to calculate the subsequent sections). Relationships between applied concentration term [O,]of the C . t product as dose and the level of inactivation of Giardia or discussed in the following paragraphs. Method 1, as Cyptosporidium were developed using relevant C . described by Finch et al. (1994), utilized Eq. [1 1] to evaluate [O,],the integrated ozone residual Wallace & Tiernan, Inc., 25 Main St., Belleville NJ, concentration. 07 109-3057 20 D. Romain et al.

t product when the equations developed by Finch et al. (1994) are utilized (Eqs. 3 to 4). This is due to the non-equivalent exponent values on the C and t where [O3Iintis the integrated ozone residual terms. The relative magnitude of the exponents can concentration (mg 03/L),and [O3If is the final weight the C . t product more heavily towards either ozone residual concentration (mg Os/L). the concentration or time tern.

Method 2 was used to calculate the average ozone Bulk Water Protocol residual concentration [03],,,over the contact time and is adapted from Langlais et al. (1991). Ozone was applied to the water samples in a semi- batch mode to achieve a pre-selected Giardia or Cryptosporidiurn inactivation level as shown in Table I. When the required ozonation time was complete, the flow of ozone into the reactor was Either [O,],,, or [03Ji,,was then substituted for [03] terminated. The ozone residual was allowed to in Eqs. [I], [3], or [4] to estimate the level .of dissipate until it was below measurable limits (c0.01 inactivation. Eq. [I21 was derived by integrating the mg 03/L using the indigo colorimetric method first-order decay equation (Eq. [9]) with respect to described earlier). Subsequently, 800 rnL of time t and then dividing by t to determine the ozonated water was transferred fiom the reactor to average ozone residual concentration. each of three narrow-neck 2.5-L amber-glass carbuoys. Chlorine was then added to the water to Time t provide nominal total chlorine residuals of 0.45, 1.8, and 4.2 mg CI,/L after 20s hours of contact time. The equation used to estimate contact time in the The treated water was incubated at either 7°C or semi-batch reactor was derived fiom the first-order 20°C. Experiments were conducted at 7OC or 20°C I decay equation (Eq. [9)]. Solving Eq. [9] for t and due to the availability of Crypfosporidium setting [O,] = 0.01 mg/L, the contact time is inactivation relationships using C . f at these estimated as: temperatures (Finch et al., 1994).

Once the chlorine contact period was complete, 1600 mL of groundwater was added to the treated water. The mixture of ground and surface waters (ratio of 2:l) was selected to simulate the typical protocol The value [O,],= 0.01 mg/L was selected for two used at the Mannheim WTP, Ontario, Canada. The reasons. First, this is the lowest residual that can be addition of groundwater to the treated-water resulted reliably measured using the indigo colorimetric in a dilution of the chlorine residual by 'a factor of method. Second, a residual below this concentration three. Residuals of 0.15, 0.6, and 1.6 mg C12/L were will not contribute significantly to the C - t product sought. The residual concentrations were selected and hence to the inactivation credit achieved due to following a review of available literature to ozone disinfection. represent a range of typical chlorine residual The contact time t exerts only a limited effect on the concentrations observed upon entry into a water distribution system. The 2.5-L carbuoys were not C . t product as defined by the SWTR since there are sealed headspace fiee (a total of 2.4 L of water was equivalent exponent values on the C and t. The t added) to maintain the proper proportions of surface terms cancel, with time t only remaining in the exponential term as shown in Eq. [14]. and grqund water. Monochloramine was formed by adding an ammonia chloride solution to the chlorinated water to achieve a mass ratio of 5:l C12:NH3as N, as per Mannheim WTP protocol. The .t= C [O,] x t= r (I - exp (-tq . I))) [I41 ammonia solution was prepared by adding ammonium chloride to pH 8 buffered ~illi-~~~ Contact time has a more pronounced effect on the C water. Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 21

Table I: Desired inactivation Levels and Associated C . t Products

Level of Microbial Microbe Log Inactivation C t 7°C 20°C Inactivation p 6LIt0.95 p 23t.64

Low Giardia 0.5 0.29' - - Medium CVP~~ 1 .O - 3 .4b - High CVP~O 3 .O - 10.3~ -

Low Giardia 0.5 0.10' - - Medium Cvpto 1 .O - - 1 .22b High CCYpto 3.0 - - 3 .7b

Based on SWTR (USEPA, 1991). Based on Finch et 01. (1994). Table II: Results of Water Quality Analysis for the Mannheim WTP and Well K21

I Parameter I Units I wTP I Well K21 1

PH 7.28 7.69 NPOC mg CL 4.8 2.1 Alkalinity mg CaC03/L 1 18k2.9 275f 2.5 Turbidity NTU 3.5 0.15 W-254 Bromide

The water from the 2.5 L carbuoys was then ~esultsand Discussion subdivided into seven' headspace-free 250-mL bottles, to simulate successive distribution system Water Quality residence times of 0, 1, 2, 3, 8 days. Analysis of the water for at least one residence time in each For the purpose of conducting bench-scale experiment was performed in duplicate and one experiments, "treated water" was collected at a post- other bottle was filled to serve as a backup. settling (pre-ozonation) location from the Mannheim WTP, Waterloo, Ontario, Canada. Groundwater was The incubation temperature was calculated as the collected at the same time from Waterloo's well weighted average of temperatures of the K21. The water quality parameters for both waters ozonatedlchlorinated water and the groundwater. are shown in Table 11. Groundwater was mixed with Groundwater was added at 10°C since this surface water in a ratio of 2: 1 prior to entering the represented the typical year round temperature of the distribution system at the Mannheim WTP. groundwater source. Treated water was either at Groundwater was added to ozonated/chlorinated 7°C or 20°C, the temperatures at which the water water in a ratio of 2:l following a 1 day contact was ozonated. Therefore, the incubation period, prior to ammonia addition. temperatures were 9°C (for the 7°C disinfected water) and 13.3"C (for the 20°C disinfected water). Applied Dose-Inactivation Relationships The complete protocol for the bulk water experiments is summarized in Figure 1. A first-order ozone decay coefficient ko, was 22 D. Romain et al.

determined for each ozone decay kinetic test. The Cyptosporidium at 7°C and 20°C. Operational decay coefficients are listed in Table III for relationships between Giardia and Cryptosporidium experiments performed at 7OC and 20°C. A plot of inactivation and applied dose are shown in Figures 3 decay coefficients vs. applied ozone dose was and 4, respectively. Contact times used in the developed as shown in Figure 2. Well-defined experiments ranged from 1.5 to 38 minutes for the relationships are observed to exist between the first- 7°C temperature water, and 0.9 to 16 minutes for the order decay coefficients and the applied dose at each 20°C temperature water. These relationships may temperature. Until demand is met, there is no then be used to determine the applied dose to obtain measurable residual and the decay is undefined. a desired level of inactivation (Table IV). Recall that "ozone demand" is defined as the point where an ozone residual is measurable. Ozone consumed during the "demand" period is reacting with material that is quickly oxidized; however, some reactive material remains. The decay coefficient decreases as the applied ozone dose (20°C and 7°C) increases. A lower decay coefficient indicates that there is less material to react with the residual ozone. The ozone decay coefficient will approach its auto- decomposition value as all the ozone oxidizable compounds have reacted. That is, ozone will decay (22 hri~ontactPeriod) at the rate it would if there were no material remaining in the water to react with. Similar results Add Groundwater have been reported by Oke et al. (1996), who 2: 1 (G:S) at 10°C developed mathematical relationships between various water quality characteristics and ozone decay rates. Since ozone decay does not follow a simple first-order decay relationship over a range of 5:l (C1i:N) different doses, the incorporation of the decay coefficient into equations describing ozone residual 250-mLBottles concentration and contact time is beneficial. fl Because of the non-simple ozong' first-order decay, Incubate at 13.3"C and 9°C Method 2 as described eeBilie;, was selected to calculate ozone residual concentration. It is not as straightforward as Method 1, but it does incorporate Figure 1: Summary of Bulk Water ~x~drimental more information about the decay kinetics by Protocol . inclusion of decay coefficient term ko3.

The decay coefficients ko, and initial ozone residuals Bulk Water Experiments [O3Iocan be entered into Equation [13] to determine the contact time r. The average ozone residual Three experiments were conducted at the high [03],,,can be determined using Equation [12], if ko,, temperature (20°C ozonation and 13.3"C incubation) while two experiments were conducted at the low [03]o,and t are known. Concentration and time may then be defined as [03],,,and t, respectively. temperature (7OC ozonation and 9°C incubation). Both desired and achieved log inactivations are The level of Giardia inactivation can be determined shown in Table V. The operational curves served by substituting [03],,,and r into Equation [I]. This well when estimating applied ozone dosages at 20°C procedure is described in detail by Romain (1996). for the 3-log Cryptosporidium and 0.5-log Giardia Similarly, the level of Cryptosporidium inactivation inactivation levels. A +0.2-log inactivation error can be determined by substituting [03],,,and t into was observed when attempting to obtain a desired 1- Equation [3] for tests conducted at 7°C and Equation log Cryptosporidium inactivation. The operational [4] for 20°C tests. , Applied dose-inactivation curves did not estimate inactivations at 7OC. relationships were developed for both Giardia and Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 23

Table III: Summary of Ozone Residual Decay Experiments

Applied Decay Coefficient

Ozone 10310 k03 Tuz'

(mg 03fL) (mg o&) (m1n-I) (mi4 R' No. of Observations

Ozonation at 7°C , I

Ozonation at 20°C

In 2 a Half-life, TIlz= - ko, Table IV: Required Applied Ozone Doses for Desired Inactivations

Microbe Desired Log Applied Dose (mg OJL) , Reference Inactivation Figure 7°C 20°C

Giardia 0.5 0.96 1.32 3 CTP~O 1 .O 1.43 1.84 4 crypt0 3.0 2.0 4.2 4

Chlorine Modeling incubation temperature expeiiments, respectively. The error term is the standard deviation of all data

Free chlorine, monochloramine, and total chlorine points divided by the average residual. , concentrations were measured throughout the course of all bulk water experiments. Following the Zero-, first-, and second-order curves were fit to the addition of ammonia, monochloramine was the experimental monochloramine data. Only dominant species constituting 83+15% and 93*4% monochloramine was modeled since it represented of the total chlorine residual for the 13.3"C and 9°C most of the total chlorine residual present. Also, 24 D. Romain et al. monochloramine in natural waters has been shown al. (1996) and are of the same order of magnitude as to react to form CNCl (Smith and Singer, 1994, and those measured in this research (1.27-1.63 x 10" Jacangelo. et al., 1989) and therefore is of primary min-'). interest. Relationships for zero-, first-, and second- order reactions are shown as Equations [IS], [16] and [17], respectively.

d [NH, Cl] = -~[NH,cI]~ dt where [NH2Cl] is the monochloramine concentration 1 2 3 4 (mg CI2/L), t is the time (hrs), and k is the decay Applied Dose (mg O&) coefficient.

The decay coefficient for each reaction order was Figure 2: First-Order Decay Coefficient, kq , vs. Applied Dose for both 7OC and 20°C. determined for all experimental data by minimizing the error of the sum of squares. The sum of the Cyanogen Chloride Modeling squares of the difference between the value determined utilizing either the zero-, first-, or Multi-Constituent Cyanogen Chloride Model second-order equations and. the experimentally measured value are minimized. Equation (181 is an Three multi-constituent models were developed on example of the minimizing function for first-order the basis of Equation 20. decay. Sminminimize (C (~H2C1]obtcrvcd - ~2~l]prcdic1cd)~)[18] drCNC'l = k.[~~~~l]~(lnact~cxp dt where:. [~2Cl]predictcd= w2cI]0exp(-kt) [201 [l91 where [CNCI] is the cyanogen chloride The least squares analysis was performed using a concentration @g/L), t is the contact time (hrs), k* is commercial spreadsheet5. The results of the least- the reaction rate coefficient (determined squares analysis are shown in Table VI. First-order experimentally), [NH2CI] is the monochloramine decay was selected to model monochloramine - residual concentration (mg C12/L), Inact is the kinetics since it had the lowest sum of squares. R- negative log inactivation (Inact - In N ) of squared values were only calculated for the first- ( Nl order models since the zero- and second-order Cryptosporidium (dimensionless), E is the activation models were not examined further. The R-squared energy (9, T is the temperature (K), R is the gas values are quite low indicating a low correlation constant (8.314 JK), and 4 P & S are between data and the first-order models. A possible experimentally determined coefficients explanation for this result is that zero-order reaction (dimensionless). The form of this equation is similar kinetics were observed to more appropriately to one proposed by McKnight and Reckhow (1992) characterize monochloramine residual decay at very for chlorine and acetaldehyde decay. The term, low levels (c0.1 mg C12/L). Inact, in Equation [20] is used in lieu of an initial formaldehyde concentration. Formaldehyde is a Monochloramine first-order decay coefficients of suspected intermediate in the formation of CNCl 1 .O- 1.5 x 10" min" have been reported by Haas et (Smith and Singer, 1994). The use of this surrogate is justified if formaldehyde formation is considered to be a function of inactivation (inactivation is a ' Microsoft Excel 5.0 Solver, Microsoft Corp., Redwood function of applied dose) and formaldehyde is WA . assumed to behave according to first-order kinetics. Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 25

20 4.0 18 5 3.5 g 16 3.0 2 14 12 5 '5 ID -i2.0 P0 1 B $ 1.5 5 6 'a 2 4 -p 1.0 2 2 0.5 0 0.0 0 I 2 3 4 s (mg Amlied Dox W) Applied Dox (mg W)

Figure 3: Operational Relationship 'Between Inactivation Figure 4: Operational Relationship Between Inactivation and Applied Dose for Giardia at both 7°C and 20°C. and Applied Dose for ~r~~tos~oridiurnat both 7°C and 20°C.

2.0 2.0 1.8 1.8 1.6 1.6 1.4 1.4 i.2 2a 2 1.2 3 1.0 1 g A:: 0.8 UF 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 0 24 48 T?. 96 120 144 168 192 0 24 48 12 % I20 144 I68 192 Time (hrr) Tim (hrs)

Figure 5: Effect of inactivation level on CNCl formation at Figure 6: Effect of inactivation level on CNCl formation at a 9°C incubation temperature: 0.5-log Giardia inactivation, a 13.3"C incubation temperature: 0.5-log Giardia initial total chlorine residual of 1.28 mg C12/L; and 1.4-log inactivation, initial total chlorine residual of 0.48 mg C12iL; Cyptosporidium inactivation, initial total chlorine residual 1.2-log Cryptosporidium inactivation, initial total chlorine of 1.36 mg CI2/l.. residual of 0.40 mg ,C12/L; and 3.0-log Cryptosporidium inactivation, initial total chlorine residual of 0.50 rng C12/L. 26 D. Romain et al.

Table V: Desired and Experimentally Achieved Log Inactivations for Bulk Water Experiments

EXP Target Log Inactivations Lo310 kc% Trans 01 vrms

# Organisms Achieved Desired (mg OJL) (ms') (mg O&) (%)

20°C Disinfection

1,2,3 CVP*~ 3.0 3.0 0.74 0.30 1.27 3 1 4,5,6 Giardia 0.50 0.50 0.12 0.89 0.62 47 7, 8,9 Crypt0 1.18 1.OO 0.25 0.7 1 0.64 35

7°C Disinfection

101112 Cvpto 1.4 3.0 0.39 0.14 0.92 46 13,14,15 Giardia 0.50" 0.50 NA NA 0.62 63

. Assumed due to insufficient data points. NA Not Available

Table VI: . Monochloramine Modeling Results for Bulk Water Experiments

Reaction Minimum Sum k

Order of Squares (K') R~ I 9°C Bulk Water Experiments I 1 zero 1 0.41 1 1.78~10.' 1 NA ( First Second

I 13.3OC Bulk Water Experiments I Zero First Second

NA Not ~vailable-R' values for zero and second order were not evaluated. Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 27

2.0 l .8 1.6 1.4 1.2 2a - 1.0 Z, z 0.8 U 0.6 [NH2CI]O - 0.10 mg CWL 0.4 [NH2CI]O = 0.40 mg CWL 0.2 0.0 0 24 48 72 96 120 144 168 192 Timc (hn) Time (brr)

~igure8: Effect of incubation temperature on CNCl formation: 13.3"C incubation experiments had a 1.2-log Figure 7: Effect of initial monochloramine concentration on Cryptosporidium inactivation and an initial total chlorine CNCl formation at a 13.3"C incubation temperature and a residual of 1.16 mg C12/L, and 9" incubation experiments had 1.2-log Cryptosporidium inactivation. a 1.4-log Cryptosporidium inactivation and an initial total chlorine residual of 1.36 mg C12/L.

CNCI Modcl (T-w) 2.0 2 5 1.5 _' 1.0 .-L1 U E 1.0 ; C 8 0.6 0.4 0.2 0.0 0 24 48 72 96 120 144 168 192 0 24 48 72 96 120 Timc (hn) Time (hrt)

Figure 9: 1.4-log Cryptosporidium inactivation, initial total Figure 10: 3-log C~yptosporidiuminactivation, initial total chlorine residual of 1.06 mg C12/L, incubation temperature of chlorine residual of 0.24 mg C12/L, incubation temperature of 13.3". 28 D. Romain et al.

The form of Equation [20] is that expected for the (-0.40) in Equations 20 and 21 would indicate that product of two exponentially decaying compounds higher levels of Cryptosporidium inactivation result (CNCI and formaldehyde). in lower CNCl concentrations. This is counterintuitive since CNCl formation has been Isothermal equations were developed to model CNCl hypothesized to result fiom an intermediate reaction formation at each temperature and an equation was with formaldehyde, an ozonation by-product (Smith also developed to model CNCl .over a range of and Singer, 1994). Formaldehyde formation has temperatures (between g0C and 13.3OC). Isothermal also been reported to increase with increasing ozone models do not include the Arrhenius temperature dose (Andrews, '1993, and Zhou et al., 1992). An modification term, exp -L . An integrated form increase in formaldehyde production with an ( RJ increase in ozone dose would imply an increase of of the equation which was used to evaluate the CNCl since formaldehyde Serves as an intermediate coefficients in Equation 20 is shown below. in CNCl. production. Smith and Singer (1994) and Andrews (1993) reported increased CNCl formation k ' [CNCI] = - ~2~1]a(~nact)Bexp with increased dose. Smith and Singer (1994) also 6 report that there exist other intermediates which are involved in the CNCl formation reaction, including CH2=NCI. Oxidation of an intermediate in the where Const is an integration constant. It is CNCI formation pathway of this specific water important to note that the level of inactivation is matrix may occur resulting in the inverse expressed in terms of Cryprosporidium inactivation. relationship between inactivation level and CNCl For Giardia inactivation experiments, the level of formation at 13.3OC. If an intermediate compound Ctyprosporidium inactivation achieved during the that is limiting the reaction is not in excess, CNCI same experiment must be used as the input value. formation may be dampened. For example, 0.19-log and 0.76-log Ctyplosporidium inactivations represent 0.5-log Table VII: Coefficients for Isothermal CNCl Formation Giardia inactivations at 7OC and 20°C, respectively. Equations Coefficient 9°C 13.3"C The coefficients in Equation [21] were evaluated using ~olver'. Detailed calculations have been previously presented by Romain (1 996). The coefficients for these equations are shown in Table VII. The standard deviation, s, of the models as. calculated using Equation 122) (Box et al., 1978) are 0.13pgIL and 0.15pg/L for the temperatures of goand 13.3'. respectively.

where n is the number of measured data points, and a k is the number of parameters being fitted. Setting E = 0 results in exp I producing an isothermal model. An exponential value (aand pin Equations [20] and Const was set to 0.26 ,ug/L, .the average [CIvcr]~in [21]) approaching zero indicates that Experiments 4 and 5. monochloramine residual concentration and log Const was set equal to 0 a,the average initial Cryptosporidium inactivation have less weight in the [CNCd concentration. CNCl formation equation. A positive exponent indicates a proportional relationship between CNCl formation and the variable, and a negative exponent A positive associated with the 9°C experiments indicates a inversely proportional relationship. does not contradict the negative value observed for Using the values for p at 13.3OC from Table VII the 13.3"C experiments. The inactivation levels in Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 29 the low temperature experiments do not cover the required to develop temperature dependent range of inactivations achieved for the high equations. temperature experiments (0.5-log Giardia inactivation to 3.0-log Cryptosporidium inactivation Single Constituent Cyanogen Chloride for the 13.3"C experiments compared to 0.5-log Model Giardia inactivation to 1.4-log Cryptosporidium inactivation for the 13.3"C experiments). There was A model was developed which could be used negligible difference in CNCl formation in the without a numerical water quality model framework. 13.3OC experiments when comparing. 0.5-log The single constituent model is shown below. Giardia inactivation to 1.2-log Cryptosporidium k' inactivation. The effect of the level of inactivation [CNCI] = - [~1~~1]0"(1nacty(1 - exp (-a))+ on CNCl formation at and 13.3"C is shown in 6 Figures 5 and 6, respectively. An increase in CNCl Const 1241 formation is observed for an increasing inactivation where w2ClIo is the initial monochloramine level for the 9°C experiments, while a decrease in residual concentration (mg CI2/L). Equation 24 is CNCl formation is observed for an increasing the integrated form of Equation 20 with exp -,= inactivation level for the 13.3OC experiments. It can ( 2 be concluded from these results that increasing the 1. Coefficients in Equation [24] were determined level of inactivation at the high temperature will using the same methodology as the multi-constituent result in lower CNCl concentrations reaching the model. The single constituent models for incubation consumer. At low temperatures, an increase in temperatures of 9°C and 13.3OC are shown in inactivation would result in higher CNCl Equations [25] and [26], respectively. concentrations reaching the consumer. [CNCI] = 0.95[~~~~1]~~~~~~(1nact)~~'~~(1 - exp Monochloramine concentration had a significant (-0.028t)) + 0.26 PSI effect on CNCl formation at 13.3OC as illustrated by [CNCI.] = 1.4 1[~~~Cl.]~~.'~~(~nact)~.~~ (1 - exp the an a = 0.14. This is as expected. The exponent (4.033t)) (26) tern on the 9°C experiments was not significant and had a negligible effect on CNCl formation. The effect of monochloramine residual on CNCI Incorporation of' the Arrhenius temperature formation is shown in Figure [73 for 13.3"C modification term to develop a single constituent temperature experiments. equation which could account for temperature variations was not sought following the problems The coefficient associated with the time term (6 in with convergence in formulating the rnulti- constituent model. Equations [25] and [26], once exp (-a)) is essentially the same for both developed for a specific water, can be utilized as a temperatures (~0.28). This indicates that residence quick "back of envelope" calculation to determine time effects on CNCl formation are independent of potential CNCl concentrations reaching consumers if temperature. residence time is how. An individual can simply substitute the desired inactivation level, Inact, the Equation [23] represents the general CNCl formation monochloramine concentration entering the model incorporating a variable temperature term. distribution system, [NH,ClIo, and the residence time t from the treatment plant to the point of interest.

(-%)exp (-0.027r) The accuracy of the single constituent model however may be questionable since it lacks the Equation 23, developed using Solver, was observed incorporation of pipe wall effects that could be to be highly unstable. The lack of stability was accounted for by a calibrated numerical water probably due to the relatively small range of quality model. Pipe wall effects on CNCl temperatures (a 4.3Odifference) used in the formation/decay were not identified at the time of experiments. A larger range of temperatures may be this research but can be determined by conducting a 30 D. Romain et al. sampling program and subsequent numerical water quality model calibration. It is hypothesized by the 1. Monochloramine concentration had less of an authors that CNCl formation may be dampened due effect on low temperature CNCl formation then to the biodegration of formaldehyde (an intermediate on high temperature formation. serving as a precursor in CNCl formation) by biological activity in the bulk fluid and the biofilm 2. The low temperature isothermal model (9°C) on pipe walls (Baribeau et al., 1994, and Levi el al., predicts a proportional relationship between 1993). The reduction in the availability of CNCl formation and inactivation level while the formaldehyde may decrease CNCl formation, if high temperature isothermal model (13.3"C) formaldehyde is the limiting substance in the CNCl predicts an inverse relationship. formation pathway. If CNCl formation is reduced by pipe wall biofilm, the stand-alone model will When all data are used to develop the general CNCl predict higher CNCl concentrations reaching formation equation (Equation [23]) two numerical consumers than actually occur. The single phenomena will occur: the proportional and inverse constituent model would therefore provide relationships with respect to CNCl formation aAd conservative estimates of CNCl concentrations inactivation level will almost cancel each other out reaching consumers. as shown in Equation 1231 by the Inact exponent equal to -0.012, the proportional effect of Summary of Bulk Water Experiments monochloramine concentration on CNCl formation will be dampened by the slightly inverse relationship Two example plots of CNCl formation as predicted predicted by the low temperature experimental data. by the isothermal multi-constituent models (CNCl Because of these phenomena,. a general CNCl Model) using Equation 20 with T = 0, the single formation predictive equation would poorly model constituent model (CNCI Model (MO)) which was CNCl forrnation over many of the experimental developed using only initial monochloramine conditions investigated in this research. . concentrations using Equations [25] and [26], and the general form of the multi-constituent model (CNC1 Model (T=Var)) are shown in Figures 9 and 10. The first-order monochloramine decay model is also plotted on each graph W2Cl Model) to illustrate the correlation between the reduction in monochloramine concentration and the formation of CNCI.

As shown in Figures 9 and 10, CNCl formation is predicted accurately by both the isothermal model and the single constituent model. Monochloramine data is accurately modeled using the first order decay model. The general multi-constituent model, however, does not predict CNCl formation accurately for the high temperature experiments Figure 11: Comparison of predicted and actual mean while producing an accurate model representing low cyanogen chloride (CNCI) concentrations for all temperature experimental data. The isothermal experiments. equations predicting CNC1 concentration were compared to the observed CNCl concentrations in Figure 11. The points were normally distributed with an R' of 0.6. If the points in the upper left hand Conclusions comer were eliminated, an R* of 0.86 would be calculated. Experiments were conducted to develop DBP and disinfectant residual kinetic relationships with the After reviewing all CNCl data and the equations aim of incorporating them into a multi-constituent which were used to model CNCl forrnation the water quality model. General conclusions are listed following observations may be reported. below: Modeling Cyanogen Chloride Kinetics in Distribution Systems: C-t Protocol 31

Future Work 1. A inverse relationship was observed between log inactivation of Cryptosporidium and CNCl A natural extension to this research is to incorporate formation at 1 3.3OC, indicating that an increase the advection-dispersion equations which include in ozone dose to meet higher levels of CNCl formation and monochloramine decay terms Cryptosporidium inactivation will result in into a numerical multi-constituent water quality lower CNCl concentrations in the distribution framework. The complete model could then be system. It has been hypothesised that an calibrated using field data. The calibrated model intermediate in the CNCl formation pathway could then be used to determine hydraulic, and pipe other than formaldehyde was oxidized in this wall effects on CNCl formation within a distribution specific water during ozonation, thus limiting system. In addition, the model could be expanded to CNCl formation. include more variables which may have an effect on CNCl formation such as precursor material (organic 2. The isothermal multi-constituent CNCl carbon), concentrations of constituents such as formation equations developed in this study are formaldehyde and other DBPs, as well as water of a form that may be incorporated into a water quality characteristics such as pH. Seasonal water quality model. Advection-dispersion equations quality variations in addition to waters obtained including the CNCl formation and from other sources should also be investigated in rnonochloramine decay terms at g0C are shown terms of applied dose-inactivation and CNCl in Equations 27 and 28, respectively. formation relationships.

afCNC11 + B[CNCI] + a2[CNCI] + Fundamental work is required to further investigate at ax ax2 the factors which affect cyanogen chlonde kinetics. 0.027[~~~~1]~~.~'~(1nact)~.'~~exp (-0,028t) = 0 [27] It is unknown at what ratio of free chlorine to monochloramine that cyanogen chlonde will form as opposed to decay.

Acknowledgments

The authors wish to acknowledge Hankin Atlas Advection-dispersion equations including the CNCl Ozone Systems Ltd. for the loan of an ozone formation and monochloramine decay terms at ' generator and monitors, technical support, and 13.3OC are shown in Equations [29 ] and [30], providing partial financial support through a Natural respectively. Sciences and Engineering Research Council a[CNCIl + B[CNCI] + a2[CNCI] (NSERC) Industrial Scholarship. NSERC Canada is at ax ax also acknowledged for providing direct financial + 0.045 [~~~~1]~.'~~(1nact)".~~exp (-0.03 1t) =O [29] assistance for this research. The authors acknowledge the Regional Municipality of Waterloo including the personnel at the Mannheim WTP, specifically Franklyn Smith and Brian Pett, who contributed both time and energy in support of this research. In addition, the authors acknowledge 3. ~onochloraminedecay was observed to be best Professor Susan Andrews, University of Waterloo, described by first-order decay kinetics when Ontario, Canada, Department of Civil Engineering, compared to zero- and second-order decay for providing advice concerning the cyanogen kinetics. chloride extraction method.

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