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Home , Bromate, Bromine dioxide

PRODUCTION IN CONTACTORS

Richard S. Yates, Graduate Research Assistant Michael K. Stenstrom, Professor and Chairman Department of Civil Engineering University of California, Los Angeles, 90024

Abstract A pilot-scale study of the ozonation of surface waters containing moderate levels of .(Br-) was conducted in order to collect kinetic parameters suitable for modeling the production of bromate. Operating in a pre- ozonation mode, the two surface waters were dosed under conditions designed to theoretically provide greater than 0.51ogto inactivation levels for Giardia. Key results from the experimental study and kinetic analysis of bromate formation in these two waters are:

1) Bromate production results from rapid free radical processes. The slower, recursive reactions involving the direct oxidation of bromide and by ozone are insignificant. 2) Ozone residual is the controlling factor in the rate and extent of bromate formation.

3) Hypobromite and hypobromous acid are formed primarily as minor byproducts of oxybromine radical decay, and do not play a significant role as precursors at pHs less than 9.0.

4) Naturally occurring organic matter plays a complex role in production and consumption of both radicals and possibly oxybromine radicals.

5) Gas-liquid contactor hydrodynamics play a critical role in bromate formation, influencing mass transfer rates, peak ozone residuals, spatial-temporal concentration gradients, and liquid backmixing phenomena.

INTRODUCTION

Boomate Toxicity Oral feeding studies involving rodents have shown that the ingestion of bromate (Br03) via drinking water can promote the formation of renal tumors (Kurokawa et al., 1987). Given this data, the United States Environmental Protection Agency (USEPA) has classified Br03 as a possible human carcinogen, and is likely to propose a maximum contantinant level in the range of 5 - 10 ,ug/L .

Initial mechanistic studies on the toxicity of Br03 have focused on the

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formation of 8-hydroxy-deoxyguanosine (8-OHdG), an oxidation byproduct (1) 03 + Br- -~ BrO- + 02 of the DNA guanosine, as a possible cause for the production of renal kt = 160 M-t s-' tumors (Kasai, 1987). As guanosine has the lowest oxidation potential, E' = 0.71 V, of the DNA bases, guanosine acts preferentially as an electron source 03 + BrO- - Br- + 202 (2) for the reduction of other DNA bases, as well of radical adducts as most k2 = 330 M"t s-t other organic and inorganic radicals (Jovanovic and Simic, 1986). + BrO +02 (3) At acidic pHs, as may occur .under physiologic conditions, BrO3 is a 03 Br0' -" moderately strong oxidant, E' =1.15 V, with reaction rates generally k3 = 100 M-? s t proportional to (H +)2SFigure 1) (Noyes, 1980; Jwo and Chang, 1989). Under (4) these conditions, Br03 is known to react directly with a number of aromatic 03 + Br02 - Br03 + 0 compounds, particularly hydroxy-aromatic and amino-aromatic compounds, k4 = > 1 x "~ M-i s-t generating aromatic radicals (Orban and K6r6s, 1978; Herbine and Field, In this model, the oxidation of hypobromite (BrO-) to bromite (BrO,) is the 1980). Furthermore, the decay of Br03 under strongly acidic conditions result, control strategies exhibits complex autocatalytic behavior (Field et al., 1972). As a result, a rate controlling step in the formation of BrO3. As a for minimizing BrO3 formation have been based primarily on minimizing number of other oxidants, such as dioxide (Br02), bromite (Br02), reduction and bromine (Br2), which are capable of generating organic radicals and hypobromite (BrO-) concentrations, either through pH brominated organic species, may be cyclically regenerated during the (5,6) reduction of BrO3 (Noyes, 1980). In particular, Br02 (E =1.33 V) is known HOBr : H+ + Br0- to rapidly oxidize a variety of organic compounds, and is likely to play a key PKa = 8.8 role in the formation of organic radicals under physiologic conditions (Nets et al. 1988). or reactions with ammonia (NH3) (Haag and Hoign6, 1983; Wajon and Morris, 1982; Pastina Christina, et al., 1984). Based on the lack of reaction during in vitro studies of the interaction of Br03 with guanosine, Kasai et al. (1987) concluded that the oxidation of the HOBr + NH3 + NH2Br + H2O (7,8) guanosine base resulted from indirect radical reactions, possibly involving the k7 = 7.4 x 107 M'1 s-1 hydrogen peroxide (H202) induced formation of oxygen radicals. However, kx = 0.3 s-t the details of this study were not noted, particularly the pH ranges over which this reaction was studied, and whether any substances were added to induce In a previous pilot-scale study, the formation of bromate (Br03) was found the decomposition of Br03. Based on the previous discussion, it would to increase under conditions designed to optimize the production of hydroxyl appear that it is not the simple presence of Br03, but the rate and extent of radicals (OH) (Metropolitan Water District of Southern California and James Br03 decay which control the formation of organic radicals. M. Montgomery, Consulting Engineers, Inc., 1991) The PEROXONE process, which involves the optimized pre-addition of H202 to the 03 contactor A number of kinetic models are available for modeling the decay of Br03 at influent, was found to significantly increase Br03 formation. acidic pHs in the presence of aliphatic and aromatic compounds (Edelson et al., 1979; Field and Boyd, 1985; Gydrgyi et al., 1985; Gydrgyi and Field, 1991 ; The fact that Br03 formation increased under these treatment conditions is Turanyi et al., 1993). While these models may prove to be simplistic in particularly interesting in that H202 has long been known to rapidly reduce comparison to human physiology, they may be of some use in modeling the HOBr and BrO- to Br- (Young, 1950; Buxton and Dainton, 1968). decay of BrO3 within the human gut. (9) HOBr + H202 - Br- + H + + H2O + 02 Previous Studies_ Recent studies of the formation of bromate during the ozonation of bromide- k9 = 5.8 x 104 M-t s't containing surface waters have focused primarily on the direct oxidation (10)pathway, as described in the extensive study of the oxidation of Br- to BrO3 BrO- + H202 -~ Br- + H O + 02 in distilled water by Haag and Hoign6 (1983). kta = 5 x 105 M-t si (assumed rate) Given that the rate of HOBr reduction by H202 is much greater than the rate method using ozonated surface water, the gravimetric method samples were of oxidation of BrO- by 03, particularly at a pH of 8.0, the high levels of found to have higher 03 residuals, 0.453 vs. 0.392, with equal precision for Br03 formed during these experiments could not have fbeen a result of the both methods (n=20). The apparent difference between the two methods with 03 losses oxidation of BrO- or HOBr by 03, OH, or other oxidizing radicals. appears to be due to a negative bias of the volumetric method Furthermore, it would appear that the oxidation of Br- by OH, not 03 resulting from offgassing during turbulent thin layer flow down the neck of the volumetric glassware, as well as 03 decay prior to bulk mixing during the (11,12)OH + Br- ; BrOH- neck filling portion of sampling. M-1 S1 k1l= 1.1 x1010 .3 x 107 1 Hydrogen Peroxide k12 =3 s method with is the initial reaction in the formation of BrO3 under these conditions Hydrogen peroxide was analyzed by the enzymatic fluorescence (Zehavi and Rabani, 1972). modifications as suggested by Zika and Saltzman (1982) and Zepp et al. (1988). 03 was stripped from solution using a oil-free compressor with the diameter spherical diffuser at the bottom of These conclusions are supported by the results of testing involving the pre- gas passing through a one-inch addition of NH3 to 03 contactor the graduated cylinder. The stripping procedure was followed to eliminate influent. At concentrations up to 0.5 mg- resulting from N11, NH3 was found to have little impact on the formation of BrO 03 residuals and the consequent artifact formation of H2O, 3 (Krasner p-hydroxyphenylacetic acid- during sample et al., 1993). As the rate of reaction of NH3 with HOBr is extremely rapid, the reaction between 03 and even at low pHs, the lack of any significant impact on addition. The fluorescence reagent was prepared as described by Kok et al. BrO3 production peroxidase was used indicates that Br03 formation results from reactions not involving the HOBr (1986) with the exception that 50 mg/L of horseradish and BrO- species. in the preparation of 100 niL, of fluorescence reagent (Zepp et al., 1988).

Based on this analysis, further pilot scale tests were conducted to examine Bromate the chromatography using bicarbonate-carbonate impact of contactor operations on the kinetics of BrO; formation by a Bromate was analyzed by presumed free radical mechanism. eluent and a 200 pL injection loop (Krasner et al., 1993). During the period over which these experiments were conducted, the minimum reporting level METHODS for Br03 concentration was lowered from 5 ug/L to 3 ug/L. Unless otherwise noted, 03 residuals were allowed to decay within the sample Q3 residuals bottles. Sample quenching was accomplished by the addition of sufficient upon bottle filling. 03 residuals were measured by a gravimetric adaptation of the standard diethylamine to produce a 100 ppm solution volumetric indigo technique. The volume of ozonated water added to a flask Carbon and UV Absorbance containing indigo was determined by weighing the flask prior to sampling and Bromide. Total Organic after sampling, with the Bromide, and total organic carbon were measured in accordance to method difference being equal to the sample volume. 03 measured in a 1 cm cell residual were calculated from the formula description in Standard Methods. UV absorbance was at 260 nm. 03 (mg/L) = (ABS * TV) Blank - (ABS * TV) Sample 0.42*SV*1 Surface Waters Two surface which are imported to the Southern California region were East Branch aqueduct, where ABS = sample absorbance at 600 studied. State Project Water (SPW), taken from the nm of the experiments . SPW is impacted by saline water TV = total volume = SV + indigo aliquot (mL) was used in the majority SV prior to transport to Southern California reservoirs. As a result, Br- levels = sample volume (ML) range of 0.15-0.45 mg/L. 1 = absorbance pathlength (cm~ have varied over the past several in the 0.42 = E / MW = (20,000 M-1 cm- /48,000 mg/mole) Colorado River Water (CRW) was used in a number of experiments to From this compare Br03formation in different source waters. CRW typically contains formula it can be seen that the standard formula is a specific case was added of this more general equation. less than 0.08 mg/L of Br-. For the experiments with CRW, Br- as the NaBr salt. Further descriptions of the two surface waters can be found JMM (1991) In a comparison of the gravimetric method and the standard volumetric the report by MWDSC and Contactors (22,23) 03 + Br02 : 03 + BrO2 Two Contactors, 50 L and 100 L, were constructed of PVC, with portions near k22 = 1 x 105 M-t s-t the diffusers constructed of clear PVC. Both were constructed and operated k23 = 5 x 10 M"t st intermittently for a year prior to the onset of this study. Both were equipped with approximately 25 sample taps with the majority placed near the Furthermore, the acid dissociation constant for (HBr02) was diffusers. The sample taps were 1/4" O.D. teflon tubing with the flow (24?5)controlled during sampling by a 1/4" stainless steel ball valve. HBr02 - H+ + BrO2 pK. = 4.9 The 50 L contactor was constructed with 3" O.D. pipe and was approximately 1050 cm in total length. The downflow, gas-liquid contacting portion of the was assume to be equal to 4.9, rather than the value of 2 expected using the contactor was 525 cm in length, with the 1" diameter spherical diffuser placed Pauling relationship for oxoacids. This value is based on recent reevaluations 20 cm above the bottom. The horizontal flow portion, 75 cm in length, was of the kinetics and thermodynamics for the decay of BrO2 (Massagali et al, the intermediate portion between the downflow leg and the 475 cm upflow 1970; Field and F6sterling, 1986). portion. The 100 L contactor, constructed of 6.4" O.D pipe, was 550 cm in length, with the diffuser placed at the mid-portion of the contactor. Both These decay initiating reactions, along with the following reaction, Contactors were operated at water flow rates ranging from 5 to 20 gpm. 03 + Br2 --~ 03 + Br2 (26) 03 was generated from hospital-grade oxygen using laboratory scale 03 k26 = 5 x 109 M-t s-1 (assumed rate) generators. Gas concentrations in most experiments were typically 2.0% (w/w), as measured by UV absorbance. which is analogous to the oxidation of Br2 by H02, would also explain the . (1990) that in solutions with very high Br- levels, OH Kinetic Models results of Sayato et al radicals were responsible for the conversion of Br- to HOW (Sutton and Downes, 1972). A similar reaction involving the oxidation of C12 by 03 has BRDOM Model (Bielski, 1993). The radical reactions were modeled using the RISO model to account for recently been reported oxyradical ; behavior the various bromine and oxybromine species were INEFIAL RESULTS modeled using the NDRC-NIST inorganic radical database as the primary reference source and guide (Bjergbakke et al., 1984; Bjergbakke et al., 1989; Observed Rate of BrO4-Formation Neta et al., 1988). Organic radicals were modeled primarily on reaction sets Br03 in the two waters is a rapid process (Table 1). described in the database compiled by Neta et al., (1990). Reaction The formation of sets Furthermore, it is scaled to the rate and extent which the 03 residual decays, describing key reactions of HC03-C03' system as well as impact of NH3 of 03 as would be expected from the direct reaction were included in the BRDOM model as well. and not to the lifetime model. A comparison of the actual 131703 formation to the predicted Br03 the direct reaction model is included to further highlight The stiff, coupled, nonlinear differential equations, comprised of formation, based on 65 species the deficiencies of the direct reaction model. The concept that Br03 and 190 reactions, were integrated using a reaction kinetics modeling program formation is dependent on 03 residual decay and not 03 residual lifetime is utilizing a variable-step adaption of Gear's method and a sparse Jacobian in Table 2 which compares the production of Br03 in two matrix (Braun et al., 1988). further illustrated different waters. As shown, the two water had similar levels of Br03 despite pronounced differences in 03 decay rates. Direct Oxidation Model formation The direct oxidation model, as proposed by Haag and Hoigne (1983), was Scavenging altered so that the oxidation of BrO2 by 03 would be analogous to the OH Radical Radical scavenging experiments, using isopropyl alcohol (IPA) as the primary reversible oxidation reaction of chlorite (Haag and Hoigne, 1983; Klaning et that the rapid oxidation of Br- by OH to be the key al, 1985; Mining et al., 1984). OH scavenger, show reaction in initiating the formation of Br03 (Table 3). The minimal scavenging effect found at the lowest IPA concentration, 0.3 mg/L, again suggests that the oxidation of HOW and BrO-, in this case by

OH + HOBr -" BrO + H2O sequential increments over an extended period of time. Table 5 compares the (13) experiments to the results of the experiments where k13=2.0x109 M-1 s 1 Br03 formation in these 03 was applied in a single dose. As shown, Br03 formation shows little + dependence on accumulated 03 dose, but is highly dependent on 03 residual. OH BrO- - BrO + OH- (14) =4.2x109 M-1 s-1 k14 The results of these recycle experiments are similar to the results of bench- extended 03 doses are required to OH radicals, plays little, if any, role in BrO; scale experiments conducted where production in these waters produce measurable quantities of Br03 in surface waters containing moderate (Klaning and Wolff, 1985; Buxton and Dainton, 1968). Had these played reactions levels of Br- (Krasner et al., 1991; Siddiqui and Amy, 1993; Glaze et al., a significant part in the formation of BrO3, a 50% reduction should mass transfer and have resulted. 1993). To better mimic both Br03 formation and the decay of 03 residuals within pilot-scale and full-scale 03 contactors, future Further bench-scale experiments should revert back to using concentrated aliquots of analysis of the impact of IPA addition on Br03 formation shows that Br03 production actual reductions are aqueous 03 for dosing experiments . Alternately, to lower less than the theoretical reductions based on future 03 contactors should be designed to maintain competition kinetics between IPA and Br- for in full-scale facilities, OH radicals. This is due to low 03 residuals throughout the contactor. the scavenging of OH radicals primarily by naturally occurring dissolved organic matter (DOM) (Hoigne et al., 1987; Haag and Yao, 1991). In a number of experiments, the impact of the gas-liquid mixing zone above the 03 diffuser on Br03 formation was studied. In the first experiment, the OH + DOM -" 'DOM + OH- (15) by gas-liquid interfacial - possibility that the formation of Br03 is influenced k15 2 x 104 L/mg s-1, [DOM) = TOC (mg/L) reactions was investigated. This was checked by comparing the production of Br03 in a low Br - (0.08 mg/L) surface water where additional Br- (035 At higher 03 doses, similar results are found, with Br03 formation reduced two different locations. In the first below the mg/L) was added to the water flow at detection limit, when sufficient IPA was added (Table 3). At the added to the contactor influent. In the second run, Br- was higher 03 doses, the run, Br- was actual reductions in BrO3 formation agreed fairly well added just downstream of the 03 diffuser in the gas free reaction zone. Both with the predicted reductions, based on the kinetic competition for OH similar Br03 levels, with the second run having a between Br- runs were found to have and IPA (Wolfenden et al., 1982). slightly higher level of Br03 formation. These two runs confirm that Br03 forms primarily as the result of the decay of 03. OH + CHOH(CH3) -" 'COH(CH3)2 + H2O (16) k16 = 1.9 x 10~ M-1 s-t In the second experiment, the impact of gas-liquid hydrodynamic on Br03 formation was investigated. In a number of runs, the formation of Br03 in In similar experiments using ethanol as a radical scavenger, .7 cm) diameter - 50 L contactor used in the majority of experiments different somewhat the 3" (7 results were found. While ethanol reacts with OH at the same rate was compared to a 6.4" (16.2 cm) diameter - 100 L contactor. The primary as IPA, ethanol was much more effective in lowering Br03 production, even difference between the two contactors was the impact of different superficial when compared on a molar basis (Table 4) (Wolfenden et al., 1982). This water velocities on the mass transfer zone when operated at similar appears to be due primarily to the enhanced decay rate of 03 in the presence volumetric flow rates. In the 3" - 50 L contactor, the high superficial water of ethanol (Staehelin and Hoigne, 1985). Alternately, this phenomena may velocities led to well defined hydrodynamics, with the water flow dominating be explained by the fact that the primary oxidation byproduct of ethanol, the the hydrodynamics of the gas-liquid mixing zone, resulting in a compressed hydrated form of acetaldehyde, reacts more quickly with OH than does 03 mass transfer zone. As a result, 03 residuals measured just downstream ethanol (Schuchmann and ion Sonntag, 1988; Wolfenden et al., 1982). In of the 03 diffuser were similar to the applied dose. Furthermore, little Br03 contrast, acetone reacts much more slowly with OH than does IPA formation occurred within the gas-liquid mixing zone. (Wolfenden et al., 1982). In contrast, the operation of the 6.4" - 100 L at superficial velocities similar Q-4 Contactors - Dose and Residual to those likely to be found in full scale contactors resulted in poorly defined To further explore the relationship between 03 dose, 03 residual, and BrO3 hydrodynamics within the gas-liquid mixing zone immediately above the formation, a number of experiments were conducted with the contactor diffuser. In general, the hydrodynamics were governed by the rise and operated in a recycle mode. In these experiments, 03 was applied in small coalescence of gas bubbles, resulting in the formation of convection cells

483 482

directly above the diffuser. The reaction zone within this region could be the OH- induced decay of the bromide radical (Br) back to OH and Br- furthered defined by extensive backmixing within this relatively high 03 would be the dominant reaction. The pH of the water was raised from 7.8 residual zone. As a result, the effluent from the 6.4" - 100 L contactor was to 9.0 and then to 9.7. As shown in Table 7, the pH increase resulted in a found to have higher levels of BrO3 than the 3" - 50 L even when operated reduction of Br03 of only 30% - 41%. Further kinetic modeling with the at similar 03 doses and volumetric flow rates (Table 6). Furthermore, the BRDOM model showed that while reaction (18) would control the fate of the initial downstream 03 residual measurements were far less than the applied Br radical, the conversion of bicarbonate (HC03) to carbonate (CO3-) at 03 dose. This indicates that a significant portion of the 03 dosed into the these pHs resulted in the significant production of Br03. 6.4"- 100 L contactor decays within the gas-liquid mixing zone. As a result, the majority of Br03 formation in the 6.4" - 100 L contactor occurred within At the pHs typically found in this study, 7.0 - 8.0, the slow oxidation of the gas-liquid mixing zone, and not downstream of the diffuser. Furthermore, bicarbonate (HCO3) the disparity between initial 03 residuals in the two contactors, even when treating the same water, indicates that the concept of "03 demand", when OH + HCO3 - C03 + H O (19) applied to full-scale contactors is an unwitting ad )Qc s-1 description of the k19 =34 - 8 x 06 M impact of contactor hydrodynamics on dispersion and subsequent decay, not an indicator of general water quality, nor a measure of easily oxidized played a minor role (Buxton et al. 1988; Holcman et al, 1987). However at constituents. higher pHs, where carbonate (C03') concentrations become appreciable, the plays a critical role in forming an alternate pH faster reaction OH with C03- Variations reaction involving the carbonate radical (C03) (Buxton et al., 1988). A decrease in the influent pH from the initial value of 8.0 to 7.0 prior to (20)ozonation resulted in decreases in Br03 formation of 45% - 60% when OH sulfuric OH + C03" -" CO + - acid was used to lower the pH. Alternately, when the coagulant km =4x1PM_I s"t FeCl3 was added to the contactor influent and the pH reduced from 8.0 to 7.0, essentially no change in Br03 formation was found. While the decrease pathway for BrO- shifted from in Br03 formation At these higher pHs, the main reaction on the addition of acid is often assumed to result from a (10), to oxidation by CO3 (Buxton and Dainton, equilibrium-based reduction in BrO available for reduction by H202, reaction - reaction, the decrease in 1968). Br03 formation appears to be due to the reductions in the efficiency of OH radical generation at lower pHs. This conclusion is supported by the lack of C03 + Br0 - -+ C02- + BrO (21) change in Br03 formation in the Fe3+ - 03 system. -t t k2t =4.3x10~M s The oxidation of DOM results in the formation of peroxyorganic radicals. results, there would appear to be at least two key pH The rate of peroxyorganic radical decay is pH dependent, typically increasing Given these modeling as dependent pathways for the formation of Br03. Furthermore, this high pH the pH of the water is raised (Bothe et al., 1977). However at low pHs, minimized through the rate of peroxyorganic radical decay pathway in which BrO- is now the key precursor maybe may be slow enough to allow for the of bromamine . direct reaction of 03 with some of the slower decaying radicals. As a result, the addition of NH3 and formation 03 is consumed without generating OH radicals. At the high doses of FeC13 (-100,uM) Bromide Levels used in this run, Fe3+ may impinge on these reactions by either .22 mg/L to 0.39 mg/L and 0.79 mg/L complexing with DOM, prior to oxidation or possibly, Increasing the initial Br levels from 0 by outcompeting 03 for BrO3 formation. The increases result from increased the oxidation of peroxyorganic radicals (Brault and Neta, 1984). Either case was found to increase probabilites of reaction between OH and Br-. Furthermore, increased Br - would allow for the radical decay of 03 resulting in the formation of OH the reactions radicals. levels will act to stabilize the Br radicals which through (22,23) Br2An attempt was made to reduce BrO3 formation by raising the pH so that Br + Br- k22 = 1 .1 x1010 M-r st k23 = 5 x 104 st OH + Br- = BrOH- : Br + OH- (11,12,17,18) k =3.3x106 st 17 which may allow for more reactions with other oxidants (Mamou et al. 1977). k18=13 x1010M"tst

48 4 485 DISCUSSION conditions, it is apparent that the reaction rate between Br and 03 is From these experiments it can be shown that Br03 formation is a fairly rapid extremely fast, k3o - 1 x 1010 M-t s-t. However, given the methods used to process. Furthermore, the formation of Br03 was shown to be initiated by the determine this rate constant, this rate estimate can hardly be considered to OH radical oxidation of of Br-, and is highly sensitive to residual 03 be a reliable value. concentrations and relatively insensitive to total 03 doses. CONCLUSIONS A skeleton model describing the key reactions (FIgure 2) in the BRDOM In surface waters containing moderate levels of Br- and DOM it can be model can be described by the following reactions. expected that the formation of OH will lead to the oxidation of Br- and the possible formation of Br03. A number of conditions can be imposed on the 0 02 (24) operation of a full scale contactor in order to minimize Br03 formation. 3 + 02'03+ include contactor operation at low 03 ± O' + 02 (25) These operating conditions may 03 with minimal backmixing. However, as 03 serves may O- + H2O + OH + OH- (26) concentrations, and purposes, the impact of low 03 concentration operation on other process criteria is uncertain, particularly with respect to disinfection. OH + Br- --4 -+ BrOH- + Br + OH- (11,12,18,19) Br + 03 -+ BrO + 02 (27) Further work in this area should be conducted with filtered water, operating some of the more 2BrO + H_2O - _Br02 + HOBr + H+ (28) in a post-ozonation mode. It is likely that the removal of 03 + BrO2 --> 03 + Br02 (29) easily oxidized constituents during the sedimentation and filtration process 2BrO2 + H2O - Br03 + Br02 + 211+ (30) may improve process predictability and stability.

With the exception of reaction (27), all the reactions in this skeleton model ACKNOWLEDGEMENTS are generally accepted reactions. Without reaction (27), the BRDOM defaults The authors would like to thank the management and staff of the Water to being an Quality Division of the Metropolitan Water District of Southern California extended version ofthe Richardson model, which like the direct of this oxidation model, underpredicts BrO; formation, but to a lesser degree than for their material support and analytical assistance during the course the direct oxidation model. study. While a number of people provided invaluable assistance, the authors would like to single out Ching Kuo, Mike Sclimenti, and Laurie Yeager for their contributions. In the gas phase, 03 is known to react with Br radicals, resulting in the formation of bromine monoxide (BrO) (Michael et al., 1978).

(27)Br + 03 -" BrO + 02

A similar aqueous phase reaction was postulated by Haruta and Takeyama (1981).

In an attempt to further elucidate Br radical chemistry an excess of 11202 was added to the contactor influent in one experiment in an attempt to scavenge Br radicals through the reaction

(31)Br + 11202 - Br- + H+ + H02 k22 = 5 x 109 M-1 s-1

(Sutton et al., 1965). Assuming an aqueous phase reaction between Br and 03, with rate constant similar to that found in the gas phase, 6 x 10 M-1 s-t, the excess of 11202 would still have quenched Br and eliminated Br03. However, Br03 production was reduced only 47%. Given the reaction

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Chem. and in a few 20:51-62 Kinet. radical scavenging by humic substances: role in ozonation photochemical processes for the elimination of micropollutants . In Buxton, G.V., and F.S. Dainton. (1968) The radiolysis of aqueous solutions Abstracts_", Environmental Chemistry Division, of oxybromine "Preprint Extended compounds ; the spectra and reactions of BrO and American Chemical Society, Denver, Colorado, April 5 - 10, 1987. Br02. Pros. Roy. Soc. A. 304:427-439 of radical- Edelson, Holcman, J., E. Bjergbakke, K. Sehested. (1987) The importance D., R.M. Noyes, and R.J. Field. (1979) Mechanistic details ofthe radiolysis of aqueous carbonate/bicarbonate. Belousov-Zhabotinsky radical reactions in pulse oscillations . II. The organic reaction subset. In Proceedings 6 h Tihanv Symposium on Radiation Chemistry, pp. Int. J. Chem. Kin. 11:155-164. eds., H. Stillman Field, 149-153 . P. Hedvig, L. Nyikos, and R. Schiller, R.J., and P.M. Boyd. (1985) Bromine-hydrolysis control in the cerium Florida ion-bromate Publishers, Boca Raton, ion-oxalic acid-acetone Belousov-Zhabotinskii oscillator. Jovanovic, S.L., and M.G. Simic. (1986) One-electron redox potentials of J. Phys. Chem. 89:3707-3714. . J. Phys. Chem. 90:974-978. Field, RJ., and H.D. purines and pyrimidines F6sterling. (1986) On the oxybromine chemistry rate Jwo, J.J., and E.F. Chang. (1989) Kinetic study of the initial phase of the constants with the cerium in the Field-K6r6s-Noyes bromate and gallic acid. the mechanism of uncatalyzed oscillatory reaction of potassium Belousov-Zhabotinskii reaction: The equilibrium HBr02 + J. Phys. Chem. 93:2388-2392. HBr03 + + H + : 2BrO2 H2O. J. Phys. Chem. 90:5400-5407. Kasai, H., S. Nishimura, Y. Kurokawa, and Y. Hayashi. (1987) Oral Field, RJ., E. K6r6s, and R.M. Noyes. (1972) Oscillations in Chemical administration of the renal carcinogen, , specifically Systems. 11. Thorough Analysis of Temporal Oscillation in the produces 8-hydroxydeoxyguanosine in rat target organ DNA. Bromate-Cerium-Malonic Acid. J. Amer. Chem. . Glaze, W Soc. 94:8649-8664. Carcinogen. 8:1959-1961 .H., H.S. Weinberg, and J.E. Cavanaugh. (1993) Evaluating the Klaning, U.K., and K. Sehested. (1984) Ozone formation in laser flash formation of brominated DBPs during ozonation. J. AWWA. 85:1 :96- photolysis of oxoacids and oxoanions of and bromine. J. 103. Chem. Soc. Faraday Trans. 80:2969-2979. _ Gy6rgyi, L., M. Varga, E. Kdrds, RJ. Field, and P. Ruoff. (1989) Klaning, U.K., and T. Wolff. (1985) Laser flash photolysis of HCIO, CIO , Simulations of the iodide ion perturbed uncatalyzed Belousov- HBrO, and BrO- in aqueous solution. Reactions CI and Br atoms. Ber. Zhabotinskii oscillator with 1-hydroxy-4-(2- Bunsenges Phys. Chem. 89:243-245. (methylamino)propyl)benzene. J. Phys. Chem. 93:2836-2843. Kok, G.L., K. Thompson, and A.L. Lazrus. (1986) Derivitization technique Gy6rgyi, L., and RJ. Field. (1991) Simple models of deterministic chaos in for the determination of peroxides in precipitation. Anal. Chem. the Belousov-Zhabotinsky reaction. J. Phys. Chem. 95:6594-7002. 58:1192-1194.

. (1988) The rapid h\dration of the Krasner, S.W., J.T. Gramith, E.G. Means, N.L. Patania, I.N. Schuchmann, M.N ., and C. con Sonntag Najm, and E.M. A pulse radiolysis study of acetaldehyde in aqueous Aieta. (1991) Formation and control of brominated ozone acetyl radical. by- solution. J. Amer. Chem. Soc. 110:5698-5701. products. Pres. at AWWA Annual Conf. Philadelphia, PA. June 23- 27, 1991 . Siddiqui, M.S., and G .L. Amy. (1993) Factors affecting DBP formation ozone-bromide reactions. J. AWWA. 85:1 :63-72. Krasner, S.W., W.H. Glaze, H.S. Weinberg, P.A. Daniel, I.N. Najm. (1993) during Staehelin, J., and J. Hoigne. (1985) Decomposition of ozone in water in the Formation and control of bromate during ozonation of waters inhibitors of containing bromide presence of organic solutes acting as promoters and . J. AWWA. 85:1:73-81. . Tech. 19:1206-1213. Kurokawa, Y., Y. Matsushima, N. takamura, T. radical chain reactions . Environ. Sci Imazawa, and Y. Hayashi. J.W. Boag, and B.D. Michael. (1965) Radiolysis (1987) Relationship between the duration of treatment Sutton, H.C., G.E. Adams, and the yields and kinetics in the pulse radiolysis of incidence of renal cell tumors in male F344 rats administered A.J. potassium solutions. In Pulse Radiolysis, pp. 61-81. M. Ebert, J.P. Keene, bromate. Jap. J. Cancer. Res. (Gann):78:358-364. Press London Mamou, A., J. Rabani, and D. Behar. Swallow, and J.H. Baxendale, eds. Academic (1977) On the oxidation of Br by OH Downes. (1972) Reactions of the HO, radical in radicals, studied by pulse radiolysis. J. Phys. Chem. Sutton, H.C., and M.T. 81:1447-1448. solution with bromine and related compounds . J. Chem. Soc. Massagali, A., A. Indelli, and F. Pergola. (1970) Kinetic investigation of the aqueous decomposition of Faraday Trans. I. 68:1498-1507. bromite. Inorg. Chim. Acta. 4:593-596. Field. (1993) Analysis and simplification Metropolitan Water District of Southern Turanyi, T., L. Gyorgyi~ and R.J. California and James M. model of the Belousov-Zhabotinsky reaction. J . Phys. Montgomery, Consulting Engineers, Inc. (1991) PtlQLScale of the GTF Evaluation of Chem. 97:1931-1941 . Ozone and PEROXON American Water Works . (1991) The elucidation of peroxyl Association. Denver, Colorado von Sonntag, C., and H.P. Schuchmann in aqueous solution with the help of radiation-chemical Michael, J.V., J.H. Lee, W.A. Payne, and L.J. Stief. (1978) Absolute rate of radicals the reaction methods. Angew. Chem. Int. Ed. Engl. 30:1229-1253. of bromine atoms with ozone from 200 to 360 K. J. Radical-cations as reference Chem. Phys. 68:4093-4097. Wolfenden, B.S., and R.L. Willson. (1982) studies of one-electron transfer reactions: pulse Neta, P., R.E. Huie, and A.B. Ross. (1988) Rate constants of chromagens in kinetic reactions of radiolysisstudies of 2,2'-azinobis-(3-et hylbenzthiazoline-6-sulphonate) . inorganic radicals in aqueous solution. J. Phys. Chem. Ref. Data. 17:1027-1284. J. Chem. Soc. Perkin Trans. II (1982) 805-812 reduction of bromtc acid by hydrobromic acid in Neta, P., R.E. Huie, and A.B. Ross. (1990) Rate constants for Young, H.A. (1950) The reactions of the presence of hydrogen peroxide. J. Amer. Chem. Soc. 72:3310- peroxyl radicals in fluid solutions. J. Phys. Chem. Ref. Data. 19(2):413-513. 3312. The oxidation of aqueous bromide ions Noyes, R.M. (1980) A generalized mechanism for Zehavi, D., and J. Rabani. (1972) the bromate-driven radicals. A pulse radiolysic invesigation. J. Phys. Chem. oscillators controlled by bromide. J. Phys. Chem. 102:4644-4649. by hydroxyl Orban, M., and 76:312-319. E. K6rds. (1978) Chemical oscillations during the uncatalzed Effects of aquatic humic reaction of aromatic Zepp, R.G., Y.I. Skurlatov, L.F. Rittmiller. (1988) compounds with bromate. 1. Search for chemical hydrogen peroxide using peroxidase- oscillators. J. Phys. Chem. 82:1672-1674. substances on analysis for triarylamines or p-hydroxyphenylacetic acid. Pastina Cristina, S., M.T. Azure, H.J. Workman, and E.T. Gray, Jr. catalyzed oxidations of (1984) Envir. Tech. Lett. 9:287-298. Decomposition of bromamines in aqueous solution: preliminary report ozone and hydrogen of the decomposition Zika, R.G., and E.S. Saltzmann. (1982) Interaction of kinetics and disproportionation of NHZBr. In for the analysis of H,OZ in air. hemWater Chlorination: stt y, Environmental peroxide in water: implications Imndct and Health Lett. 9:231-234. Effects. Vol, 5., pp. 763-774. R.L. Jolley, et al., eds. Lewis Publishers Geophys. Res. Chelsea, Michigan. Richardson, L.B., D.T. Burton, G.R. Helz, and J.C. Rhoderick . (1981) Residual oxidant decay and bromate formation in chlorinated and ozonated sea-water. Water Res. 15:1067-1074. Sayato, Y., K. Nakamuro, M. Hayashi, and H. Sano. (1990) Formation of active bromine from bromide ion by aqueous ozonation. Chemosphere 20:309-315.

491 490

Br03 + 6H+ + 6e- C 16 C p) w ' w w w 1-15V o O 0 0 o O a Q I BrO2 + 4H + + H2O + 5e- v m CO __ -1.15V +4 N ¢ ? O O 0 N m m 0 1 .33V z a 0 O I 1 HBr02 + 3H + +H20 + 4e- I- O m ma) D co 3l mN m--v -2.48V +3 m O 3.48V = 2 x 1.74V (BrO ?) . m O ~ mv - vv . - ,- w o a n n n O HOW + 2H20 + H + + 2e- w c') 04 -5.96V N N N N N N O (D CIS Cl) ~ cr)) r r 0.70V w0 Br +3H20+e- is u) rc) co (0 co o) a) v) 0) a) C/) 0 m co comes r,-: 1.57V -Z6V co 0 0 ai ri ai vi ri O Q 11/2Br 2 + 3H20 + e- w n ~ ~ r` J .'- v) N N N N 7 7 7 7 m 0 0 000 000001 1 1 -

1.09V 1.96V w 0 0 000 00000 0 o °) N N (V 0 Br + 3H20 -8.62V

Fic, I

TABLE 3. THE IMPACT OF OH RADICAL SCAVENGING ON THE PRODUCTION OF Br03 ) a)) CV) C Initial 03 Predicted x Z- 03 IPA 03 Residual Br03 O W N m O Dose Dose Br- Residual Half-ute Br03 Dir Rxns Q a` o (m9A) (mgn (mg/1) (mgn) - (s) (VO/I) (p9/1) W 11- U- C ~_ 1.0 0 0.28 0.91 19 15 0.1 O 00 1 .0 0.3 0.28 0.88 17 13 0.1 T O m 1 .0 3.0 0.28 0.80 10 8 0.02 1 .0 6.0 0.28 0.71 9 <5 0.01

Z m a? 2.0 0 0.28 1 .86 34 33 2 C*) 0 2.0 18 0.28 1 .07 24 < 5 0.3 u7 O a) X 4.0 0 0.29 3.31 80 122 17 Q 4.0 24 0.29 3.00 29 12 3 _ _cu 0 _ 0m U) Lo 4.0 0 0.17 3.79 122 180 23 C (D C; C 4.0 150 0.17 6.28 20 < 3 3 M O n 7.0 0 0.29 6.26 118 303 69 U- 7.0 12 0.29 5.82 78 61 38 0 w 7.0 24 0.28 6.64 40 50 33 I- N M m ' Gas Enirainment Z C C 0 W TABLE 4. THE IMPACT OF DIFFERENT ALCOHOLS ON Br03 0 0 ma a: T FORMATION 0 1 Initial 03 U 03 Alcohol Alcohol 03 Residual (V Q Dose Dose Dose Residual Half-Lffe Br03 JW W (mg/1) (mg/1) (NM) (mg/1) (s) (ug/I) m Q Ethanol Ethanol H 1 .0 0 0 0.85 18 15 1 .0 1 22 0.78 11 3 1 .0 2 43 0.62 10 < 3 1 .0 4 87 0.59 7 < 3 1 .0 6 130 0.56 6 < 3 1 .0 8 174 0.52 5 < 3- IPA IPA 1.0 0 0 0.91 19 15 1.0 0.3 5 0.88 17 13 1.0 3 50 0.80 10 8 1 .0 6 100 0.71 9 < 5 1 .0 12 200 0.80 8 < 5

494 495 TABLE 5. IMPACT OF 03 RESIDUAL & 03 DOSE ON BrO3 FORMATION

SINGLE DOSE Initial Initial 03 03 03 H202 Residual g C9 U) Dose Residual Residual Half-Life Br03 Z N (") V (m9A) (mg/1) (mg/1) (s) (u9/U O

1 .0 0.91 - 19 15 U 2.0 1 .86 0.087 34 33 w 4.0 3.31 0.070 122 Q ce) -0 80 Z M M 303 O .05 7.0 6.26 - 117 a) co Q = RECYCLE OPERATION (0.4 mg/I per pass) O Accumul. Initial Initial 03 03 03 H202 Residual C9 ;O O) 00 T Dose Residual Residual Half-Ue Br03 0 rn E rr-N c (1) `. oo (m9p) _ (mg/) (mg/1) LL - (p9n) O F- 0.4 0.13 - 0.4 < 5 U c) u) 1 .4 0.23 - 2 <5 F- Z '~ rc') tp QZO 2.4 0.33 - 6 6 vo E *-'t rNch O f- Q. 4) _ 3.3 0.37 --- 10 12 U Q > 4.4 0.36 - 18 16 5.4 0.34 --- 23 19 O ~ ,,o., N N 6.4 0.35 --- 24 25 LL U N a) E U `") cp U C") -4cD: 0) RECYCLE OPERATION (0.2 mg/I per pass) O E0 Q`° ~r Accumul. Initial Initial 03 aM co N 03 03 H202 Residual 0 (0 Dose Residual Residual Half-Life Br03 N W 0 0 0 0 II m~nL_ (mg/I) (mgAI) (s) (NgAI) w r- ,- CV N J O o E I m 0.20 - 0.033 - < 3 0.67 0.04 0.038 2 < 3 1 .34 0.13 -- 2 <3 2.00 0.17 0.061 2 < 3 2.67 0.22 0.060 6 < 3 4.00 0.19' 0.035 7 8

SPW,pH8.0, 24-26deg C, Br- from 0.28 to 0.29 mg/I, velocities from 7.5 to 17.5 cm/s

497 496

TABLE 8. IMPACT OF Br- LEVELS ON BROMATE FORMATION

Initial 03 03 03 Residual

T O co T ~ co N n M T T r- Dose Br- Residual Half-Life Br03 _ {1 _1' 09 I S , .q F1 -a q? J T T O Nv M to r) M IRT 1 .0 0.22 0.83 22 5 +- N C") tr co V N ,- O OOC 2 1 .0 0.39 0.86 23 12 1 .0 0.79 0.88 25 28 c0 ~. :3 O },'a co :_ p) T r- qr q co O Nr co co N O cOcoENv O O ,- r ~ T T T cr) ix: O m F % c~. a.- 0 Z + --Q2-- DOM * + OH U 0 O Br~ O (/) 4) O N co co oN = w 2 Z Z H 0 U w w Br+ w 0 000 00 coor" W Q OH c6 r,: r,: c6 r,: r,: ofotE e/r \3 J. DOM O Br2 a o [Br-03]J\ / BrO v) Br2 ~'o c "zo w c") N p) 000 00 000 J T T T Br02 ao O El N CV N N N 03 oHl m / + DOM H \ _ - HOBr o HOBr + Br .-- BrO , o 3 \. Br02 rs1o2 - Br +03 ,,~ro2 Br "'Br204

Br03 + Br02 03 +Br + 2H+