Minimizing bromate formation with cerium dioxide during ozonation of bromide-containing water

This work investigated the effect of several metal oxides including alpha-FeOOH, alpha-Fe(2)O(3), gamma-FeOOH, and CeO(2) on bromate formation potential (BFP) during ozonation of bromide-containing water. Results indicate that CeO(2) could most effectively minimize the BFP among these metal oxides taking ozonation alone as control. The BFP minimization by O(3)/CeO(2) favored a relatively low Br(-) concentration (i.e., <1.0mgL(-1)) and pH<7. Water temperature ranging from 5 to 25 degrees C had no significant impact on the percent reduction of BrO(3)(-). Further investigation indicates that the effective BFP minimization can be ascribed to neither the surface adsorption of BrO(3)(-) or Br(-) on CeO(2) nor the surface reduction of BrO(3)(-) to HOBr/OBr(-) by CeO(2). It seems to have relationship with the activity of surface Ce(IV) sites. The CeO(2) can lower the concentration of H(2)O(2) which is formed during ozone decomposition and promotes BrO(3)(-) formation. Another possible reason for the BFP minimization is that the CeO(2) could possibly reduce BrO() to HOBr/OBr(-) during the decomposition of H(2)O(2).     

Ammoniacal bromamines: a review of their influence on bromate formation during ozonation

Ammonia can inhibit the formation of bromate in ozonated drinking water by reacting with free bromine (HOBr/OBr-), an intermediate in bromate formation, to form bromamines. Bromamines do not participate in bromate formation, however, they will decay due to autonomous decomposition and through reaction with ozone and hydroxyl radicals. The reaction with ozone controls the overall decay rate. This reaction also results in a net loss of ammonia from the system, leading to the possibility that all ammonia may be oxidized before the ozone residual in the water is eliminated, allowing bromate formation to resume. This paper presents a review of our understanding of bromamine chemistry and identifies areas that are not adequately understood, which may prevent an accurate estimation of ammonia's impact on bromate formation.     

Investigating synergism during sequential inactivation of Bacillus subtilis spores with several disinfectants

The sequential application of ozone, chlorine dioxide, or UV followed by free chlorine was performed to investigate the synergistic inactivation of Bacillus subtilis spores. The greatest synergism was observed when chlorine dioxide was used as a primary disinfectant followed by secondary disinfection with free chlorine. A lesser synergistic effect was observed when ozone was used as the primary disinfectant, but no synergism was observed when UV was used as the primary disinfectant. When free chlorine was used as the primary disinfectant (i.e., sequential application in the reverse order), the synergistic effect was shown only when chlorine dioxide was applied as the secondary disinfectant. The synergistic effect observed could be related to damage to the spore coat during primary disinfection, suggested by the loss of proteins from spores during disinfectant treatment. The greatest synergism observed by the chlorine dioxide/free chlorine pair suggested that common reaction sites might exist for these disinfectants. The concept of percent synergistic effect was introduced to quantitatively compare the extent of synergistic effects in the sequential disinfection processes.     

Adsorptive ozonation of 2-methylisoborneol in natural water with preventing bromate formation

This paper presents an application of our newly developed adsorptive ozonation process using a high silica zeolite adsorbent (USY) for drinking water treatment. First, the adsorption of 2-methylisoborneol (2-MIB) on USY in a river water/pure water mixture was clarified by a batch-type adsorption experiment. The results showed that 2-MIB was adsorbed on USY; however, almost all of the adsorbed 2-MIB was desorbed over time. The desorption rate was increased with the ratio of river water to pure water, indicating that compounds dissolved in the river water, such as natural organic matter (NOM), prevent the adsorption of 2-MIB on USY. Second, the ability of the river water to consume ozone was confirmed in an experiment using a USY-packed column reactor. The ozone consumption was obviously increased by the presence of USY, indicating that USY-adsorbing compounds dissolved in the river water (probably small size NOM) consumed the ozone. However, the rapid ozone consumption was occurred by 6-8 s in the retention times when 3.14-4.38 mgL(-1) of water dissolved ozone was fed, this rapid ozone consumption lasted no more than these times. This result revealed that the rapid consumption of ozone by the adsorptive compounds in our process could be avoided within a certain retention time (6-8 s; especially for the river water used in this study) when enough concentration of ozone (3.14 mgL(-1) or more; same above) was supplied. We therefore performed a trial in which 2-MIB dissolved in river water was continuously decomposed using a USY-packed column with various ozone concentrations. In the process, the adsorptive compound dissolved in the river water adsorbed and reacted with ozone in the parts of the apparatus upstream of the column, while the adsorption and decomposition of 2-MIB took place in the parts of the apparatus downstream of the column. This resulted in a sufficient 2-MIB decomposition with minimizing bromate ion formation.     

Modeling of bromate formation by ozonation of surface waters in drinking water treatment

The main objective of this paper is to try to develop statistically and chemically rational models for bromate formation by ozonation of clarified surface waters. The results presented here show that bromate formation by ozonation of natural waters in drinking water treatment is directly proportional to the "Ct" value ("Ctau" in this study). Moreover, this proportionality strongly depends on many parameters: increasing of pH, temperature and bromide level leading to an increase of bromate formation; ammonia and dissolved organic carbon concentrations causing a reverse effect. Taking into account limitation of theoretical modeling, we proposed to predict bromate formation by stochastic simulations (multi-linear regression and artificial neural networks methods) from 40 experiments (BrO(3)(-) vs. "Ctau") carried out with three sand filtered waters sampled on three different waterworks. With seven selected variables we used a simple architecture of neural networks, optimized by "neural connection" of SPSS Inc./Recognition Inc. The bromate modeling by artificial neural networks gives better result than multi-linear regression. The artificial neural networks model allowed us classifying variables by decreasing order of influence (for the studied cases in our variables scale): "Ctau", [N-NH(4)(+)], [Br(-)], pH, temperature, DOC, alkalinity.     

Disinfection of Bacillus subtilis spores with chlorine dioxide: a bench-scale and pilot-scale study

Chlorine dioxide (ClO2) inactivation of Bacillus subtilis ATCC 19659 spores was examined at pilot-scale during periods representative of winter and summer temperature extremes at the Britannia Water Treatment Plant in Ottawa, Canada. In addition, bench-scale experiments using the same source water (Ottawa River, Ontario, Canada), as well as buffered and unbuffered laboratory waters were conducted using B. subtilis spores. Bench-scale inactivation of B. subtilis spores by ClO2 was similar to reported values for Cryptosporidium parvum (both organisms being more resistant to ClO2 than Giardia lamblia), suggesting the possibility that these spores may be used as potential indicators for protozoan parasites. Additionally, spore inactivation was observed to be influenced by pH in laboratory (distilled deionised water) water but not in Ottawa River water. At pilot-scale, spore inactivation was influenced by water temperature: a ClO2 dose of 2.5 mg/L resulted in a spore inactivation of approximately 2.0 log10 and 0.5 log10 at water temperatures of 23.2d egrees C and 5.2 degrees C, respectively. Chlorite concentrations remained below both the US EPA maximum contaminant level of 1.0 mg/L and the maximum contaminant level goal of 0.8 mg/L for up to 2.0log10 B. subtilis inactivation.     

N-nitrosodimethylamine (NDMA) formation during ozonation of dimethylamine-containing waters

Ozonation of aqueous solutions of dimethylamine (DMA) leads to the formation of nitrosodimethylamine (NDMA). The yield of reaction is low (below 0.4% in relation to DMA) and increases with increasing pH. Contact time, ozone/DMA ratio and radical scavengers are other variables controlling the yield of reaction. Data from the literature and observed ozonation by-products suggest that nitrosation of DMA might be responsible for nitrosamine generation. NDMA can be recognized as a by-product of ozonation of DMA in water, which is formed in a specific, but reasonable, range of ozone/DMA ratios. The reaction may have potential importance for water treatment technology assuming reasonable micrograms per liter of DMA concentrations in raw waters.     

The impact of selected water quality parameters on the inactivation of Bacillus subtilis spores by monochloramine and ozone

Selected water quality parameters-pH, dissolved organic carbon, turbidity (NTU), and temperature-were tested for their potential effects on ozone and monochloramine inactivation of Bacillus subtilis spores. In oxidant demand-free phosphate-buffer, temperature had the strongest influence on inactivation kinetics when using ozone, pH had a smaller but significant impact on B. subtilis spore inactivation with both monochloramine and ozone. Where monochloramine was applied, modeling and experimental measurements confirmed that dichloramine levels were too low to produce significant inactivation effects under these experimental conditions. It was demonstrated that oxidant demand-free phosphate buffer may not be an adequate environmental analogue for inactivation responses in natural waters.     

Investigating synergism during sequential inactivation of MS-2 phage and Bacillus subtilis spores with UV/H2O2 followed by free chlorine

A sequential application of UV as a primary disinfectant with and without H₂O₂ addition followed by free chlorine as secondary, residual disinfectant was performed to evaluate the synergistic inactivation of selected indicator microorganisms, MS-2 bacteriophage and Bacillus subtilis spores. No synergism was observed when the UV irradiation treatment was followed by free chlorine, i.e., the overall level of inactivation was the same as the sum of the inactivation levels achieved by each disinfection step. With the addition of H₂O₂ in the primary UV disinfection step, however, enhanced microbial inactivation was observed. The synergism was observed in two folds manners: (1) additional inactivation achieved by hydroxyl radicals generated from the photolysis of H₂O₂ in the primary UV disinfection step, and (2) damage to microorganisms in the primary step which facilitated the subsequent chlorine inactivation. Addition of H₂O₂ in the primary disinfection step was also found to be beneficial for the degradation of selected model organic pollutants including bisphenol-A (endocrine disruptor), geosmin (taste and odor causing compound) and 2,4-D (herbicide). The results suggest that the efficiency of UV/free chlorine sequential disinfection processes, which are widely employed in drinking water treatment, could be significantly enhanced by adding H₂O₂ in the primary step and hence converting the UV process to an advanced oxidation process.     

Effects of temperature and chemical addition on the formation of bromoorganic DBPs during ozonation

The effects of temperature and addition of OH radical scavengers/enhancers or HOBr scavenger on the formation of bromoorganic disinfection byproducts (DBPs) from ozonation of six raw waters were studied in true batch reactors. The formation of bromoorganic DBPs during ozonation generally increased with the increase of temperature, but might also decrease for the waters with somewhat higher values of specific UV absorbance (SUVA). The addition of hydrogen peroxide, ethanol, or ammonium dramatically decreased the formation of bromoorganic DBPs; t-butanol addition significantly increased the formation of bromoorganic DBPs; bicarbonate addition might increase or decrease bromoorganic DBP formation depending on the water source. For all the waters treated with the chemical addition, the level of total organic bromine (TOBr) varied with the same pace as that of ozone exposure (CT), which suggests that TOBr formed during ozonation may be used to estimate the CT, a measure for the achieved degree of disinfection. The results demonstrate that for each water, the correlation between TOBr and CT was less affected by the change of chemical composition of the water than that between BrO(3)(-) and CT; for a given chemical composition and temperature of a water, there generally were well-defined relationships between TOBr and CT, and bromoform and CT just as that between BrO(3)(-) and CT. The possible mechanisms behind the linear functions of TOBr or BrO(3)(-) versus CT were given. Further study is needed to examine whether the trends found in this research can be applicable for the high SUVA waters.     

Synergistic effect of sequential or combined use of ozone and UV radiation for the disinfection of Bacillus subtilis spores

This study was performed to evaluate the inactivation efficiency or synergy of combined ozone and UV processes (combined ozone/UV process) or sequential processes (ozone-UV, UV-ozone) compared with individual unit processes and to investigate the specific roles of ozone, UV and the hydroxyl radical, which is formed as an intermediate in the combined ozone/UV process. The Bacillus subtilis spore, which has often been used as a surrogate microorganism for Cryptosporidium parvum oocysts, was used as a target microorganism. Compared to individual unit processes with ozone or UV, the inactivation of B. subtilis spores by the combined ozone/UV process was enhanced under identical conditions. To investigate the specific roles of ozone and UV in the combined ozone/UV process, sequential ozone-UV and UV-ozone processes were tested for degrees of inactivation. Additionally, the experiment was performed in the presence and absence of tert-butyl alcohol, which acted as a hydroxyl radical scavenger to assess the role of inactivation by the hydroxyl radical in the combined ozone/UV process. Among the five candidate processes, the greatest synergistic effect was observed in the combined ozone/UV process. From the comparison of five candidate processes, the hydroxyl radical and ozone were each determined to significantly enhance the overall inactivation efficiency in the combined ozone/UV process.     

Transformation of dissolved organic matter during ozonation: effects on trihalomethane formation potential

Transformation of dissolved organic matter (DOM) during ozonation results in a higher reduction in trihalomethane formation potential (THMFP) relative to dissolved organic carbon (DOC). This study was conducted to determine the effect of DOM transformation after ozonation on THM formation and to elucidate the difference in THMFP and DOC removal. Changes in DOC, THMFP, reactivities of the hydrophilic and hydrophobic DOC, and phenolic-OH were determined to explain the difference in THMFP and DOC removal after ozonation. Higher reduction in THMFP (24-46%) relative to DOC (10-16%) was obtained and was attributed to the following: transformation of DOM from a more reactive hydrophobic DOC (microg THM produced per mg organic carbon) to a less reactive hydrophilic DOC and to the decrease in the reactivities of both the hydrophobic and hydrophilic DOC after ozonation. The results also showed decrease in phenolic-OH indicating the oxidation of some reactive sites like resorcinol or meta-dihydroxy benzene ring structures, which are prone to chlorine substitution, consequently decreasing the reactivity of the organic carbon to form THM. These changes in DOM led to a significant decrease in THMFP with no remarkable removal in DOC.     

Impact of a magnetic ion exchange resin on ozone demand and bromate formation during drinking water treatment

The objective of this research was to examine the impact of a magnetic ion exchange resin (MIEX) on ozone demand and bromate formation in two different ozonated waters at bench scale. The first raw water had a high bromide ion concentration, a high ozone demand, and was highly colored. Based on experimental findings from the first water, the second water was selected as a model water in which more controlled experiments were performed. The waters were treated with the MIEX resin using jar test procedures to find the optimal MIEX dosage based upon the removal of ultraviolet (UV)-absorbing substances, dissolved organic carbon (DOC), and bromide. The optimal resin dosage was chosen for bulk MIEX treatment and subsequent ozonation in a semi-batch reactor. The ozone demand and formation of bromate were analyzed as a function of ozone dosage and dissolved ozone concentration for the MIEX pre-treated water, and compared to the results obtained by ozonating the water without MIEX pre-treatment. The results indicate that pre-treatment of the water with the MIEX resin significantly reduces total organic carbon, DOC, UV absorbance, color, and to some extent, bromide. MIEX pre-treatment of the water prior to ozonation substantially lowered the ozone demand and formation of bromate during subsequent ozonation.     

Residual oxidant decay and bromate formation in chlorinated and ozonated sea-water

Oxidant decay and bromate formation were studied under light and dark conditions in 5.15 and 30‰ artificial sea-water and 5‰ natural estuarine water following ozonation or chlorination. For both oxidants, light exposure accelerated the residual oxidant decay rates which were inversely related to sample salinities in artificial sea-water. Significant quantities of bromate were produced in light-exposed, chlorinated samples with an initial residual oxidant concentration of 70 μM (5mg l⁻¹ as total residual chlorine) but not at lower residual oxidant concentrations or in non-photolyzed samples. No bromate was formed in any of the chlorinated natural estuarine water samples. Bromate production was much greater in ozonated samples than in chlorinated ones and was formed in two distinct stages. Photolytic bromate formation decreased with increasing bromide concentration in both chlorinated and ozonated artificial sea-water. Bromate formation was completely inhibited in the presence of NH₃-N and estuarine sediment. The same free radical mechanism is proposed for both ozone-induced and photolytic-induced bromate formation in artificial sea-water.     

The effects of combined ozonation and filtration on disinfection by-product formation

The effects of combined ozonation and membrane filtration on the removal of the natural organic matter (NOM) and the formation of disinfection by-products (DBPs) were investigated. Ozonation/filtration resulted in a reduction of up to 50% in the dissolved organic carbon (DOC) concentration. Furthermore, humic substances were converted to non-humic substances, with changes in the humic and non-humic substance concentrations of up to −50% and +20%, respectively. Ozonation/filtration resulted in the formation of partially oxidized compounds from NOM that were less reactive with chlorine, decreasing the concentration of simulated distribution system total trihalomethanes (SDS TTHMs) and simulated distribution system halo acetic acids (SDS HAAs) by up to 80% and 65%, respectively. Reducing the molecular weight cut-off (MWCO) of the membranes resulted in reductions in the concentrations of SDS TTHMs and SDS HAAs. Using a membrane with a 5 kD MWCO, the minimum gaseous ozone concentration required to bring about effective NOM degradation and meet regulatory requirements for chlorinated DBPs was 2.5 g/m³.     

Biofiltration for removal of BOM and residual ammonia following control of bromate formation

Nitrification was developed within a biological filter to simultaneously remove biodegradable organic matter (BOM) and residual ammonia added to control bromate formation during the ozonation of drinking water. Testing was performed at pilot-scale using three filters containing sand and anthracite filter media. BOM formed during ozonation (e.g., assimilable organic carbon (396-572 microg/L), formaldehyde (11-20 microg/L), and oxalate (83-145 microg/L)) was up to 70% removed through biofiltration. Dechlorinated backwash water was required to develop the nitrifying bacteria needed to convert the residual ammonia (0.1-0.5 mg/L NH(3)-N) to nitrite and then to nitrate. Chlorinated backwash water resulted in biofiltration without nitrification. Deep-bed filtration (empty-bed contact time (EBCT) = 8.3 min) did not enhance the development of nitrification when compared with shallow-bed filtration (EBCT = 3.2 min). Variable filtration rates between 4.8 and 14.6 m/h (2 and 6 gpm/sf) had minimal impact on BOM removal. However, conversion of ammonia to nitrite was reduced by 60% when increasing the filtration rate from 4.8 to 14.6 m/h. The results provide drinking water utilities practicing ozonation with a cost-effective alternative to remove the residual ammonia added for bromate control.     

Association and decontamination of Bacillus spores in a simulated drinking water system

The objective of this work was to elucidate the disinfectant susceptibility of Bacillus anthracis Sterne (BA) and a commercial preparation of Bacillus thuringiensis (BT) spores associated with a simulated drinking water system. Biofilms composed of indigenous water system bacteria were accumulated on copper and polyvinyl chloride (PVC) pipe material surfaces in a low-flow pipe loop and uniformly mixed tank reactor (CDC biofilm reactor). Application of a distributed shear during spore contact resulted in approximately a 1.0 and 1.6 log₁₀ increase in the number of spores associated with copper and PVC surfaces, respectively. Decontamination of spores in both free suspension and after association with biofilm-conditioned pipe materials was attempted using free chlorine and monochloramine. Associated spores required 5- to 10-fold higher disinfectant concentrations to observe the same reduction of viable spores as in suspension. High disinfectant concentrations (103 mg/L free chlorine and 49 mg/L monochloramine) yielded less than a 2-log₁₀ reduction in viable associated spores after 60 min. Spores associated with biofilms on copper surfaces consistently yielded higher Ct values than PVC.     

Disinfectant decay and disinfection by-products formation model development: chlorination and ozonation by-products

Comprehensive disinfectant decay and disinfection by-product formation (D/DBP) models in chlorination and ozonation were developed to apply to various types of raw and treated waters. Comparison of several types of models, such as empirical power function models and empirical kinetic models, was provided in order to choose more robust and accurate models for the D/DBP simulations. An empirical power function model based on dissolved organic carbon and other parameters (Empirically based models for predicting chlorination and ozonation by-products: haloacetic acids, chloral hydrate, and bromate, EPA Report CX 819579, 1998) showed a strong correlation between measured and predicted trihalomethane (THM) and haloacetic acid (HAA) formation for raw waters. Internal evaluation of kinetic-based models showed good predictions for chlorine decay and THM/HAA formation, but no significant improvements were observed compared to the empirical power function model simulations. In addition, several empirical models for predicting ozone decay and bromate (ozonation disinfection by-product) formation were also evaluated and/or developed. Several attempts to develop kinetic-based and alternative models were made: (i) a two-stage model (two separate decay models) was adapted to ozone decay and (ii) an ozone demand model was developed for bromate formation. Generally, internal evaluation of kinetic-based models for ozone decay showed significant improvements, but no significant improvements for the simulation of bromate formation were observed compared to the empirical power function model simulations. Additional efforts were performed to reduce the gaps between specific models and their actual application. For instance, temperature effects and configuration of ozone contactors were considered in actual application.     

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60-80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.     

Filtration methods for recovery of Bacillus anthracis spores spiked into source and finished water

Spores of Bacillus anthracis Sterne strain were recovered from 100 ml and 1 L volumes of tap and source waters using filtration through a 0.45 um filter, followed by overnight culture on agar plates. In a set of experiments comparing sheep red blood cell (SRBC) plates with a chromogenic agar formulation designed by R & F Laboratories, with a spiking dose of 47 plate-enumerated spores in 100 ml tap water, the mean spore recoveries were 34.0 and 30.8 spores, respectively. When a spiking dose of 100 fluorescence activated cell sorter(FACS)-enumerated spores was used in 100 ml potable water, the average recovery with SRBC plates was 48 spores. Detection efforts with spiking doses of 35 and 10 spores in 1 L tap water were successful, but recovery efforts from spiked 1 L volumes of source water were problematic due to the concomitant growth of normal spore-forming flora. Recoveries were also attempted on 10 L volumes of tap water. For a spiking dose of 100 spores, mean recovery from six replicates was 11 spores (±6.8, range 2–20), and for a spiking dose of 10 spores, mean recovery from six replicates was 2.3 spores (±3.5, range 0–9). Efforts were also made to “direct detect” spores via polymerase chain reaction (PCR) on washes from filters. When spiking 534 spores in 100 ml, 9/9 replicates of spiked tap water, 6/6 source water replicates, and 0/3 unspiked controls were positive by lef PCR. When 534 spores were spiked into 1 L tap water, the lef PCR was unsuccessful; however, using the nested vrrA PCR resulted in 4/9 spiked samples, and 0/3 unspiked controls, testing positive. Our results indicate that an inexpensive and user-friendly method, utilizing filtration apparatus commonly present in many water quality testing labs, can readily be adapted for use in detecting this potential threat agent.