Bromate Formation during Ozonation of Bromide Containing Drinking Water- a Pilot Scale Study

The effect of bromide ion concentration, pH, temperature, alkalinity, and hydrogen peroxide content on bromate formation was studied. Increase in pH was found to give the greatest increase in bromate formation. Also increase in the ozonation temperature, bromide ion concentration and hydrogen peroxide content increased the observed bromate concentration. Only increased alkalinity decreased the bromate formation during the ozonation experiments. Bromate formation exceeded the EU limit value for bromate ion, 10 μg/l, when the initial bromide ion concentration was around 100 μg/l, except for the alkalinity of 1.4 mmol/1, when the bromate formation was 9.4 μg/l.     

Results Of Bromide And Bromate Monitoring At Several Water Treatment Plants

The ozonation of water is a widely used technology within the water industry. Recent toxicological studies have shown that high bromate ion intake induces a high incidence of tumors in rats. Bromate ion formation from oxidation of water containing bromide ion was examined at nine treatment plants and one pilot. We found bromate ion (> 2 μg/L) in drinking water containing bromide ion when treated with ozone at pH greater than 7.0, even in the presence of ammonia. Bromate ion formation increased with the applied ozone dose. But bromate ion must be considered also as a byproduct of commercial sodium hypochlorite solutions. Under commercial conditions, chlorine dioxide and granular activated carbon had no effects on bromate levels.     

Use of Ozone for Disinfection and Taste and Odor Control at Proposed Membrane Facility

Zone 7 of Alameda County Flood Control and Water Conservation District, in coordination with Black & Veatch, conducted a 9-month pilot study to determine preliminary design parameters for a new water treatment plant (WTP). The pilot study was performed to verify the performance of membrane filters and to establish preliminary design parameters for the submerged membrane process, followed by ozonation and biological granular activated carbon filtration. The pilot testing was conducted using water from the Patterson Pass WTP reservoir. The process included coagulation with either ferric chloride or polyaluminum chloride, flocculation, sedimentation, membrane filtration, ozonation, and filtration using biological granular activated carbon (BAC). The goals of the study were as follows:

1. Determine the potential effectiveness of ozone and BAC for removing geosmin and MIB.

2. Determine the impacts of different levels of pathogen inactivation, i.e., 0.5-log Giardia and 2-log virus inactivation.

3. Monitor the formation of bromate under various conditions of ozone oxidation for different levels of pathogen inactivation as well as for taste and odor control, and evaluate bromate mitigation strategies, if necessary.

The results of the study showed that the use of ozone achieved 2.0-log virus inactivation and 0.5-log Giardia inactivation. It also decreased the disinfection by-product formation and effectively controlled geosmin and removed a significant fraction of the MIB during a taste and odor event. Because the raw water bromide concentrations were low, bromate formation remained below the regulated level of 0.010 mg/L. However, in one instance, bromate mitigation was utilized by applying sulfuric acid to lower the pH to less than 7.1, which reduced bromate formation to less than 0.010 mg/L.     

Effect of Ozonation on Trihalomethane and Haloacetic Acid Formation and Speciation in a Full-Scale Distribution System

Disinfection by-product (DBP) formation was evaluated before and after ozone implementation at two full-scale drinking water facilities in Las Vegas, NV USA. The two treatment plants used preozonation for primary disinfection followed by direct filtration with subsequent chlorination for secondary disinfection. DBP data was evaluated from the finished water of the two treatment plants along with six locations in the distribution system. Results showed that preozonation reduced the formation of total trihalomethanes (TTHM) by up to 10 μg/L and the sum of five haloacetic acids (HAA5) by up to 5 g/L. These reductions were primarily due to decreases in the di- and trichlorinated DBPs such as chloroform, bromodichloromethane, and trichloroacetic acid. Ozonation appeared to shift the speciation of TTHMs and HAA5 to favor increased formation of the di- and tribrominated species such as bromoform, chlorodibromomethane, and dibromoacteic acid. A bromide mass balance showed that <30% of the raw water bromide was accounted for by the formation of TTHMs (8–21%), HAAs (2–3%) and bromate (5%). Reducing the concentration of THMs and HAAs is often not the primary purpose of ozonation, but it can assist utilities in meeting regulatory requirements during drinking water treatment.     

Impact of Water Temperature on Resolving the Challenge of Assuring Disinfection While Limiting Bromate Formation

Intensive pilot studies were performed to study the impact of ozone dose (0.6 to 3.5 mg/L), pH (6.0 to 7.5), and contact time (12 to 38 min) on bromate (BrO₃) formation, for different sand-filtered water qualities from the Neuilly-sur-Marne Treatment Plant (COT = 1.3 to 2.2 mg/L, TAC = 190 to 230 mg CaCO₃, [Br^?] = 25 to 50 μg/L, and T = 5°C to 26°C). Whatever the water quality studied, the main factors influencing bromate formation were ozone dose, pH, and a cross factor between them. Bromate formation was shown to be proportional to bromide concentration, and to increase only slightly with temperature, depending on the ozone dose and the pH. As on the contrary temperature has an important impact on disinfection, especially when considering Cryptosporidium inactivation, resolving the challenge of ensuring disinfection while limiting bromate formation was shown to be quite easily achievable, at intermediate temperature, and with more stringent conditions at high temperature (because of bromate formation) or at low temperature (because of disinfection).     

Modeling Bromate Formation During Ozonation

Bromate formation has been identified as a significant barrier in the application of ozone during water treatment for water sources that contain high levels of bromide. Bromate has been identified as a possible human carcinogen and bromate levels in drinking water are strictly controlled at 10 μg/L in most developed countries. Various models have been proposed to model bromate formation during ozonation based on raw water quality, ozone dose and contact time. Two main approaches for modeling have been used: an empirical regression modeling methodology and kinetic-based methodology. Currently, the benefit of the bromate models lies in their ability to show how process parameters may impact on the amount bromate formed.     

Empirically and Theoretically–Based Models for Predicting Brominated Ozonated By–Products

During water treatment, ozonation of waters containing bromide ion producesboth organic and inorganic disinfection byproducts. Bromide ion concentrations in U.S. waters range from 0.01 to 2 mg/L (Krasner, 1989). Bromoformand dibromoacetic acid (DBAA) are the major organic byproducts and bromateion is the major inorganic byproduct derived from ozonation. Bromoform is a known carcinogen and the existence of bromate ion in water supplies also is of public health concern (Lykins, 1986). Bromate ion causes renal failure and hearing loss in laboratory animals and in human beings (Kruithof, 1992). The provisional guideline for bromate ion as proposed by the World Health Organization is 25 pg/L and may be exceeded in water treatment processesusing ozone. Also draft drinking water regulations in the U.S. will specify a maximum contaminant level (MCL) of 10 µg/L for bromate ion and a bestavailable treatment (BAT) of pH adjustment.     

Parameters Affecting the Formation of Bromate Ion During Ozonation

Batch type ozone experiments conducted on aquatic humic substances solutions spiked with bromide ion were developed to evaluate the importance of various parameters that may affect the formation of bromate ion during ozonation. The nature of the NOM, the alkalinity, the bromide ion content and the presence of ammonia were found to significantly affect the bromate ion production. Temperature and pH can be considered as minor factors. The ozonation of a clarified surface water using a continuous flow ozone contactor have shown that the addition of a low quantity of ammonia (0.05 to 0.1 mg/L NNH₄ ⁺) appeared to be an interesting option for controlling the bromate formation. On the contrary, the addition of hydrogen peroxide may enhance or reduce the bromate ion production, depending on the applied hydrogen peroxide/ozone ratio.     

Minimizing Bromate Concentration by Controlling the Ozone Reaction Time in a Full-Scale Plant

The latest European Directive 98/83/CE (5 December 1998), concerning the quality of water intended for human consumption, has set a two-stage parametric value for bromate. Bromate concentration will comply with 25 μg/L after December 25, 2003, and with 10 μg/L after December 25, 2008. Bromate formation in water is generally due to bromide oxidation during the ozonation stage. Due to higher temperatures, this latter parametric value is often exceeded in summer. Minimizing bromate levels is thus a crucial problem for drinking water producers. A bromate-minimizing strategy consists of shortening the reaction time between ozone and water. This can be done by neutralizing dissolved ozone residual with bisulfite at the exit of the ozone reactor chamber and/or by managing the introduction of ozone in different chambers depending on the water flow rate. This is only possible if, in our case, the disinfection goal for ozone is respected toward bacteria and viruses. The CT value must comply with 1.6 mg/min/L. In our plants, this value could be very large due to high contact time in and after leaving the ozone reactors.     

Bromate in Drinking Water A problem in Switzerland?

Ozonation of bromide-containing waters causes the formation of bromate which is considered to be potentially carcinogenic. An investigation in Switzerland on water works using ozone (85) has shown that the new drinking water standard of 10?µg/L for bromate is generally not exceeded. This is mainly due to the relatively small bromide concentrations which are typically below 25?µg/L. There is a characteristic relationship between bromate formation and the ozone exposure in a particular water type. This can be used to estimate the integral ozone exposure from the bromate formation which allows the assessment of the efficiency of the disinfection. This new concept is illustrated by means of two examples.     

Chlorination by-products in surface water treatment process

Chlorine disinfection is carried out for the purpose of sterilization of microbes existing in drinking water. Chlorination may cause the formation of disinfection by-products (DBPs) by the reaction of free chlorine with humic substance in the water. In particular, the DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloketones exist in tap water. The US Environmental Protection Agency (US EPA) suggests 80 μg/L THMs and 60 μg/L HAAs as maximum contamination levels for drinking water. This study was performed to detect the level of DBPs in drinking water and to measure disinfection by-product formation potential (DBPFP) of raw water with four different properties. After 24 h of chlorination, the measured level of trihalomethane formation potential (THMFP), haloacetic acid formation potential, and haloacetonitrile formation potential ranged from 55.0 to 102.6 μg/L, from 9.1 to 23.6 μg/L, and from 10.3 to 33.6 μg/L, respectively. DBPFP was the highest at pH 7.0 and increased with the reaction time. Among the DBPFP, THMFP was detected more frequently than the others. In the treated water, DBPs were measured with a mean value of 47.0 μg/L. Chloroform, dichloroacetic acid, trichloroacetic acid, and dichloronitrile all known as hazardous compounds, were measured as major parts of DBPs.     

Ozonation at Belle Glade,Florida : A Case History

In October 1984, the city of Belle Glade, FL installed a two-stage ozonation process for the treatment of lake water high in organics (av TOC 30 mg/L; up to 75 mg/L), high in color (av 100 color units; up to 500), and high in THM concentrations, at times nearly 1,000 μ/L. The new treatment process applied 3 mg/L of ozone to the raw water ahead of the flash mix basin, lime softening, alum and polymer coagulation, clarification, recarbonation, and addition of 3 mg/L ozone prior to filtration. Post-chlorination then produced distribution system THM concentrations averaging 124 μg/L. Distribution of THMs shifted from 85% chloroform by the original process to 40% after adoption of ozonation, the balance comprising brominated species (but not bromoform).

In 1987, the treatment process was modified by adding chlorine and ammonia at the outlets of the pre- and intermediate-stages of ozonation and abandoning free chlorination. This has further reduced the distribution system THM levels to 20-30 μg/L. Filtered water turbidity and color have been improved. The use of chloramines after ozonation controls the nuisance aquatic growths in the clarifiers and recarbonation basins (caused by ozonation alone), and produces a combined chlorine residual which can be maintained throughout the distribution system. Periodic use of free chlorine in the distribution system is required to prevent elevated heterotrophic plate counts and the formation of excessive concentrations of nitrite ion due to biological regrowth and nitrification.     

Bromate control in phenol-contaminated water treated by UV and ozone processes

Formation of bromate is of a great concern whenever ozone-based technologies are used for treating highly bromide-containing water ever since bromate was classified as a potential carcinogen. Saudi Arabian groundwater is coincidentally high in bromide content, and the potential of forming bromate during the treatment of such water is high. This study investigated the extent of bromate formation under different treatment conditions of ozone-based Advanced Oxidation Processes (AOPs) when used for the treatment of phenol-contaminated water. The results of the study showed that continuous ozonation at a rate of 1 L/min has completely removed 50 ppm of phenol from contaminated water in less than 5 min. However, as high as 8.85 ppm of bromate (BrO₃⁻) was detected when treating the water which has high concentration of bromide ion (5 ppm). Results also showed that by adjusting the pH to 6 and adding ammonia (NH₃) at a dosage of 1.5 ppm, bromate formation was diminished drastically to non-detected levels.     

Comparing Static Mixer Performances at Pilot and Full Scale for Ozonation,Inactivation of Bacillus subtilis,and Bromate Formation in Water Treatment

The potential benefits of using a static mixer for ozone dissolution was evaluated through comprehensive pilot- and full-scale studies under a variety of operating conditions and source waters. The static mixer pilot unit was operated side-by-side to a full-scale plant which also employed static mixers for ozonation. Based on the results obtained from this pilot study (and at other sites), it appears that an optimal ozone dose (≤0.5mgO₃/mgC) applied through a static mixer dissolution system integrated with a well-designed downstream contactor can result in enhanced microbial inactivation while keeping bromate formation below 10μg/L.     

Effects of Ozonation on AOC Content of Humic Finnish Groundwater

The effects of ozonation on assimilable organic carbon (AOC) content of humic groundwater were investigated in batch experiments on three different groundwaters used as drinking water in Finland. All water samples had quite high concentrations of iron (range 2–10 mg/L) and manganese (range 0.1–0.2 mg/L) and therefore combined ozonation and filtration is a possible water purification method. The ozone dosage used varied from 0 to 16.6 mgO₃/L (ΔO₃/TOC?=?0–1.6). The ozone treatment increased the AOC concentration in the groundwater samples to different degrees. For example, an ozone dose of 3.9 mg/L increased the AOC concentration in different water as follows: from 49 μg/L to 55/L, from 7 μg/L to 119 μg/L and from 23 μg/L to 226 μg/L.     

水厂深度处理工艺中臭氧投加量探讨

臭氧生物活性炭深度处理是降低水中微量有机物的关键净化工艺。为确定臭氧的合理投加量,利用小试装置开展了臭氧氧化对砂滤池出水的研究。结果表明:随着臭氧投加量的增加,CODMn、总有机碳(TOC)的去除率均有所增加,但幅度弱于UV254;当臭氧的投加量达到3.0 mg/L时,臭氧氧化后的生物可降解溶解性有机碳(BDOC)可增加30%以上,UV254与TOC的比值趋于稳定;砂滤出水的溴离子浓度为100~300μg/L的情况下,当臭氧的投加量达到3.5 mg/L时仍未检测到溴酸盐。综上所述黄浦江原水水厂深度处理工程运行时,臭氧的投加剂量控制在2.5~3.5 mg/L是安全合理的。     

Characteristics of Natural Organic Matter and Formation of Chlorinated Disinfection By-Products from Two Source Waters that Respond Differently to Ozonation

This study investigated the characteristics of natural organic matter (NOM) in two different raw surface water sources that respond differently to ozonation: one for which ozonation decreases the disinfection by-product (DBP) formation potentials (i.e., Capilano Reservoir, Vancouver, Canada), and one for which ozonation does not (i.e., South Thompson River, Kamloops, Canada); and evaluated the effect of ozonation on these characteristics and on the DBP formation potential of the different size and polar fractions of the NOM. Although the South Thompson River and the Capilano Reservoir waters had relatively similar total organic carbon concentrations, the characteristics of the NOM (e.g., size and polar distribution, specific UV absorption), in these water sources differed significantly. In general, no clear and consistent trend was observed with respect to the tendency of different size and polar fractions of NOM to generate DBPs. Nonetheless, the results from the present study suggest that hydrophobic NOM has a higher tendency to form DBPs. In addition, when considering individual size and polar fractions, specific UV absorption was a good overall indicator of the DBP formation potential for a given water source. The effect of ozonation on South Thompson River and Capilano Reservoir waters also differed significantly. For both source waters, ozonation appeared to have a greatest effect on the more hydrophilic fractions, generally increasing the DBP formation potential of the smaller more hydrophilic NOM, while generally decreasing that of the larger more hydrophilic NOM. The beneficial effect of ozonation on reducing haloacetic acid (HAA) formation potentials was due to a reduction in both the dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potentials, while the negative effect of ozonation on increasing HAA formation potentials was due to an increase in the DCAA formation potentials. The results from the present study clearly indicate that the use of ozone as a primary disinfectant does not necessarily reduce the DBP formation potential of NOM in all water sources, further demonstrating the complex structure of NOM and the fact that NOM from different sources cannot be simply treated as one entity and compared with one another.     

Effect of Ammonia and Chloramine Pretreatment during the Ozonation of a Colored Groundwater with Elevated Bromide

Ozone coupled with pre-chloramination was evaluated as an effective color removal and bromate control method for groundwater at Mesa Water's Well #8. A modified solution ozone test procedure was employed to simulate the sidestream ozone injection. Satisfactory color removal (<10 PtCo CU) was achieved with 2 mg/L of ozone in the presence or absence of preformed monochloramine or ammonia. While bromate formation was reduced by 67% and 83% with 0.3 and 0.6 mg/L of ammonia-N alone, respectively, 68% and 92% of bromate formation was suppressed with 1.0 and 2.0 mg/L of monochloramine as Cl₂, respectively. Only the pre-treatment with 2.0 mg/L of monochloramine provided sufficient bromate control to meet its maximum contaminant level of 10 μg/L. UV and fluorescence analyses showed effective destruction of color-causing organics by ozone in the presence of preformed monochloramine.     

纳米金属氧化物催化臭氧氧化抑制溴酸盐形成的效能研究

通过纯水的模拟研究,探讨了纳米SnO2和纳米TiO2催化臭氧氧化抑制溴酸盐形成的情况及不同条件下纳米TiO2的抑制效能.结果表明,纳米SnO2催化及纳米TiO2催化均能有效抑制溴酸盐的形成,相对单独臭氧氧化条件溴酸盐生成量分别降低了45.81％和74.10％;光照对纳米TiO2催化抑制溴酸盐形成的效能影响不大;反应温度在10～26℃之间时,随着温度的升高,纳米TiO2催化抑制溴酸盐形成的作用越明显;纳米TiO2催化抑制溴酸盐生成的效能随着Br-初始质量浓度的增加和pH的上升而降低.     

Prediction of Bromate Formation Using Multi-Linear Regression and Artificial Neural Networks

The main objective of this study was to develop simple models for the prediction of bromate formation in ozonated bottled waters, using rapidly and practically measurable raw water quality and/or operational parameters. A total of 6 multi-linear regression (MLR) with or without principal component analysis (PCA) and 2 artificial neural networks (ANN) models with multilayer perceptron architecture were developed for the prediction of bromate formation. PCA was employed to better identify relations between variables and reduce the number of variables. Experimental data used in modeling was provided from the ozonation of samples from 5 groundwater sources at various applied ozone dose and contact time. MLR models#1 and #2 well-predicted bromate formation although correlations (i.e., the signs of regression constants) among pH (as input variable) and bromate concentrations did not agree with the chemistry. MLR model#6, containing practical input parameters that are measured on-line in full-scale treatment plants, adequately predicted bromate formation and agreed with the chemistry, although fewer input parameters were used compared to MLR#1 and #2. Although both of the ANN models exhibited high regression coefficients (R²) (0.97 for both) ANN#1 was found to provide better prediction of bromate formation based on mean square error (MSE) values. However, since ANN#2 included easily measurable input parameters it may be practically used by water companies employing ozonation. Results overall indicated that ANN models have stronger prediction capabilities of bromate formation than MLR models. ANN modeling appears to be a strong tool in situations where the relations between variables are non-linear, interactive and complex, as in the bromate formation by ozonation.