Reduction of bromate to bromide coupled to acetate oxidation by anaerobic mixed microbial cultures

Bromate, a weakly mutagenic oxidizing agent, exists in surface waters. The biodegradation of bromate was investigated by assessing the ability of mixed cultures of micro-organisms for utilization of bromate as electron acceptor and acetate as electron donor. Reduction of bromate was only observed at relatively low concentrations (<3.0 mM) in the absence of molecular oxygen. Under these conditions bromate was reduced stoichiometrically to bromide. Unadapted sludge from an activated sludge treatment plant and a digester reduced bromate without lag period at a constant rate. Using an enrichment culture adapted to bromate, it was demonstrated that bromate was a terminal electron acceptor for anaerobic growth. Approximately 50% of the acetate was utilized for growth with bromate by the enrichment culture. A doubling of 20 h was estimated from a logarithmic growth curve. Other electron acceptors, like perchlorate, chlorate and nitrate, were not reduced or at negligible rates by bromate-utilizing microorganisms.     

Ozone decomposition of 2-methylisoborneol (MIB) in adsorption phase on high silica zeolites with preventing bromate formation

This work elucidates the applicability of our newly developed adsorptive ozonation process for the decomposition of 2-methylisoborneol (MIB), a typical taste and odor chemical, without the formation of possibly carcinogenic bromate ions. First, zeolite adsorbents were screened for their ability to adsorb MIB with a batch-type adsorption experimental apparatus and a flow-type decomposition experimental apparatus included an adsorbent-packed column. The USY zeolite with the highest silica to alumina ratio (SiO(2)/Al(2)O(3) molar ratio=70) showed the best performance as an adsorbent. Using this adsorbent, an ozonation experiment on an MIB solution including bromide ions was performed under various retention times using the flow-type apparatus. As a result, sufficient decomposition of MIB was achieved with preventing bromate formation.     

Seawater ozonation: effects of seawater parameters on oxidant loading rates,residual toxicity,and total residual oxidants/by-products reduction during storage time

The efficacy of ozonation in different seawater conditions provides an improvement in the water quality and promotes the increment of dissolved oxygen. By-products (bromine, bromate, and bromoform) formation is directly proportional to the ozonation time. Ozone-produced oxidants remain toxic in both closed and dark containers for at least 4 days; however, during long storage period (35 days) in dark and cold conditions, these residual oxidants decrease slowly. These results have practical implications for both the installation of ozone systems on ships ballast water or for recirculating aquaculture system for inactivating undesirable organisms present in seawater.     

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.     

Pilot Study on Pre-Ozonation Enhanced Drinking Water Treatment Process

The enhancement of TOC, COD_Mn, and UV₂₅₄ reduction in the conventional drinking water treatment process by pre-ozonation was investigated in South China on treating dam source water with a pilot plant consisting of pre-ozonation, coagulation-sedimentation, and filtration units. Pre-ozonation enhanced the reduction of NOM in the conventional coagulation-sedimentation and filtration process, and the total removals of UV₂₅₄, COD_Mn and TOC were improved for 34.6%, 18.1% and 15.3%, respectively by the adoption of pre-ozonation under an ozone dose (in ozone consumption base) of 0.85 mg/L. The enhancement of UV₂₅₄ and COD_Mn removals was mainly achieved through direct ozonation on humic substances, and that for TOC removal was achieved through biodegradation in sand filtration. In comparison with the TOC removal of 38%, a removal of 49% was acquired for SDS-THM under a pre-ozonation dose of 0.80 mg/L, indicating the selective removal of THMFP. The reduction of SDS-THM paralleled the reduction of COD_Mn to a significant degree, suggesting that the COD_Mn might be an effective surrogate parameter for SDS-THM if the raw water does not contain the reductive inorganic matters. Although the source water contains 13.2–27.0μg/L bromide, the formation of bromate was negligible when the ozone dose was below 1.0 mg/L.     

Ozone and chlorine dioxide: Similar chemistry and measurement issues

The chemical reactions associated with ozone and chlorine dioxide can be complicated and involve numerous intermediates. When ozone is applied, the presence of reactive intermediate species (O₂ ^‐, O₃ ^‐, OH, HO₂, HO₂ ^‐, and H₂O₂) influence the extent of oxidation that takes place and determines the amount and types of by‐products formed. Similarly, when chlorine dioxide is applied the amount of intermediate (Cl₂O₂) formed determines whether chlorine dioxide producing reactions or chlorate ion forming reactions occur. Ozone and chlorine dioxide are excellent agents for inactivating Cryptosporidium and Giardia. Microbiologically, each of the agents are very reactive. In the case of ozone, typically each molecule undergoes a one‐electron change. The mechanism of chlorine dioxide inactivation involves a recycling process whereby chlorine dioxide is reduced to chlorite ion followed by the “regeneration” of chlorine dioxide that continues to react within the cell over and over again. Chlorite ion also has oxidizing power and in some cases, is a biocide. When ozone and chlorine dioxide are used in combination, it is important that the chlorine dioxide application follow the ozone treatment to prevent the formation of unwanted by‐products such as ClO₃ ^‐.     

Remediation of bromate-contaminated groundwater in an ex situ fixed-film bioreactor

Use of a pilot-scale fixed-film bioreactor was investigated for remediation of bromate contamination within groundwater. Bromate reduction with stoichiometric production of bromide was observed, providing supporting evidence for complete reduction of bromate with no production of stable intermediates. Reduction of 87-90% bromate from an influent concentration of 1.1 mg L(-1) was observed with retention times of 40-80 h. Lower retention times led to decreases in bromate reduction capability, with 11.5% removal at a 10 h retention time. Nitrate reduction of 76-99% from a 30.7 mg L(-1) as NO(3)(-) influent was observed at retention times of 10-80 h, although an increase in nitrite production to 2.7 mg L(-1) occurred with a 10 h retention time. Backwashing was not required, with the large plastic packing media able to accommodate biomass accumulation without decreases in operational efficiency. This study has provided proof of concept and demonstrated the potential of biological bromate reduction by fixed-film processes for remediation of a bromate contaminated groundwater source.     

Ozonation of drinking water: part II. Disinfection and by-product formation in presence of bromide,iodide or chlorine

Ozone is an excellent disinfectant and can even be used to inactivate microorganisms such as protozoa which are very resistant to conventional disinfectants. Proper rate constants for the inactivation of microorganisms are only available for six species (E. coli, Bacillus subtilis spores, Rotavirus, Giardia lamblia cysts, Giardia muris cysts, Cryptosporidium parvum oocysts). The apparent activation energy for the inactivation of bacteria is in the same order as most chemical reactions (35-50 kJ mol(-1)), whereas it is much higher for the inactivation of protozoa (80 kJ mol(-1)). This requires significantly higher ozone exposures at low temperatures to get a similar inactivation for protozoa. Even for the inactivation of resistant microorganisms, OH radicals only play a minor role. Numerous organic and inorganic ozonation disinfection/oxidation by-products have been identified. The by-product of main concern is bromate, which is formed in bromide-containing waters. A low drinking water standard of 10 microg l(-1) has been set for bromate. Therefore, disinfection and oxidation processes have to be evaluated to fulfil these criteria. In certain cases, when bromide concentrations are above about 50 microg l(-1), it may be necessary to use control measures to lower bromate formation (lowering of pH, ammonia addition). Iodate is the main by-product formed during ozonation of iodide-containing waters. The reactions involved are direct ozone oxidations. Iodate is considered non-problematic because it is transformed back to iodide endogenically. Chloride cannot be oxidized during ozonation processes under drinking water conditions. Chlorate is only formed if a preoxidation by chlorine and/or chlorine dioxide has occurred.     

O3/UV过程中溴酸盐生成的研究

臭氧在处理含溴水的过程中会产生具有致癌性的溴酸盐。本文研究了O3/UV氧化法在处理含溴水的过程中溴酸盐生成量的变化规律,与单独臭氧氧化和单独紫外氧化的结果做对比分析,并应用于处理自然水体。研究结果表明：单独臭氧氧化过程中会产生一定量的溴酸盐,并随反应时间逐渐增多,低pH值有利于减少溴酸盐的生成量;在相同条件下,紫外光辐射的氧化过程中基本不产生溴酸盐,但反应速率较慢;O3/UV联用氧化法处理过程中溴酸盐的变化规律与臭氧氧化法中类似,但溴酸盐生成量减少了70%;O3/UV联用氧化法处理自然水体的效果优于单独臭氧氧化,溴酸盐生成量减少了24%。     

Study on By-Products of Ozonation during Ammonia Removal under the Existence of Bromide: Factors Affecting Formation and Removal of the By-Products

Factors affecting the formation of by-products of ozonation during ammonia removal under the existence of bromide were investigated. The presence of reducible N compounds could significantly reduce the formation of bromate and brominated organics; however, it was difficult to completely prevent formation of the by-products. It was therefore concluded that while the method used in this study was an effective process to decompose ammonia, it should be applied to the treatment of wastewaters containing low concentration of TOC. For power plant condensate demineralization wastewater containing TOC of 3 to 4mg/L, TOX formed during ammonia removal ranged from 0.20 to 0.30 mgBr L^?1. The only halogenated organic substance of the power plant wastewater detected on GC spectrum was bromoform, whose concentration varied from 0.11 to 0.14 mg L^?1. Column test results indicated that bromate could almost completely be decomposed to bromide by activated carbon under proper space velocity and pH. Activated carbon was also very effective in adsorption of CHBr₃: 1 g activated carbon adsorbed ca. 20.3 mg of CHBr₃.