pH effect on the formation of THM and HAA disinfection byproducts and potential control strategies for food processing

Chlorine-based sanitizers have seen wide spread use in food sanitation. The reaction of chlorine species with organic matter is a concern for two reasons. Available chlorine can be "used up" by organic compounds resulting in a lower amount of chlorine available for disinfection. Another concern is that some forms of chlorine can react with some organic compounds to form toxic halogenated disinfection byproducts(DBPs). Many studies have been conducted to evaluate the role of hypochlorous acid(HOCl) and hypochlorite ion(OCl–) in the production of DBPs with a particular interest in the production of trihalomethanes(THMs) and haloacetic acids(HAAs). Since most of the chlorine reactions are pH dependent, pH is found to have a significant effect on the formation of chlorine DBPs. In many cases, the concentration of THMs decreases and HAAs increases as pH decreases. pH also plays an important role in the determination of the type and amount of DBPs formed, with lower, more acidic, pHs resulting in the formation of less chloroform. This review summarizes the information from the literature on the role of chlorine-based sanitizers as affected by pH in the formation of different types of DBPs. Alternative novel strategies to minimize the formation of DBPs are also discussed.

Disinfection byproducts and halogen-specific total organic halogen speciation in chlorinated source waters——The impact of iopamidol and bromide

This study investigated the speciation of halogen-specific total organic halogen and disinfection byproducts(DBPs) upon chlorination of natural organic matter(NOM) in the presence of iopamidol and bromide(Br^-).Experiments were conducted with low bromide source waters with different NOM characteristics from Northeast Ohio,USA and varied spiked levels of bromide(2-30 μmol/L) and iopamidol(1-5 μmol/L).Iopamidol was found to be a direct precursor to trihalomethane(THM) and haloacetic acid formation,and in the presence of Br^-favored brominated analogs.The concentration and speciation of DBPs formed were impacted by iopamidol and bromide concentrations,as well as the presence of NOM.As iopamidol increased the concentration of iodinated DBPs(iodo-DBPs) and THMs increased.However,as Br^-concentrations increased,the concentrations of nonbrominated iodo-and chloro-DBPs decreased while brominated-DBPs increased.Regardless of the concentration of either iopamidol or bromide,bromochloroiodomethane(CHBrClI) was the most predominant iodo-DBP formed except at the lowest bromide concentration studied.At relevant concentrations of iopamidol(1 μmol/L) and bromide(2 μmol/L),significant quantities of highly toxic iodinated and brominated DBPs were formed.However,the rapid oxidation and incorporation of bromide appear to inhibit iodoDBP formation under conditions relevant to drinking water treatment.

消毒副产物生成势测定方法的优化研究

提出新的DBPs生成模型,并进行DBPFP测定方法优化,优化因素包括投氯量、消毒时间和p H-温度联合因素。在优化投氯量时,发现低投氯量下五种DBPs生成量与投氯量之间存在明显的线性关系,线性拟合的确定性系数（R2）均大于0.980。优化消毒时间时,提出了ttrend的概念,发现8种DBPs的ttrend均包括3 d这一时间点。在pH-温度联合因素优化时,得到CHCl3、CHCl2Br、CHClBr2和C2Cl4生成量响应曲面拟合的R2均大于0.970,拟合效果较好;但三种卤乙酸生成量响应曲面拟合的R2为0.6710.874,拟合效果一般。这可能是因为pH-温度联合因素对卤乙酸生成量的影响较小,或试验过程引入过大误差造成模型残差过大。得到优化的DBPFP测定方法是投氯量为5 mg/L,消毒时间为3 d,pH值为7.5,温度为11℃。可根据DBPs生成量与三个优化因素的关系,使用DBPs生成模型和DBPFP测定值计算出不同条件下水样消毒过程中的DBPs生成量。