Influencing factors of disinfection byproducts formation during chloramination of Cyclops metabolite solutions

Effects of reaction time, chlorine dosage, pH and temperature on the formation of disinfection byproducts(DBPs), were investigated during the chloramination of Cyclops metabolite solutions. The results showed that some species of DBPs like trichloromethane(TCM), dichloroacetic acid(DCAA) and trichloroacetic acid(TCAA) could accumulate to their respective stable values with a progressive elevation in reaction time and monochloramine concentration. And 1,1,1-2-trichloropropanone(1,1,1-TCP) content decreased correspondingly with a continuous increase of reaction time. The amounts of chloral hydrate(CH), chloropicrin(TCNM), 1,1,1-TCP and DCAA firstly increased and then decreased with increasing monochloramine doses. Higher temperature resulted in a decrease of CH, dichloroacetonitrile(DCAN), 1,1-dichloropropanone(1,1-DCP), 1,1,1-TCP, DCAA and TCAA concentration. pH affected the formation of the different DBPs distinctly. TCM accumulateded with the increase of pH under 9, and DCAA, TCAA, CH and 1,1-DCP decreased continuously with increasing pH from 5 to 10, and other DBPs had the maximum concentrations at pH 6–7.     

Characterization of halogenated DBPs and identification of new DBPs trihalomethanols in chlorine dioxide treated drinking water with multiple extractions

Chlorine dioxide(ClO_2) is a widely used alternative disinfectant due to its high biocidal efficiency and low-level formation of trihalomethanes and haloacetic acids. A major portion of total organic halogen(TOX), a collective parameter for all halogenated DBPs, formed in ClO_2-treated drinking water is still unknown. A commonly used pretreatment method for analyzing halogenated DBPs in drinking water is one-time liquid–liquid extraction(LLE), which may lead to a substantial loss of DBPs prior to analysis. In this study, characterization and identification of polar halogenated DBPs in a ClO_2-treated drinking water sample were conducted by pretreating the sample with multiple extractions. Compared to one-time LLE, the combined four-time LLEs improved the recovery of TOX by 2.3 times. The developmental toxicity of the drinking water sample pretreated with the combined four-time LLEs was 1.67 times higher than that pretreated with one-time LLE.With the aid of ultra-performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, a new group of polar halogenated DBPs, trihalomethanols,were detected in the drinking water sample pretreated with multiple extractions; two of them,trichloromethanol and bromodichloromethanol, were identified with synthesized standard compounds. Moreover, these trihalomethanols were found to be the transformation products of trihalomethanes formed during ClO_2disinfection. The results indicate that multiple LLEs can significantly improve extraction efficiencies of polar halogenated DBPs and is a better pretreatment method for characterizing and identifying new polar halogenated DBPs in drinking water.     

Total organic halogen (TOX) in human urine: A halogen-specific method for human exposure studies

Disinfection by-products(DBPs) are a complex mixture of compounds unintentionally formed as a result of disinfection processes used to treat drinking water. Effects of long-term exposure to DBPs are mostly unknown and were the subject of recent epidemiological studies. However,most bioanalytical methods focus on a select few DBPs. In this study, a new comprehensive bioanalytical method has been developed that can quantify mixtures of organic halogenated compounds, including DBPs, in human urine as total organic chlorine(TOCl), total organic bromine(TOBr), and total organic iodine(TOI). The optimized method consists of urine dilution, adsorption to activated carbon, pyrolysis of activated carbon, absorption of gases in an aqueous solution, and halide analysis with ion chromatography and inductively coupled plasma-mass spectrometry. Spike recoveries for TOCl, TOBr, and TOI measurements ranged between 78% and 99%. Average TOCl, TOBr, and TOI concentrations in five urine samples from volunteers who consumed tap water were 1850, 82, and 21.0 μg/L as X~-, respectively.Volunteers who consumed spring water(control) had TOCl, TOBr, and TOI average concentrations in urine of 1090, 88, and 10.3 μg/L as X~-, respectively. TOCl and TOI in the urine samples from tap water consumers were higher than the control. However, TOBr was slightly lower in tap water urine samples compared to mineral water urine samples, indicating other sources of environmental exposure other than drinking water. A larger sample population that consumes tap water from different cities and mineral water is needed to determine TOCl, TOBr, and TOI exposure from drinking water.     

TIC-Tox: A preliminary discussion on identifying the forcing agents of DBP-mediated toxicity of disinfected water

The disinfection of drinking water is a major public health achievement; however, an unintended consequence of disinfection is the generation of disinfection by-products (DBPs). Many of the identified DBPs exhibit in vitro and in vivo toxicity, generate a diversity of adverse biological effects, and may be hazards to the public health and the environment. Only a few DBPs are regulated by several national and international agencies and it is not clear if these regulated DBPs are the forcing agents that drive the observed toxicity and their associated health effects. In this study, we combine analytical chemical and biological data to resolve the forcing agents associated with mammalian cell cytotoxicity of drinking water samples from three cities. These data suggest that the trihalomethanes (THMs) and haloacetic acids may be a small component of the overall cytotoxicity of the organic material isolated from disinfected drinking water. Chemical classes of nitrogen-containing DBPs, such as the haloacetonitriles and haloacetamides, appear to be the major forcing agents of toxicity in these samples. These findings may have important implications for the design of epidemiological studies that primarily rely on the levels of THMs to define DBP exposure among populations. The TIC-Tox approach constitutes a beginning step in the process of identifying the forcing agents of toxicity in disinfected water.     

臭氧预氧化强化混凝对二级出水中DON作用机制探讨

城市污水厂出水越来越多被中水回用或排入河流间接地作为下游水源水,其中所包含的溶解性有机氮(dissolved organic nitrogen,DON)被认为是含氮消毒副产物(nitrogenous disinfection by-products,N-DBPs)的前体物,受到国内外学者的高度关注.为探讨臭氧预氧化强化混凝对二级出水中DON作用机制,不仅分析了不同相对分子量和亲疏水性DON组分变化,而且还考察氯化消毒副产物(disinfection by-products,DBPs)生成潜势;最后结合三维荧光(3DEEM)分析技术,对强化混凝前后DON组成、化学结构特征进行研究.结果表明,臭氧预氧化可以显著提高混凝对DON、DOC和UV254去除效果,其中DON最大去除率提高到3.7倍;pH对臭氧预氧化强化混凝有着重要的影响.随着pH值的增加,DON、DOC和UV254去除率呈下降趋势;Ca~(2+)是臭氧预氧化提高混凝效果的关键因素.随着臭氧浓度增加到8 mg·L~(-1)时,ζ电位由-33 m V上升到-8 m V,Ca~(2+)浓度则从116 mg·L~(-1)下降到89 mg·L~(-1).ζ电位和溶解性Ca~(2+)浓度的线性关系(R~2=0.97)可以表明,只有当Ca~(2+)浓度较高时臭氧预氧化才能显著地提高混凝效果;臭氧预氧化强化混凝处理后,相对大分子量(20×103)和疏水性DON所占比例显著下降,相对小分子量(6×103)和亲水性DON所占比例增加.DBPs的生成潜势总和明显降低,由120.1μg·L~(-1)下降到65.2μg·L~(-1);最后,经3DEEM光谱分析可知,在臭氧预氧化强化混凝过程中DON浓度和DBPs生成潜势变化与3DEEM光谱中3个主要荧光峰有关,分别代表色氨酸类蛋白质、芳香族类蛋白质和富里酸类物质.     

Formation of disinfection byproducts in typical Chinese drinking water

Eight typical drinking water supplies in China were selected in this study. Both source and tap water were used to investigate the occurrence of chlorinated disinfection byproducts (DBPs), and seasonal variation in the concentrations of trihalomethanes (THMs) of seven water sources was compared. The results showed that the pollution level for source water in China, as shown by DBP formation potential, was low. The most encountered DBPs were chloroform, dichloroacetic acid, trichloroacetic acid, and chlorodibromoacetic acid. The concentration of every THMs and haloacetic acid (HAA) compound was under the limit of standards for drinking water quality. The highest total THMs concentrations were detected in spring.     

Characteristics of typical dissolved black carbons and their influence on the formation of disinfection by-products in chlor(am)ination

● The physicochemical and structural properties of DBC were characterized. ● The effects of DBC on DBPs and DBPFP generation during disinfection were evaluated. ● The DBPs and DBPFP generation during chlor(am)ination were compared. Dissolved black carbon (DBC) released from biochar can be one of the potential disinfection by-products (DBPs) precursors in the dissolved organic matter pool. However, the physiochemical and structural properties of DBC and the effects on the development of DBPs and DBP formation potential (DBPFP) during the disinfection process remain unclear. In this study, the characteristics of two kinds of DBC, namely, animal-derived DBC (poultry litter DBC, PL-DBC) and plant-derived DBC (wheat straw DBC, WS-DBC), were investigated. The effects of different kinds of DBC on the evolution of DBPs and DBPFP in chlorine and chloramine disinfection processes were compared with natural organic matter (NOM). The results showed that the total DBPs concentrations derived from PL-DBC, WS-DBC and NOM were similar during chlorination (i.e., 61.23 μg/L, 64.59 μg/L and 64.66 μg/L, respectively) and chloramination (i.e., 44.63 μg/L, 44.42 μg/L and 45.58 μg/L, respectively). The lower total DBPs and DBPFP concentrations in chloramination could be attributed to the fact that the introduction of ammonia in chloramine inhibited the breaking of the bond between the disinfectant and the active group of the precursor. Additionally, DBC presented much lower total DBPFP concentrations than NOM in both chlorination and chloramination. However, both kinds of DBC tended to form more monochloroacetic acids and haloacetamides than NOM, which could result from the higher organic strength, higher protein matter, and nitrogen-rich soluble microbial products of DBC.     

Formation of disinfection by-products during sodium hypochlorite cleaning of fouled membranes from membrane bioreactors

•HAAs was dominant among the DBPs of interest. •Rising time, dose, temperature and pH raised TCM and HAAs but reduced HANs and HKs. •Low time, dose and temperature and non-neutrality pH reduced toxic risks of DBPs. •The presence of EPS decelerated the production of DBPs. •EPS, particularly polysaccharides were highly resistant to chlorine. Periodic chemical cleaning with sodium hypochlorite (NaClO) is essential to restore the membrane permeability in a membrane bioreactor (MBR). However, the chlorination of membrane foulants results in the formation of disinfection by-products (DBPs), which will cause the deterioration of the MBR effluent and increase the antibiotic resistance in bacteria in the MBR tank. In this study, the formation of 14 DBPs during chemical cleaning of fouled MBR membrane modules was investigated. Together with the effects of biofilm extracellular polymeric substances (EPS), influences of reaction time, NaClO dosage, initial pH, and cleaning temperature on the DBP formation were investigated. Haloacetic acids (HAAs) and trichloromethane (TCM), composed over 90% of the DBPs, were increasingly accumulated as the NaClO cleaning time extended. By increasing the chlorine dosage, temperature, and pH, the yield of TCM and dichloroacetic acid (DCAA) was increased by up to a factor of 1‒14, whereas the yields of haloacetonitriles (HANs) and haloketones (HKs) were decreased. Either decreasing in the chlorine dosage and cleaning temperature or adjusting the pH of cleaning reagents toward acidic or alkaline could effectively reduce the toxic risks caused by DBPs. After the EPS extraction pretreatment, the formation of DBPs was accelerated in the first 12 h due to the damage of biofilm structure. Confocal laser scanning microscopy (CLSM) images showed that EPS, particularly polysaccharides, were highly resistant to chlorine and might be able to protect the cells exposed to chlorination.