腐殖酸特性及其对三卤甲烷形成的影响

以提取腐殖酸和商品腐殖酸为对象,研究了不同腐殖酸对加氯消毒后三卤甲烷生成量的影响,并对腐殖酸特性进行了分析。结果表明,伊春腐殖酸比松花江腐殖酸和商品腐殖酸具有更高的三卤甲烷生成量、生成速度和更高的卤代活性。松花江腐殖酸和商品腐殖酸中的芳香结构、不饱和双键的分子较少,分子质量较大,而伊春腐殖酸中芳香结构和不饱和双键的分子较多,分子质量较低。小分子质量和含不饱和双键的有机物通常是消毒副产物的主要前体物,因而伊春腐殖酸加氯消毒后的三卤甲烷生成量比松花江腐殖酸和商品腐殖酸高。     

臭氧催化氧化与BAC联用控制氯化消毒副产物

研究了臭氧催化氧化与生物活性炭联用技术对氯化消毒副产物（DBPs）的控制效能。结果表明：常规工艺出水中分子质量为2000u左右的疏水性有机物是氯化消毒副产物的主要前质，其占DOC与UV254的比例分别为70％和80％，并与UV254有良好的线性相关性，故可用UV254作为DBPs前质的替代指标。臭氧催化氧化与生物活性炭联用对DBPs前质的去除效果显著，其中臭氧催化氧化可有效去除三卤甲烷（THMs）前质中的疏水性有机物及部分亲水性有机物，并提高了DBPs前质的可生化性，是给水深度处理中控制THMs前质的主要工艺环节。臭氧催化氧化／生物活性炭对UV254的控制是减少DBPs生成的一条有效途径。     

氯化消毒条件及污水水质对生成THMs、HAAs的影响

系统地研究了消毒务件和水质在城市污水氯化消毒过程中对生成三卤甲烷和卤乙酸的影响。结果表明，投氯量对三卤甲烷和卤乙酸生成量的影响最大，投氯量为40mg／L时的生成量分别约是投氯量为5mg／L时的30倍和70倍。三卤甲烷浓度随反应时间和温度无明显变化，而卤乙酸浓度在反应2h后达到峰值并在之后逐渐降低，且随温度的升高呈下降趋势。pH对两类副产物生成的影响几乎相反，近中性条件下的三卤甲烷生成量最多而卤乙酸生成量最少。水中氨氮浓度的增加会导致三卤甲烷生成量略有下降，而卤乙酸浓度却大幅上升。溴离子浓度升高将导致三卤甲烷和卤乙酸生成量显著增加，其中三氯甲烷浓度下降，三溴甲烷浓度显著上升，混合取代的三卤甲烷浓度先增加后减少。与此类似，二氯乙酸和三氯乙酸浓度随溴离子浓度的增加而减少，含溴卤乙酸浓度则有不同程度的增加。反应温度、反应时间、pH和氨氮对污水消毒副产物生成的影响与已报道的饮用水消毒中的作用规律存在显著差异，甚至截然相反，这为有针对性地选取消毒工艺参数提供了依据。     

臭氧/陶瓷膜集成工艺的饮用水安全性研究

从微生物安全和消毒副产物前体物控制两个方面对混凝、臭氧/陶瓷膜和生物活性炭集成工艺进行了中试研究。结果表明,膜出水中粒径2μm的颗粒数低于10个/mL,大肠杆菌、菌落总数、隐孢子虫和贾第虫均为零,从而有效保障了工艺出水的微生物安全。臭氧投量为3mg/L时,中试工艺对UV254和DOC的去除率分别为83%和73%,对三卤甲烷、卤乙酸和三氯乙醛前体物的去除率分别为77%、76%和83%,其中对三氯甲烷、二氯乙酸和三氯乙酸前体物的去除率分别为81%、79%和77%。集成工艺能有效控制病原微生物和大幅降低水中消毒副产物前体物含量,显著改善饮用水的安全性。     

二氧化钛光催化降解腐殖酸的试验研究

研究了不同pH条件下二氧化钛(TiO2)对腐殖酸的吸附和光催化降解过程,重点考察了腐殖酸降解过程中UV254、A436、TOC、SUVA254、AOC的变化.结果表明:随着pH值的升高,Ti02对腐殖酸的吸附率下降;当腐殖酸初始浓度为10 mg/L、初始pH=7、二氧化钛投量为2g/L时,反应2 h后,对UV254、A436、TOC的去除率分别可达98.21%、99.11%、71.02%,SUVA254值由初始的7.58 L/(mg·m)持续降低至0.467 L/(mg·m),AOC浓度则先升高后降低.     

强化混凝对微污染水源水消毒副产物的去除研究

通过对微污染水源水的强化混凝试验,研究不同的聚合氯化铝投加量对消毒副产物三卤甲烷生成势、UV254及TOC的影响。结果表明,增加聚铝投加量时三卤甲烷生成势呈现下降的趋势,当聚铝投加量为2.7mg/L时,三卤甲烷生成势的去除由原水的238.9μg/L降至114.5μg/L,去除率高达52.07%,四次试验的平均去除率达40%;投加不同聚铝量后UV254呈现下降的趋势,当聚铝投加量为2.7mg/L时,UV254由原水的0.070降至0.042,去除率达40%,且四次试验的平均去除率达到32.32%;投加不同聚铝量后TOC呈现下降的趋势,当聚铝投加量为2.7mg/L时,TOC的去除由原水的3.231mg/L降至1.226mg/L,去除率高达62.06%,四次试验的平均去除率达到48.48%。     

混凝/微滤去除滦河水中不同分子质量有机物的效果

采用混凝/微滤工艺处理滦河水,以DOC、UV254、THMFP为指标考察了处理前、后水中有机物的分子质量分布.结果表明,原水中的有机物以溶解性小分子有机物为主,该部分有机物是生成THMs的主要物质,其中分子质量为1-3 ku的有机物生成THMs的能力最强;混凝/微滤工艺对分子质量>10 ku的DOC的去除效果较好,在各个分子质量区间,对UV254的去除率均高于对DOC的;系统对THMFP的去除率约为40%.     

臭氧活性炭工艺对三卤甲烷前体物的去除性能研究

通过两组试验对水厂臭氧活性炭深度处理工艺去除三卤甲烷前体物的性能进行了研究。结果表明:…臭氧活性炭工艺能有效去除TOC和UV254;对三卤甲烷前体物去除效果显著,去除率达40%以上;臭氧氧化对三卤甲烷前体物去除能力较小,活性炭滤池过滤去除效果显著。经臭氧活性炭工艺处理的水加氯消毒后三氯甲烷生成量较处理前可减少50%以上。臭氧活性炭工艺能有效降低消毒生成三卤甲烷的风险。     

城市饮用水水源水质的变化特性分析

从季节性差异分析了我国东北某城市两座水源地水库的浊度、CODMn氨氮、UV254三卤甲烷生成潜能(THMFP)、叶绿素a的变化规律.结果表明,B水库原水水质要好于A水库,两座水库原水浊度、有机物和三卤甲烷前驱物含量均呈季节性变化;A水库CODMn最高值为6.5 mg/L,最低值为2.8 mg/L;B水库CODMn最高值为5.0 mg/L,全年的最低值0.5 mg/L出现在3月;B水库叶绿素a在春夏之交变化较明显,A水库和B水库六个月内叶绿素a的平均值分别为36.53和22.25 mg/m3,UV254平均值分别为0.11和0.112 cm-1.     

强化混凝去除水源水中三卤甲烷前体物的研究

通过小试试验，研究了通过调整混凝剂聚氯化铝的投加量进行强化混凝，对两种不同水质的水源水中TOC、UV254及三卤甲烷前体物。结果表明，强化混凝能有效提高对TOC、UV254及三卤甲烷前体物去除效果，对TOC的去除率分别达到52.11%和41.25%，对UV254的去除率分别达到29.23%和63.33%，对三卤甲烷前体物的去除率分别达到50.62%和44.75%。     

Disinfection by-product formation following chlorination of drinking water: Artificial neural network models and changes in speciation with treatment

Artificial neural network (ANN) models were developed to predict disinfection by-product (DBP) formation during municipal drinking water treatment using the Information Collection Rule Treatment Studies database complied by the United States Environmental Protection Agency. The formation of trihalomethanes (THMs), haloacetic acids (HAAs), and total organic halide (TOX) upon chlorination of untreated water, and after conventional treatment, granular activated carbon treatment, and nanofiltration were quantified using ANNs. Highly accurate predictions of DBP concentrations were possible using physically meaningful water quality parameters as ANN inputs including dissolved organic carbon (DOC) concentration, ultraviolet absorbance at 254 nm and one cm path length (UV₂₅₄), bromide ion concentration (Br⁻), chlorine dose, chlorination pH, contact time, and reaction temperature. This highlights the ability of ANNs to closely capture the highly complex and non-linear relationships underlying DBP formation. Accurate simulations suggest the potential use of ANNs for process control and optimization, comparison of treatment alternatives for DBP control prior to piloting, and even to reduce the number of experiments to evaluate water quality variations when operating conditions are changed. Changes in THM and HAA speciation and bromine substitution patterns following treatment are also discussed.     

Characteristic transformation of humic acid during photoelectrocatalysis process and its subsequent disinfection byproduct formation potential

In this study, degradation of humic acid (HA) via photoelectrocatalysis (PEC) process and corresponding disinfection byproduct formation potential (DBPFP) were investigated. Particularly, structure variation and subsequent DBPFP of HA during PEC treatment were correlated. The PEC process was found to be effective in reducing dissolved organic carbon concentration by 75.0% and UV absorbance at 254 nm by 92.0%. Furthermore, 90.3% of haloacetic acids formation potential and 89.8% of trihalomethanes formation potential were reduced within 180 min. Based on molecular weight and resin fraction results, it was demonstrated that HA with large aromatic, hydrophobic and long aliphatic chain organics were transformed into small and hydrophilic organics during PEC process. Combined with the fourier transform infrared spectra and ¹³C nuclear magnetic resonance spectra analysis of HA fractions, it was concluded that phenolic hydroxyl and conjugated double bonds tended to be attacked by hydroxyl radicals during PEC process; these groups were reactive with chlorine to produce disinfection byproducts (DBP), especially trihalomethane and trichloroacetic acid. By contrast, amino, carboxyl and alcoholic hydroxyl groups were relatively difficult to be oxidized during PEC process; these groups had the potential to form dichloroacetic acid during chlorination. Results of these studies confirmed that PEC process was a safe and effective technique to decrease DBP formation significantly in water treatment plant.     

Potential impact of chlorination of Sandy bottom swimming areas on drinking water sources

The concentrations of trihalomethanes and haloacetic acids, disinfection by‐products (DBPs) of chlorine, were measured in sandy bottom swimming areas to determine their potential impact on surface and ground water that are sources of drinking water. Total trihalomethanes and individual haloacetic acid concentrations in several swimming area samples were higher than the drinking water standards (current and proposed). Individual trihalomethanes (except bromoform) also exceeded ground and surface water release standards. No release standard exists for haloacetic acids. The DBPs, while exceeding standards, would be diluted by the ground water and microbially degraded prior to reaching the drinking water plant. So while DBPs from swimming areas contributed to groundwater concentrations, the current drinking water standards could still be met using source waters impacted by chlorinated swimming areas. It is suggested, though, that any release of chlorinated DBPs to surface and ground water be minimized to obtain the highest quality water sources for drinking water.     

Formation and fate of chlorination by-products in reverse osmosis desalination systems

Chlorination by-products may be formed during pretreatment or posttreatment disinfection in reverse osmosis (RO) desalination systems, potentially posing health, aesthetic and ecological risks. To assess the formation and fate of by-products under different conditions likely to be encountered in desalination systems, trihalomethanes, dihaloacetonitriles, haloacetic acids, and bromophenols were analyzed in water samples from a pilot-scale seawater desalination plant with a chlorine pretreatment system and in benchscale experiments designed to simulate other feed water conditions. In the pilot plant, RO rejection performance as low as 55% was observed for neutral, low-molecular-weight by-products such as chloroform or bromochloroacetonitrile. Benchscale chlorination experiments, conducted on seawater from various locations indicated significant temporal and spatial variability for all by-products, which could not be explained by measured concentrations of organic carbon or bulk parameters such as SUVA₂₅₄. When desalinated water was blended with freshwater, elevated concentrations of bromide in the blended water resulted in dihaloacetonitrile concentrations that were higher than those expected from dilution. In most situations, the concentration of chlorination by-products formed from continuous chlorination of seawater or blending of desalinated water and freshwater will not compromise water quality or pose significant risks to aquatic ecosystems.     

Chlorination of humic substances in aqueous solution: Yields of volatile and major non-volatile organic halides

In this paper, we present the study of the effect of chlorination contact time, of the chlorine/carbon ratio and of the bromide concentration on the major halogenated products in the case of chlorinated humic substance solutions at neutral pH. The yields of chloroform, of trichloroacetic acid and of dichloro-acetic acid increase with the increase in reaction time and in chlorine dosage. Various values for the yield are given for chlorinated commercial humic acid solutions and for chlorinated solutions of aquatic fulvic and humic acids. The simultaneous presence of trihalomethanes precursors and bromides in the solution leads to the formation of organo-brominated products. Total trihalomethanes increase with the increase of bromide concentration.     

DPB formation in breakpoint chlorination of wastewater

The formation of trihalomethanes (THMs) and haloacetic acids (HAAs), two major disinfection by-products (DBPs), from the breakpoint chlorination of three diluted yet buffered (pH 7.0) wastewater effluents was studied. The concentrations and distributions of THMs and HAAs species varied among different effluents at different zones of the breakpoint curves. Nevertheless, some common trends were observed. The formation of chloro-only THMs and HAAs, after normalization with the carbon contents of the effluents, increased with increasing the specific UV absorbance (SUVA) of the effluents but the dependency is not valid for bromo- or bromochloro-DBPs. The formation of THMs and HAAs showed no significant inclination with increasing chlorine dosages up to the breakpoint, but increased sharply beyond the breakpoint dosing level. Bromine incorporations into THMs and HAAs increased with an increasing bromide to DOC molar ratio. In addition, the bromine incorporation was also found to be highly dependent on the chlorine dosage and the bromide to ammonia ratio. A longer reaction time increased the yields of THMs and HAAs and was found to favor the formation of dihalogenated HAAs. A two-stage correlation between the total THMs and the total HAAs was found for each wastewater effluent.     

Ozone enhanced removal of natural organic matter from drinking water sources

The use of ozone as a pre-oxidant or intermediate oxidant in drinking-water treatment is becoming increasingly common. The ozonation of natural source waters containing natural organic matter produces biodegradable by-products such as organic acids, aldehydes, and ketoacids. These organic by-products serve as carbon source for bacteria, potentially causing regrowth problems in distribution systems. The measurement of biodegradable dissolved organic carbon (BDOC) provides quantitative insight into the amount of BDOC that is present. In drinking-water treatment, removal of BDOC can also reduce the formation potential of chlorination disinfection by-products such as trihalomethanes and haloacetic acids. Removal of BDOC was optimal at an applied ozone:DOC ratio of 2:1 (mg/mg) for source waters containing DOC levels ranging from 3 to 6 mg/liter. The use of biotreatment resulted in a 40–50% decrease in DOC, a 90–100% reduction in aldehydes, and a 40–60% reduction in trihalomethane formation potential. No removal of bromate ion and dibromoacetic acid was observed. A positive correlation was obtained between BDOC and assimilable organic carbon; both parameters indicate a tendency to plateau at an applied ozone/DOC weight ratio of 2:1.     

Low trihalomethane formation in Korean drinking water

Organics in water have the potential to generate harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) during the chlorination process. To clarify the regulatory implications of Korean THMs levels which appear to be significantly lower than those in the US where the Stage 1 and 2 D/DBPs rule has been promulgated, the characteristics of THMs formation were investigated on five major river waters in Korea. Water samples were taken from 12 water treatment plants on five major rivers that serve as drinking water sources for more than 90% of the Korean population. Trihalomethane formation potential (THMFP), total organic halide formation potential (TOXFP) and ultraviolet absorbance at 254 nm (UV(254)) were determined and compared with those from US data. A survey of existing data [J Korean Soc Water Qual; 16(4) 2000b 431-443] provided evidence that THMs levels in treated drinking water in Korea were one-third of those reported in the US. The lower THMs levels were mainly attributable to the differences in the level and THMFP of dissolved organic carbon (DOC). The DOC levels and the THMFP normalized to DOC were approximately 60% of those in the US. Results which combined could quantitatively account for the lower THMs levels (i.e. 0.6 x 0.6 approximately 1/3) in Korea. The observed Korean THMs levels were over-predicted by the THMs model () developed in the US. The level of THMFP was found to be similar if normalized for aromaticity as measured by UV(254). These findings suggest that: (i) the case for more stringent THMs control is not likely to be a high priority among issues of drinking water quality in Korea; and (ii) significant variation of THMFP level may exist over different geographic regions; hence (iii) independent THMs models should be developed to make accurate predictions for different regions.     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.     

Seasonal variations of disinfection by-product precursors profile and their removal through surface water treatment plants

A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV(254)), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.