The effects of UV disinfection on drinking water quality in distribution systems

UV treatment is a cost-effective disinfection process for drinking water, but concerned to have negative effects on water quality in distribution system by changed DOM structure. In the study, the authors evaluated the effects of UV disinfection on the water quality in the distribution system by investigating structure of DOM, concentration of AOC, chlorine demand and DBP formation before and after UV disinfection process. Although UV treatment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV_254, SUVA₂₅₄, the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular weight) significantly, the increase of low molecular fraction was observed after UV treatment, in dry season. Chlorine demand and THMFP are also increased with chlorination of UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights of broken DOM are not low enough to be used directly by microorganisms in distribution system. Nonetheless, modification of DOM structure can affect water quality of distribution system as it can increase chlorine demands and DBPs formation by post-chlorination.     

The effect of inorganic precursors on disinfection byproduct formation during UV-chlorine/chloramine drinking water treatment

Ultraviolet (UV) disinfection is being increasingly used in drinking water treatment. It is important to understand how its application to different types of water may influence finished water quality, particularly as anthropogenic activity continues to impact the quality of source waters. The objective of this study was to evaluate the effect of inorganic precursors on the formation of regulated and unregulated disinfection byproducts (DBPs) during UV irradiation of surface waters when combined with chlorination or chloramination. Samples were collected from three drinking water utilities supplied by source waters with varying organic and inorganic precursor content. The filtered samples were treated in the laboratory with a range of UV doses delivered from low pressure (LP, UV output at 253.7 nm) and medium pressure (MP, polychromatic UV output 200-400 nm) mercury lamps followed by chlorination or chloramination, in the presence and absence of additional bromide and nitrate. The regulated trihalomethanes and haloacetic acids were not affected by UV pretreatment at disinfection doses (40-186 mJ/cm²). With higher doses (1000 mJ/cm²), trihalomethane formation was increased 30-40%. While most effects on DBPs were only observed with doses much higher than typically used for UV disinfection, there were some effects on unregulated DBPs at lower doses. In nitrate-spiked samples (1-10 mg N/L), chloropicrin formation doubled and increased three- to six-fold with 40 mJ/cm² MP UV followed by chloramination and chlorination, respectively. Bromopicrin formation was increased in samples containing bromide (0.5-1 mg/L) and nitrate (1-10 mg N/L) when pretreated with LP or MP UV (30-60% with 40 mJ/cm² LP UV and four- to ten-fold increase with 40 mJ/cm² MP UV, after subsequent chlorination). The formation of cyanogen chloride doubled and increased three-fold with MP UV doses of 186 and 1000 mJ/cm², respectively, when followed by chloramination in nitrate-spiked samples but remained below the World Health Organization guideline value of 70 μg/L in all cases. MP UV and high LP UV doses (1000 mJ/cm²) increased chloral hydrate formation after subsequent chlorination (20-40% increase for 40 mJ/cm² MP UV). These results indicate the importance of bench-testing DBP implications of UV applications in combination with post-disinfectants as part of the engineering assessment of a UV-chlorine/chloramine multi-barrier disinfection design for drinking water treatment.     

氯化消毒副产物NDMA的生成与控制研究进展

NDMA（N-Nitrosodimethylamine）是水处理领域新近发现的一种氯化消毒副产物,由于其具有检出率高、致癌风险大、难以有效去除等特性,已成为国际关注的重要水质问题之一。饮用水中的NDMA主要产生于氯化消毒过程,尤为严重的是氯胺消毒过程,而臭氧和过氧化氢氧化基本不产生NDMA。NDMA为亲水性小分子有机物,常规处理和深度处理均难于有效去除,而且管网中的浓度显著高于出厂水。目前控制饮用水中NDMA的常用方法是紫外线照射,但能耗较高。其他方法如延长自由氯接触时间和采用高铁酸盐预氧化、反渗透、臭氧／过氧化氢高级氧化工艺等也可以不同程度地控制NDMA及其前体物。     

深度处理污染河水的反渗透膜污染特性与防治

对以受污染河水为原水的反渗透系统膜污染问题进行了分析，初步认定反渗透膜污染是以生物粘泥、铁的氧化物及有机物为主的综合污染，而预处理的不完善、清洗方案选择不合理以及杀菌措施不够是导致膜污染的主要原因，最后提出了相应的解决办法。     

再生水用于地下回灌的加氯消毒研究

针对城市污水厂二级出水用于地下回灌的两种深度处理工艺,确定了达到消毒要求的加氯量,并且研究了加氯消毒对有关水质参数DOC、AOX、CHCl3、CCl4、UV254等的影响。研究发现,有效氯投加量在8mg/L左右时,水中细菌总数与总大肠菌群数均能达到我国饮用水卫生标准。加氯后水的DOC值变化不大,AOX值则有较明显的增大,CHCl3浓度略有增加,CCl4基本维持在加氯前的水平,UV254值也较加氯前有所增大。研究结果还表明,粒状活性炭处理工艺在污水深度处理流程中对去除消毒副产物（AOX）及其前驱物发挥着重要的作用。     

UV-induced effects on chlorination of creatinine

Ultraviolet (UV) irradiation is commonly employed for water treatment in swimming pools to complement conventional chlorination, and to reduce the concentration of inorganic chloramine compounds. The approach of combining UV irradiation and chlorination has the potential to improve water quality, as defined by microbial composition. However, relatively little is known about the effects of this process on water chemistry. To address this issue, experiments were conducted to examine the effects of sequential UV₂₅₄ irradiation/chlorination, as will occur in recirculating system of swimming pools, on disinfection byproduct (DBP) formation. Creatinine, which is present in human sweat and urine, was selected as the target precursor for these experiments.     

Some aspects of renovation of domestic sewage

Renovation of domestic sewage up to drinking water quality is discussed in a treatment consisting of screening. aeration. clarification, filtration, break point chlorination. dechlorination. reverse osmosis. carbon adsorption and ozone oxidation.     

Sequential UV- and chlorine-based disinfection to mitigate Escherichia coli in drinking water biofilms

This study was designed to examine the potential downstream benefits of sequential disinfection to control the persistence of Escherichia coli under conditions relevant to drinking water distribution systems. Eight annular reactors (four polycarbonate and four cast iron) were setup in parallel to address various factors that could influence biofilm growth in distribution systems. Eight reactors were treated with chlorine, chlorine dioxide and monochloramine alone or in combination with UV to examine the effects on Escherichia coli growth and persistence in both the effluent and biofilm. In general, UV-treated systems in combination with chlorine or chlorine dioxide and monochloramine achieved greater log reductions in both effluent and biofilm than systems treated with chlorine-based disinfectants alone. However, during UV-low chlorine disinfection, E. coli was found to persist at low levels, suggesting that the UV treatment had instigated an adaptive mutation. During UV-chlorine-dioxide treatment, the E. coli that was initially below the detection limit reappeared during a low level of disinfection (0.2 mg/L) in the cast iron systems. Chloramine was shown to be effective in disinfecting suspended E. coli in the effluent but was unable to reduce biofilm counts to below the detection limit. Issues such as repair mechanism of E. coli and nitrification could help explain some of these aberrations. Improved understanding of the ability of chlorine-based disinfectant in combination with UV to provide sufficient disinfection will ultimately effect in improved management and safety of drinking water.     

MBR、MCR处理微污染水的膜污染比较

膜污染是影响膜反应器稳定运行的重要原因之一，为此考察了膜生物反应器(MBR)和膜混凝反应器(MCR)处理微污染地表水时的运行状况，并对膜比通量的变化进行了比较，发现MBR的膜污染情况比MCR的严重。MCR和MBR的膜组件经物理、化学清洗后膜比通量分别恢复至新膜比通量的99．7％和76．9％，物理清洗对此的贡献较大。经分析发现，MCR中无机污染占优势，主要污染元素是Fe；MBR中微生物和有机物是膜污染的主要组成，而无机污染物则主要是铁盐和磷酸盐。     

Identification and understanding of fouling in low-pressure membrane (MF/UF) filtration by natural organic matter (NOM)

An understanding of natural organic matter (NOM) as a membrane foulant and the behavior of NOM components in low-pressure membrane fouling are needed to provide a basis for appropriate selection and operation of membrane technology for drinking water treatment. Fouling by NOM was investigated by employing several innovative chemical and morphological analyses.

Source (feed) waters with a high hydrophilic (HPI) fraction content of NOM resulted in significant flux decline. Macromolecules of a relatively hydrophilic character (e.g. polysaccharides) were effectively rejected by low-pressure membranes, suggesting that macromolecular compounds and/or colloidal organic matter in the hydrophilic NOM fraction may be a problematic foulant of low-pressure membranes. Moreover, the significant organic fouling that is contributed by polysaccharides and/or proteins in macromolecular and/or colloidal forms depends on molecular shape (structure) as well as size (i.e. molecular weight). More significant flux decline was observed in microfiltration (MF) compared to ultrafiltration (UF) membrane filtration. MF membrane fouling may be caused by pore blockage associated with large (macromolecular) hydrophilic molecules and/or organic colloids. In the case of UF membranes, the flux decline may be caused by sequential or simultaneous processes of surface (gel layer) coverage during filtration. Morphological analyses support the notion that membrane roughness may be considered as a more important factor in membrane fouling by controlling interaction between molecules and the membrane surface, compared to the hydrophobic/hydrophilic character of membranes. Membrane fouling mechanisms are not only a function of membrane type (MF versus UF) but also depend on source (feed) water characteristics.     

Drinking water and health hazards in environmental perspective

Among the present environmental issues drinking water quality and more specifically organic micropollutants receive not the highest priority. The long tradition of potable water quality assurance and the sophisticated evaluation methodologies provide a very useful approach which has great potential for wider application in environmental research and policy making.Water consumption patterns and the relative importance of the drinking water exposure route show that inorganic water contaminants generally contribute much more to the total daily intake than organic micropollutants. An exception is chloroform and probably the group of typical chlorination by-products. Among the carcinogenic organic pollutants in drinking water only chlorination by-products may potentially increase the health risk. Treatment should therefore be designed to reduce chemical oxidant application as much as possible.It is expected that in the beginning of next century organic micropollutants will receive much less attention and that the present focus on treatment by-products will shift to distribution problems. Within the total context of water quality monitoring microbiological tests will grow in relative importance and might once again dominate chemical analysis the next century.As disinfection is the central issue of the present water treatment practice the search for the ideal disinfection procedure will continue and might result in a further reduction in the use of chemical oxidants.     

A field study evaluation for mitigating biofouling with chlorine dioxide or chlorine integrated with UV disinfection

The drinking water industry is continually seeking innovative disinfection strategies to control biofouling in transmission systems. This research, conducted in collaboration with the East Bay Municipal Utility District (EBMUD) in California, compared the efficacy of chlorine dioxide (ClO2) to free chlorine (Cl2) with and without pre-treatment with low-pressure ultraviolet (UV) light for biofilm control. An additional goal was to determine disinfection by-product (DBP) formation with each disinfection strategy. Annular reactors (ARs) containing polycarbonate coupons were used to simulate EBMUD's 90-mile aqueduct that transports surface water from a source reservoir to treatment facilities. ARs were dosed with chemical disinfectants to achieve a residual of 0.2 mg/L, which is a typical value mid-way in the aqueduct. The experiment matrix included four strategies of disinfection including UV/ClO2, ClO2, UV/Cl2 and Cl2. Two ARs acted as controls and received raw water (RW) or UV-treated water. The data presented show that the UV/ClO2 combination was most effective against suspended and attached heterotrophic (heterotrophic plate count, HPC) bacteria with 3.93 log and 2.05 log reductions, respectively. ClO2 was more effective than Cl2 at removing suspended HPC bacteria and similarly effective in biofilm bacterial removal. UV light alone was not effective in controlling suspended or biofilm bacteria compared to treatment with ClO2 or Cl2. Pre-treatment with UV was more effective overall for removal of HPC bacteria than treating with corresponding chemical disinfectants only; however, it did not lower required chemical dosages. Therefore, no significant differences were observed in DBP concentrations between ARs pre-treated with UV light and ARs not pre-treated. Disinfection with ClO2 produced fewer total trihalomethanes (TTHMs) and haloacetic acids (HAAs) than chlorination but did produce low levels of chlorite. These data indicate that replacing Cl2 with ClO2 would further control microbiological re-growth and minimize TTHM and HAA formation, but may introduce other DBPs.     

The fate of wastewater-derived NDMA precursors in the aquatic environment

To assess the stability of precursors of the chloramine disinfection byproduct N-nitrosodimethylamine (NDMA) under conditions expected in effluent-dominated surface waters, effluent samples from four municipal wastewater treatment plants were subjected to chlorination and chloramination followed by incubation in the presence of inocula derived from activated sludge. Samples subjected to free chlorine disinfection showed lower initial concentrations of NDMA precursors than those that were not chlorinated or were disinfected with pre-formed chloramines. For chloraminated and control (unchlorinated) treatments, the concentration of NDMA precursors decreased by an average of 24% over the 30-day incubation in samples from three of the four facilities. At the fourth facility, where samples were collected on three different days, NDMA precursor concentrations decreased by approximately 80% in one sample and decreased by less than 20% in the other two samples. In contrast to the low reactivity of the NDMA precursors, NDMA disappeared within 30 days under the conditions employed in these experiments. These results and measurements made in an effluent-dominated river suggest that although NDMA may be removed after wastewater effluent is discharged, wastewater-derived NDMA precursors could persist long enough to form significant concentrations of NDMA in drinking water treatment plants that use water originating from sources that are subjected to wastewater effluent discharges.     

Transition in fouling mechanism in microfiltration of a surface water

The main disadvantage of membrane filtration is membrane fouling, which remains as the major obstacle for more efficient use of this technology. Information about the constituents that cause fouling is indispensable for more efficient operation. We examined the changes in both foulant characteristics and membrane morphology by performing the pilot-scale filtration test using one microfiltration membrane. During the operation, we cut the membrane fibers three times, and the components that caused irreversible fouling were extracted by acid or alkaline solution. We found that the characteristic of inorganic matter extracted by acid solution completely differed depending on the filtration period. A large amount of iron was extracted in the second chemical cleaning, while manganese was the dominant component of the extracted inorganic matter in the third chemical cleaning. The analysis of Fourier transform infrared (FTIR) and cross polarization magic angle spinning carbon-13 (CPMAS (13)C) nuclear magnetic resonance (NMR) demonstrated that the contribution of humic substances and carbohydrate in the organic foulant had increased as fouling developed. The changes in the major foulant have no relation with the fluctuation in feed water. The analysis of membrane morphology illustrated that the cake layer started to build up after the blockage of membrane pores. Based on the above results, we hypothesized the following fouling mechanism: the pores were covered or narrowed with relatively large particles such as iron, carbohydrate or protein; small particles such as manganese or humic substances blocked the narrowed pores; and finally an irreversible cake layer started to build up on the membrane surface.     

Analysis of trihalomethanes in drinking water using headspace-SPME technique with gas chromatography

In many drinking water treatment plants, the chlorination process is one of the main techniques used for the disinfection of water. This disinfecting treatment leads to the formation of trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform. In this study, headspace-solid-phase microextraction (HS-SPME, 85 microm carboxen/polydimethylsiloxane fiber) technique was applied for the analysis of THMs in drinking water. The effects of experimental parameters such as kinds of SPME fiber, the volume ratio of sample to headspace, the addition of salts, magnetic stirring, extraction temperature, extraction time and desorption time on the analysis were investigated. Analytical parameters such as linearity, repeatability and limit of detection were also evaluated. The results of THMs from the survey of Seongnam (Korea) drinking water samples showed that the highest total trihalomethane and chloroform were 24.03 and 13.34 microg/l, which were well within the Korean drinking water quality standard of 100 and 80 microg/l, respectively.     

Investigation of microbial inactivation efficiency of a UV disinfection system employing an excimer lamp

An ultraviolet (UV) disinfection reactor based on excimer lamp technology was designed by integration of the results of numerical simulations based on computational fluid dynamics and a fluence rate (E') distribution model for cylindrical excimer lamps. The E' distribution model was developed based on a point source approach that accounts for absorption, dissipation, reflection, and refraction within the reactor system. A prototype reactor was constructed with a xenon-bromide excimer lamp and an internal spiral baffle. Experiments were conducted on the reactor to test its effectiveness for disinfection of drinking water in situations where the use of mercury-based UV sources is restricted or undesirable; a similar design approach could be used to develop an excimer UV reactor for disinfection of other fluid media, including wastewater or air.     

Low- and medium-pressure UV inactivation of microsporidia Encephalitozoon intestinalis

Newly recognized waterborne pathogens such as microsporidia are being detected in the world's water supplies with increasing frequency. Many of these organisms have been shown to cause negative health impacts for both immunocompetent as well as immunocompromised individuals. It is imperative that these emerging pathogens be investigated for their ability to resist both traditional and novel disinfection technologies that are currently in use or under consideration for drinking water treatment. Low- and medium pressure UV light is at the cutting edge of disinfection technologies for the drinking water industry. While previous UV disinfection studies have focused on the inactivation of Cryptosporidium and Giardia as well as viruses and common bacteria, this research reports the ability of low- and medium pressure UV light to inactivate > 3.6 log10 of microsporidia Encephalitozoon intestinalis spores at a dose of 6 mJ/cm2 or higher as determined using a cell culture approach.     

浅谈饮用水消毒中常用的几种方法

对饮用水消毒中常用的几种方法进行了介绍，对这几种方法进行了比较，认为在目前国内的饮用水消毒处理中次氯酸钠发生器消毒是比较好的一种，而紫外线消毒法是今后可能取代传统的化学消毒法并且具有广阔应用前景的一种绿色环保高效的消毒方法。     

Chlorination disinfection by-products, public health risk tradeoffs and me

Since 1974 when trihalomethanes (THMs) were first reported as disinfection by-products (DBPs) in drinking water, there has been an enormous research effort directed at understanding how DBPs are formed in the chlorination or chloramination of drinking water, how these chlorination DBPs can be minimized and whether they pose a public health risk, mainly in the form of cancer or adverse reproductive outcomes. Driven by continuing analytical advances, the original DBPs, the THMs, have been expanded to include over 600 DBPs that have now been reported in drinking water. The historical risk assessment context which presumed cancer could be mainly attributed to exposure to environmental carcinogens played a major role in defining regulatory responses to chlorination DBPs which, in turn, strongly influenced the DBP research agenda. There are now more than 30 years of drinking water quality, treatment and health effects research, including more than 60 epidemiology studies on human populations, directed at the chlorination DBP issue. These provide considerable scope to reflect on what we know now, how our understanding has changed, what those changes mean for public health risk management overall and where we should look to better understand and manage this issue in the future.     

Pipeline materials modify the effectiveness of disinfectants in drinking water distribution systems

We studied how pipe material can modify the effectiveness of UV- and chlorine disinfection in drinking water and biofilms. This study was done with two pipe materials: copper and composite plastic (polyethylene, PE) in a pilot scale water distribution network. UV-disinfection decreased viable bacterial numbers in the pilot waterworks and outlet water of pipes on average by 79%, but in biofilms its disinfecting effect was minor. Chlorine decreased effectively the microbial numbers in water and biofilms of PE pipes. In outlet water from copper pipes, the effect of chlorination was weaker; microbial numbers increased back to the level before chlorination within a few days. In the biofilms present in the copper pipes, chlorine decreased microbial numbers only in front of the pipeline. One reason for weaker efficiency of chlorine in copper pipes was that its concentration declined more rapidly in the copper pipes than in the PE pipes. These results means that copper pipes may require a higher chlorine dosage than plastic pipes to achieve effective disinfection of the pipes.