Inactivation of indigenous coliform bacteria in unfiltered surface water by ultraviolet light

This study examined the potential for naturally occurring particles to protect indigenous coliform from ultraviolet (UV) disinfection in four surface waters. Tailing in the UV dose-response curve of the bacteria was observed in 3 of the 4 water samples after 1.3-2.6-log of log-linear inactivation, implying particle-related protection. The impact of particles was confirmed by comparing coliform UV inactivation data for parallel filtered (11 microm pore-size nylon filters) and unfiltered surface water. In samples from the Grand River (UVT: 65%/cm; 5.4 nephelometric turbidity units (NTU)) and the Rideau Canal (UVT: 60%/cm; 0.84 NTU), a limit of approximately 2.5 log inactivation was achieved in the unfiltered samples for a UV dose of 20 mJ/cm2 while both the filtered samples exhibited >3.4-log inactivation of indigenous coliform bacteria. The results suggest that particles as small as 11 microm, naturally found in surface water with low turbidity (<3NTU), are able to harbor indigenous coliform bacteria and offer protection from low-pressure UV light.     

Effect of pre- and post-UV disinfection conditions on photoreactivation of fecal coliforms in wastewater effluents

Photoreactivation of microorganisms following UV disinfection can represent a disadvantage to using UV technology for wastewater treatment since recovery may, in some cases, reach several logs. Thus, decreasing photoreactivation can lead to considerable savings in capital and operating costs. Objectives of this study were to determine pre- and post-UV irradiation conditions which could decrease fecal coliform (FC) photoreactivation in wastewater effluents. Results indicated that delaying exposure to photoreactivating light for 3 h suppressed photoreactivation after relatively low UV doses of 10 and 20 mJ/cm². Moreover, at least 440 lux (0.065 mW/cm²) of visible light was needed to initiate photoreactivation. Additionally, photoreactivation decreased significantly when samples were exposed to visible light simultaneously or prior to UV irradiation. This was more significantly observed for winter samples, where photoreactivation decreased by nearly 50%. Finally, summer FC populations were more sensitive to inactivation and less able to photoreactivate than winter populations. The effect of visible light on photoreactivation levels may be explained by several photo-mechanisms of FC photolyase, such as photodecomposition of the MTHF co-factor and reduction of FAD.     

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。     

Impact of microparticles on UV disinfection of indigenous aerobic spores

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.     

紫外线和氯组合方式对大肠杆菌灭活效果的影响研究

系统地比较了紫外线和氯不同的组合方式对大肠杆菌的灭活效果.结果表明,紫外线和氯联合顺序消毒在一定程度上提高了消毒效果,但不同的组合方式以及两者不同的剂量对灭活效果都有影响.紫外线和氯先后作用的消毒效果优于紫外线和氯同时消毒.先氯后紫外线消毒时,加较高浓度的氯且短时间接触即可达到较好的消毒效果;先紫外线后氯消毒时,氯剂量越大则灭活率越高,若氯浓度相同而接触时间不同,则灭活效果差别不大.     

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。     

Systematic features in the study of humic substances in natural surface waters

The article has considered systematic approaches to the investigation of humus substances of natural surface water. It has been shown that the use of chromatographic methods for extraction humic matter from water and investigation of their molecular-weight distribution is accompanied by losses of these compounds owing to phenomena of irreversible adsorption. The comparative assessment of the methods of determining concentration of humus mater, in particular, spectrophotometry and fluorescent spectroscopy as well as methods based on the results of determination of water color and reaction of azo-combination using diazotized 4-nitroaniline has been made.     

Field observations on the occurrence of new indicators of disinfection efficiency

This paper summarizes studies on the presence of acid-fast and yeast organisms in wastewater and water treatment plants and in surface water. These organisms were found to satisfy three of Bonde's criteria for indicator organisms: presence whenever pathogens are likely to be present; resistance at least equal to that of pathogens; and lack of regrowth in the post-treatment environment. This, plus prior data, indicates that these organisms are at least as acceptable as indicators of disinfection efficiency than the coliform group.     

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。     

Empirical rate equation for trihalomethane formation with chlorination of humic substances in water

Trihalomethane (THM) in drinking water is formed by chlorination of humic substances. In this study, the rates of THM formation in aqueous solution of humic acid were examined under various conditions. The following rate equation was obtained empirically. [THM] = k (pH − a)[TOC][Cl₂]₀^mtⁿ.

Here, [THM] is the concentration of total THM after t h, [TOC] and [Cl₂]₀ are the concentrations of total organic carbon and chlorine dose, k is the rate constant and a, m and n are parameters. The values of k, a, m and n for humic acid as reagent were obtained as 8.2 × 10⁻⁴ (l^mmg^−mh⁻ⁿ), 2.8, 0.25 and 0.36, respectively. The activation energy was obtained as 37 kJ mol⁻¹. Further, it was proved that the above equation could be applied to the rates of THM formation from precursors in actual river and lake waters.     

Study on chlorine disinfection of pond effluent

Chlorine disinfection experiments were conducted to investigate the die-off patterns of the fecal coliforms when present in waste stabilization pond effluents containing from 100 to 400 mg l⁻¹ algae. The fecal coliform inactivation was observed to occur at two rates, i.e. an initial rapid kill followed by a slower kill. The magnitude of inactivation was found to be proportional to the initial chlorine dose and contact time and inversely proportional to the algal concentration. A mathematical model was developed to predict the fecal coliform survival ratio during the chlorination of the pond effluent. When compared with the experimental data, the predicted results had a correlation coefficient of 0.981.     

Influence of cations on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids

The influence of cations (Na(+), Ca(2+) and Mg(2+)) on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic acids (FAs) (Norman landfill leachate fulvic acid (NLFA) and Suwannee River fulvic acid (SRFA)) and dissolved humic acids (HAs) (Suwannee River humic acid (SRHA) and Leonardite humic acid (LHA)) was examined using steady-state fluorescence spectroscopy at pH 4, 7 and 10 as a function of cation concentration (up to 25-100mM). Regardless of pH and cation concentration, PRODAN quenching by FA was unaffected by cations. However, interactions between PRODAN and HA decreased in the presence of cations at pH 7 and 10. Cation concentrations below the HA charge density resulted in the greatest decrease of PRODAN quenching, while very little additional decrease in PRODAN quenching occurred at cation concentrations above the HA charge density. This suggests that as the HA carboxylic acid functional groups form inner sphere complexes with divalent cations, intramolecular interactions result in a contraction of the HA molecular structure, thereby preventing PRODAN from associating with the condensed aromatic, electron accepting moieties inherent within HA molecules and responsible for PRODAN quenching. However, once the HA carboxylic acid functional groups are fully titrated with divalent cations, PRODAN quenching is no longer significantly influenced by the further addition of cations, even though these additional cations facilitate intermolecular interactions between the HA molecules to form supramolecular HA aggregates that can continue to increase in size. Regardless of FA and HA type, pH, cation type and concentration, the lack of blue-shifted fluorescence emission spectra indicated that micelle-like hydrophobic regions, amenable to PRODAN partitioning, were not formed by intra- and intermolecular interactions of FA and HA.     

The effect of humic acids on the cytotoxicity of silver nanoparticles to a natural aquatic bacterial assemblage

The effect of a terrestrial humic acid (HA) and a river HA on the cytotoxicity of silver nanoparticles (AgNPs) to natural aquatic bacterial assemblages (0 μM, 2.5 μM and 5 μM) was measured with spread plate counting. The effect of HA (20 and 40 ppm) on the cytotoxicity of AgNPs ranging in size between 15 and 25 nm was tested in the presence and in the absence of natural sunlight. The experiment was a full factorial, completely randomized design and the results were analyzed using the General Linear Model in SAS. LSMEANS was used to separate the means or combinations of means. Significant main effects of all independent variables, plus interaction effects in all cases except HA/LI and HA/AgNPs/LI were observed. The toxicity of AgNPs to natural aquatic bacterial assemblages appears to be concentration dependent for concentrations between 0 μM and 5 μM. The data indicate that the light exposure inhibited viability more than the darkness exposure. The HA treatment groups in the presence of light showed greater reduced viability count compared to darkness exposure groups. The inhibition of bacterial viability counts by AgNPs exposure was less in the light treatment groups containing a terrestrial HA compared to that with a river HA. Difference in the extent of reactive oxygen species formation and adsorption/binding of AgNPs was speculated to account for the observed phenomenon.     

饮用水中氯化消毒副产物的控制研究进展

探讨了DBPs的形成机理及其种类,然后介绍了DBPs对人体的健康风险,并总结了目前国内外控制DBPs的方法,为饮用水高效安全消毒技术的进一步研究提出了意见和建议。     

Removal of THMP by nanofiltration: Effects of interference parameters

An experimental investigation is conducted to evaluate the effects of interference parameters on the performance of nanofiltration for removal of trihalomethane precursors (THMPs). The influence of operating pressure, feed THMPs concentration, pH, presence of other ions (Ca²⁺ and Mg²⁺), and suspended solids on nanofiltration performance are determined. The effect of membrane precompaction is studied as well. Membrane performance for reversible and irreversible compaction is compared. Pretreated surface water from a pond is used as the feed water in the study to simulate the practical conditions in water treatment industries. Experimental results show that precompacted membrane has a higher rejection capacity. Higher pressure, feed THMP concentration, and suspended solids increase rejection. However, overall flux variation due to these parameters is found to be negligible. On the other hand presence of divalent ions reduce the rejection capacity. Generally rejection is found to be greater than 90% for a precompacted membrane, which turned out to be well suited for industrial scale application of nanofiltration for removal of THMPs.     

Bioaccumulation and toxicity of copper as affected by interactions between humic acid and water hardness

This study evaluated the effects of water hardness and humic acid (HA) on the acute and chronic toxicity of copper to Daphnia pulex and on its accumulation by D. magna. Hardness had little effect on either the acute (3-day) or the chronic (42-day) toxicity of copper. Humic acid significantly reduced both the acute and chronic toxicity of copper when added to waters having hardnesses of 58, 115 and 230 mg l^?1 as CaCO₃. The effect, per unit of HA, on chronic toxicity was very similar for soft and medium water but less in hard water. At each of two HA concentrations, copper was chronically more toxic in hard water than in either medium or soft water. Bioaccumulation of copper varied with relative hardness and HA concentration and this was further affected by age at exposure. For 1-day-old animals, an increase in either hardness or HA- or any combination of the two, tended to decrease bioaccumulation. Results for 7-day-old animals were in general agreement except for animals exposed to copper in hard water at an intermediate HA concentration. These animals accumulated significantly more copper in the presence of HA. This agrees with the fact that this concentration of HA also increased the chronic toxicity of copper in hard water. Both of those phenomena are probably due to the displacement of Cu²⁺ from HA by competition from the increased concentrations of Ca²⁺ and Mg²⁺. The fact that HA had the opposite effect on copper accumulation by young animals in hard water could not be explained.     

Sorption of trichloroethylene by organo-clays in the presence of humic substances

We examined trichloroethylene sorption by organo-clays [hexadecyltrimethylammonium (HDTMA) and didodecyldimethylammonium (DDDMA) exchanged smectites (SWy-1 and SAz-1)] in aqueous solutions both in the presence and absence of humic substances (Aldrich humic acid and peat fulvic acid). The results indicated the uptake of humic substances by organo-clays and the effects of humic substances on trichloroethylene sorption by organo-clays were dependent on the type of organo-clay and humic substance. Selection of an appropriate combination of clay and organic cation can optimize the removal of trichloroethylene as well as humic substances from aqueous solutions by organo-clays. Organo-clays may be an alternative to activated carbon sorbents in some specific water treatment processes.     

光触媒在饮用水处理中的作用研究

目前,水源污染日益严重,同时,传统消毒剂Cl2将与水中的有机物合成大量的致癌或致诱变的副产物,对人们的身体健康带来了很大的危害。光催化氧化在去除饮用水中有机物污染物及消毒副产物方面具有突出优点,本文主要就其在饮用水处理中的研究进行综述,并提出了今后研究方向。     

Formation, adsorption and separation of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances

A significant portion of the unidentified disinfection byproducts (DBPs) in chlorinated drinking water can be attributed to high molecular weight (MW)-chlorinated DBPs (above 500 Da) that may have adverse health effects. In this work, issues on the formation, adsorption and separation of high MW-chlorinated DBPs were investigated by introducing radioactive (36)Cl into humic substance samples. The results show that the amount of high MW-chlorinated DBPs during chlorination decreased with the increase of contact time from 1 to 120 h, increased with the increase of pH from 5.5 to 9.5, and was less in the ultrafiltered samples from Suwannee River fulvic acid than from Suwannee River humic acid. The high MW-chlorinated DBPs were found to be effectively adsorbed by activated carbon and be possibly reduced to Cl(-) by activated carbon, but not to be readily desorbed from the activated carbon. Those high MW-chlorinated DBPs were demonstrated to be incapable of resolution into discrete peaks by any of the three liquid chromatography columns studied. The significant implications of these results are discussed.     

Chlorine dioxide disinfection of drinking water—An evaluation of a treatment plant

A treatment plant for lake Kinneret water, comprising treatment by two filtration steps, flocculation and disinfection with chlorine dioxide, was studied with a view to evaluating the effect of ClO₂ disinfection on drinking water quality and determining the optimal mode of operation for the treatment plant. Four modes of operation were studied and the optimal mode was defined as that in which the flocculant (aluminium sulphate) was introduced before the first, and ClO₂ after the second, filtration.

The finished water contained a residue of approx. 0.2 mgl⁻¹ ClO₂, approx. 0.35 mgl⁻¹ ClO₂⁻ and low concentrations of suspended matter (1.5 mgl⁻¹) and of chlorophyll (0.1 μgl⁻¹). Trihalomethane concentrations were negligible, and the bacteriological quality of the water was within the health authorities' requirements. It was shown that disinfection of treated water (after flocculation and filtration) was much more effective than that of raw water. Furthermore, disinfection in the optimal mode prevents accumulation of high chlorite concentrations leaving a residue of ClO₂.