Microbiology, chemistry and biofilm development in a pilot drinking water distribution system with copper and plastic pipes

We studied the changes in water quality and formation of biofilms occurring in a pilot-scale water distribution system with two generally used pipe materials: copper and plastic (polyethylene, PE). The formation of biofilms with time was analysed as the number of total bacteria, heterotrophic plate counts and the concentration of ATP in biofilms. At the end of the experiment (after 308 days), microbial community structure, viable biomass and gram-negative bacterial biomass were analysed via lipid biomarkers (phospholipid fatty acids and lipopolysaccharide 3-hydroxy fatty acids), and the numbers of virus-like particles and total bacteria were enumerated by SYBR Green I staining. The formation of biofilm was slower in copper pipes than in the PE pipes, but after 200 days there was no difference in microbial numbers between the pipe materials. Copper ion led to lower microbial numbers in water during the first 200 days, but thereafter there were no differences between the two pipe materials. The number of virus-like particles was lower in biofilms and in outlet water from the copper pipes than PE pipes. Pipe material influenced also the microbial and gram-negative bacterial community structure in biofilms and water.     

The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes

We studied the effects of flow velocity on the formation of biofilms and the concentration of bacteria in water in copper and plastic (polyethylene, PE) pipes. The formation of biofilms increased with the flow velocity of water. The increase in microbial numbers and contents of ATP was clearer in the PE pipes than in the copper pipes. This was also seen as increased consumption of microbial nutrients in the pipeline system. This indicates that the mass transfer of nutrients is in major role in the growth of biofilms. However, the increased biomass of biofilms did not affect microbial numbers in the water. Rapid changes in water flow rate resuspended biofilms and sediments which increased the concentrations of bacteria and copper in water. The disturbance caused by the changing water flow was also seen as an increase in the particle counts and water turbidity recorded with online instrumentation.     

Survival of Mycobacterium avium in a model distribution system

A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50microg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53 degrees C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.     

Principally New Technology Of Preparing Drinking Water Of Sanitary-Hygienic Purpose

The analysis of water disinfection technology by chemical reagents and physical methods was made, showed their advantages and disadvantages. The main disadvantages of chlorination is high toxicity of chlorine and its extremely dangerous compounds—organochlorine derivatives, which are not completely removed by existing methods of water purification. Substantiated is introduction of a new standard for water treatment at water management boards by natural disinfectants—carbon dioxide and ultraviolet radiation after coagulation and filtration to prevent biofouling of pipes and for disinfecion. It will allow us to give up the technology of chlorination of tap water with its negative effects.     

Drinking water and biofilm disinfection by Fenton-like reaction

A Fenton-like disinfection process was conducted with Fenton's reagent (H₂O₂) at pH 3 or 5 on autochthonous drinking water biofilms grown on corroded or non-corroded pipe material. The biofilm disinfection by Fenton-like oxidation was limited by the low content of iron and copper in the biomass grown on non-corroded plumbing. It was slightly improved by spiking the distribution system with some additional iron source (soluble iron II or ferrihydrite particles appeared as interesting candidates). However successful in situ disinfection of biofilms was only achieved in fully corroded cast iron pipes using H₂O₂ and adjusting the pH to 5. These new results provide additional support for the use of Fenton's processes for cleaning drinking water distribution systems contaminated with biological agents or organics.     

Role of discontinuous chlorination on microbial production by drinking water biofilms

Microbial quality in water distribution systems is strongly affected by the development of microbial biofilms. Production and release of microbial cells by the biofilm affect microbial levels in the water column and in some cases this fact constitutes a public health concern. In this study, we attempt to analyze in which way the existence of different episodes of chlorine depletion affects both biofilm formation and microbial load of an artificial laboratory system. The work was carried out using two parallel packed bed reactors both supplied with running tap water. One of the reactors was used as a control and was permanently exposed to the action of chlorine. In the other reactor, chlorine was neutralized at selected times during the experiment and for periods of variable length. During the experiment the concentration of total and viable cells from the effluent was monitored at the exit of each of the reactors. The data obtained were used to estimate microbial production from the biofilms. As an average, release of microbial cells to the water phase increased tenfold in the absence of chlorine. The results also indicate that disinfectant efficiency against the biofilm was not recovered when chlorine returned to normal levels after each event of chlorine neutralization. Cell viability in the water phase in the presence of chlorine was low at the beginning of the experiment but increased 4 orders of magnitude after five neutralization periods. Therefore, subsequent episodes of chlorine depletion may accelerate the development of microbial communities with reduced susceptibility to disinfection in real drinking water systems.     

热水地面辐射采暖常用加热管材水力计算

介绍了热水地面辐射采暖常用管材的水力计算方法,得出了6种常用管材的水力计算表并绘制了水力线算图。对塑料管材和金属Cu管材进行水力比较,结果表明相同条件下Cu管材水力较优;在塑料类管材中,PE—X管材水力较优。     

Reversible shift in the α-, β- and γ-proteobacteria populations of drinking water biofilms during discontinuous chlorination

As disinfection strategies could support a shift of some bacterial populations, the biodiversity of drinking water biofilms depending on the disinfectant concentrations was explored. The effect of different chlorine sequences applied for several weeks (0.1-0.4-0.1 mg Cl₂ L⁻¹ or vice versa) was tested on the abundance of the α-, β- and γ-proteobacteria populations, used as indicators of changes in bacterial populations within drinking water biofilms. Using dynamic (industrial pilot) and batch (bench scale) conditions, our work demonstrated the ability of the 3 proteobacteria subclasses to re-organize following discontinuous chlorinations. The β- and γ-proteobacteria subclasses were favoured by high free residual chlorine concentrations (0.4 mg Cl₂ L⁻¹) while α-proteobacteria population was sensitive to this oxidant level. The proteobacteria population shifts within the biofilm exposed to discontinuous chlorination were reversible. The resilience of the biofilm proteobacteria populations exposed to oxidant stress questioned the emergence of bacterial population less sensitive to chlorine.     

供水管网中AOC、消毒副产物的变化规律

以西南L市的供水管网为研究对象,以可同化有机碳（AOC）、三卤甲烷（THMs)、卤乙酸（HAAs)为评价指标,研究了不同季节给水管网中水质的变化情况,结果表明：三卤甲烷在管网中只受余氯的影响,其含量一般随管道长度的增加而增加;卤乙酸和AOC在管网中的变化受余氯和微生物活性的影响,其含量一般随管网延伸而先增加后减少,温度越高则下降越快,温度和余氯是管网中控制消毒副产物和AOC浓度的重要因素。     

Microbiological and Trihalomethane Responses to Booster Chlorination

Two zones of a water distribution supply area receiving treated surface water were used to study the effect of booster chlorination on bacterial regrowth. In the first year of the study general patterns of bacterial regrowth were observed, and in the second year one of the areas was booster chlorinated at the outlet from a surface reservoir. In both years of the study the heterotrophic plate counts showed a seasonal pattern. In the second year there was a large increase in plate counts from mid-July to October in both of the study areas. During this period, booster chlorination was unable to prevent bacterial regrowth. The addition of chlorine to produce an initial free chlorine residual of 0.5 mg/1 resulted in a reduction in bacterial numbers, but with further retention in the distribution system bacterial regrowth occurred. There was little increase in the trihalomethane (THM) concentration following booster chlorination, but booster chlorination appeared to increase the assimilable organic carbon concentration.     

从节能角度分析绿色建筑中常用塑料给水管材的选用

该文计算出绿色建筑中常用各种管径的塑料给水管材与相应公称直径的PE63级（PN=1.0MPa）给水用聚乙烯管单位长度水头损失的比值K,对比分析各种规格塑料给水管材的K值,从节能角度出发结合绿色建筑冷水及中水给水系统,提出选用塑料给水管材的合理化建议。     

Studies on vinyl chloride migrating into drinking water from polyvinyl chloride pipe and reaction between vinyl chloride and chlorine

To determine the conditions for the migration of vinyl chloride monomer (VCM) into water from polyvinyl chloride (PVC) pipes and to examine the reaction between VCM and the chlorine present in drinking water, we studied the migration of VCM into water. It was found that migration of VCM into water from PVC pipes (containing 29.5 ppm VCM) could only be detected by using an apparatus that prevented volatilization of VCM and increasing the surface area of the pipe wall in contact with the water. The amount of VCM which could undergo action of the chlorine in the water decreased markedly with the age of the pipes and when the pH was lowered. VCM occurred in the water was converted to chloroacetaldehyde, chloroacetic acid, etc., by its reaction with chlorine, while the amounts of these reactants varied with pH of the solution was changed.     

饮用水氯胺辅助消毒的效果及有机卤化物含量变化

与氯消毒相比,氯胺消毒能有效降低消毒副产物的生成量.昆山市在水厂清水池加氯消毒后,将氯胺用作维持管网水质的辅助消毒剂,使管网水质监测点的消毒剂余量和细菌总数合格率从92.8%上升到99.5%,管网消毒效果得到明显改善.在有机物含量较高的情况下,与氯消毒相比,采用氯胺辅助消毒可降低饮用水中可吸附有机卤素(AOX)含量达48%,因而在保证清水池和出厂水消毒效果的前提下,应尽量降低清水池的投氯量,以使氯消毒副产物含量控制在较低水平.通过对三卤甲烷、氯苯和卤乙酸等氯化消毒副产物含量的测定分析,证实氯胺消毒可大幅降低饮用水中的有机卤化物含量,这与对可吸附有机卤素的测定结果是一致的.     

Chlorine decay in drinking-water transmission and distribution systems: pipe service age effect

Water quality can deteriorate in the transmission and distribution system beyond the treatment plant. Minimizing the potential for biological regrowth can be attained by chlorinating the finished water. While flowing through pipes, the chlorine concentration decreases for different reasons. Reaction with the pipe material itself and the reaction with both the biofilm and tubercles formed on the pipe wall are known as pipe wall demand, which may vary with pipe parameters. The aim of this paper was to assess the impact of the service age of pipes on the effective chlorine wall decay constant. Three hundred and two pipe sections of different sizes and eight different pipe materials were collected and tested for their chlorine first-order wall decay constants. The results showed that pipe service age was an important factor that must not be ignored in some pipes such as cast iron, steel, cement-lined ductile iron (CLDI), and cement-lined cast iron (CLCI) pipes especially when the bulk decay is not significant relative to the wall decay. For the range of the 55 years of pipe service age used in this study, effective wall decay constants ranged from a decrease by -92% to an increase by +431% from the corresponding values in the recently installed pipes. The effect of service age on the effective wall decay constants was most evident in cast iron pipes, whereas steel pipes were less affected. Effective chlorine wall decay for CLCI and CLDI pipes was less affected by service age as compared to steel and cast iron pipes. Chlorine wall decay constants for PVC, uPVC, and polyethylene pipes were affected negatively by pipe service age and such effect was relatively small.     

自由氯、氯胺和顺序氯化对饮用水消毒效果的试验研究

研究了自由氯、氯胺和顺序氯化三种消毒方式对大肠埃希氏菌和粪肠球菌的灭活效果.结果表明,自由氯浓度越高,对细菌的灭活速率和最终灭活率越大;氯胺浓度越高,对细菌的灭活速率和最终灭活率越大;顺序氯化消毒效果优于单独使用自由氯或氯胺时的消毒效果.同时,还探讨了pH和温度对三种消毒方式的影响.     

Influence of pipe material and surfaces on sulfide related odor and corrosion in sewers

Hydrogen sulfide oxidation on sewer pipe surfaces was investigated in a pilot scale experimental setup. The experiments were aimed at replicating conditions in a gravity sewer located immediately downstream of a force main where sulfide related concrete corrosion and odor is often observed. During the experiments, hydrogen sulfide gas was injected intermittently into the headspace of partially filled concrete and plastic (PVC and HDPE) sewer pipes in concentrations of approximately 1000 ppm_v. Between each injection, the hydrogen sulfide concentration was monitored while it decreased because of adsorption and subsequent oxidation on the pipe surfaces. The experiments showed that the rate of hydrogen sulfide oxidation was approximately two orders of magnitude faster on the concrete pipe surfaces than on the plastic pipe surfaces. Removal of the layer of reaction (corrosion) products from the concrete pipes was found to reduce the rate of hydrogen sulfide oxidation significantly. However, the rate of sulfide oxidation was restored to its background level within 10-20 days. A similar treatment had no observable effect on hydrogen sulfide removal in the plastic pipe reactors. The experimental results were used to model hydrogen sulfide oxidation under field conditions. This showed that the gas-phase hydrogen sulfide concentration in concrete sewers would typically amount to a few percent of the equilibrium concentration calculated from Henry's law. In the plastic pipe sewers, significantly higher concentrations were predicted because of the slower adsorption and oxidation kinetics on such surfaces.     

Multiobjective optimization of water quality and rechlorination cost in water distribution systems

To comprehensively describe the effect of residual chlorine and disinfection by-products (DBPs) on water quality in water distribution systems (WDS) and optimize rechlorination cost, this study developed a multi-objective optimization model of water quality and rechlorination cost. Firstly, chlorine decay and DBPs formation were simulated using EPANET_MSX. An improved non-dominated sorting genetic algorithm II (NSGA-II) with real code was used to optimize the multiobjective model and Pareto fronts could be obtained under different conditions. The results showed that Pareto fronts obtained by average value were better than those obtained by standard deviation and multiplication. Moreover, with the number of boosters increased, maximum value of water quality increased and rechlorination cost decreased. Wall chlorine decay constants were the most important on Pareto fronts, followed by the number of chlorination nodes, proportional coefficients of trihalomethanes (THMs) generation based on residual chlorine consumption, and THMs concentration.     

臭氧/氯消毒中藻类有机物生成消毒副产物的特征

饮用水源地藻华会释放大量藻类有机物(AOM),AOM与氯消毒剂反应生成的消毒副产物(DBPs)会给饮用水用户带来不容忽视的健康风险。为此,探究了臭氧/氯消毒对AOM结构和DBPs生成的影响。结果表明,臭氧氧化能有效去除AOM中芳香蛋白和酚类、叶绿素a、藻蓝蛋白结构物质,但是对腐殖酸类结构的去除效果相对较差。DBPs生成总量随臭氧投加浓度的升高而增加,其中主要是三氯甲烷(TCM);卤代乙腈和卤代酮的生成总量随臭氧投加浓度的变化趋势不明显。延长臭氧接触时间会明显增加1 h氯化中TCM的生成量,氯化24 h时DBPs生成总量与臭氧接触时间无关。在臭氧/氯消毒过程中,AOM的DBPs生成潜能低于天然有机物(NOM)。AOM有利于一溴一氯乙腈的生成,而NOM会生成更多的二氯乙腈。     

浅谈给水管聚丁烯PB、聚乙烯PE与铜管的选择

比较了铜管与聚丁烯PB管、聚乙烯PE管的综合材料性能、施工性能和经济性能,认为PB管、PE管的性价比高于铜管,更适用于全装修住宅或高品质住宅小区.     

Synergistic effect of the sequential use of UV irradiation and chlorine to disinfect reclaimed water

The effectiveness of UV and chlorination, used individually and sequentially, was investigated in killing pathogenic microorganisms and inhibiting the formation of disinfection by-products in two different municipal wastewaters for the source water of reclaimed water, which were from a microfilter (W1) and membrane bioreactor (W2) respectively. Heterotrophic plate count (HPC), total bacteria count (TBC), and total coliform (TC) were selected to evaluate the efficiency of different disinfection processes. UV inactivation of the three bacteria followed first-order kinetics in W1 wastewater, but in W2 wastewater, the UV dose-response curve trailed beyond approximately 10 mJ/cm² UV. The higher number of particles in the W2 might have protected the bacteria against UV damage, as UV light alone was not effective in killing HPC in W2 wastewater with higher turbidity. However, chlorine was more effective in W2 than in W1 for the three bacteria inactivation owing to the greater formation of inorganic and organic chloramines in W1 wastewater. Complete inactivation of HPC in W1 wastewater required a chlorine dose higher than 5.5 mg/L, whereas 4.5 mg/L chlorine gave the equivalent result in W2 wastewater. In contrast, sequential UV and chlorine treatment produced a synergistic effect in both wastewater systems and was the most effective option for complete removal of all three bacteria. UV disinfection lowered the required chlorine dose in W1, but not in W2, because of the higher chlorine consumption in W2 wastewater. However, UV irradiation decreased total trihalomethane formation during chlorination in both wastewaters.