给水管网中铁稳定性问题及其研究进展

介绍了给水管网中出现的铁稳定性问题,分析了管网水中铁不稳定的原因和危害,总结了国外关于铁稳定性问题的相关理论,提出我国应开展铁稳定性的相关研究.     

BDOC值对管网水生物稳定性的影响

目前降低给水管网中生物可降解性有机碳(BDOC)已成为水厂迫切需要解决的主要问题，为此以东北某水厂为例，研究了出厂水的BDOC阈值问题，并对出厂水BDOC浓度对给水管网中游离性细菌、吸附性细菌的再生长的影响进行了探讨。结果表明，出厂水BDOC浓度阈值为0．2mg／L；当BDOC浓度发生变化时，游离性细菌变化量没有吸附性细菌变化量大。     

模拟管网系统主体水浊度变化规律研究

以氯胺为消毒剂,炭滤后出水为实验用水,通过模拟管网系统中试实验,研究了水力工况、pH值、水温及铁释放对管网主体水浊度变化的影响。结果表明:水力工况、pH值、水温及铁释放对管网水浊度的变化影响显著。随着流速增加,浊度相应增加;水力工况的突然改变是引起浊度上升的主要原因;给水管网长时间以某一流速稳定运行时,部分引起浊度的物质会发生二次沉淀。pH越低,浊度上升速率越快。温度的急剧变化是引起管网水浊度短时期内突然上升的重要原因。相同时间段内,温度变化幅度越大,浊度上升幅度越大。管网水浊度与总铁含量存在一定的线性关系,浊度随总铁含量的增加而升高;铁的释放是导致管网水中色度、浊度等水质指标增加的重要原因。     

西安市饮用水中铁含量的变化趋势分析

针对西安市饮用水中铁含量的变化规律建立了时间序列模型,分析了近几年该市水源水、出厂水、管网水中铁含量在整个供水系统中演变的时空变化规律,结果显示该市饮用水中铁含量具有明显的周期性、季节性和不稳定性的变化特点.在模型建立的基础上,按其变化规律预测了将来可能发生的延续及变化,诊断结果令人满意,拟合结果相关性可高达0.7以上,预测精确度也可达到0.862.确定了该市饮用水铁超标主要是由于原水水质污染、不完善的水处理工艺和长距离的原水输送造成的.     

城市供水管网铁稳定性控制研究进展

针对当前城市供水管网中铁释放引发的管网水质问题,重点阐述了供水管网中铁释放的机理,总结了管网水力条件、生物因素及化学因素对铁释放的影响规律及管网水铁释放控制技术措施,并对城市供水管网铁稳定性控制的研究方向进行展望。     

城市供水管网铁稳定性控制研究进展

针对当前城市供水管网中铁释放引发的管网水质问题,重点阐述了供水管网中铁释放的机理,总结了管网水力条件、生物因素及化学因素对铁释放的影响规律及管网水铁释放控制技术措施,并对城市供水管网铁稳定性控制的研究方向进行展望。     

北方某高校管网水质生物稳定性的研究

目前关于饮用水安全性的研究大都集中在出厂水水质上，对给水管网中水质的变化则重视不够，而给水管网在整个供水体系中占有重要的地位，对保障水质安全起关键作用。为此，结合北方某高校校园管网的水质监测数据，分析了管网水中异养细菌的生长情况及其影响因素。结果表明，沿水流方向管网水质变得越来越差，至管网末梢时自由余氯、浊度、细菌总数等都劣于国家饮用水卫生标准；影响该管网水质生物稳定性的主要因素为AOC、自由余氯、浊度、有机物等。     

水质变化对某市供水管网中铁释放的影响及控制作用研究

为研究某市供水管网中铁释放的控制技术措施,对管龄为20~30年的灰口铸铁管内壁的腐蚀瘤进行分析,主要组成物质为Fe_3O_4和FeOOH;利用实验室管段动态模拟反应器,选择腐蚀较严重的铸铁管进行浸泡试验,定量分析了水中无机化学水质参数的变化对水中铁释放能力的影响,并推导出该市管网铁临界释放速率。试验结果表明:铁释放速率与水中p H值、碱度浓度呈负相关性,与氯离子和硫酸根离子含量呈正相关性。对于此类水体,铁的临界释放速率为0.375mg/(m~2·h),控制铁稳定的条件为pH大于7.5,碱度大于250mg/L,氯离子浓度小于94mg/L,硫酸根离子小于146mg/L。     

丹江口水源对北方某市管网铁释放影响的研究

针对丹江口水库水源调入北方某受水区城市后对管网水质可能造成的影响,开展了初步的模拟管网中试研究。从北方某受水区城市的实际管网中挖取了历史通水水源不同的4个地点的无内衬铸铁管并运输至丹江口中试基地,搭建了4套管网模拟系统,并在水源切换为丹江口水源水后对模拟管网进、出水水质进行了6个月的连续跟踪监测。中试结果表明:丹江口水库水的拉森指数在0.5左右,低于该北方受水城市的地表水但高于其地下水,具有微弱的腐蚀性。水源切换后,原通地下水的管道铁释放量最高,呈现"黄水"现象,切换75 d后逐渐达到稳定,"黄水"现象消失;而原通地表水为主的3套管道系统只在水源切换初期铁释放量较高,约30 d后铁释放趋于稳定并一直维持在较低的水平。管网水的铁释放量与出水浊度存在明显的正相关性。水源切换后伴随总铁释放量的增加,管网出水的pH值、总碱度、总硬度、溶解氧浓度明显降低。不同管道对水源切换响应的差异与其内壁的管垢特征不同有关,长期通地下水的管道内部管垢较薄且无明显分层特征,而长期通地表水的管垢较厚且多呈瘤状分布,具有明显的分层特征。     

给水管网中细菌总数快速预测模型的建立与应用

对选定实际给水管网的水质进行了长期监测,研究了水质与细菌总数的相关关系,分析确定了与细菌总数相关性较高且易于测定的水温、自由余氯、总余氯、浊度及UV254等5项指标.应用多元线性回归分析建立了实际给水管网中细菌总数的快速预测模型.经验证,该模型预测的准确度为64.55%,能够用于实际给水管网中细菌总数的快速预测,可为保障供水管网水质微生物学指标的安全提供快速、可靠的技术支持.     

Removal of soft deposits from the distribution system improves the drinking water quality

Deterioration in drinking water quality in distribution networks represents a problem in drinking water distribution. These can be an increase in microbial numbers, an elevated concentration of iron or increased turbidity, all of which affect taste, odor and color in the drinking water. We studied if pipe cleaning would improve the drinking water quality in pipelines. Cleaning was arranged by flushing the pipes with compressed air and water. The numbers of bacteria and the concentrations of iron and turbidity in drinking water were highest at 9 p.m., when the water consumption was highest. Soft deposits inside the pipeline were occasionally released to bulk water, increasing the concentrations of iron, bacteria, microbially available organic carbon and phosphorus in drinking water. The cleaning of the pipeline decreased the diurnal variation in drinking water quality. With respect to iron, only short-term positive effects were obtained. However, removing of the nutrient-rich soft deposits did decrease the microbial growth in the distribution system during summer when there were favorable warm temperatures for microbial growth. No Norwalk-like viruses or coliform bacteria were detected in the soft deposits, in contrast to the high numbers of heterotrophic bacteria.     

Application of biological processes for the removal of arsenic from groundwaters

Bacteria are widespread, abundant, geochemically reactive components of aquatic environments. In particular, iron-oxidizing bacteria, are involved in the oxidation and subsequent precipitation of ferrous ions. Due to this property, they have been applied in drinking water treatment processes, in order to accelerate the removal of ferrous iron from groundwaters. Iron also exerts a strong influence on arsenic concentrations in groundwater sources, while iron oxides are efficient adsorbents in arsenic removal processes. In the present study, the removal of arsenic (III and V), during biological iron oxidation has been investigated. The results showed that both inorganic forms of arsenic could be efficiently treated, for the concentration range of interest in drinking water (50-200microg/L). In addition, the oxidation of trivalent arsenic was found to be catalyzed by bacteria, leading to enhanced overall arsenic removal, because arsenic in the form of arsenites cannot be efficiently sorbed onto iron oxides. This method comprises a cost competitive technology, which can find application in treatment of groundwaters with elevated concentrations of iron and arsenic.     

固定化菌种处理锈蚀管网出水的研究

发生内腐蚀的管道出水往往使出厂饮用水水质部分超标,遂进行了相关的深度净化技术研究。从除铁除锰滤池中的成熟滤砂洗脱下滤膜,以铁锰细菌的选择性培养基进行分离纯化,共培养出5株铁锰降解菌。通过试验发现,铁锰降解菌在铁、锰共存的培养基中的生长情况要好于只含铁基质的,而在只含有锰的基质中不生长。将降解有机物的工程菌和铁锰降解菌固定在同一个反应器的不同滤料上并处理管网出水(浊度为1.5NTU、色度≥25倍、有腥味),结果表明,一体式固定菌种反应器对铁、锰和高锰酸盐指数的去除率可达98%、96%和55%,处理出水的浊度<0.5NTU,色度<15倍,没有嗅味。     

Disinfectant efficacy of chlorite and chlorine dioxide in drinking water biofilms

The drinking water industry is closely examining options to maintain disinfection in distribution systems. In particular this research compared the relative efficiency of the chlorite ion (ClO2-) to chlorine dioxide (ClO2) for biofilm control. Chlorite levels were selected for monitoring since they are typically observed in the distribution system as a by-product whenever chlorine dioxide is applied for primary or secondary disinfection. Previous research has reported the chlorite ion to be effective in mitigating nitrification in distribution systems. Annular reactors (ARs) containing polycarbonate and cast iron coupons were used to simulate water quality conditions in a distribution system. Following a 4 week acclimation period, individual ARs operated in parallel were dosed with high (0.25mg/l) and low (0.1mg/l) chlorite concentrations and with high (0.5 mg/l) and low (0.25mg/l) chlorine dioxide concentrations, as measured in the effluent of the AR. Another set of ARs that contained cast iron and polycarbonate coupons served as controls and did not receive any disinfection. The data presented herein show that the presence of chlorite at low concentration levels was not effective at reducing heterotrophic bacteria. Log reductions of attached heterotrophic bacteria for low and high chlorite ranged between 0.20 and 0.34. Chlorine dioxide had greater log reductions for attached heterotrophic bacteria ranging from 0.52 to 1.36 at the higher dose. The greatest log reduction in suspended heterotrophic bacteria was for high dose of ClO2 on either cast iron or polycarbonate coupons (1.77 and 1.55). These data indicate that it would be necessary to maintain a chlorine dioxide residual concentration in distribution systems for control of microbiological regrowth.     

Fate of Escherichia coli experimentally injected in a drinking water distribution pilot system

Detection of coliforms and E. coli in drinking water distribution systems can be explained by accidental contaminations and/or growth of these bacteria in the network. This last point still remaining debatable, an experiment was carried out with two E. coli strains (E. coli O126:B16 and one isolated from a drinking water distribution system) separately injected in a drinking water distribution pilot plant continuously fed with drinking water. The work aimed to study (i) the partition of the injected bacteria between the water phase and the indigenous biofilm phase and (ii) the kinetic of disappearance or growth of these bacteria.Depending on the strain, 1–50% of injected bacteria adsorbed within a few hours to the indigenous bacterial biofilm. During the first 5–7 days, both E. coli populations behaved similarly: the total number of injected bacteria decreased more quickly than the theoretical washout (death, lysis, predation, ...). Then the number of these bacteria slowly increased and at day 9–12, the number of recoverable injected bacteria became higher than the predictable number calculated from the theoretical washout. This result clearly proves that both E. coli strains are able to grow at 20°C in the absence of residual chlorine in a distribution network system largely colonized with an autochthonous population. However, colonization of the network by E. coli strains was only partial and transient.     

Occurrence of nitrifying bacteria and nitrification in Finnish drinking water distribution systems

Microbiological nitrification process may lead to chemical, microbiological and technical problems in drinking water distribution systems. Nitrification activity is regulated by several physical, and chemical, and operational factors. However, the factors affecting nitrification in the distribution systems in boreal region, having its specific environmental characteristics, are poorly known. We studied the occurrence and activity of nitrifying bacteria in 15 drinking water networks distributing water with very different origin and treatment practices. The waters included chloraminated surface water, chlorinated surface water, and non-disinfected groundwater. The networks were located in eight towns in different parts of Finland. Our results showed that nitrifying bacteria are common in boreal drinking water distribution systems despite their low temperature. Surprisingly high numbers and activities of nitrifiers were detected in pipeline sediment samples. The numbers of ammonia-oxidizing bacteria and their oxidation potentials were highest in chloraminated drinking water delivering networks, whereas the nitrite-oxidizing bacteria were present in the greatest numbers in those networks that used non-disinfected groundwater. The occurrence of nitrifying bacteria in drinking water samples correlated positively with the numbers of heterotrophic bacteria and turbidity, and negatively with the content of total chlorine. Although nitrifying bacteria grew well in drinking water distribution systems, the problems with nitrite accumulation are rare in Finland.     

Effect of PVC and iron materials on Mn(II) deposition in drinking water distribution systems

Polyvinyl chloride (PVC) and iron pipe materials differentially impacted manganese deposition within a drinking water distribution system that experiences black water problems because it receives soluble manganese from a surface water reservoir that undergoes biogeochemical cycling of manganese. The water quality study was conducted in a section of the distribution system of Tegucigalpa, Honduras and evaluated the influence of iron and PVC pipe materials on the concentrations of soluble and particulate iron and manganese, and determined the composition of scales formed on PVC and iron pipes. As expected, total Fe concentrations were highest in water from iron pipes. Water samples obtained from PVC pipes showed higher total Mn concentrations and more black color than that obtained from iron pipes. Scanning electron microscopy demonstrated that manganese was incorporated into the iron tubercles and thus not readily dislodged from the pipes by water flow. The PVC pipes contained a thin surface scale consisting of white and brown layers of different chemical composition; the brown layer was in contact with the water and contained 6% manganese by weight. Mn composed a greater percentage by weight of the PVC scale than the iron pipe scale; the PVC scale was easily dislodged by flowing water. This research demonstrates that interactions between water and the infrastructure used for its supply affect the quality of the final drinking water.     

Control of Coliform Growth in Drinking Water Distribution Systems

The occurrence of coliforms in drinking water distribution systems may be explained by (i) inadequate water treatment, (ii) post-treatment contamination, or (iii) coliform growth in the network. In order to confirm the third hypothesis, a 24 h-starved dense suspension of Escherichia coli was injected into an experimental water distribution system. Results from this experiment clearly indicate that E. coli may find ecological conditions in drinking water distribution systems which will allow growth, particularly in the biofilm phase. Chlorination is an appropriate tool to limit coliform much more easily than the total heterotrophic bacterial biomass. However, in all cases, biofilm associated bacteria are more difficult to kill than suspended bacteria, because of chlorine consumption by the pipe material, and because of a diffusion-limited reaction between chlorine and the biofilm.     

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.     

Impact of particles on sediment accumulation in a drinking water distribution system

Discolouration of drinking water is one of the main reasons customers complain to their water company. Though corrosion of cast iron is often seen as the main source for this problem, the particles originating from the treatment plant play an important and potentially dominant role in the generation of a discolouration risk in drinking water distribution systems. To investigate this thesis a study was performed in a drinking water distribution system. In two similar isolated network areas the effect of particles on discolouration risk was studied with particle counting, the Resuspension Potential Method (RPM) and assessment of the total accumulated sediment. In the ‘Control Area’, supplied with normal drinking water, the discolouration risk was regenerated within 1.5 year. In the ‘Research Area’, supplied with particle-free water, this will take 10-15 years. An obvious remedy for controlling the discolouration risk is to improve the treatment with respect to the short peaks that are caused by particle breakthrough.