【作者】 周玲玲；

【导师】 李圭白；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2010， 博士

【摘要】 由于各国对饮用水消毒副产物重视程度的提高,相对稳定和消毒副产物生成量较少的氯胺作为二次消毒剂被越来越多的水厂采用。在给水管网中,氯胺能够在一定程度上灭活水中和管壁生物膜中的微生物,但同时可能会与水中及生物膜中的有机物发生反应,释放出一定量的微生物可利用有机物为异养细菌在管网中的再生长提供底物。而氯胺消毒的另一个问题是由于氯胺衰减在水中释放出氨氮而引起氨氧化细菌(AOB)的生长,导致管网中硝化作用的发生,引起异养菌的大量繁殖。本文通过模拟管网系统及实际管网采样测定,系统地研究了氯胺消毒管网中微生物生长现象、硝化作用及管网内余氯衰减的问题,并探讨了氯胺消毒管网水的微生物安全性影响因素及其控制方法,以期为保障氯胺消毒管网微生物安全性提供科学依据。利用模拟管网系统RAB反应器,以松花江为水源的哈尔滨某水厂出水为研究对象,研究氯胺消毒对不同管材上生物膜形成的影响及控制效果,并探讨了管材和余氯胺等因素对管壁生物膜形成的影响。结果表明,在不加消毒剂时,生物膜中异养菌浓度明显增加,而在有氯胺情况下运行,可以较好地控制生物膜中细菌的浓度。在有、无氯胺存在条件下,铜质挂片上的异养菌数量明显低于不锈钢挂片;氯胺对管壁生物膜和水中细菌具有一定控制作用,但低浓度的氯胺(0.5~0.75mg/L)不能阻止给水管壁生物膜的形成和水中悬浮菌浓度的增加。以大肠杆菌生物膜为研究对象,对比研究了氯和氯胺对该生物膜的灭活,并首次提出两种消毒剂对生物膜的氧化作用溶出物对细菌再生长的影响。在相同CT值,氯浓度的提高对生物膜中细菌的灭活效果明显;而在相同氯胺浓度,氯胺对生物膜细菌灭活效果是由CT值决定的,而氯胺浓度的提高对灭活率的提高不起主要作用。氯和氯胺对生物膜的氧化作用都会造成水中生物可利用有机碳(AOC)、生物可利用磷(MAP)浓度的增加,并增加了水的细菌生长潜能(BRP),因而在管壁生物膜存在的情况下,消毒剂的存在会造成管壁中物质的溶出,促进水中微生物的生长。利用模拟管网系统RAB反应器,研究了有机物浓度、氯氨比与硝化生物膜形成的关系,并探讨了pH值、温度、氯胺浓度对管网硝化作用的影响,以及三种消毒剂对硝化作用的控制。结果表明:氯氨比对于硝化作用影响不显著,而有机物水平对硝化作用有显著影响,高有机物较低有机物水平硝化程度高。提高pH值可能改变化合态氯胺的种类和将氯胺能够维持更高的水平,硝化作用也得到了一定程度的控制。在较低水温时(13±2℃),一定浓度氯胺对水和生物膜中AOB灭活后,停止投加氯胺,由于AOB生长速率很低,AOB的浓度增加不显著。但当水温提高到22±2℃后,AOB浓度有回升的趋势,较高的温度会影响AOB的生长速率。氯胺对硝化作用的控制依赖于氯胺的浓度,作用时间和温度。亚氯酸根转而使用氯胺较单纯使用氯胺可以有效的控制管网中的硝化作用。对硝化细菌代谢产物与异养菌生长的关系进行研究时发现,硝化细菌产生的溶解性微生物产物和死亡的AOB可以作为异养细菌生长底物的补充,促使异养细菌繁殖。对氯胺在管网中的衰减的研究表明,随温度的升高,氯胺自身的分解速度增加;而氯氨比的提高,氯胺趋于不稳定,氯胺的衰减量和衰减速率均高于低氯氨比的情况。在pH值6.0-8.9的范围内,pH值越高,氯胺的稳定性越高,衰减量和衰减速率越低。高氯胺浓度下氯胺的衰减量远大于低浓度氯胺的衰减量,并且高氯氨比下其衰减速度加快。亚硝酸氮可以促进氯胺的衰减,当管网系统中发生硝化作用,产生的亚硝酸氮迅速与氯胺发生反应,导致氯胺的衰减,其与氯胺具有较快的反应速率,促进作用在初始阶段体现得更为明显。有生物膜存在时,氯胺的衰减速率是自来水中的一半左右,也就是说生物膜对氯胺衰减的贡献占氯胺衰减系数的一半左右,可见生物膜是管网系统中造成消毒剂衰减的重要部分。实际管网取样的水质参数和潜能分析,验证了在实验室对硝化作用得到的结果。由于消毒剂会与水中及管壁生物膜进行反应以及自身衰减而造成浓度降低,使管网中的微生物大量繁殖和导致硝化作用的发生。因而给水管网中维持一定量的消毒剂余量是保证饮用水微生物安全性的一个重要手段。实际管网水样的水质参数分析,与实验室得到的硝化作用的结果有较好的对应关系。更多还原

【Abstract】 In response to new limits on disinfection byproducts (DBPs), drinking water utilities in many countries are implementing chloramination for the purpose of distribution system disinfection. Although the use of chloramines resulted in inactivation bacteria, chloramines will react with organic matter in bulk water and biofilm. The chloramines consumed in the bulk and biofilm will release microbial assimilated organic carbon (AOC) which can serve as a source of energy for heterotrophic bacteria localized and reproduced in the bulk water and biofilm. Another significant concern associated with this practice is nitrification caused by the growth of ammonia-oxidizing bacteria (AOB) in the distribution, which is associated with an increase in heterotrophic plate count (HPC) bacteria. In this study, bacteria growth, nitrification, chloramines decay and the controlling method of microbial safety was investigated. The primary objective of this research was to develop scientific basis regarding the microbial safety in model distribution system and site sampling using chloramines for secondary disinfection.Two Rotating Annular Bioreactors (RABs) with copper and stainless steel pipe materials were adopted to investigate the effects of these two pipe materials and chloramines disinfection on biofilms formation. The result indicated that the heterotrophic bacteria concentration increased in the absence of chloramines, but the bacteria concentration in biofilm can be controlled in the presence of chloramines. The count of bacteria in copper slide was lower significantly than in steel slide in the absence and presence of chloramines. The control of HPC in bulk water and biofilm was achieved by chloramines, but low level chloramines (0.5-0.75mg/L) cannot prevent the formation of biofilm and bacteria regrowth in bulk water.Take Escherichia coli biofilm as the research objective, the comparative study was conducted regarding to the inactivation effect on the biofilm applying chlorine and chloramines. Two kinds of disinfectant oxidation on biofilm were observed for the first time. The released oxidation product from biofilm will stimulate heterotrophic bacteria regrowth. Chlorine inactivation effect on biofilm increased with the chlorine concentration increasing on the same CT value, but chloramines inactivation effect highly depend on CT value on the same chloramines concentration. Using chlorine and chloramines resulted in release AOC and microbial assimilated phosphorus (MAP) from biofilm and increase the bacteria regrowth potential (BRP).The study used a bench-scale approach to evaluate the impact of organic matter level and chlorine to ammonia-N ratio on the incidence and potential establishment of nitrifying biofilm within simulated water distribution system. The temperature and pH effect on nitrification also studied insimulated distribution system. The finding from this study clearly indicated that organic matter level influence significantly on nitrification, but chlorine to ammonia ratio is not the factor for nitrification. Obvious symptom of nitrification occurred at high level organic matter. Increasing pH level can stabilize and increase the chloramines concentration, which can control AOB concentration to some extent. Chloramines controlling for nitrification depend on chloramines dosage and temperature.Relationship was observed between heterotrophic bacteria growth and metabolic product produced by AOB. The formation of soluble microbial products (SMP) by AOB and dead AOB can provide a supplementary organic substrate for heterotrophic bacteria.It was found that auto-decomposition rate of chloramines increased with temperature increasing. Chloramines show unstable at high chlorine to ammonia ratio. Chloramines were more stable at higher pH level. Nitrite is typically found in distribution system due to nitrification. The presence of nitrite accelerates the chloramines decay. The chloramines decay rate caused by biofilm is 50% of total decay rate in simulated distribution system, which indicated that chloramines decay largely attribute to biofilm in distribution system.Because of disinfectant can react with organic matter in bulk water and biofilm and auto-decompose. The disinfectant concentration decreased will lead to bacteria growth in distribution system. It is important that maintain appropriate concentration disinfectant to guarantee microbial safety of drinking water.更多还原