【作者】 贲岳；

【导师】 陈忠林；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2009， 博士

【摘要】 随着社会、经济的发展,公众对饮用水水质的要求越来越高,但大量污水的直接排放或不达标排放造成饮用水水源中的有机污染尤其是氮污染问题越来越严重。由于水中硝基化合物的化学毒性较高,其常被视为水体重要的氮污染标志,城镇生活污水是氮污染的主要来源,因而水循环系统中城镇污水的有效处理是保证水源水水质的关键步骤。对氯硝基苯(pCNB)是水中常见的硝基化合物,其毒性大、难自然降解,被美国EPA列为优先控制的污染物。掌握此类含氮化合物在污水生化处理过程中的转化规律并有效控制其在水中的含量,是保证污水处理效能、提高饮用水水源水质、降低饮用水安全风险的根本保障。本文在对我国北方某市的水源水及市政污水进行水质调查分析的基础上,针对水中存在的硝基含氮化合物——pCNB进行了生物转化降解研究。考察了好氧与厌氧条件下各相关因素对生物转化降解pCNB效能的影响,鉴定了pCNB的降解产物,并由此推测出生物转化降解水中pCNB的反应途径,同时探讨了pCNB对水处理系统内微生物生态学的影响。研究发现含氮化合物是可以相互转化的,pCNB对微生物硝化作用的抑制使得亚硝酸盐氮(NO2--N)含量升高,NO2--N在水中可与二级胺或具有二级胺结构的有机含氮化合物反应,形成强致癌的N-亚硝基二甲胺(NDMA),因此,探讨了污水中生物降解副产物——NDMA在其生成前质物存在时各因素对其存在形态的影响,分析了NDMA的生物合成途径及其降解规律。首先,针对北方某市的水源水及市政污水水质进行了调查研究。研究表明:给水及市政污水出水中的常规指标(如TOC、COD、UV254、TN、TP等)基本达到饮用水与污水排放标准;水中含有大量的有机氮类化合物,污水中pCNB的含量是水源水中的2.4倍,给水与污水中的有机含氮化合物分别占总氮的23.4%和31%;给水与污水的消毒实验表明,氯或氯胺消毒后有大量含氮消毒副产物生成,如卤乙腈,以及新型含氮消毒副产物亚硝基二乙胺(NDEA)和NDMA生成。以pCNB作为目标污染物,污泥经过驯化后,可以克服pCNB对污泥活性的抑制作用,pCNB在处理过程中可以得到较好的转化、降解与矿化。在适宜的厌氧反应条件下,污泥可以在1h内把低浓度的pCNB完全转化降解为对氯苯胺(pCA);好氧条件下,污泥对pCNB的总去除率为85%左右,其中,约48%的pCNB因曝气挥发到空气中;SBR法在厌氧4h,好氧处理8h后可以有效地去除pCNB,去除率在95%以上。厌氧污泥通过还原反应将pCNB降解为对氯苯胺(pCA)和苯胺(AN);好氧污泥通过部分还原途径和氧化途径降解pCNB,并使其开环最终达到矿化。为了辅助系统的工艺设计和更加合理的调控系统运行,进行了pCNB对系统处理效能的影响研究,并从生态学的角度对系统中微生物的种类组成及数量变化进行了分析。实验表明:微量pCNB对好氧污泥代谢活性的抑制作用强于厌氧污泥,尤其是pCNB严重抑制了细菌的硝化作用,使得系统内NO2--N积累含量升高,但经过驯化后,pCNB对好氧与厌氧污泥的毒性均可以减小;当水中存在微量pCNB时,其严重影响了污水处理系统中的微生物组成及数量,使得系统中微生物的数量及种类明显减少,但经过驯化后菌群数量有所上升。由于水中pCNB的存在,使得NO2--N含量升高,即增加了生物代谢副产物——NDMA的前质物浓度,在适宜条件下,微生物在反硝化及硝化阶段均可以合成一定量的NDMA,最高生成量均出现在系统运行30min-60min时,且反硝化阶段生成的NDMA量明显高于硝化阶段;活性污泥微生物对直接投加到污水中的NDMA没有吸附和降解效能,但可高效降解微生物自身合成的NDMA;硝化阶段与反硝化阶段生物合成NDMA的途径略有不同,除了传统的亚硝化途径外,本文提出了一种新的NDMA生物合成途径,即羟胺(HA)与二甲胺(DMA)反应生成不对称二甲肼(UDMH) , UDMH可被氧化生成NDMA。同时研究了NDMA对微生物的抑制作用,由于NDMA的水溶性较大,其不易被生物富集,因而NDMA对微生物的毒性弱于pCNB。更多还原

【Abstract】 The organic pollution especially the nitrogen pollution in water, resulting from the direct or inacceptable discharge of wastewater, has received considerable public interest in recent years. Due to their chemical toxicity, nitrate compounds are often considered as important signs of nitrogen pollution in water. Urban wastewater has been proved to be a major source of nitrogenous pollutants, so the effective treatment of urban sewage becomes the key step to improve water quality in the water cycle system. p-Chloronitrobenzene (pCNB) is typical and ordinary nitro- compounds. Being high-toxic but hardly degraded, they have been treated as priority control pollutants by the U.S. EPA. It is necessary and crucial to master the biotransformation law of these nitro- compounds in wastewater treatment process.Building on the quality analysis of water and municipal wastewater in a city of northern China, biotransformations of pCNB (nitro-compound) was investigated in the research. Effects of several parameters on the efficiency of pCNB biodegradation were studied; final products of pCNB biodegradation were identified and pathways of pCNB biodegradation in water were proposed, meanwhile, the effect of pCNB in systemic microecology was studied. The research found that nitrogen compound can be translated into each other and the microbial nitrification inhibition of pCNB makes nitrite content increased, when there are precursors such as secondary amine (DMA etc.) or tertiary amine with secondary-amine structures in water, biodegradation byproduct——NDMA can be biosynthesized. With precursor of NDMA formation in water, effects of factors on the existent pattern of NDMA were studied; biosynthesis pathways and biodegradation of NDMA were analyzed.First, quality of source water and municipal wastewater in a city of northern China were surveyed and analyzed. Results show that: conventional parameters (TOC, COD, UV254, TN, TP, etc.) of both source water and municipal wastewater could achieve water standards and effluent sewage standards; a great deal of organic nitrogenous pollutants have been detected in water, they account for 23.4% and 31% of TN in source and wastewater, respectively, and the concentration of pCNB in municipal sewage is about 2.4 times as that in source water; disinfection researches of source and waste water indicate that the generation amount of nitrogen byproduct, such as halogen acetonitriles(HANs), N-nitrosodiethylamine (NDEA) and N-Nitrosodimethylamine (NDMA) have been found largely generated both in source and waste water for over 1 and 10 days’disinfection.With pCNB as the target pollutant, the inhibition of sludge activity produced by pCNB was removed after a period of domestication, and then pCNB was well transformed, degraded and mineralized by microbes in the treatment process. Under appropriate anaerobic conditions, low concentrations of pCNB can be completely biotransformed into chloroaniline (pCA) within an hour; in aerobic conditions, the total pCNB removal was about 85%, including 48% volatile of pCNB into air because of aeration; In the SBR process, 95% pCNB was effectively degraded after anaerobic treatment for 4h and aerobic treatment for 8h. pCNB can be reduced to chloroaniline (pCA) and aniline (AN) by anaerobic sludge; In the biodegradation of pCNB by aerobic sludge, Benzene ring can be opened through some reduction and oxidation reactions, the mineralization was achieved ultimately.In order to provide more theoretical basis for the design and operation of system, the impact of pCNB on the efficiency of the system was investigated. Furthermore, microbial species composition and the biomass changes were ecologically analyzed. Experimental results show that: the inhibition of metabolic activity produced by trace pCNB on anaerobic sludge is stronger than that on anaerobic sludge, especially, the inhitbition of microbial nitrification by pCNB makes nitrite accumulated and the concentration of NO2--N is increased, but these two inhibitions can be reduced after domestication; the coexistence of NDMA and pCNB in water resulted in obvious reduction of microbe species and biomass in sewage treatment system, after a period of domestication, the systematic biomass increased.Because of pCNB in water, the concentration of NO2--N as an intermediate product in wastewater treatment is increased. When there are precursors in water, NDMA as biodegradation byproduct can be biosynthesized in the course of nitrification and denitrification, the maximum of NDMA in the system was obtained at the reaction time of 30min-60min, NDMA produced in the denitrification stage was obviously higher than that in the nitrification stage; The added NDMA can neither be adsorbed nor degraded by activated sludge, but the bio-synthesized NDMA can be efficiently degraded by microbes themselves; The biosynthesis way of NDMA in denitrification are slightly different from that in nitrification. A new pathway of NDMA biosynthesis was proposed: asymmetric dimethylhydrazine (UDMH), products of hydroxylamine (HA) reacting with dimethylamine (DMA), can be oxidized to NDMA. Due to its high water-soluble, NDMA is hardly bio-enriched, so the toxicity of NDMA on microorganisms is much weaker than pCNB.更多还原