硝酸盐转化过程中反硝化与异化还原为铵的竞争机理研究

Nitrate pollution in natural water bodies has become a serious problem threatening the safety of drinking water and health. Biological denitrification is considered to be the best option for removing nitrogen from water bodies because of its efficiency and moderate cost. However, recent studies have found that dissimilatory nitrate reduction to ammonium (DNRA) occupy a position and cannot be ignored in nitrate transformation. DNRA converts nitrate to ammonium rather than N2, so the nitrogen cannot be removed from water bodies efficiently. Consequently, the research for the mechanism of competition between denitrification and DNRA has important value in improving the efficiency of nitrate removal and preventing the byproducts accumulation in nitrate removal process..This project aims to isolate and identify denitrifying bacteria and DNRA bacteria, and understand the physiological and biochemical property of these two kinds of microorganisms, and study their characteristic of nitrate reduction. To study the impact of growth factors on denitrification and DNRA, and to determine the key microbial processes and mechanisms of nitrate reduction. Meanwhile, the characteristics and evolution rule of microbial community in nitrate removal systems will also be studied by 16S rDNA clone library methods, and the mechanism of competition between denitrification and DNRA will be explained from the point of microbiology. This project will provide theoretical and technical support for the nitrate treatment.

水体硝酸盐污染严重威胁居民的饮水安全和身体健康，反硝化作用具有高效低耗的特点，被认为是去除水体中硝酸盐负荷的主要途径。但近年发现，硝酸盐异化还原为铵（DNRA）途径在硝酸盐转化过程中占有不可忽视的地位，NO3--N通过DNRA 途径被转化为NH4+-N，氮素仍然滞留在水体中，未能达到彻底脱氮的目的。因此，硝酸盐转化过程中反硝化与DNRA的竞争机理研究，对于提高反硝化效率，防止副产物的积累有重要的研究价值。.本项目拟通过实验分离鉴定反硝化菌和DNRA菌，认识这两类微生物的生理生化特征，并研究其硝酸盐还原特性；探究各生长因子对反硝化反应以及 DNRA 反应的影响，明确硝酸盐转化的关键微生物过程与竞争机理；同时采用16S rDNA克隆文库法研究硝酸盐去除系统内的微生物群落特征及演变规律，从微生物角度对反硝化与DNRA的竞争机理进行阐释，为硝酸盐污染的治理提供理论依据。

生物反硝化是环境中去除硝酸盐负荷的有效方法，本项目首先针对混合菌群研究了碳源、C/N以及温度对反硝化和硝酸盐异化还原为铵（DNRA）的影响，之后分离反硝化细菌和具有DNRA功能的细菌，研究生长因子对他们的影响，并研究了不同细菌在硝酸盐还原中的竞争协同机理。研究表明以活性污泥作为反硝化菌源，以麦秆、锯末、可生物降解塑料以及甲醇、乙醇和葡萄糖为碳源时，硝酸盐转化过程以反硝化为主，DNRA过程轻微，氨氮积累量较少。同时研究发现C/N值越大、温度越高，则氨氮中间积累越严重。从活性污泥和水稻土中分离出两株不同的硝酸盐还原菌H6和D5，鉴定菌株H6为Pseudomonas nitritireducens，D5为 Klebsiella sp.。研究发现碳源对H6和D5还原硝酸盐有重要的影响，乙酸钠和柠檬酸钠均可作为H6、D5的碳源，对H6来说，乙酸钠是最佳碳源，36h内硝酸盐去除效率便达到98.7%，整个过程中无亚硝酸盐积累，有少量氨氮积累，而对于D5来说，柠檬酸钠是最佳碳源，36h内，硝酸盐的去除率便达到94.4%，但中间过程亚硝酸盐积累严重，而且积累的氨氮浓度明显高于以乙酸钠为碳源时的浓度。另外研究发现，不同细菌所需的最佳碳氮比并不一致，以乙酸钠为碳源时，当C/N为2:1、3:1和5:1时H6可以有效的去除硝酸盐氮，而对于D5，当C/N为2:1时，去除率仅有77.9%，只有当C:N为3:1和5:1时，去除率才能达到90%以上。温度同样会对H6、D5还原硝酸盐产生重要的影响。将H6和D5混合来还原转化硝酸盐，当以柠檬酸钠和乙酸钠为碳源时，36小时内，去除率便分别达到91.3%和96.8%，高于H6以柠檬酸钠为碳源和D5以乙酸钠为碳源时的硝酸盐去除率，而且在实验结束时无亚硝酸盐氮检出。实验中出现氨氮的积累，当以柠檬酸钠为碳源时，积累量最大。因此当利用反硝化法去除水体内的硝酸盐时，将不同的细菌一起使用可以有效避免碳源对于硝酸盐去除效果的限制，扩大碳源的选择，而且在不同细菌的相互协同下，可以有效去除过程中产生的副产物，本研究对于污水处理过程中提高反硝化效率，避免副产物积累有重要的指导意义。