零价铁介导硝酸盐还原-氨氧化的反应机制研究

With the low-cost and high-efficiency, anaerobic ammonia oxidation (Anammox) process attracted much attention by researchers. The simultaneous removal of nitrate and ammonium (SRNA) was mainly via heterotrophic denitrification associated with Anammox process. However, this approach has shortcomings in excessive sludge production and the inhibition of organic on Anammox bacteria was also inevitable. The zero-valent iron (ZVI) has been widely used in remediation of groundwater since it is non-toxic and strong reducing. In theory, the nitrate can be reduced to nitrogen gas with nitrite as the intermediate which could provide the electron acceptor for the followed Anammox process. If the SRNA process can be accomplished with ZVI-assisted, that would be a process of complete no extra energy input resulting a nonpollution green treatment technology. For this proposal of scientific significance and application value, an experimental research project is intended to carried out. In the laboratory-scale reactor, the ZVI-assisted SRNA process mediate by Anammox micro-organisms was studied. The main objectives of this project are to: clarify the reaction mechanisms, recognize the functional microbial populations mediated the reactions as well as their characteristics, explore the main factors affecting the reactions, seek the effective methods and measures to control the material transformation pathway in the whole process.The proposed study will provide a technological principles to support the development of new economical and high efficient biological SRNA processes based on Anammox technology, also, expand the understanding in metabolic versatility of Anammox bacteria.

Anammox工艺以其经济性和高效性引起了研究者的广泛关注。氨氮和硝酸盐同步去除方法主要为通过异养反硝化耦合Anammox反应。但该方法存在污泥产量大，有机物抑制厌氧氨氧化反应等不足。零价铁具有无毒害和较强还原力等优点，在水体修复中已经得到广泛的应用。在零价铁作用下硝酸盐可被还原成氮气，其中间产物亚硝氮可做为Anammox反应电子供体，以此实现氨和硝酸盐的同步转化。若该过程得以有效实现，将使氨和硝酸盐的生物去除过程完全无需外加能量、成为绿色无污染的生物除氮技术。本项目围绕这一具有重要科学意义课题，拟以Anammox菌为接种物进行零价铁介导的氨氮和硝酸盐同步转化过程的深入研究，进一步明确该过程的反应机制，了解作用微生物的种群特征，探明影响反应的主要因素，寻求有效控制反应过程中物质转化途径的条件和调控手段，为开发新型生物脱氮工艺提供技术原理，丰富对Anammox菌多代谢途径的认识。

本项目围绕Anammox细菌代谢底物多样性的特征，聚焦Anammox培养物以零价铁为电子供体还原硝酸盐这一过程，探讨了硝酸盐的转化途径以及Anammox菌在硝酸盐还原过程中的作用，回答了两个关键科学问题：（1）Anammox培养物以硝酸盐为底物的培养过程中，所需的氨和亚硝氮究竟是由Fe0/Fe2+的化学还原作用产生？还是由生物还原作用产生？（2）Anammox微生物参与了硝酸盐还原的哪一个环节？. 主要结论为：在缺氧条件下，Anammox微生物以零价铁为电子供体还原硝酸是生物转化与化学转化共同作用的结果。通过表达narG基因，Anammox细菌将硝酸盐还原为亚硝酸盐，但其并未表达nrfA基因，因此未参与亚硝酸盐异化还原为氨的过程，而Fe0/Fe2+的化学还原作用是Anammox细菌获取氨的主要途径。同时，其他共生微生物通过参与不同的代谢活动，也对Anammox细菌以硝酸盐为底物的生长代谢起到积极作用。通过上述转化途径，Anammox细菌可以利用硝酸盐为底物进行生长代谢。这一过程中，硝酸盐和总氮的转化效率同时受到温度和Fe/NO3-N比的共同影响，而pH在4.0 - 7.4范围内对该过程影响并不显著。当控制温度在25.5℃ - 30.0 ℃、Fe/NO3-N比在31 - 48范围内，硝酸盐去除率可超过90%、总氮去除率大于75%。. 本项目的研究，为探明Anammox细菌还原硝酸盐提供了关键的基因学证据，揭示了Anammox培养物中硝酸盐转化的客观规律，丰富了对于Anammox细菌多种底物代谢能力的认知，这是本项目的科学意义。同时，项目研究成果为应用Anammox技术处理含硝酸盐废水提供了理论依据。更重要的是，Anammox工艺中会产生约占总氮11%的硝酸盐副产物，导致出水中总氮不达标，而本项目为实现厌氧氨氧化工艺的硝酸盐原位处理提供了一种新思路。