甲烷-膜生物反应器(MBfR) 耦合化学吸收还原烟气中NOx的过程机制研究

It is an economical and effective approach to remove NOx from flue gas by biological reduction coupled with chemical absorption. It is conducive to the enrichment of slow-growing autotrophic microorganisms in methane-fed membrane biofilm reactor(MBfR). The enrichment of microorganisms improves the reduction efficacy of Fe(II)EDTA-NO and Fe(III)EDTA. However, the exact mechanism has not yet been clarified. We develop a chelated absorption-biological reduction integrated system with methane oxidation coupled to denitrification(MO-D) and Fe(III)EDTA reduction using CH4-based Membrane biofilm reactor(MBfR) for NOx removal. It is explored to the key impact factors for Fe(II)EDTA-NO and Fe(III)EDTA reduction. It is evaluated the function and contribution of Fe(II)EDTA. Operating conditions and parameters of denitrification in CH4-MBfR will be optimized. The mechanism and metabolic pathway of denitrifying of Fe(II)EDTA-NO coupled methane oxidation and the reduction of ferric iron and its fate are studied. With the aid of molecular biology technology, the microbiological effects on the surface of hollow fiber membrane are investigated. It is analyzed the expression characteristics of key enzymes and genes in functional microbe in the MBfR system. It is a new attempt to develop NOx chelate absorption coupled with biological reduction in MBfR using methane as the sole electron donor and carbon source. The proposed project is expected to provide theoretical basis for the industrial application of the chelated absorption- microbial reduction integrated process for removal of NOx from flue gas.

烟气中的NOx经络合吸收，由微生物还原成氮气，是NOx处理经济有效的途径。以甲烷为电子供体的膜曝气膜生物反应器有利于富集慢速生长微生物，从而提高Fe(II)EDTA-NO和Fe(III)EDTA的还原效能，但确切的作用机制尚未阐明。本课题拟基于甲烷-MBfR系统中反硝化甲烷氧化/Fe(III)EDTA还原的生物膜体系，探明影响Fe(II)EDTA-NO和Fe(III)EDTA还原的关键因素，评估Fe(II)EDTA的作用和贡献，考察甲烷基质-MBfR工艺反硝化运行条件及效能优化的控制参数；探明甲烷氧化Fe(II)EDTA-NO反硝化机制、代谢途径和铁转化还原与归趋；借助分子生物学技术，探索甲烷基质膜界面的微生物学效应，解析系统中功能菌群关键酶及基因的表达特征。本课题以甲烷-膜生物反应器还原NOx络合吸收产物的全新尝试，为生物还原耦合络合吸收处理烟气中NOx的工业化应用提供理论依据。

相对于传统的化学脱硝，以络合吸收-微生物还原为核心的NOx控制工艺是经济、可持续新型生化技术。本项目以CH4/H2等无机电子供体，还原NOx络合吸收产物，构建了NOx络合吸收-MBfR生物还原体系，探索了甲烷/氢自养反硝化菌和铁还原菌等功能微生物的快速富集培养方法，反硝化菌和铁还原菌的竞争与协同关系、铁对生物脱氮的影响及微生物特征等。主要研究结果：经响应曲面法优化得出，pH 6.3，Fe(Ⅱ)/EDTA 摩尔比1: 1.1，温度32 ℃ 时，是Fe(II)EDTA络合吸收 NO 的最佳条件。以甲烷为唯一电子供体的铁还原菌比甲烷反硝化菌更易富集。在初始DO为3.0 mg·L-1无硝酸盐存在的条件下，60d左右可以成功富集甲烷基质铁还原菌，铁还原效率可达0.12 mM·d-1。经100 d富集，以甲烷为唯一电子供体的反硝化菌效率可达80%以上，反硝化速率为0.85-0.95 mg-NO3--N·L-1·d-1。CH4-MBfR系统因充足的甲烷供给和MBfR高效的气液传质，大幅提高了甲烷的利用率，反硝化速率可达27.45 mg-NO3--N·L-1·d-1。当硝酸盐和Fe(III)EDTA共存条件下，Fe(III)有利于促进甲烷反硝化，而硝酸盐的存在会抑制铁还原，以甲烷为唯一电子供体的反硝化相对于铁还原要优先利用。体系中同时存在基于好氧/厌氧甲烷氧化的铁还原菌和反硝化菌以及甲烷氧化古菌，如Methylocystis、Methanobacterium等。与甲烷电子供体不同，以氢为唯一电子供体的反硝化菌有同步反硝化和铁还原性能，对氧气不敏感，而氢为电子供体的铁还原菌对氧气极其敏感。快速启动具有同步反硝化和铁还原的H2-MBfR系统的有效方法是富集成功自养反硝化菌后，直接启动Fe(III)EDTA还原。本项目研究为推进烟气生物脱硝、铁还原协同自养脱氮工艺开发提供理论支撑。