垃圾填埋场渗滤液处理系统高强度N2O释放成因及微生物学机制

Because of the specific characteristics of leachate quality, a large amount of nitrous oxide (N2O) could be emitted from leachate treatment, which is an important anthropogenic source of N2O in waste sector. Little is known about the reason for significant N2O emissions during the leachate treatment, especially in the mechanisms of community succession and gene regulation of functional microorganism in this special niche. This project aims to investigate the effects of factors (e.g., ammonia, landfill age, salinity, dissolved oxygen) on N2O emissions during the processes of nitrification and denitrification using raw leachate combined with synthetic wastewater, and to identify the key environmental factor using statistical analysis. The variations of interspecies relationship between keystone species and nitrogen-cycle functional bacteria will be studies using high-throughput sequencing technology, aiming to reveal the microbial response to key environmental factor and the effects on N2O emissions. The N2O generation pathways under different environmental conditions will be quantified using stable isotope labeling method, and subsequently validated with functional gene abundance and expression by quantitative PCR. Moreover, the quantitative relationship among environmental factors, microorganism and N2O emissions will be established by combining the multivariate statistics and model analysis, and the strategies to mitigate N2O emissions will be further proposed. The implementation of this project will improve our understanding of the mechanisms of N2O emission during leachate treatment, and provide a reliable theoretical guidance for inventory protocols and emission mitigation of greenhouse gas.

垃圾填埋场渗滤液因其水质特征在处理过程中会释放高强度的N2O，是N2O重要的人为释放源。渗滤液处理过程中N2O释放现象的成因，特别是在该特殊生境下氮循环微生物的群落演替及基因调控机制尚不清晰。本项目拟采用实际渗滤液结合配水的方法，研究氨氮、COD/N、盐度、溶解氧等因子对硝化和反硝化过程N2O释放的影响，辨识关键因子；运用高通量测序技术研究基石物种、氮循环功能微生物种群变化规律，揭示关键因子驱动下微生物的响应过程及其对N2O释放的影响；利用稳定同位素标记技术研究不同环境因子条件下N2O的产生途径，与功能基因丰度及其表达水平相互验证；结合多元统计分析，构建环境-微生物-释放量之间的定量关系，并提出降低N2O释放的调控策略。本项目的研究成果有助于深入理解渗滤液处理过程中N2O的释放机制，为制定温室气体减排方案提供可靠的理论依据。

垃圾填埋场渗滤液处理系统或将成为固体废物处理过程温室气体的释放热点，却未引起足够的重视。通过对不同等级的填埋场渗滤液处理系统长期原位监测发现，渗滤液一旦进入生化处理单元N2O便成为主要释放的温室气体，尤其是硝化池成为N2O释放热点。填埋场温室气体排放量的计算不应只关注库区甲烷释放，渗滤液处理过程释放大量的N2O可占填埋场温室气体总排放量的一半以上。因此，在编制填埋场温室气体排放清单时，需将N2O考虑在内。区别于城市生活污水特征的渗滤液高氨氮、高COD和高盐的水质特征可能是引起N2O高强度释放的原因。在设置不同的实验室小试处理，利用先进的测序技术并结合多元统计分析识别影响N2O释放的关键水质因子和关键群落组成。研究结果表明，COD是N2O释放的关键影响因子，进水有机物浓度越低系统释放的N2O越多，而氨氮和氯化物浓度影响较小。一旦进水超出设定范围，氨氮和氯化物浓度同样可能引起N2O的强烈释放。黄杆菌属（Flavobacterium）和亚硝化单胞菌属（Nitrosomonas）是引起N2O高强度释放的两种核心功能菌，进水COD的增加可能促进黄杆菌反硝化菌的增殖，抑制亚硝化单胞菌的生长，从而减少了N2O的释放。而丰度高Castellaniella unclassified和Saprospiraceae unclassified是关键基石物种，可能在维持细菌群落稳定性方面发挥关键作用。进一步地，构建了处理系统氮平衡情景分析工艺流程导致了N2O产生和释放的时空异质性，利用稳定同位素标记的方法明确各处理单元硝化和反硝化途径对N2O产生的贡献比例。反硝化池绝大部分的N2O由反硝化途径产生，而硝化池硝化和反硝化途径对N2O的产生贡献各近一半。硝化阶段产生的N2O要远高于反硝化阶段。在各池中产生的N2O绝大部分在原位释放，极少部分跟随水流进入下一阶段延迟释放。该部分的结果表明，进行渗滤液生化处理时应多关注硝化阶段产生的N2O，通过调整溶解氧等操作参数创造更好的硝化条件从而降低N2O的产生是可行的减排方式。本项目全面完成计划目标，研究结果有助于深入理解渗滤液处理过程N2O释放机制，为制定温室气体减排方案提供可靠的理论依据。