污泥蚯蚓堆肥N2O生成特性及蚯蚓作用机制的分子解析

The emission of greenhouse gases in waste disposal process has been concerned by the society widely due to the global warming. Vermicomposting offers a cost-effective, easy management and environmental friendly alternative to stabilize the sewage sludge, which has potential in the treatment and recycling of sludge from the small wastewater treatment plant. Although previous researches have shown that the vermicomposting also had certain N2O emission flux, the production characteristics of N2O and the earthworm’s ecological mechanism on the formation of N2O during vermicomposting of sewage sludge remains to be further studied. In this study, dewatered excess sludge generated from wastewater biological treatment process was treated by vermicomposting. Firstly, the dynamics of N2O emission and its influencing factors is stated by determining the N2O fluxes during vermicomposting under different initial parameters. Moreover, the pathway of N2O production and the influencing mechanism of earthworm on the formation of N2O were explored by asymmetric isotopic 15N in the molecular structure of N2O (site preference). Furthermore, quantitative PCR and high-throughput sequencing are employed to reveal the effect of earthworm on the abundance and diversity of gene amoA and nosZ, and then to clarify the microbiological mechanism of earthworm on the production of N2O in the vermicomposting. The findings of the study is not only able to reveal the formation mechanism of N2O, but also help to reduce the emission of N2O, and then to optimize the operation performance and expand the application prospect of the vermicomposting.

温室效应的加剧使得废弃物处理过程中温室气体的排放引起广泛关注。蚯蚓堆肥基建费用低、绿色生态友好，在中小型污水厂污泥资源化过程中具有较大潜力。研究表明，蚯蚓堆肥亦释放一定的氧化亚氮（N2O）。然而，对于污泥蚯蚓堆肥N2O的生成特性以及蚯蚓在N2O生成中的作用机制，尚有待探索。本研究拟采用蚯蚓堆肥处理污泥，以不同工艺参数下N2O的排放情况为主线，明确蚯蚓堆肥过程中N2O的生成规律及其影响因素；以N2O分子结构中同位素15N的不对称分布为依据，探讨蚯蚓堆肥N2O的生成途径及蚯蚓对N2O产生机制的影响；以定量PCR和高通量测序为手段，揭示蚯蚓对氨单加氧酶（amoA）和N2O还原酶（nosZ）基因丰度和多样性组成等的影响，阐明蚯蚓调控蚯蚓堆肥N2O生成的微生物学机制。研究结论不仅可以从微观层面揭示蚯蚓堆肥N2O的生成机理，且有助于针对性地提出N2O的减排措施，优化蚯蚓堆肥，扩大其应用前景。

蚯蚓堆肥基建费用低、绿色生态友好，在中小型污水厂污泥资源化过程中具有较大潜力，然而蚯蚓堆肥亦释放强温室气体N2O。本研究采用蚯蚓堆肥处理污泥，考查了不同工艺参数下N2O的排放情况及影响因素；探讨了蚯蚓堆肥N2O的生成途径及蚯蚓对N2O生成机制的影响；揭示了蚯蚓调控污泥蚯蚓堆肥N2O生成的微生物学机制。主要结论有：（1）污泥蚯蚓堆肥过程中会产生一定量的N2O。C/N比是影响N2O生成的最主要因素，其次为温度，含水率对其影响最小。从堆肥腐熟度和降低温室效应角度出发，添加稻草等高C/N比农林废弃物提高污泥C/N比，可以有效削减污泥蚯蚓堆肥过程中N2O的生成。（2）蚯蚓能够加快堆肥过程中氮素的转化过程，促进堆肥过程中N2O的生成。提高蚯蚓密度亦可增大N2O的生成。N2O稳定同位素SP值显示，蚯蚓堆肥过程中N2O的来源较为复杂，硝化和反硝化均可导致堆肥初期N2O的生成，而后期主要为硝化作用途径。蚯蚓通过促进硝化作用增加了污泥蚯蚓堆肥N2O的生成，蚯蚓肠道内的反硝化亦为堆肥过程中N2O的重要来源。（3）蚯蚓能够提高堆肥系统中总细菌群落结构的多样性，促进堆肥过程中氮素的矿化和硝化作用。蚯蚓提高了氨氧化细菌amoA的数量，而抑制了反硝化细菌nirS和N2O还原酶基因nosZ的数量，从而增加了N2O的生成。在堆肥过程中，蚯蚓的存在显著提高了硝化菌Nitrosospira的丰度，而抑制了反硝化菌Ralstonia和Pseudomonas的生长。蚯蚓肠道内微生物群落结构与堆肥基质差异较大，Firmicutes为主导优势菌。蚯蚓肠道对nosZ有削减作用，使其成为污泥蚯蚓堆肥过程N2O生成的热区。