Variable sediment methane production in response to different source-associated sewer sediment types and hydrological patterns: Role of the sediment microbiome.

Production of methane (CH4), an essential anthropogenic greenhouse gas, from municipal sewer sediment is a problem deserving intensive attention. Based on long-term laboratory batch tests in conjunction with 16 s rRNA gene sequencing and metagenomics, this study provides the first detailed assessment of the variable sediment CH4 production in response to different pollution source-associated sewer sediment types and hydrological patterns, while addressing the role of the sediment microbiome. The high CH4-production capability of sanitary sewer sediment is shaped by enriched biologically active substrate and dominated by acetoclastic methanogenesis (genus Methanosaeta). Moreover, it involves syntrophic interactions among fermentation bacteria, hydrogen-producing acetogens and methanogens. Distinct source-associated microbial species, denitrifying bacteria and sulfate-reducing bacteria occur in storm sewer and illicit discharge-associated (IDA) storm sewer sediments. This reveals their insufficient microbial function capabilities to support efficient methanogenesis. Hydrogenotrophic methanogenesis (genus Methanobacterium) prevails in both these sediments. In this context, storm sewer sediment has an extremely low CH4-production capability, while IDA storm sewer sediment still shows significant carbon emission through a possibly unique mechanism. Hydrological connections promote the sewer sediment biodegradability and CH4-production capability. In contrast, hydrological disconnection facilitates the prevalence of acetoclastic methanogenesis, sulfate-reducing enzymes, denitrification enzymes and the sulfur-utilizing chemolithoautotrophic denitrifier, which drastically decreases CH4 production. Turbulent suspension of sediments results in relative stagnation of methanogenesis. This work bridges the knowledge gap and will help to stimulate and guide the resolution of 'bottom-up' system-scale carbon budgets and GHG sources, as well as the target CH4 abatement interventions.