IMPACTS OF SEWAGE CONCENTRATION ON METHANE EMISSION AND MICROBIOLOGICAL MECHANISMS IN SEWAGE COLLECTION SYSTEMS
Municipal sewers are an important potential source of greenhouse gases such as methane,with a wide range of influencing factors.The characteristics of methane production and discharge in pipelines,the transformation of substrates and the microbial function mechanisms under different water quality conditions still need to be further analyzed.This study investigated the volatile fatty acids(VFAs)content and methane emission characteristics in sewage pipeline systems under different sewage concentrations(100~700 mg COD/L)via static simulations.The results showed that the higher the effluent COD concentration in the pipeline system,the higher the production of VFAs and methane.Compared with low-concentration sewage(100 mg COD/L),the VFAs production in high-concentration sewage pipeline systems(500 and 700 mg COD/L)was increased by 2.4,4.1 times,respectively,while the methane emission was increased by 8.1 and 21.0 times.Mechanism analysis revealed that high-concentration sewage in the pipeline system favored the enrichment of anaerobic microorganisms involved in hydrolysis,acidogenesis,and methane production.This led to the upregulation of functional gene expression associated with extracellular hydrolysis(e.g.,dacC),intracellular metabolism(e.g.,yhdR),fatty acid generation(e.g.,pta),and methane generation(e.g.,ftr,fwd),thereby enhancing microbial methane production metabolism.Partial least squares path modeling(PLS-PM)analysis indicated that the functional microbial community(λ=0.721)and the expression of related metabolic genes(λ=0.640)were the main factors influencing methane production and emission in sewage pipelines,while sewage COD concentration was a secondary factor(λ=0.623).
municipal sewer collection systemsewage concentrationsubstrates transformationmethane emission fluxfunctional genes