The Characteristics and Estimation of Greenhouse Gas Emission in the Urban Sewer System

The carbon emission fluxes in the urban sewer systems and the microbial community structure in sewer sediments remain unclear. In this study, a sewer system located in southern China was utilized to investigate the water quality characteristics, carbon emission flux, and microbial community structure in sediment. The results showed that the chemical oxygen demand loss rates in the branch pipe and sub-main pipe were 27.1% and 14.1 %, respectively. The estimated carbon emission flux revealed a total carbon emission flux from the sewer system was 1.39 kg CO2-eq/m3 and the emissions fluxes of methane and carbon dioxide were 0.87 kg CO2-eq/m3 and 0.51 kg CO2-eq/m3, accounted for 62% and 36.4%. Microbial community structure analysis revealed that methanogenic archaea in the sediments of the branch pipes and sub-main pipes were Methanobacterium, Methanosaeta, and Methanobrevibacter. The methanogenic activity of sewer sediments was further assessed. This study further confirmed that the branch pipe and sub-main pipe were the main sources of carbon emission and methane and carbon dioxide are the main greenhouse gases in the sewer system. This study furnishes novel insights for the control of carbon emissions in municipal sewage systems.