The Characteristics and Estimation of Greenhouse Gas Emissions from Urban Sewer Systems in Southern China

Carbon emission fluxes in 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. 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 was estimated by the carbon emission factor method. The results revealed that the total carbon emission flux from the sewer system was 1.39 kg CO2-eq/m3 and the emission fluxes of methane and carbon dioxide were 0.87 kg CO2-eq/m3 and 0.51 kg CO2-eq/m3, accounting for 62% and 36.4%. The microbial community structure was analyzed by 16S rRNA. The results indicated that the methanogenic archaea in the sediments of the branch pipe and sub-main pipe were Methanobacterium, Methanosaeta, and Methanobrevibacter. The methanogenic activity of the sewer sediments was further assessed. This study further confirmed that the branch pipe and sub-main pipe were the main sources of carbon emissions 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.