Quantifying Methane Influx from Sewer into Wastewater Treatment Processes

Wastewater treatment contributes substantially to methane (CH₄) emissions, yet monitoring and tracing face challenges because the treatment processes are often treated as a "black box". Particularly, despite growing interest, the amount of CH₄ carryover and influx from the sewer and its impacts on overall emissions remain unclear. This study quantified CH₄ emissions from six wastewater treatment plants (WWTPs) across China, utilizing existing multizonal odor control systems, with a focus on Beijing and Guiyang WWTPs. In the Beijing WWTP, almost 90% of CH₄ emissions from the wastewater treatment process were conveyed through sewer pipes, affecting emissions even in the aerobic zone of biological treatment. In the Guiyang WWTP, where most CH₄ from the sewer was released at the inlet well, a 24 h online monitoring revealed CH₄ fluctuations linked to neighborhood water consumption and a strong correlation to influent COD inputs. CH₄ emission factors monitored in six WWTPs range from 1.5 to 13.4 gCH₄/kgCOD_rem, higher than those observed in previous studies using A²O technology. This underscores the importance of considering CH₄ influx from sewer systems to avoid underestimation. The odor control system in WWTPs demonstrates its potential as a cost-effective approach for tracing, monitoring, and mitigating CH₄.