Greenhouse gas emissions from a sewage contact oxidation emergency treatment plant after destruction by an earthquake and tsunami

Differences in greenhouse gas emissions and microbial communities between underground and conventionally constructed wastewater treatment plants

Large quantities of greenhouse gases (GHGs) are emitted into the atmosphere during wastewater treatment. In this study, GHG and microbial samples were collected from four wastewater treatment plants (WWTPs), and their differences and relationships were assessed. The study showed that, compared with conventionally constructed WWTPs, well-established gas collection systems in underground WWTPs facilitate comprehensive collection and accurate accounting of GHGs. In aboveground WWTPs, capped anoxic ponds promote methane production releasing it at 2-8 times the rate of uncapped emissions, in contrast to nitrous oxide emissions. Moreover, a stable subsurface environment allows for smaller fluctuations in daily GHG emissions and higher microbial diversity and abundance. This study highlights differences in GHG emission fluxes and microbial communities in differently constructed WWTPs, which are useful for control and accurate accounting of GHG emissions.

Advancing greenhouse gas emission factors for municipal wastewater treatment plants in China

Estimations of greenhouse gas (GHG) emissions from municipal wastewater treatment plants (MWTPs) remain significant uncertainties in China owing to a lack of reliable emission factors (EFs). This study developed a framework to obtain multi-level (technology, province, and nation) GHG EFs of MWTPs using a database containing 3107 MWTPs in China and published site-specific monitoring data. Results show that GHG EFs of different technologies range widely from 180.0 to 615.7 g CO₂-eq/t wastewater, and significant differences are also observed among different provinces in China (190.5-600.3 g CO₂-eq/t wastewater), which are generally lower than the previous estimates. It confirms the importance of more detailed technology classification and considering the technological disparity of different provinces in refining GHG estimations of MWTPs. To test the feasibility of the developed EFs, we compared GHG emissions from MWTPs based on multi-level EFs at different spatial and temporal scales. Similar estimation results imply that selecting corresponding EF depending on the availability of activity data would simplify GHG estimations of MWTPs without sacrificing much accuracy. This study contributes a set of well-developed EFs to improve the estimates of GHG emissions from MWTPs, and also offers a method to develop GHG EFs for other sectors.