An overview of environmental co-benefits and trade-offs to reduce greenhouse gas emissions in municipal wastewater management

Many opportunities are available to reduce greenhouse gas (GHG) emissions associated with municipal wastewater management. The vision of low -carbon or carbon -neutral operation of wastewater treatment plants is emerging. Is the vision of low -carbon wastewater management consistent with improving environmental performances? Here, we explored this question using wastewater management life cycle assessment studies that had scenarios with GHG emissions reduction through alternative wastewater treatment options, sludge treatment options, and resource recovery options. Among these options that contribute to GHG emissions reduction, integrating resource recovery (i.e., water, biogas, phosphorus) appears to have greater chances of co -benefits (especially on acidification, eutrophication, and photochemical oxidant formation). In contrast, shifting sludge disposal practices require more attention to their potential trade-offs (especially on eutrophication and toxicity). It is evident that achieving GHG emissions reduction oftentimes involves compromising on other environmental performances. While more GHG emissions reduction and environmental co -benefits can be seen in most of the scenarios and impact categories (over 75% combining), achieving GHG emissions reduction can still lead to deteriorating of at least one of the environmental impact categories in over half of all the scenarios. Instead of exclusively focusing only on GHG emissions mitigation, abatement strategies from municipal wastewater management systems should also consider harnessing environmental co -benefits and alleviating unintended environmental trade-offs. Identifying the potential contributing factors behind environmental trade-offs can also represent opportunities for optimizing the design and operation of these GHG emissions reduction options. Into the future, wastewater management needs to adopt a broader systems perspective considering the wider system boundary and environmental scope.