Towards more accurate life cycle assessment of biological wastewater treatment plants: a review

Life cycle assessment (LCA) has been proved to act as a desirable tool to evaluate the environmental impacts of wastewater treatment plants (WWTPs). However, the application of LCA methodology in the field of wastewater treatment is still in progress. This paper has made a review of the LCA studies dealing with biological (activated sludge) WWTPs, with the aim to provide qualitative interpretation of the associated environmental impact categories: eutrophication potential, global warming potential, toxicity-related impacts, energy balance, water use, land use and other impact categories. Possible sources for each impact category of WWTPs are summarized in order to provide information about the critical aspects in WWTP systems that might influence LCA results. Moreover, recent development and the application status of characterization models for each impact category have been reviewed. The analysis indicates that it is important to carry out site-specific LCA studies on WWTPs. The specificity is most typical for the eutrophication potential and toxicity-related impact categories, which need implementation of spatial differentiated characterization methods, considering the emission location, spatial dimensions (transfer between environmental compartments) and even properties of pollutants. Although remarkable progresses have been obtained, their applications in the field of wastewater treatment are still limited. For the global warming potential impact category, it is most crucial to calculate accurately the greenhouse gas (GHG) emissions, because nitrous oxide (N2O) and methane (CH4), as well as fossil origin carbon dioxide (CO2) in wastewater have the potential to make considerable contributions. In the end, prospective is made about which aspects in WWTPs are candidates for further LCA studies. Overall, there is still room for pursuing more accurate results when applying LCA to WWTPs