Life cycle assessment of wastewater treatment in developing countries: A review.

Within developing countries, wastewater treatment (WWT) has improved in recent years but remains a high priority sustainability challenge. Accordingly, life cycle assessment (LCA) studies have recently started to analyse the environmental impacts of WWT technologies on the specific context of less developed countries, mainly in China and India. This work presents a comprehensive review of this knowledge with the aim of critically analysing the main conclusions, gaps and challenges for future WWT-related LCAs in developing countries. The most commonly assessed technologies in the 43 reviewed articles are different variations of activated sludge and extensive treatments applied in decentralized systems; however, studies focused on advanced technologies or new sources of pollution (e.g. micropollutants) are still lacking. Goal and system boundaries are normally clearly defined, but significant stages for some technologies such as the construction and sludge management are frequently not included and functional units should be defined accordingly to specific conditions in developing countries. At the inventory level, a more concise description of sources and technical parameters would greatly improve the quality of the LCAs along with accountability of direct greenhouse gas emissions. Eutrophication and global warming are the two most commonly assessed impacts; however, the calculation of terrestrial ecotoxicity when the sludge is used for agricultural purposes, of water use and of the land use change impacts associated to extensive technologies should be encouraged. The estimation of more site-specific databases, characterization factors (especially for eutrophication) or normalization and weighting values combined with more affordable access to background databases and LCA software, would deeply increase the accuracy of WWT-related LCAs in developing countries. An increased usage of the uncertainty analysis should be encouraged to assess the influence of these gaps in the final interpretation of the results. The review finishes with a summary of the main challenges and research gaps identified and with specific guidelines for future researchers to avoid the most common shortcomings found in the reviewed studies.