Assessment of upgrading WWTP in southwest China: Towards a cleaner production

Abstract This work comprehensively assessed two scenarios of a WWTP (before and after upgrading, respectively) in southwest China, on the basis of their treatment performance, operational cost, energy demand, as well as environmental impacts. The scenario before upgrading adapted conventional anaerobic-aerobic system, whereas that of after upgrading improved the treatment scale and quality by expanding the biochemical tanks and elevating tertiary treatment with a membrane tank. Our results implied that the treatment performance of the WWTP was notably enhanced after upgrading, in particular, for chemical oxygen demand (COD) and nitrogen removal. The microbes responsible for nitrification and denitrification showed a relatively higher abundance compared with those before upgrading. In turn, energy demand and costs consumption per m3 of wastewater also increased. This increment was predominantly caused by the intensive energy load and the substantial uses of multiple chemicals in secondary and tertiary treatment without systematic optimization. Subsequently, environmental impacts were escalated in the scenario after upgrading. The dominating impact category in both scenarios was Marine Aquatic Ecotoxicity Potential (MAEP), whereas the Abiotic Depletion-fossil (ADP (fossil)) was also considerably affected after upgrading because of the increasing use of chemicals. The results indicate that upgrading the WWTP significantly improved the treatment performance, however, inevitably brought additional impacts as the scale enlarged accompanied by more unit input to meet the stringent treatment standards. Thus, actions and strategies are in need to balance trade-offs among treatment performance, energy and costs consumption, and environmental impacts for current and future projects towards a cleaner production.