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.

本工作根据污水处理厂的处理性能、运营成本、能源需求和环境影响，综合评估了西南地区污水处理厂（分别为改造前和改造后）的两种情景。升级前方案采用常规厌氧-好氧系统，升级后方案通过扩大生化池和提升膜池三级处理，提高处理规模和质量。我们的结果表明，污水处理厂的处理性能在升级后显着提高，特别是化学需氧量 (COD) 和脱氮。与升级前的微生物相比，负责硝化和反硝化的微生物显示出相对更高的丰度。反过来，每 m ^{3 的}能源需求和成本消耗废水量也有所增加。这一增长主要是由于能源负荷密集以及在二级和三级处理中大量使用多种化学品而没有进行系统优化造成的。随后，场景升级后的环境影响升级。两种情景中的主要影响类别是海洋水生生态毒性潜力 (MAEP)，而非生物耗竭化石 (ADP (fossil)) 在升级后也因化学品使用的增加而受到相当大的影响。结果表明，污水处理厂升级改造显着提高了处理性能，但不可避免地带来了额外的影响，因为规模的扩大伴随着更多的单位投入来满足严格的处理标准。因此，