Environmental Performance of Chlorella sp.-Based Phytoremediation Across Multiple Wastewater Scenarios: A Comparative Life Cycle Assessment

This study assesses the environmental performance of three wastewater treatment setups through an attributional, gate-to-gate life cycle assessment (functional unit: 1 m3 of treated wastewater): (Sc1) a traditional municipal wastewater treatment plant, (Sc2) an aquaculture recirculation system using microalgae, and (Sc3) a domestic system combining UASB pretreatment with microalgae polishing. Inventory data were analyzed in SimaPro with ReCiPe 2016 Midpoint (Hierarchist) across seven effect categories. Robustness was tested through sensitivity analyses (±20%) of power consumption and influent characteristics, as well as an additional scenario exploring the offset of methane-recovery electricity. The global warming impact remained consistent across scenarios, ranging from 60.5 to 65.1 kg CO2-eq·m−3, indicating no significant difference within the operational parameters. In most categories, power consumption and influent-related burdens were the main contributors, while the impacts from flocculants and microalgae inoculum were minimal. Sc3 showed a lower freshwater eutrophication potential compared to Sc1 and Sc2 (0.028 vs. approximately 0.049 kg P-eq·m−3). Normalization highlighted human carcinogenic toxicity and aquatic ecotoxicity as key impact categories. The methane-offset scenario caused only slight changes at low CH4 outputs, suggesting that energy recovery depends on context.