Life cycle impact and economic assessment of decentralized strategies to treat source-separated wastewater

Decentralized wastewater treatment and recycling strategies have the potential to address the water scarcity issues facing a large percentage of the population. Compared to centralized wastewater treatment facilities, decentralized wastewater treatment with source separation is a potential solution to cost-effective wastewater treatment. This study performed a comprehensive life cycle impact assessment and techno-economic analysis comparison on five treatment scenarios for two source-separated wastewaters (blackwater and graywater). The treatment scenarios were composed of different combinations of three currently available and scalable technologies: activated sludge, anaerobic digestion (AD), and membrane filtration. Activated sludge is utilized to treat source-separated wastewater. Anaerobic digestion is applied to convert the sludge to biogas for energy generation. The membrane filtration including ultrafiltration and reverse osmosis further polish the treated wastewater for discharge or recycling. The results elucidated that Treatment B utilizing activated sludge and membrane filtration to treat blackwater and graywater separately, and then applying anaerobic digestion to reduce the activated sludge amount and generate methane energy had overall better environmental and technoeconomic performances among the studied treatment scenarios. Treatment B had a water recovery efficiency of 99.9 % with a minimum net energy demand of 4.2 kWh-e/m3 recycled water, as well as lower treatment cost. As for the pharmaceutical and personal care products (PPCPs) removal and EcoToxicity, Treatment B shows a comparable performance. The study demonstrated that synergistic combination of activated sludge, AD, and membrane technologies on source-separated wastewaters can create an environmentally friendly, technically sound, and economically feasible decentralized solution to treat wastewater. Meanwhile, the study also indicated that biological treatments are critical to remove PPCPs in the wastewater and alleviate their environmental impacts.