Does resource recovery and utilization improve environmental and economic performance of rural wastewater treatment plants? A case study in Xiamen, China.

Wastewater treatment (WWT) has been recognized as a major source of greenhouse gas emissions. Rural WWT often lags behind urban areas due to insufficient infrastructure construction and lack of funding to maintain operation. Selection of optimal WWT technologies in rural areas requires that environmental impacts and costs are traded-off across the entire lifecycle, including the construction, operation, and demolition phases. This study compared the lifecycle environmental impacts of different rural WWT technologies, incorporating both positive and negative externalities into the cost-benefit analysis (CBA). Results showed that the environmental and economic performance during the construction phase of small-scale rural WWT was critical, especially for the Source-separated Wastewater Treatment (SWWT), where construction contributed over 50 % of its environmental impacts and 70 % of its costs. SWWT exhibited the lowest carbon emissions, with wastewater reuse offsetting approximately 17 % of its emissions. However, its ranking of economic performance was worse due to high construction costs, meaning it is likely to be considered desirable only if a lower discount rate (<1.7 %) was used. Monetizing both positive and negative externalities can improve the economic performance of the SWWT. Notably, when positive externalities are included, its net present value remains non-negative (1.3 CNY/m³) even at discount rates as high as 10 %. Given its diverse revenues and low operation costs, SWWT is more suitable for low-income rural areas. This study proposed a framework in selecting rural WWT, considering both the construction and operation phases while integrating externalities into CBA. This can offer more informed policy insights (such as carbon price and tiered price) to support the development of sustainable rural WWT strategies.