Optimization of wastewater treatment strategies using life cycle assessment from a watershed perspective

Increasing the environmental sustainability of wastewater treatment contributes to the construction of sustainable urban water systems, especially for developing countries. Life cycle assessments (LCA) have quantified the environmental implications of overly-sophisticated discharge standards. However, studies on these topics provide limited practical guidance, as real policy concerns are rarely incorporated in the assessment process. One such concern is watershed management by satisfying the water quality limit (WQL) of the receiving environment. To manage sustainable wastewater treatment from a watershed perspective, this study integrates LCA with water quality models to facilitate the decision process. By parameterizing the WQL as a constraint condition, a hierarchical priority structure is established in the environmental index system, and alternatives that satisfy the WQL are screened, and compared in terms of life cycle burdens. This study investigates the effect of considering WQL on the evaluation of wastewater treatment strategies, using an urban sewage system case study in China. In wastewater treatment plants (WWTPs), determining discharge levels based on the WQL of the receiving river, contributes to specific control of WWTPs with reduced life cycle burdens, compared with the "one size fits all" administrative strategy. Considering the influence of non-point source pollution (urban runoff), results demonstrate that only relying on wastewater treatment is unlikely to reliably satisfy the WQL. This study highlights the importance of utilizing an integrated policy to coordinate the treatment of wastewater and urban runoff for watershed management, by coupling enhanced wastewater treatment intensities with the green and gray storm water management infrastructures. This integrated policy quantitatively showed advantages in terms of stable control of water pollution, and less dependence on the self-purification capacity of the receiving river.