Tracing the Consumption Origins of Wastewater and Sludge for a Chinese City Based on Waste Input–Output Analysis

Water scarcity and pollution are grand challenges to sustainability. We developed a high-resolution wastewater input–output model for a Chinese city, Xiamen, incorporating detailed information on the treatment and quality of wastewater and sludge. We estimated consumption-based wastewater and sludge footprints of products (W2F and SF, respectively). Significant differences were found between the amounts of direct discharge (scope 1) and W2F (scopes 1–3), indicating the need to consider W2F in making plans for future wastewater management strategies. Reflecting its high organic content, food-related consumption was found to be a significant contributor to sludge generation. Scenario analyses were conducted to assess the effects of a shift from the traditional Chinese diet to the European diet and the anticipated industrial growth. Attempts were also made to establish links between the direct wastewater discharge of households and the final consumption of food items through human excretion, or the postconsumption footprints. It was found that the postconsumption W2F outweighed the preconsumption W2F for five out of nine food items, while the postconsumption SF outweighed the preconsumption SF in all cases except one. This research provides a scientific basis to identify the economy-wide fate of wastewater and sludge and to frame a policy for sustainable wastewater and sludge management.