Search

Sludge management poses a great challenge to China's urbanization process as the number of wastewater treatment plants increases and the discharge standards are strengthened. China's sludge production rate is still low compared with developed countries but is undergoing a rapid growth due to increasing urbanization. Sludge management requires a systematic solution which integrates environmental effectiveness, social acceptability, and economic affordability based on a life cycle approach. In this study, we assess the environmental and economic performance of hydrothermal-pyrolysis technology (HPT), an emerging technology for sludge disposal. Climate change, human toxicity, costs, beneficial use of sludge and land occupation are used as indicators to compare HPT with conventional disposal methods, including incineration with two water contents, landfill, and compost. A particle swarm optimization (PSO) model based on the LCA results (PSO-LCA) was built to find a sustainable sludge management system in Xiamen. HPT was the most favorable scenario for sludge disposal overall, but given capacity restrictions and a trade-off between indicators, the optimal disposal proportion was for landfill to account for 9.3% of total sludge disposal, incineration with water content of 80% to account for 35.9%, HPT to account for 28.9% and compost to account for the remaining 25.9%. As further dewatering contributes a significant fraction to human toxicity effects and economic performance, the amount of dewatering should be selected based on the subsequent disposal process. The PSO-LCA method provides scientific evidence to inform decision makers to find a sustainable sludge management plan in accordance with wastewater features and socioeconomic conditions in Chinese cities.

Urban waste management is a complex social-ecological system that requires broader stakeholder participation and widespread environmental awareness. However, further investigation is required to identify interdependencies among different stakeholders and improve their interactions within the system. This research took Xiamen, a Chinese city, as a case study, which was one of 8 Chinese pilot cities that implemented waste separation in 2000 and one of the 46 key cities participating in a new separation policy since 2017. We used stakeholder analysis (SA), social network analysis (SNA) and ecological network analysis (ENA) to identify the characteristics of different stakeholders, their network structure, and the beneficiaries and contributors to the urban waste separation management (UWSM) system. The research conducted a comparison of resident’s participation before and after the new waste separation policy, as well as a comparison among different stakeholders in the new policy. The results showed that all stakeholders had a high level of satisfaction in 2017, but that satisfaction levels decreased with distance from the downtown area. Residents were more willing to participate in waste separation in 2017 than in 2012. Based on their powers and interests, stakeholders were divided into 4 categories that had different network centrality. The ecological relationships between stakeholders were mainly exploitative and competitive which may cause potential inefficiency; powerful stakeholders did not benefit the whole system and the least powerful stakeholder was the largest contributor. The combined application of these methods were complementary to help diagnose information flow problems in the socio-ecological system. Policy implications to further promote mutualism in UWSM are discussed.