Resource reclamation of municipal sewage sludge based on local conditions: A case study in Xi'an, China

With the dramatic increase in sludge resulting from rapid urbanization, the need to optimize sludge resource recovery and utilization technologies is particularly urgent. However, there is a large deviation between the optimized technologies using the optimal selection method and the actual situation. This study established an adaptation to local conditions-based sludge recovery technology evaluation mode to solve this problem. The principle of this evaluation method relies on the combination of sludge recovery and local industrial structure, focusing on the resource and energy recovery rate. The Vlsekriterijumska Optimizacija I Kompromisno Resenje (VIKOR method) based on the modified entropy weighting method was developed to determine most sustainable option in the decision-making process. An evaluation index system was constructed related to sludge disposal's technical characteristics with 15 indicators under five main dimensions: environmental impact, economic impact, entropy change, resource utilization rate, and regional suitability. The new evaluation method was applied in Xi'an, China. It was found that sewage sludge recovery technologies followed the order: brick-making, cement kiln, composting, power generation, landfill, and incineration, with Q_J of 0, 0.222, 0.264, 0.437, 0.598, and 1, respectively. Using brick-making, cement kiln, and composting as critical recovery processes, coupled with power generation as the supplementary process, the sewage sludge can be reasonably recovered in Xi'an, implying that the integrated recovery process achieved environmental and economic apex. The sludge recovery evaluation method based on adaptation to local conditions in this study can provide a helpful reference for municipal sludge disposal and recovery in big and medium-sized cities.