The Assessment Of Municipal Sewage Sludge Treatment And Disposal Technologies

In this paper, the sewage sludge treatment and disposal technologies were studied to build the methodology for technology assessment. At the same time, the sewage sludge treatment and disposal technologies were evaluated with cost-benefit analysis method and fuzzy comprehensive evaluation method, and the corresponding evaluation index system and assessment process were set up. A fuzzy comprehensive evaluation system was developed. Finally, the fuzzy comprehensive evaluation method was applied to assess the sewage sludge treatment and disposal technologies and choose the best sewage sludge disposal technical process for Suzhou city which was taken as a case.The investment costs, operating costs and direct benefits of sewage sludge treatment and disposal technologies were estimated with cost-benefit analysis method. The results showed that the investment costs and operating costs per ton dry sludge decreased with the scale of the wastewater treatment plants increasing and were affected by the processing of the plants. For centralized disposal technologies, the investment costs and operating costs per ton dry sludge increased with the sequence of landfill, compost and land use, making construct materials, desiccation and incineration. The direct benefit of making construct materials was about 333-1055Y per ton dry sludge, much higher than other centralized disposal technologies.For comprehensive assessment, an evaluating index system which consisted of the goal layer, rule layer, and layer of specific indicators was constructed. Furthermore, it's the first time to propose the regional coordination performance as an indicator for the assessment of sludge treatment and disposal technologies in China, emphasizing the principle of act according to circumstance. Meanwhile, the ananlytic hierarchy process (AHP) and fuzzy comprehensive evaluation method were determined to calculate the values of weights and scores of sludge disposal technical processes respectively. A user-friendly fuzzy comprehensive evaluation system was developed, which could support the calculation processes effectively. As a case study, the fuzzy comprehensive evaluation method was applied to assess the sludge disposal technical processes in Suzhou, including sludge incineration, landfill, land use and making construction materials. Combined with expert consultation result, the value of the weight of each indicator was calculated with AHP. The results showed that the weights of the indicators in the rule layer decreased in order of environmental impact performance, economic performance, regional coordination performance, technical performance and resource utilization performance. For specific indicators, the top five indicators, whose weights were larger than others, were unit operating costs, air pollution, soil pollution, recyclability and social acceptability. The priority of the sludge treatment and disposal technologies in Suzhou City was making construct materials, incineration, land-use and landfill, which was consistent with the socioeconomic development features, envioronmental protection demand and existing infrastructures of Suzhou, providing a reference for Suzhou to select the best sludge treatment and disposal technical process.The research results were very significant to perfect the methodology for the assessment of sewage sludge treatment and disposal technologies, as well as to accelerate the scientific choices of sewage sludge treatment and disposal technologies and improve the environment quality.