Four commonly used sewage sludge treatment techniques in China are compared, each with and without the combination of anaerobic digestion; composting, co-combustion in power plant, thermal drying-incineration, and cement manufacturing. Life cycle assessment (LCA) is used to quantify the environmental burden, while exergetic life cyde assessment (ELCA) is supplemented to measure the resources conversion efficiency. Afterward, abatement exergy is adopted to determine their degree of environmental sustainability, so that all environmental issues associated with resource use and environmental emissions can be solved simultaneously. Results show that anaerobic digestion is an effective pretreatment approach to reduce environmental burden. Thermal drying-incineration is preferable to co-combustion and cement production, since fossil fuel combustion is the dominant cause of emissions. Composting poses a positive effect to mitigate global wanning, but it introduces high heavy metals to the soil, Results from ELCA reveal that thermal techniques present higher resources conversion efficiency than a biological system. Adopting anaerobic digestion obviously improves the performance of composting, but it has reduced the total energy recovered in thermal techniques. For process improvements, an efficient sludge predrying is important; and the use of a combined heat and power system can. also provide more effective recovery of energy.
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