[Environmental impacts of sewage treatment system based on emergy analysis]

"Integrated sewage treatment system" (ISTS) consists of sewage treatment plant system and their products (treated water and dewatered sludge) disposal facilities, which gives a holistic view of the whole sewage treatment process. During its construction and operation, ISTS has two main impacts on the environment, i.e., the consumption of resources and the damage of discharged pollutants on the environment, while the latter was usually ignored by the previous researchers when they assessed the impacts of wastewater treatment system. In order to more comprehensively understanding the impacts of sewage treatment on the environment, an analysis was made on the ISTS based on the theories of emergy analysis, and, in combining with ecological footprint theory, the sustainability of the ISTS was also analyzed. The results showed that the emergy of the impacts of water pollutants on the environment was far larger than that of the impacts of air pollutants, and NH3-N was the main responsible cause. The emergy consumption of ISTS mainly came from the emergy of wastewater and of local renewable resources. The "sewage treatment plant system + landfill system" had the highest emergy utilization efficiency, while the "sewage treatment plant system + reclaimed water reuse system + incineration system" had the lowest one. From the aspect of environmental sustainability, the "sewage treatment plant system + reclaimed water reuse system + landfill system" was the best ISTS, while the "sewage treatment plant system + incineration system" was the worst one.