| Sweage treatment has become an important part for the sustainable development of livestock breeding, since its huge volume, large impact area and significant adverse effects on ambient environment. As a method based on energy analysis, emergy evaluation considered the contributions of natural capital and economic inputs. It makes the incomparable flows like materials, energy and currency comparable by qutifying them in equivalent units, solar emjoules. Emergy analysis has been applied to the evaluation of different kinds of socioeconomic and environmental system in various regions widely. Take consideration of sewage treatment plant system and their product (treated water, dewatered sludge) disposal facilities,"integrated sewage treatment system"(ITS) were formed in this paper. Afterwards, the traditional emergy analysis indicators, the improved emergy analysis indicators and the ecomomic evaluation indices were exploited to assess the environmental sustainability and economic benefits of ITSs. Meanwhile, the impacts of concomitant emissions were estimated by emergy theory, to quatify its environmental effects of resource consumed and pollutants discharged from constrction to the use of an intergrated sewage treatment system. The results showed that:(l)"Sewage treatment plant system+incineration system+treatred water reuse system" has the largest amount of emergy input, following by "sewage treatment plant system+compost system+treatred water reuse system" and "sewage treatment plant system+landfilling system+treatred water reuse system","sewage treatment plant system+landfilling system" is the lowest one. The emergy inputs of all subsystems from high to low are sewage treatment plant system, treated water reuse system, incineration system, compost system and landfilling system.(2)The number of emergy flows for ITSs in a descending order as:waste influent, local renewable resources, purchased renewable resources, purchased nonrenewable resources and local nonrenewable resources. Total emergy inputs main came from waste influent (77.74%～78.66%) and local renewable resources (17.58%～18.03%).(3)Among all water pollutants, NH3-N has the biggest value of emission impacts, TP is the second one, and followed by BOD5, COD has the smallest. For air pollutants, dust, SO2and CO2is the order. In general, the impact of water pollutants were much significant than air pollutants, the former accounted for at least97%of total impacts of emissions.(4)"Sewage treatment plant system+landfilling system" had the lowest emergy consumption density, implies it has the highest emergy utilization efficiency; on the contrary,"sewage treatment plant system+incineration system+treatred water reuse system" has the highest emergy consumption density, which indicates it has the lowest mergy utilization efficiency. In a ITS, the emergy consumption of per TP treated is the biggest, secondly NH3-N and the smallest is COD.(5)"Sewage treatment plant system+incineration system+treatred water reuse system" has the largest currency flow input while "sewage treatment plant system+landfilling system" has the smallest. Currency flow of an ITS consists of purchased nonrenewable resources and purchased renewable resources, and the former is bigger.(6)"Sewage treatment plant system+landfilling system" is the most competitive one in terms of economy, but it is less sustainable from the perspective of environment. Although "sewage treatment plant system+landfilling system+treated water reuse system" is less competitive in terms of economy, it is the one with the greatest environmental sustainability and the biggest ecosystem benefits, economic policy supports should be made available for popularization.(7)The improved emergy evaluation indicators performed better in reflecting the characteristics of intergrated sewage treatment system. In a certain assessment, emergy analysis indices should be proposed according to characteristics of a specific system, in particular, the impacts of emissions should be considered. |
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