两个污水处理系统的能值与经济综合分析

Emergy and economic evaluations of two sewage treatment systems

运用改进的能值评价指标和经济指标对构建的两个污水处理综合系统("污水处理厂处理+脱水污泥填埋"及"污水处理厂处理+脱水污泥填埋+中水回用")进行了环境可持续性和经济竞争力的综合分析。改进的能值指标(能值产出率SEYR、环境负载率SELR、环境可持续发展指数SESI和能值受益率SEBR)是在考虑研究对象废物及产物能值对环境影响的基础上提出的,更好地反映了系统的特征。结果表明,中水回用系统的增加有利于提升系统的环境可持续发展能力;"污水处理厂处理+脱水污泥填埋+中水回用"系统较"污水厂处理+脱水污泥填埋"系统的经济竞争力差,但却拥有更强的可持续发展能力,有利的经济政策能够刺激其更好的推广运用。

The pressure arising from continuous increase in productivity on the ambient environment and the concomitant pollution threat call for integrated and more efficient environmental protection systems.Sewage treatment systems are technological means to handle the pollution resulting from the production activities,and environmental sustainability and economic viability are two important assessment parameters.Based on the traditional emergy analysis indicators（emergy yield ratio EYR,environmental loading ratio ELR,environmental sustainability index ESI and emergy benefit ratio EBR）,the improved emergy indices（SEYR,SELR,SESI and SEBR,respectively） were proposed for assessing two integrated sewage treatment systems after considering effects of the waste and the product in this study.In addition,three economic evaluation indicators（the net income NI,the profitability ratio PR and economic investment ratio per unit sewage IR） were also exploited to evaluate and compare two constructed integrated sewage treatment systems（i.e.,＇sewage treatment plant＋dewatered sludge landfilling＇ and ＇sewage treatment plant＋reclaimed water reuse＋dewatered sludge landfilling＇）.Emergy evaluation and economic analysis are complementary approaches,with emergy evaluation focusing on the environmental support and effects of a production system while economic analysis method paying more attention to the market value of the products.Hence,a combination of them allows to gain a better understanding of overall performance of a sewage treatment ecosystem in terms of both environment and economy.The systems considered here were integrated with livestock sewage treatment systems,as the systems not only included the sewage treatment plant,but also were composed of treated water and dewatered sludge disposal options.This may give a whole picture of the ecological economic performance of the treatment of livestock sewage.The results showed that,system 2（＇sewage treatment plant＋reclaimed water reuse＋dewatered sludge landfilling＇） has a much greater environmental sustainability index than system 1（＇sewage treatment plant＋dewatered sludge landfilling＇） suggesting the former is much more sustainable,and that incorporation of a reclaimed water reuse system is a valuable way for promoting the sustainability of a sewage treatment system since the reuse system of reclaimed water not only produced new water resources from reclaimed water but also saved the cost for discharging treated water which is charged according to the relative regulations.System 2 is less competitive than system 1 as NI of system 1 is higher（2.4620×106 Yuan/a）,PR and IR of system 1 are 1.38 and 0.72 times of system 2,respectively.System 2 is a more environmentally benign system,however,it′s not competitive in terms of economy.Thus,economic policy supports should be made available for popularization of system 2 which may include charge for direct waste discharge of untreated or insufficiently treated sewage,and economic compensation for reclaimed water reuse.