Sustainability Evaluation Of Hospital Sewage Treatment System Based On Emergy Theory

The more and more dewatered sludge is increasingly challenging the sustainable development of sewage treatment plants. In order to assess the comprehensive benefit s of sewage treatment process, it is necessary to construct sewage treatment ecosyste m through integrating sewage treatment subsystem, treated water disposal subsystem and dehydrated sludge disposal subsystem into a system. Only by this way can we co mpare the comprehensive performances of different scenarios so as to provide suggest ions for engineering designers and decision-makers. As one of important system analy sis tools, the emergy analysis is fit for evaluating the comprehensive benefits of sewag e treatment systems. Due to rooting in researching natural ecosystem, the traditional e mergy analysis does not consider the impact of emissions because there are not so-call ed wastes in natural ecosystem. However, sewage treatment process belongs to man-made system, there exist all kinds of wastes and/or products in its total life cycle, and this is different from natural ecosystem. Therefore, the traditional emergy analysis ne eds to be improved so as to consider the impact of emissions, and then it can be applie d to evaluating sewage treatment process. Here, this paper put forward a quantifying method for impact of emissions based on emergy, and the impact of emissions was int egrated into the traditional emergy indicators to describe the comprehensive performa ncesof an ecological sewage treatment system. Next, Zhuo-Ke-Ji hospital sewage treatment system, as a case, was researched using the proposed methods and index system."sewage treatment subsystem+sludge incineration subsystem" has been constructed to compare the each subsystem comprehensive benefits by evaluating sustainability of subsystems and combining the size of the weighing coefficients of each subsystem. The results show that the improved emergy analysis method are more suitable for evaluating the sustainability of an ecological sewage treatment system; waste utilization can improve the sustainability of ecological sewage treatment system; Sludge incineration subsystem has the highest sustainable index weighing coefficients of5.6,and the sustainable index weighing coefficients of sewage treatment subsystem is0.9899.Therefore, the sludge incineration subsystem has a higher contribution than the sewage treatment subsystem to the whole sewage treatment ecosystem sustainability. Finally, this paper put forward the related suggestions.