A Research On Environmental Sustainability Of Two Tap Water Supply Systems Based On Emergy

With the rapid growth of population and the increasing urbanization,the demand of urban tap water has increased dramatically.In order to meet the increasing demand of tap water,tap water plants,as one of important municipal infrastructures in society,have been developed fast.In the context of the fast economic growth and the ecological civilization building,energy conservation and emission reduction is still the work that to be continued after the twelfth five-year plan period to achieve win-win results for economic development and environmental improvement.Water supply system has made great contribution to China's economic development;however,it also leads to serious resources and environmental problems and affect the sustainable development of the society as a whole.Therefore,it has very important practical significance and theoretical value to evaluate the resource efficiency,environmental impact and sustainability of the entire water supply system.Emergy analysis considers natural contribution to economic activities and concentrates on the interaction between human and nature and the related resources efficiency and environmental impact.Therefore,it has been widely used to evaluate the comprehensive performance of all kinds of systems with different scales.However,traditional emergy analysis ignores the impact of emissions when evaluating a certain process,thus this method needs to be improved to quantity the impact of emissions,and then the related indicators should be also adjusted.This study adopted emergy analysis method to evaluate the sustainability of water supply system.Emissions' impacts are quantified through integrating eco-indicator 99,dilution method,disability adjusted life years and land occupation into traditional emergy analysis.Then this paper puts forward the improved emergy indicator system to evaluate the energy efficiency,environmental and economic performances of a tap water supply plant in Jiangsu Province(plant A)and a tap water supply plant in Shanxi Province(plant B).The results are summarized as follows:(1)As for emergy flows,for plant A,the local renewable resource inputs,the purchased renewable resource inputs and the purchased nonrenewable resource inputs account for 34.39%?4.47% and 61.13% of total emergy inputs,respectively.Among the purchased non-renewable inputs,thermal power contributes the largest,followed by operation cost and polyaluminium chloride.For plant B,the local renewable inputs,the purchased renewable inputs and the purchased nonrenewable inputs account for 41.19%?3.05% and 55.76% of total emergy inputs,respectively.Among the purchased non-renewable inputs,polyaluminium chloride contributes the largest,followed by thermal power and operation cost.In a word,thermal power,polyaluminium chloride and operation cost are the three largest contributors to the total input except the raw water.And plant A has higher share of nonrenewable input than plant B.(2)The unit emergy value of plant A and plant B attains 7.13E11 sej/m3 and 1.64E12sej/m3 based on the baseline 12.0E24 Sej/a,respectively.That is to say,plant A has higher resources utilization efficiency than plant B.(3)As far as emissions' impact is concerned,for plant A,ecological service and economic loss contributes shares of 5.45% and 94.55% to the total emissions' impact,respectively.Therein,67.36% of ecological service is needed to dilute pollutants of water;79.48% of economic loss comes from impacts of dust emissions on human health.For plant B,ecological service and emergy loss contributes shares of 27.04% and 72.96% to the total emissions' impact,respectively.Therein,55.29% of ecological service is needed to dilute air pollutants;35.69% of emergy loss comes from impacts of dust emissions on human health.(4)According to the indicator results,plant B has smaller environmental impact,higher economic benefit and higher sustainable development level than plant A.(5)For the two tap water plants,the pollution emissions' impact reduces their economic benefit,raises their environmental loading and weakens their comprehensive performance to different degrees.Comparatively speaking, plant A has a greater impact on the environment.(6)Based on the analysis of the specific water purification process of plant A and B,we can optimize the input structure and improve the comprehension performance of them through choosing the method of hydraulic mixing and adding the moderate amount of potassium permanganate.Finally,this paper presents the corresponding suggestions for improving the comprehensive performance of tap water pants,including(1)optimizing water purification technologies;(2)strengthening energy management;(3)optimizing energy structure;(4)strengthening the management of indirect pollution sources.