A Sustainability Study On A Municipal Solid Waste Incineration Plant Based On Emergy

In recent years,with the growth of China’s population,the development of economy,the increase of urbanization and the improvement of living standards,municipal solid waste（MSW）has increased by an annual rate of 8%to 10%.China has become the largest generator of MSW in the world.According to the statistic data,the delivering quantity of Chinese MSW reached about 178 million tons in 2014,and it will attain approximately 282million tons by 2020,which has exceeded the biosphere’assimilative capacity and induced numerous detrimental impacts.Nowadays,the predominant practices of MSW disposal in China include landfill（65.5%）and incineration（32.5%）.However,with the increasing scarcity of land and the negative impacts of landfill,more and more studies show that landfill is not a sustainable way,MSW incineration is becoming an attractive choice.In fact,MSW incineration technology has possessed increasing market share in China in recent years.E.g.the number of MSW incineration plants has significantly increased from47 in 2003 to 220 in 2015 and the quantity of incinerated MSW has also risen from 3.7million tons in 2003 to 61.7 million tons in 2015.But this technology cannot be absolutely perfect;there are also a series of problems during the course of the construction and operation of MSW incineration plants due to resources and energy consumption and the related direct and indirect pollution emissions,which require extra resources input to eliminate these pollutants and could cause other adverse impacts on human and environment before those pollutants attain safe level.With the concept of―Blue MSW incineration plants‖being put forward,what is urgently needed in this country is enhancing the resources comprehensive utilization rate of MSW incineration plants through technical integration.In order to reflect the characteristic of MSW incineration plants,this paper integrated dilution method,Eco-indicator 99 method,disability adjusted life years（DALY）method,land-use into the emergy analysis so as to quantify pollution emissions’impacts.And then the improved emergy based indicators were proposed to assess the comprehensive performance of MSW incineration systems.One existing incineration plant in Sichuan Province,China,as a case study,was evaluated using the proposed method and the related indicators.Three alternative scenarios（scenario 1:the incineration subsystem+the bottom ash（BA）landfill subsystem;scenario 2:the incineration subsystem+the concrete paving brick production subsystem using BA as raw material;scenario 3:the incineration subsystem+the non-burnt wall brick production subsystem using BA as raw material）were set up from a life cycle viewpoint for an overall comparison.This study aimed to explore how to make the resource comprehensive utilization level of the MSW incineration plant higher and more sustainable.The results show that:（1）As for the emergy flow analysis,the input emergy for scenario 1 is 8.21E+19 sej/yr,of which the waste resource utilization input（W_R）,free renewable input（R₁）,the purchased renewable input（F_R）and the purchase nonrenewable input（F_N）accounted for20.32%,4.21%,2.39%and 73.08%respectively.For scenario 2,the input emergy is1.90E+20 sej/yr;therein,W_R,R₁,F_R and F_N account for 23.71%,1.86%,1.15%and73.28%of the total input emergy respectively.For scenario 3,the input emergy is1.28E+20 sej/yr;therein,W_R,R₁,F_R and F_N has share of 35.20%,2.70%,1.60%and60.50%respectively.In general,the proportion of the purchased nonrenewable emergy input in each scenario is the highest,followed by the emergy input of the waste resource utilization.（2）As for the emissions’impacts,the total value of pollutant’emissions’impact for the three scenarios is 1.67E+18 sej/yr,of which ecological service and emergy loss account for 1.77%and 98.23%respectively.The most ecological service is used to dilute cadmium（Cd）,and the greatest emergy loss is derived from carbon dioxide（CO₂）.Therefore,the cadmiu（Cd）and carbon dioxide（CO₂）in flue gas should be paid more attention.（3）As far as the results of emergy indicators are concerned,the cost per unit waste disposal（CUWE）of three scenarios is 8.59E+13 sej/t,1.65E+14 sej/t and 1.24E+14 sej/t respectively;the ratio of positive output（PRO）is 1.225,2.861 and 1.230 respectively;the improved environmental loading ratio（IELR）of three scenarios is 2.715,2.742 and 1.533,respectively;the improve environmental sustainability index（IESI）is 0.451,1.043 and0.803 respectively.Generally the indicator CUWE show the superiority of scenario 1,the indicator PRO highlights the advantage of scenario 2,the indicator IELR shows the lowest environmental loading of scenario 3,and the indicator IESI means the highest sustainability level of the scenario 2.（4）For the three scenarios analyzed,the pollution emissions reduce their economic benefit between 2.15%⁵.46%and raise their environmental loading between0.02%⁰.05%,the pollution emissions affect their environmental sustainability index between 2.17%⁵.51%.In summary,pollutant’emissions slightly affect their performances.（5）Resource utilization of bottom ash in scenarios 2 and 3 enhances their environmental sustainability compared to the scenario 1.Compared with scenarios 3,the scenario 2 has better comprehensive performance.Based on the above research results,the following suggestions are put forward:（1）Independently researching and developing MSW incineration equipment and technologies suitable for the characteristics of China’s MSW to realize its localization;（2）Reducing the amount of MSW generated from the source;（3）Promoting and implementing the MSW collection system;（4）Reasonable resource utilization of bottom ash after MSW incineration.The scenario 2 should be advocated and prioritized in this study.However,enterprises must also strengthen the management of raw materials and pay attention to the control of air pollutants,and care product market demand;（5）Establishing an open information system for the public;（6）Improving the system of MSW fee;（7）China’government should provide more support for the utilization of waste resources.