| To deal with the serious situation caused by the excessive generation and disposal of municipal solid waste(MSW),MSW classification has been of great concern currently in China.The overall aim of this study was to systematically understand the improvement of MSW classification on the environmental benefit of terminal disposal from the perspective of MSW integrated management and further achieve a theoretical foundation to optimize the formulation of the MSW integrated management system.In this study,312 samples were collected from 9 representative communities in Zhangjiagang City from September 2020 to July 2021.The proportion,bulk density and moisture content of different MSW components were measured,and their changing characteristics and relevant influencing factors were analyzed as well.The environmental benefit of MSW disposal under various scenarios of MSW different separation amounts and purities were investigated and predicted based on the life cycle assessment(LCA)method and MSW composition data obtained from Zhangjiagang City.This study summarized the characteristics and existing problems of MSW classification management in Zhangjiagang City and other cities in China,and analyzed the popularization of MSW classification management mode in Zhangjiagang City.As for the MSW composition,the proportion of food components was highest(66.57%)in Zhangjiagang City,which was at a relatively high level on a national scale.The proportion of plastic,paper,textile,ceramic,glass,metal,bamboo,toxic and hazardous components were 13.38%,13.36%,2.96%,0.72%,1.59%,0.71%,0.37%and 0.34%,respectively.There was no significant seasonal difference in MSW composition.The average moisture content of MSW in Zhangjiagang City was 58.18%,which was higher than the national average level(approximately 50%).And the average bulk density of MSW in Zhangjiagang City was 161.12 kg·m-3.For residual waste,the average proportion of food components(48.33%),average moisture content(45.11%),and average bulk density(101.15 kg·m-3)under manual supervision mode decreased by 27.40%,22.46%and 37.22%,respectively,compared with those in the unclassified communities,while the average proportion of paper(21.59%)and plastic(18.49%)increased by 61.60%and 38.90%respectively.Under the machine-assisted mode,the average proportion of food components(38.90%),average moisture content(40.35%),and average bulk density(96.51 kg·m-3)decreased by 41.57%,30.65%and 40.10%,respectively,compared with those in the unclassified communities,and the proportion of paper(24.74%)and plastic(22.19%)increased by 85.18%and 65.84%respectively.For food waste,the average proportion of food components(97.41%),average moisture content(77.65%)and average bulk density(491.67 kg·m-3)under the manual supervision mode increased by 46.33%,33.47%and 205.16%compared with unclassified communities,while plastic(1.27%)and paper(1.09%)decreased by 90.51%and 91.84%respectively.Under the machine-assisted mode,the average proportion of food components(93.07%)average moisture content(75.24%)and average bulk density(383.24 kg·m-3)increased by 39.81%,29.32%and 137.86%compared with unclassified communities,while the proportion of plastic(4.65%)and paper(1.62%)decreased by 65.25%and 87.87%respectively.In this study,the machine-assisted mode had a better effect on the classified management of residual waste,but the manual supervision mode was more conducive to the classified management of food waste.In addition,the machine-assisted mode would significantly decrease the moisture content of residual waste,and the manual supervision mode would significantly improve the bulk density of food waste at the present stage.Various factors would affect MS W classification efficiency,including MSW classification management mode,season,classification duration and property management level(take housing prices as the indicative indicator),etc.MSW classification management mode was the significant factor affecting the composition change of food waste,and the property management level was the important influencing factor.Season and classification duration would not affect the MSW composition significantly.The manual supervision mode was more conducive to improving the classification effect of food waste while the machineassisted mode had an accelerated classification effect on residual waste.In the short term,easily identifiable waste components such as plastic and paper would be significantly increased.The improvement of the environmental benefit from MSW disposal depended not only on the improvement of the MSW classification efficiency but also on the matching degree with the terminal disposal capacity.According to the average daily MSW production of 1850 t in Zhangjiagang City,the direct total environmental impact potential converted from the pollutant emission(DTEIP)and the total environmental impact potential after the conversion of power recovery were calculated based on life cycle assessment(LCA)method and MSW composition data collected from Zhangjiagang City.Under the scenarios based on the current situation of terminal disposal,when the food waste separation amount was 150 t·d-1,the DTEIP would gradually decrease with the increase of the food waste purity,which decreased by about 10%compared to that of unclassified scenario(3.41×10-10 in PET2000,the same applies hereinafter).When the food waste separation amount was above 150 t·d-1,as the separation amount and purity of food waste gradually increased,disposal of separated food waste by landfill and high purity residual waste by incineration would lead to increasing pollution,and the DTEIP would increase gradually.Under the scenarios based on the terminal disposal plan,the DTEIP(1.73×10-10-2.40×10-10)after classification was lower than that of the current terminal disposal scenarios.When the food waste treatment capacity was sufficient and the purity of food waste remained stable,the DTEIP decreased as the food waste separation amount increased.The continuous improvement of the MSW classification effect greatly promoted the environmental benefit from MSW integrated management after the terminal disposal capacity expanded according to the plan.Under the scenarios based on the current situation of terminal disposal,the total environmental impact potential after the conversion of power recovery was-1.18×10-10--0.39×10-10,while the value was-2.31×10-10--1.82×10-10 under the scenarios based on the terminal disposal plan.Thus,recycling MSW was conducive to reducing pollution during the MSW treatment and disposal process and improving environmental benefits.According to the experience of MSW classification involved in MSW integrated management in Zhangjiagang City,promoting the matching degree between MSW classification and the terminal disposal capacity should be considered.The capacity of MSW incineration and food waste recycling could also be enhanced to improve the popularization mode and effect of MSW classification. |
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