Heavy Metal Emission During Rubber Catalytic Pyrolysis/Combustion And Life-cycle Multi-criteria Decision Of RDF Thermal Treatment

Heavy metals emission during thermal treatment of municipal solid waste(MSW)is a serious environmental problem,so it is necessary to grasp the migration characteristics of heavy metals in the thermal treatment process.And RDF thermal conversion and utilization technology is the direction of future development on waste treatment.Exploring the applicability and feasibility of the RDF thermal treatment from the perspective of resources,environment,and economy is an important art.This research content of this paper is as follows:(1)The volatilization characteristics and risk evaluation of heavy metals during the pyrolysis and combustion of rubber waste with or without molecular sieves(MS)were studied using a lab-scale tubular furnace.Nine target metals(As,Cd,Co,Cr,Cu,Ni,Pb,Zn,and Ti)were analyzed.The fitting formula for the volatilization rate of each heavy metal with temperature and MS addition amount was established.The heavy metal content in the thermal treatment residue decreased with the increment of the furnace temperature in most cases.The addition of MS during pyrolysis inhibited the volatilization of As and promoted the volatilization of Ni and Co,while during combustion it inhibited the volatilization of Pb,Zn and promoted the volatilization of Cu.For Cd,Cr,Ni,Zn and Ti,their volatilization rates during pyrolysis were significantly higher than those during combustion,whereas for As and Cu,the volatilization rates during pyrolysis were lower than those during combustion.Co and Cd had the highest monomial potential ecological risk factor,while Cu and Cr had the lowest one.The addition of MS increased the potential ecological risk during pyrolysis but reduced the potential ecological risk during combustion in most cases.The potential ecological risk during combustion was generally lower than that during pyrolysis.(2)This paper analyses environmental and economic performance of thermal utilization technologies of two different refuse derived fuel(RDF)manufactured from landfilled waste or fresh municipal waste,including incineration of landfilled RDF(I-LRDF),gasification of landfilled RDF(G-LRDF),replacement of partial coal by landfilled RDF for the cement industry(C-LRDF),incineration of municipal RDF(I-MRDF),and replacement of partial coal by municipal RDF for the cement industry(C-MRDF).The result shows that RDF thermal utilization technologies bring an economic profit of $17.29～$35.77 per ton of waste.Especially,I-LRDF has the worst effect on ecosystem quality and human health and can yield the greatest economic profit of $35.77 per ton of landfilled waste,while I-MRDF has the least impact on environment.Multi-criteria decision making(MCDM)is implemented by AHP-TOPSIS.I-MRDF has the best comprehensive performance from the perspectives of local government,industry,residents,and an “egalitarian” standpoint.The improvement of the RDF thermal utilization efficiency is the most critical factor affecting the economic benefits for the above five cases.