Carbon Emission Accounting For Low Carbon Remediation Of Contaminated Sits

With China’s economic development and industrial reform,a large number of factories have been abandoned or various types of industrial abandoned contaminated sites have been created in the processes of relocation.However,the formally laws and regulations regulating contaminated site remediation have been launched by the Chinese government in 2016.Currently,China’s contaminated remediation is still at the stage of high efficiency,high energy consumption,and high emissions,resulting in inefficient use of resources and economic waste.This will not only affect the sustainable development of the contaminated site remediation industry in the long run,but may also cause serious secondary environmental problems.Therefore,promoting the greening and low carbonization of contaminated site remediation is the "double carbon" demand of the country and the inevitable development of the industry.Therefore,this paper proposed a new low-carbon remediation concept,evaluation and optimization research framework for contaminated sites.Low-carbon remediation refers to the concept of contaminated site remediation in which carbon emissions are accounted for throughout the entire life cycle of various remediation projects,and then the most suitable low-carbon alternative for the contaminated site is selected,and the process with high carbon emissions in the remediation process are further optimized and adjusted to reduce the carbon emissions of the final remediation alternative as much as possible.This study aimed to provide a theoretical basis and practical foundation for the establishment of a low-carbon sustainable remediation system in China.A complete carbon emission accounting system is a prerequisite for the systematic design of low-carbon remediation processes.In this paper,a tiered hybrid life cycle assessment(TH LCA)carbon accounting model is constructed by process life cycle assessment(PLCA)and economic input-output life cycle assessment(EIO-LCA).The carbon accounting model includes three tiers: it accounts the carbon emissions of direct inputs of materials and energy in the site in tier 1,using the traditional PLCA method with truncation error.It can only quantify carbon emissions in the limited supply chain of soil remediation.It is based on EIO-LCA to quantify the carbon emissions of the whole supply chain in the province where the case is located in tier 2;It quantifies the nationwide emissions of the whole supply chain in tier 3,which is based on the tier 2accounting and further considers spillover effect of the cross-regional carbon emission.The three-tiers accounting model proposed in this study can include all carbon emissions at each tier of the supply chain,and can also study the total emissions with process volume,sector volume and regional spillover in a hierarchical manner.Based on this three-tiers accounting model,the key factors,sectors and regions that influence the carbon emission characteristics of each remediation solution can be identified,and corresponding emission reduction policies can be formulated.In addition,the optimal low-carbon remediation alternative should not only consider the carbon emission impact,but also its social and economic feasibility.Therefore,this paper integrates the social,economic,and environmental performance of remediation alternatives and their sensitivities based on a multi-attribute decision making approach to obtain the optimal remediation alternatives.Select a typical heavy metal contaminated site in Hubei Province as a case site,this paper further verified the feasibility of the research framework proposed in this paper by using three alternatives,including co-disposal in a cement kiln technology,ex-situ solidification and stabilization technology and ex-situ soil washing technology.Codisposal in a cement kiln technology,ex-situ solidification and stabilization technology and ex-situ drenching technology are commonly used remediation technologies for heavy metal contaminated sites The results showed that the carbon emission ranking of the three methods is stable regardless of the accounting method used,and the co-disposal in a cement kiln alternative is the lowest carbon alternative.Specifically,based on the Tier 1accounting method,the soil washing alternative emits 467.34 kg/m~3,which is the highest Tier 1 emission alternative.However,based on the tier 1 accounting method,the ex-situ solidification and stabilization has an increased cut-off error(tier 3 minus tier 1)of105.81 kg/m~3.The sensitivity analysis results indicated that if we want to reduce carbon emissions from the ex-situ solidification and stabilization and soil washing alternatives,adjustments should be taken from the solidification stabilization agent and soil washing agent.From the tier 2 and tier 3 accounting,production and supply of electric power and heat power(PSE)sectors are the most affected by all three remediation alternatives of the project,with impacts ranging from 5.21(co-disposal in a cement kiln)to 71.71(ex-situ solidification and stabilization)kg/m~3 under different alternatives.While Inner Mongolia,Xinjiang,and Shanxi are the three provinces with the highest cross-regional impacts,ranging from 0.65 to 9.83 kg/m~3,0.38 to 2.96 kg/m~3,and 0.37 to 3.91 kg/m~3,respectively.The lowest carbon spillover alternative is the co-disposal in a cement kiln,the highest alternative is the ex-situ solidification and stabilization.Considering the socio-economic and environmental impacts of the three remediation alternatives,the co-disposal in a cement kiln is the optimal low-carbon remediation alternative.If only primary carbon emissions are used as the carbon emission indicator,the co-disposal in a cement kiln alternative is still the best alternative,but its advantages are limited.If carbon emission is not considered as a reference indicator,it may lead to a bias in the selection of alternatives,and the ex-situ solidification and stabilization alternative becomes the optimal one.The model analysis framework proposed in this study is able to identify the carbon emission contribution of low carbon technologies,key aspects and raw materials for soil remediation,and provides methodological support for further optimization of soil remediation technologies.