| Industrial symbiosis(IS)has a significant impact on several aspects,such as the improvement of the utilization efficiency of resources and energy,the emission reduction of environmental pollutants,the improvement of environmental quality and so on.The hot and difficult topics in the field focus on the causes of IS,the conditions of formation,evolution,driving factors,mechanism,carbon metabolism and carbon emissions,environmental and economic benefit,symbiotic type,and the influence of IS on industrial network structure and function.The current studies,however,usually select a single time point in the process of system development to research industrial symbiosis,lacking competent understanding and empirical research for definition,evolution and driving factors of IS,as well as its influence on carbon metabolism.This paper applied backward approach that provides comprehending on how industrial network emerged over time to analyze the sequences and driving factors of IS in a typical case study of an iron and steel industrial network from 1958 to 2012.Using the method of substance flow analysis to research the effect of IS on carbon metabolism in the iron and steel industrial chain.The changes of symbiotic benefits over time have been evaluated from the environmental,economic,and ecological three aspects.Results show that the IS development in our case went through four stages,which were approximately same with the phase of environmental policies and regulations in China.Symbiotic links increased from 2 to 75 over time,with the symbiotic density from 1 to 3.26,suggesting that entities were engaging in several IS exchanges at the same time and that new entities joined in the IS network.The main guiding factors in the evolution of IS are not only the interests of enterprises and knowledge about industrial symbiosis,but also related policies and regulations.Policies and regulations have a crucial influence on the development of IS from three aspects: Source control,Process control and End-of-pipe control.These three aspects respectively,emphasis on the input of resource management,production operation management and pollutant emissions management.Moreover,IS can improve carbon metabolism efficiency and reduce the carbon in disposable wastes.The proportion of the annual average carbon in carbon dioxide(CO2)in the fourth stage decreased by 9.5% than the third stage.Meanwhile,the carbon in recycled wastes and byproducts increased from 2.0% in the third stage to 2.8% in the fourth stage.The symbiotic benefits increase with the development of IS.For environmental benefit,exchange-based IS can avoid more CO2 emission than sulfur dioxide(SO2)and nitrogen oxides(NOx).The annual average economic benefits increased from 15.048 million yuan/y in the second stage to 30.414 million yuan/y in the fourth stage.Solid waste/byproduct exchanges has a greater economic benefits than energy exchanges and water exchanges.The annual average ecological benefits increased from 35.549 million yuan/y in the second stage to 2983.425 million yuan/y in the fourth stage.The air pollutant emission reduction has the most contribution to ecological benefits,followed by the recycle of solid wastes and water.In addition,the results shows that although IS in internal companies are dominant synergy,it is worth noting that Intra-plant(or company)type symbioses reach to 21%.Hence,the network structure and the evolution of IS can be understood better through considering not only the inter-firm level and the regional or global level but also the intra-firm level.Our results can provide guidance to industrial network planning,construction,management,optimization,and reduce emissions,so as to further improve the function of industrial network. |
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