Carbon Footprint Analysis Of Agricultural Waste Recycling Based On Emergy Theory

At present,based on the goal of "carbon neutrality",the carbon pollution management of agricultural waste are the main problems urgently needed to be solved in Chinese rural areas.As one of the universal agricultural waste utilization methods in rural areas of China,biogas production can transfer the collected agricultural wastes,including crop straw and animal and poultry manure,into biogas,biogas slurry and biogas residue through the anaerobic fermentation treatment,and ultimately contribute in the production of clean energy or planting fertilizer,which has great significance to the agricultural waste treatment and resource utilization.In this study,the agricultural waste biogas production system was redefined as four parts:raw material collection,transportation,storage and production utilization stages.The biogas production project of Weilai Energy Company in Xincai County,Henan Province was taken as an example to adopt the carbon footprint theory and emergy evaluation method to analyze the greenhouse effect from agricultural waste biogas production system.In order to scientifically measure the environmental impact of the system,the carbon emission calculation models of agricultural waste comprehensive utilization system were constructed to quantify the carbon emissions and removal amounts,and the emergy-based carbon emission indicator system and emergy radius formulas according to the characteristics of biogas production were established to illustrate the relationship between the system carbon emission and resource input-output,as well as the relationship between the low-carbon sustainable development of the system and the feedstock supply radius.The calculation results of the carbon footprint analysis showed that the highest carbon emissions of the comprehensive utilization system were generated by transportation stage,and the next stages were the collection stage,production stage and storage stage.The carbon reduction effect analysis concluded that the agricultural waste recycling could greatly reduce carbon emission pollutions of 1.10×108 kgCO2eq that might be caused by waste incineration or discharge.And the outputs of electricity and organic fertilizer had replaced a total of 9.67×106 kg carbon emissions from traditional electricity and fertilizer consumption,which has significant benefits of energy saving and emission reduction to keep pace with the national"double carbon" goal and the rural revitalization strategy.It should be widely promoted in Chinese rural areas.For the carbon emission indexes based on emergy theory,it was concluded that the system has a low degree of social resource input and carbon emission loading,and had a high ability of production and low-carbon sustainable development.And the carbon emissions generated by the system were mainly related to the external purchase of non-renewable resource inputs,including electricity,production material and fossil energy,etc.Most of these inputs were high-carbon emission or energy-intensive resources,which made high carbon emission intensity of the system in the process of resource recycling and utilization.The emergy radius analysis showed that with the further enlargement of the raw material collection radius of the agricultural waste recycling system,the production efficiency and ecological sustainability of the system reached the maximum finally,and the substitution emission reduction benefit was also significantly enhanced,both of which were better than that of the optimal economic distance.From the economic point of view,agricultural waste biogas production systems require a large amount of external capital investments,in order to reduce production costs,the raw material collection centers tend to build plants near the biomass resources,which is actually limit the distance of raw material supply.The emergy radius results indicate that the ecological sustainability and alternative emission reduction benefits of biogas production can be further improved by increasing the collection radius.Therefore,the scientific study of carbon footprint analysis of agricultural waste recycling system based on emergy theory provides a new decision-making approach for the low-carbon sustainable development and rational distribution of rural agricultural waste comprehensive utilization system.