Cost-benefit Analysis Of Anaerobic-aerobic Combined Dairy Manure Management System Based On LCC

It is significant to assess the comprehensive environmental and economic benefits of dairy manure management systems which would support dairy farms to choose economically feasible and environmentally friendly manure management systems and to achieve sustainable development.In this study,a cost-benefit evaluation model of the anaerobic-aerobic combined management system for dairy manure was established based on the life cycle cost methodology,involving manure collection,anaerobic fermentation,biogas utilization,and field application.The economic and environmental impacts of the system were quantitatively evaluated,and the main processes,factors,materials and pollutants including structures and equipment raw materials were determined,and the economic and environmental costs and benefits were analyzed.The composition and characteristics of costs and benefits,as well as the comprehensive consideration of the relationship between environmental and economic costs and benefits,and a sensitivity analysis were carried out,which provide a reference for the optimization of the manure management system and the formulation of policies.The main research results as follows:（1）The main sources of annual operating costs of the manure management system are labor costs,energy consumption,and fixed asset depreciation costs,which account for35.31%,29.74%and 29.12%of the annual cost,respectively.The main processes of annual costs are anaerobic fermentation stage,treatment and utilization of biogas residue,manure collection and biogas purification and power generation;the contribution rates are 30.17%,29.31%,23.87%and 16.46%,respectively.（2）Among the eight major environmental impact categories assessed in this study,the direct energy consumption and pollutant emissions from the manure management system are main sources of seven impact categories global warming,fine particulate matter formation,ozone human toxicity,and terrestrial acidification,freshwater eutrophication,human non-carcinogenic toxicity,and fossil resource exhaustion,with a contribution rate of73.21%-98.67%.Indirect emissions from structures and equipment raw materials are the main source of human carcinogenic toxicity,the sum of the two contributions is 88.44%of total impact,which main pollutant is Cr（VI）came from production of copper and steel.The NH₃volatilization of cow manure and urine in the cattle barn and the treatment and utilization of the biogas slurry is the main contributor to the formation of fine particles and the terrestrial acidification.The heavy metals in the manure,especially zinc,are the main contributors to human non-carcinogenic toxicity.（3）The main sources of the environmental cost of the manure management system came from human non-carcinogenic toxicity,fine particulate matter and global warming,with contribution rates of 75.93%,18.79%,and 4.14%,respectively.The contribution rate of terrestrial acidification,freshwater eutrophication and human carcinogenesis toxicity were 0.67%,0.34%and 0.14%,respectively.（4）The economic benefits of the manure management system mainly come from the sales of organic fertilizers,with a contribution rate of 53.63%.The contribution rates of biogas power generation and self-use as gas are 28.01%and 18.36%respectively.The main source of environmental benefits is reduction of fine particulate matter formation,global warming,human non-carcinogenic toxicity and terrestrial acidification,which contribution rates were 47.37%,22.41%,22.01%and 6.99%,respectively.（5）The dynamic investment payback period of the manure management system is 23years,and the economic net present value of 30 is 374,700 yuan.The comprehensive environmental and economic benefits are lower than the cost,and the efficiency-cost ratio is 0.43,as social benefits（reduction of disease transmission and sanitation problems caused by direct discharge of manure）are not considered.（6）According to sensitivity analysis,enhancing biogas productivity can significantly improve the net economic and environmental benefits of the system,and increasing the efficiency of power generation and the biogas slurry is used nearby can improve the economic net income,but the increase of the net environmental income is relatively small.In the case that biogas is 100%used as fuel,a significant increase in economic net income is achieved,but the net environmental income is decreased.In summary,when only economic revenue was considered,the dairy manure management system has a long payback period and low economic net income within 30years of operation.It relies on government financial support to encourage farms adopting an anaerobic-aerobic combination management system.In the case that social benefits of the fecal sewage system are not considered,that is,avoiding the disease transmission and sanitation problems caused by the direct discharge of fecal sewage,the comprehensive environmental and economic costs are higher than the benefits.Heavy metals,especially Zn in manure,is the main environmental hazard of applying biogas residue in the field.