Study On Comprehensive Assessment Of Whole Process For Food Waste Anaerobic Digestion

With the general implementation of waste sorting policies,the scale of food waste collection and transportation in China has grown rapidly.With serious environmental pollution and shortage of energy resources,how to dispose of food waste scientifically,reasonably and efficiently has become an urgent problem to be solved.Anaerobic digestion of food waste can fully realize waste reduction and produce clean fuel gas,which is a mature technology with promising future.However,at present,there are many anaerobic digestion process technical routes of food waste,and the route selection lacks standards.The existing route assessment studies mostly are conducted from a single aspect,or focus on single-case analysis without horizontal comparison.Therefore,from the perspectives of environmental impact potential and techno-economics,the comprehensive and quantitative evaluation of whole process of food waste anaerobic digestion and the key stages-biogas utilization and digestate disposal were carried out in this article,to provide references for environmental management,decision-making planning,and technology improvement for different stakeholders involved in the food waste treatment project.Firstly,taking a 150 t/d food waste disposal project in Zhejiang Province as a case,the environmental impact assessment and techno-economic evaluation of the whole process of anaerobic digestion of food waste are carried out.The evaluation results show that the process shows strong energy saving and emission reduction effects.After anaerobic digestion,1 ton of food waste can reduce 91 kg CO₂ equivalent GHG emissions and reduce 1206 MJ of energy consumption.Due to the high energy consumption and high sewage discharge in the treatment process,the overall process would cause eutrophication effect.The biogas utilization process is the core to realize the environmental benefits of the overall process,and its contribution to mitigating climate warming and reducing fossil energy consumption accounts for 95.5%and 89.65%respectively.The digestate disposal process contributes mostly to toxicity effect and its contribution to human toxic effects and freshwater aquatic eco-toxic effects accounts for 91.5%and 98.2%respectively.The 150 t/d food waste anaerobic digestion treatment project is financially feasible,but the payback period is long,and the economics of the project are easily affected by the actual treatment scale.When the processing scale drops by 10%,the NPV of the project drops by 83.5%Therefore,ensuring that the processing scale increases is the key to maintaining the economics of the project.The income from the sales of electricity only accounts for 4.24%of the overall income.When the electricity price drops by 10%,the NPV of the project only drops by 4.55%,which has little impact on the overall economy of the project.On the basis of analysis for whole process,three biogas utilization technical routes（internal combustion engine cogeneration,micro gas turbine cogeneration and purification as vehicle gas）were evaluated.The results show that the internal combustion engine obtains the best environmental and economic benefits by virtue of its higher combined heat and power efficiency.The centralized utilization of biogas is more environmentally friendly than the decentralized use of biogas after purification.When the price of purified is 3 CNY/Nm³,the economic efficiency of the purification unit that processes 2.7 million Nm³ of biogas per year is comparable to that of the internal combustion engine cogeneration unit project.Subsequently,the three digestate disposal technical routes（landfill,incineration and composting）were evaluated,and the results showed that although composting disposal performed best in all types of environmental impacts other than toxic effects,the overall environmental benefits were the worst.Incineration of digestate with high moisture content has poor environmental benefits due to higher energy consumption.When the price of digestate fertilizer reaches 250 CNY/t,the economy of digestate composting is much better than landfill or incineration.When the price of digestate fertilizer drops to 61 CNY/t,it no longer has economic advantages.