Characteristics And Aerobic Composting Of Anaerobic Digestion Residues Of Food Waste In Lhasa

Food waste is one of the most important municipal solid waste,and it is also one of the most important categories to be collected separately.With the rapid development of Lhasa’s economy and the continuous increase of the urban population,the daily output of food waste in the urban area of Lhasa has risen sharply.The daily 2023 has reached 130 tons per day,a food waste treatment plant based on anaerobic digestion and biogas production has been built and put into operation in Lhasa.At present,about10% to 15% of food waste from the factory is disposed of by a three-phase separator and sent to a nearby landfill site for disposal,the annual amount of residue that can not be fully utilized reach 5000 ～ 7000 tons.It is an important step to realize the efficient utilization of food waste in the whole process of food waste classification,therefore it is of great significance to study the composting of the anaerobic digestion residues of food waste in Lhasa.In this paper,the residue of anaerobic digestion of food waste was used as the main raw material,and the characteristics of the residue were analyzed to determine the potential of resource utilization.In the process of aerobic composting,four factors and three levels orthogonal experiment were designed to analyze the influence of the initial C/N,the initial moisture content,the amount of microbial agent and the times of composting on the composting of food residue,according to the orthogonal test range analysis and compost maturity evaluation to determine the food residue aerobic composting process parameters.Finally,the compost efficiency,economic and environmental benefits were evaluated.The main findings of the study are as follows:1.Characteristics and utilization potential of anaerobic digestion residue of food wasteBased on the analysis of physical and chemical characteristics of food waste produced during anaerobic digestion,the results showed that the organic matter content of food residue was up to 89.59%,and it was rich in nitrogen,phosphorus and potassium,and the total nutrient content was6.58%,it is more suitable for soil utilization and can enhance soil fertility and improve soil environment than the requirement of organic matter content more than 30% and total nutrient content more than 4% in organic fertilizer.Considering the low maturity of residue,the germination index of seed is only 33%,which is not enough to be applied as organic fertilizer directly.According to the demand of resource utilization,more utilization can be realized by aerobic composting technology.2.Determination of process parameters and maturity evaluation of aerobic composting of food waste anaerobic digestion residueThe range analysis of the orthogonal test is based on the total number of days when the pile temperature exceeds 55 °C and the final seed germination index of the pile,the optimum combination of the basic process conditions of aerobic composting of anaerobic digestion residue of kitchen waste is C/N 25,the moisture content is 55%,the content of microbial agent is 1.5%,and the composting time is once a day;and the influence degree of each factor was C/N > moisture content > microbial agent content > turn-over number.Based on the analysis of the changes of the maturity indexes of each group,the authors concluded that the rapid maturity indexes suitable for aerobic composting of anaerobic digestion residue of food waste were as follows: the temperature of compost should be maintained at high temperature(> 55 ° C)for more than 5 days;p H ranged from 5.5 to 6.17,electrical conductivity from 3.02 to 3.94 m S/cm,and germination index > 85%.3.Evaluation of aerobic composting of anaerobic digestion residue of food wasteThe composting products can basically meet the basic requirements of fertilizer by comparing the composting efficiency before and after aerobic composting.Through the analysis of economic benefit,when the price of organic fertilizer is more than about 200 yuan per ton,the economic benefit of producing 1 ton fertilizer is more than zero.According to the analysis of environmental benefit,the environmental impact load of the whole process of composting food waste is 5.54.The degree of environmental benefit was eutrophication > ecotoxicity > photochemical smog pollution > environmental acidification > global warming,and the negative effect of eutrophication on environmental benefit mainly came from ammonia emission.Therefore,strengthening the management and control of emission gases can achieve the best combination of environmental benefits,economic benefits and ecological benefits.