Study On Rapid And Harmless Treatment Process Of Vegetable Wastes

Vegetables are a kind of cash crop,the development of China’s vegetable industry is more and more rapid,and with it,a large amount of vegetable waste generated by the distribution chain.Vegetable waste is extremely perishable and will cause serious environmental pollution if not treated in time.The existing vegetable waste treatment process treats it as garbage and treats its pressed water as sewage,which not only causes serious waste of resources and generates additional hazardous waste sludge,but also the process has deficiencies such as high energy consumption,high cost,easy destabilization and low treatment efficiency.In this paper,we propose a new vegetable waste treatment process based on the new method of vegetable waste treatment by coupling thermostatic anaerobic digestion,thermostatic aerobic digestion,and heat pump reheat to address the problems of existing processes and combine the characteristics of vegetable waste.Then,we carried out the experimental study of constant temperature anaerobic digestion and constant temperature aerobic digestion of vegetable waste,and compared the gas production characteristics,anaerobic digestion performance,aerobic digestion performance and treatment capacity with the analysis of harmful substances by conducting anaerobic digestion of vegetable waste with different feed forms and mixture materials,and changing the anaerobic digestion temperature,aerobic digestion temperature and aerobic digestion aeration volume,and combining the material and energy transfer and transformation characteristics of the reaction process.The feasibility and reliability of the new vegetable waste treatment process will be studied to provide theoretical basis and engineering reference for the large-scale treatment of vegetable waste.The main conclusions of this paper are as follows:(1)Different feed forms of vegetable waste had less influence on the gas production characteristics,mainly in terms of daily methane production and methane volume fraction in the late reaction period,while mixed feeds had more influence on the gas production characteristics,mainly in terms of daily gas production and methane volume fraction in the late reaction period.there was no significant difference in daily methane production and cumulative methane production between SW and SW+VW groups,and the peak of methane production occurred on day 14 in both groups.In the early stage of anaerobic digestion,the cumulative methane production in the SW+CS group was smaller than that in the other two groups,and the peak methane production occurred on day 15.The methane volume fraction of SW group,SW+VW group and SW+CS group were in descending order in the early stage of anaerobic digestion,and the methane volume fraction of SW+CS group was significantly lower than the other two groups in the late stage of reaction.After 30 days of anaerobic digestion,the cumulative methane production was from SW+CS group > SW+VW group > SW group in descending order.(2)After 30 days of medium temperature anaerobic digestion,organic matter and energy in the feedstock were gradually transferred to methane by anaerobic bacteria.the solids content and volatile solids content of the SW,SW+VW,and SW+CS groups were significantly reduced,with the VS removal rate in descending order of SW group >SW+VW group > SW+CS group.the SW group had the highest SCOD removal rate of84%,and the SW The highest removal rate of dissolved carbohydrates was 71.5% in the +VW group,indicating that the addition of straw was not conducive to the removal of raw organic matter.The highest ammonia nitrogen levels were 1143.2 mg/L,1076.8mg/L,1168.8 mg/L in the three groups,respectively,and none of them showed ammonia inhibition,and the highest VFAs levels were 4528.3 mg/L,4115.9 mg/L,5698.0 mg/L,respectively,and none of them showed acidification,and all three feedstock combinations were suitable for anaerobic digestion.the SW group,SW + VW group and SW+CS group all showed very strong correlation between the SCOD removal rate and the respective cumulative methane production,which further indicates that the energy in the organic matter was gradually transferred to biogas during anaerobic digestion.(3)During aerobic digestion,the organic matter of the digestate was degraded,and the p H value of all groups showed an increasing trend,and SCOD,ammonia nitrogen,TDS and EC showed a decreasing trend.For 48 h aerobic digestion of vegetable waste press wastewater digestate after 30 days of anaerobic digestion,TDS,EC,SCOD and ammonia nitrogen in the 30℃ group were lower than those in the 20℃group during aerobic digestion,and the organic matter removal rate was higher;the characteristics of aerobically digested digesting digestate changed similarly under 1L/min and 1.5 L/min aeration,and the treatment effect was better than 0.5 L/min.After24 h aerobic digestion,the SCOD content of the 30℃ group can be reduced to below1000 mg/L,with high treatment efficiency.(4)After 30 days of constant temperature anaerobic digestion and 24 hours of constant temperature Aerobic digestion,the SCOD of vegetable waste can be reduced to below 1000 mg/L,and the removal rate is up to 96%.Moreover,no pesticides were detected in the treated biogas slurry,and only mercury and arsenic were detected as heavy metals.The content was much lower than the specified value in the "Agricultural biogas slurry"(GB/T 40750-2021),and the biuret content was much lower than the specified value in the "Limit Requirements for Toxic and Harmful Substances in Fertilizers"(GB 38400-2019),providing a scientific basis for the harmless return of vegetable waste biogas slurry fertilizers to the field.(5)Temperature had a greater influence on the gas production characteristics of vegetable waste.The higher the anaerobic digestion temperature,the earlier the daily gas production and the daily methane production peak appeared,and the greater the gas production.The gas production rate was the highest in the 52℃ group at the beginning of the reaction,which was much higher than the other two groups.The higher the anaerobic digestion temperature,the greater the cumulative gas production and cumulative methane production,and the greater the volume fraction of methane at the beginning of the reaction.As the reaction proceeded,the methane volume fraction of the 52℃ group gradually decreased,while the methane volume fraction of the 37℃group still maintained a high level.26℃ group had lower methane production and methane volume fraction than the other two groups due to lower microbial activity.The anaerobic digestion of vegetable waste was stable at 26℃,37℃ and 52℃,and the cumulative methane yield was 52℃>37℃>26℃ in descending order,and no acidification and ammonia inhibition occurred during anaerobic digestion.The TDS removal rates of aerobic digestion were 30.2%,26.9% and 30.3%,and ammonia removal rates were 81.6%,86.9% and 89.7%,respectively.The total SCOD removal rates were 72.7%,93.9%,and 94.5%,respectively.Innovation and significance of this topic: The effects of different feed forms,mixture and temperature on anaerobic digestion of vegetable waste,and the effects of temperature and aeration on aerobic digestion are revealed,and the material and energy transfer and transformation characteristics of constant temperature anaerobic digestion and constant temperature aerobic digestion of vegetable waste are revealed,and the theoretical basis for the feasibility and reliability of the new vegetable waste treatment process is obtained,which provides theoretical basis and engineering reference for efficient and low-cost treatment and recycling of vegetable waste.