Study On Anaerobic Digestion Of Vegetable Waste

The anaerobic digestion of vegetable waste,which contains high organic matter and water,can reduce the environmental pollution caused by improper disposal of vegetable waste leaves and recover energy to alleviate future resource scarcity.Therefore,it is important to explore the anaerobic digestion process of vegetable waste and its effectiveness.In this paper,the methanogenic potential and characteristics of mixed vegetable wastes were firstly explored by using a batch fermentation unit,then a new CSTR reactor was used to treat mixed vegetable slurry,and finally EGSB and a new AF were used to treat vegetable digestate to investigate the stability,treatment efficiency and resourceful discharge of digestate from anaerobic digestion process for treating vegetable wastes.The findings of this paper are as follows:（1）Four vegetables,cabbage,kale,lettuce and rape,were selected for single and mixed fermentation,and it was concluded that both could achieve normal anaerobic digestion.The best gas production in the single vegetable group was the kale group,with TS and VS gas production rates of 947 m L/g and 1037 m L/g,respectively,and the best gas production in the mixed vegetable group was the E group,with TS and VS gas production rates of 1090 m L/g and 1418 m L/g,respectively.Compared to the mixed vegetable group,which is more suitable for anaerobic digestion engineering applications.Therefore,this paper used the mixed vegetable waste as the fermentation substrate for the next process study.（2）Anaerobic digestion of mixed vegetable wastes was studied using a new CSTR reactor,and the difference in the reactor operation effect became more and more obvious as the HRT was set to 48d,24d,16d,12d and 10d under the condition of continuous feeding.The gas production effect decreased sharply at the HRT of 10d.That is,the best treatment effect was achieved at stage IV with HRT of 12 d.The raw material gas production rate was 23.87 L/g,the TS gas production rate was403.98 L/g,the VS gas production rate was 552.38 L/g,the average methane content was 51.28%,the OLR was 0.90 g COD·L^-1·d^-1on average,the pool volume gas production rate was 0.92 g COD·L^-1·d^-1on average was 0.92 L·L^-1·d^-1,and the average COD removal rate reached 78.00%.（3）The vegetable digestate wastewater obtained from the treatment of mixed vegetable slurry by the new CSTR reactor was further treated by the EGSB reactor with HRTs of 4.4 d,3.2 d,2.5 d and 2.2 d.The best treatment effect was achieved in stage III with an HRT of 2.5 d,i.e.,the mean effluent NH₄⁺-N concentration was 139mg/L,the mean OLR was 1.79 g COD·L^-1·d^-1,the average pool volume gas production rate was 0.26 L·L^-1·d^-1,and the average COD removal rate was 78.16%.（4）A new AF reactor was used to treat the methane wastewater obtained from vegetable methane in an EGSB reactor as the fermentation substrate in two stages with HRT of 1.6 d and 0.9 d.The best treatment effect was achieved in stage II with HRT of 0.9 d.The average OLR was 0.84 g COD·L^-1·d^-1,the average pool volume gas production rate was 0.02 L·L^-1·d^-1,the average value of effluent NH₄⁺-N concentration was 242.73 mg/L,and the average COD removal rate was 72.53%.In summary,the best treatment effect was determined by measuring the indexes during the anaerobic digestion of vegetable wastes with an HRT of 12 d for the new CSTR reactor,2.5 d for the EGSB reactor,and 0.9 d for the new AF reactor.The COD content of vegetable waste was reduced from 15000～2000mg/L to450～300mg/L.Meanwhile,each kilogram of vegetable waste can produce 24L of biogas energy,and the research results can provide technical support for the engineering utilization of anaerobic digestion process of vegetable waste.