Study On The Effect Of Main Organic Components Of Kitchen Waste On The Production Of Volatile Fatty Acids

The annual production of kitchen waste in China is high,and improper treatment can cause serious environmental pollution.Kitchen waste is mainly composed of carbohydrates,proteins and lipids,and contains high organic matter,which is an ideal raw material for anaerobic fermentation to produce volatile fatty acids(VFAs).Under the influence of food supply,seasonal changes and dietary habits,the composition of kitchen waste is complex and variable,which will affect the acid production performance of anaerobic fermentation.However,there are few studies on the effect of the main organic composition of kitchen waste on the acid production performance of anaerobic fermentation.The purpose of this study is to clarify the effects of different organic components in kitchen waste on the concentration and composition of VFAs,improve the VFAs production performance of anaerobic fermentation,and realize the resource utilization of kitchen waste.The main research contents and results are as follows:Firstly,rice,chicken breast and fatty pork were used as representatives to simulate the components of carbohydrates,proteins and lipids in kitchen waste to produce VFAs from single component anaerobic fermentation.The response surface method was used to study the effects of different mixing ratios of the three representative components on the VFAs production of anaerobic fermentation.The results showed that proteins produced the maximum VFAs concentration,up to 21305 mg/L.Acetic and butyric acid,acetic acid,acetic and propionic acid were the main components of VFAs produced by carbohydrates,proteins and lipids,respectively.The maximum VFAs concentration reached 12247 mg/L when the three representative components were mixed.Response surface analysis showed that high carbohydrate and protein content was beneficial to VFAs formation.Acetic and butyric acid were the dominant VFAs produced in all groups,and the high carbohydrate content favored the synthesis of butyric acid.Secondly,the effects of process conditions and organic composition on the VFAs production performance of simulated kitchen waste anaerobic fermentation were studied by adjusting p H and increasing organic loading.The results showed that the highest VFAs concentrations were 13884,18605 and 13897 mg/L when the organic loading was 30 g VS/L and p H was 5.0,7.0and 9.0,respectively.According to the response surface analysis,when p H was 5.0,increasing carbohydrate content could promote VFAs formation,but the change of protein content had little effect.When p H was 7.0 and 9.0,high carbohydrate and protein contents were beneficial to VFAs formation.When p H was 5.0,the proportion of butyric acid was higher than that of acetic acid.When p H increased to 7.0 and 9.0,the proportion of acetic acid increased and the proportion of butyric acid decreased.The increase of p H may change the metabolic pathway of organic components,making the proportion of acetic acid gradually higher than butyric acid.When organic loading was increased to 60 g VS/L,VFAs concentration could be significantly increased to 29196mg/L,which was 56.9% higher than that under 30 g VS/L.Finally,using real kitchen waste as substrate,under the condition of organic loading of 60 g VS/L and p H 7.0,the effects on the VFAs production of kitchen waste anaerobic fermentation under different ultrasonic combined enzyme pretreatment conditions were studied.The results showed that the pretreatment conditions of ultrasonic for 10 min combined with 7 U/g amylase could increase the VFAs concentration and have less enzyme consumption.The VFAs concentration was increased by 30.9%,23.0%,and 34.0%compared with the unpretreated group,only ultrasonic for 10 min pretreatment group,and only 7 U/g amylase pretreatment group.In the study of ultrasonic combined with protease pretreatment,32 U/g protease pretreatment was the best condition,and the VFAs concentration was 31.0% higher than that of the unpretreated group.In the study of ultrasonic combined with lipase pretreatment,the pretreatment effect of ultrasonic for 5 min was better,and the VFAs concentration was 17.8% higher than that of the unpretreated group.The increase of lipase dosage did not significantly increase the VFAs concentration.The VFAs concentration in the group of ultrasonic for 10 min combined with three enzymes pretreatment was 69.8%,59.5% and 40.8%higher than that in the group of unpretreated,only ultrasonic for 10 min pretreatment and only three enzymes pretreatment,respectively.Ultrasonic for10 min combined with three enzymes pretreatment can further improve the VFAs concentration of kitchen waste.In this study,the effects of the mixing ratios of organic components in kitchen waste on the VFAs production of anaerobic fermentation were clarified,and the VFAs production performance of kitchen waste was improved through parameter adjustment and pretreatment,which contributed to deepening the understanding of the regularity of VFAs production of kitchen waste anaerobic fermentation,and provided a theoretical reference for realizing the resource-based transformation and high-value utilization of kitchen waste.