Research On Gas Production Of Enhanced Anaerobic Fermentation Of Kitchen Waste Based On Different Pretreatments

To improve the reduction and resource utilization of kitchen waste,physical and chemical characteristics of kitchen waste in representative areas of Nanjing and their seasonal differences were measured and analyzed in this study.The effects of different control parameters on the sequential batch anaerobic fermentation of kitchen waste were researched.And the effects of different pretreatment methods on organic matter removal rate and gas production efficiency of semi-continuous medium-temperature-wet anaerobic fermentation of kitchen waste were studied.The main research results are as follows:（1）The physical and chemical characteristics of kitchen waste collected from five representative areas in Nanjing were analyzed in spring and autumn.The results showed that the C/N and p H of kitchen waste in Nanjing were lower than other domestic cities,which were 12.3 and 4.2.And the contents of total solid（TS）,protein and fat were higher,which were 23.1%,27.2%and 40.6%.Seasonal changes had significant effect on the organic matter ratio（VS/TS）,protein and oil of kitchen waste.（2）The effects of anaerobic activated sludge inoculation rate,system salt content and kitchen waste oil content on the methane production and organic matter removal rate of sequential batch anaerobic fermentation of kitchen waste were studied.The results showed that the total methane production was the largest when the volatile solid（VS）ratio of sludge and kitchen waste was 2.5:1.The low concentration of salt content had no significant effect on the anaerobic fermentation of kitchen waste,while the system salt content exceeded 0.3%,the methane production by anaerobic fermentation began to be inhibited.There was a positive correlation between 0～1%oil content and methane production and VS removal rate.（3）The effects of semi-continuous medium-temperature-wet anaerobic fermentation on organic matter removal rate and gas production efficiency were studied by using liquid phase kitchen waste（S₁）and solid-liquid mixed phase kitchen waste（S₂）based on solid-liquid-oil separation pretreatment,and solid-liquid mixed phase kitchen waste by thermal-alkaline pretreatment（S₃）.The results showed that under the condition of the organic load of 2.0g VS·（L·d）^-1,semi-continuous medium-temperature-wet anaerobic fermentation of kitchen waste by different pretreatment methods had high methane concentration above 60%and high VS removal rate,with average values of 91.1%,90.6%and 91.0%,respectively.Ammonia nitrogen accumulated faster in the anaerobic fermentation stage of solid-liquid mixed-phase kitchen waste,and the ammonia nitrogen concentration increased by 43.6%after 60 days.The experimental methane potential（EMP）was overall higher during the anaerobic fermentation stage of kitchen waste by thermal-alkaline pretreatment,with an average value of 541.3 m L CH₄·g^-1VS.The EMP value decreased during the anaerobic fermentation stage of solid-liquid mixed phase kitchen waste,with an average value of 479.5m L CH₄·g^-1VS.Liquid phase kitchen waste and kitchen waste by thermal-alkaline pretreatment had higher degree of reduction and resource utilization during anaerobic fermentation.Appropriate pretreatment methods could be selected according to actual engineering conditions.（4）The effect of anaerobic fermentation on microbial community structure of kitchen waste substrate prepared by different pretreatment methods were studied.The results showed that Bacteroidetes,Cloacimonetes and Firmicutes were the most important bacterial categories in the three anaerobic fermentation systems.At the genus level,Methanosarcina and Methanoculleus were the main dominant genera of methanogen-producing archaea in the three anaerobic fermentation systems.In the three anaerobic fermentation systems,when liquid-phase kitchen waste was used as substrates for anaerobic fermentation,Methanoculleus occupied a dominant position in methanogenic archaea.On the contrary,Methanosarcina dominated when solid-liquid mixed-phase kitchen waste was used as substrates for anaerobic fermentation.The differences in the structure of the archaeal community in the above three anaerobic fermentation systems were mainly due to the influence of the ammonia nitrogen concentration.The archaeal community increased the richness and diversity in the low ammonia nitrogen concentration environment,and the succession to the acetic and hydrogenotrophic methanogenesis patterns.In the high ammonia nitrogen concentration environment,Methanosarcina,which had stronger resistance to high ammonia nitrogen concentration,became the dominant genus.