Study On Characteristics Of "Alkali Pretreatment+Bentonite" Enhancing Methane Production Of Kitchen Waste

Kitchen waste contains a large amount of biodegradable organic substances with high water content and oil content.Without proper treatment and disposal,it might cause many problems in environmental protection and treatment.Anaerobic digestion is an effective method to treat kitchen waste.It can not only degrade the biodegradable organic components in kitchen waste,but also produce renewable energy methane.However,kitchen waste is mainly composed of biodegradable carbohydrates and proteins,which is easy to cause acidification,resulting in a long lag period and low methane production in the anaerobic digestion process.Therefore,how to strengthen the performance of the anaerobic digestion system for kitchen waste is the key issue of research.Some studies have found that pretreatment and additives can effectively improve anaerobic digestion performance.However,the strategy of alkali pretreatment and bentonite addition（AP/Be）treatment to improve the anaerobic digestion of kitchen waste has not been explored.Based on this,this study was carried out from the following three aspects:（1）The effect of alkali pretreatment time（12,24,36,48 and 60h）on anaerobic digestion performance of kitchen waste was studied,and the effect of AP/Be reatment on microbial community was discussed.The results showed that AP/Be treatment could effectively improve the methane yield of anaerobic digestion,and had a significant impact on the microbial community structure of the kitchen waste anaerobic digestion.The methane yield of R₁₂,R₂₄,R₃₆,R₄₈ and R₆₀in the AP/Be treatment group was 109.3,145.3,149.7,121.8 and 101.2 m L CH₄/g VS respectively,while the R_C was only 34.8 m L CH₄/g VS.Compared with the control group,the methane yield of the treatment group increased by 214.2%,317.5%,330.0%,250.0%and 192.9%respectively.Alkaline pretreatment for kitchen waste was conducive to accelerating hydrolysis and acid production process.Meanwhile,AP/Be treatment enhanced acetoclastic methanogenic pathway and hydrogenotrophic methanogenic pathway,and improving the anaerobic digestion methane yield.Considering the methane yield and alkali pretreatment time of each group,the"alkali pretreatment time（24h）"condition was optimized.（2）On the basis of the research content,the effect of AP/Be treatment on the anaerobic digestion and methanogenic performance of kitchen waste with different total solid（TS）content（10%,13%,19%,22%and 25%）was further studied,and further analyze the change of microbial community to reveal the impact of AP/Be treatment on the methanogenic pathway of kitchen waste anaerobic digestion.The methane yield in the control group was only 59 m L CH₄/g VS,while after AP/Be treatment,the methane yield increased to 198 m L CH₄/g VS,an increase of 236%.In addition,the microbial community analysis showed that the AP/Be treatment enriched the diversity of bacterial community.At TS of 10%,AP/Be treatment significantly promoted the relative abundance of hydrogenotrophic methanogens.Under different TS content conditions,the main methanogenic pathway was different.At TS of 13%,19%,and 22%,hydrogenotrophic methanogenic pathway and acetoclastic methanogenic pathway were dominant.TS further increased to 25%,acetoclastic methanogenic pathway were dominant.（3）Based on the results of batch experience,the long-term continuous test of kitchen waste anaerobic digestion was conducted with different organic loading rate（OLR）（42,38,27 and22d）.At OLR of 3.11 and 4.04 g VS/L/d,the methane yield of the control group was 244.52and 226.82 m L/g VS,while that of the AP/Be group was 570.34 and 594.54 m L/g,which increased by 133%and 162%.The study showed that AP/Be treatment was helpful to enhance the performance and stability of kitchen waste anaerobic digestion.In addition,at OLR of 5.25g VS/L/d,the gas production of two group reactors sharply decreased.At OLR of 6.82 g VS/L/d,the gas production was completely stopped of two group reactors,resulting in the collapse of the anaerobic digestion system due to system instability.The above results indicated that appropriately increasing the OLR was beneficial to improving methane production.However,if the OLR was too high,the semi continuous system for kitchen waste anaerobic digestion is prone to acidification,leading to reaction failure.In summary,experimental studies showed that AP/Be treatment can significantly enhance the performance of kitchen waste anaerobic digestion,and was beneficial to optimizing the microbial community structure of the system.The strengthening mechanism of AP/Be treatment improving the anaerobic digestion of kitchen waste:AP/Be treatment can promote the hydrolysis of anaerobic digestion and enhance the biodegradability of food waste.In addition,AP/Be treatment help maintain the anaerobic digestion of kitchen waste in the pH range suitable for methanogenesis,as well as help to alleviate the inhibitory effect caused by VFAs accumulation inhibition.In addition,the microbial community analysis showed that the AP/Be treatment was beneficial to enrich the diversity of f bacterial community.It significantly affected the structure of archaeal community in the anaerobic digestion of kitchen waste,and promoted the hydrogentrophic methanogenic pathway.