Study On Anaerobic Digestion Of Food Waste:Effects Of Oil And Corresponding Pretreatment

Disposal of municipal solid waste,related to our sustainable development,has received increasing attention in recent years.As an important part of municipal solid waste,food waste is of high organic content and has high recycling value.Anaerobic digestion technology,through microbial action,could convert food waste into clean energy such as methane.Therefore,anaerobic digestion,not only achieves the harmless disposal of food waste,but also realizes the resource utilization of food waste,has broad prospects.Food waste in China has the characteristic of high oil content.On the one hand,the gas production potential of oil is high,on the other hand,oil has a lower hydrolysis rate,which is considered as the rate-limiting stage of anaerobic digestion.In order to improve the gas production characteristics of anaerobic digestion of food waste,in this thesis,lipase pretreatment,surfactant pretreatment,alkali pretreatment and multiple pretreatments were used to promote the hydrolysis of oil and improve the stability of the reaction system.Firstly,anaerobic digestion experiments on food waste of different oil content(0%~7%)were performed,which showed that food waste with high oil content has greater potential for methane production.However,since the degradation of oil is more difficult,the degree of degradation of organic matter after anaerobic digestion is lower.Within the experimental range,with the increase of oil content,the removal rates of TS and VS were reduced by up to 55.6% and 62.0%,while the cycle of anaerobic digestion was extended by up to 5 days.In order to accelerate the hydrolysis of oil,lipase and surfactant pretreatment were performed on the food waste before anaerobic digestion.Lipase has a significant catalytic effect on the hydrolysis of oil,within the experimental range,resulting in the increase of gas production by 31.2% at most.Surfactants could emulsify oil into small droplets and increase the contact area of oil and microorganisms,within the experimental range,resulting in the increase of gas production by 29.1% at most.The results show that the appropriate concentration of lipase and surfactant pretreatment could effectively promote the degradation of organic matter and increase the gas production of anaerobic digestion.However,excessive concentration of lipase and surfactant pretreatment caused the imbalance between the acid production stage and the methanogenesis stage,leading to the acidification in the reaction system,which exerted negative effects on the anaerobic digestion of food waste,resulting in the decrease of gas production by 42.0% at most.The alkaline pretreatment of food waste,on one hand,could promote the dissolution of complex macromolecular organic matter,on the other hand,could regulate the pH of the reaction system,which could effectively prevent acidification during the reaction process and improve the stability of anaerobic digestion.The result shows that alkaline pretreatment could effectively improve the degradation of organic waste and increase the gas production of anaerobic digestion.Compared with the blank group,the gas production of food waste with alkaline pretreatment increased by 13.4%.In order to promote the hydrolysis of oil while ensuring the stability of the reaction system,the effects of multiple pretreatments on anaerobic digestion of food waste were studied.Lipase combined with alkali pretreatment and surfactant combined with alkali pretreatment both got food waste a higher gas production.Within the experimental range,lipase combined with alkali pretreatment increased the gas production of anaerobic digestion by 45.9% and surfactant combined with alkali pretreatment increased the gas production of anaerobic digestion by 37.8%.The results show that multiple pretreatments could further increase the gas production characteristics of anaerobic digestion of food waste.