Study on the Enhanced Hydrolysis of Kitchen Grease and Promoted Anaerobic Digestion Performance by Lipase

Abstract:

The effect of lipase pretreatment on kitchen grease hydrolysis and its anaerobic digestion performance were studied with batch experiments. Firstly，the influence of enzyme dosage，ratio of water to oil，pH and temperature on the kitchen grease hydrolysis were investigated. Then，the optimized pretreatment condition was determined by response surface analysis. Finally，anaerobic fermentation of the kitchen wastewater with grease were carried out to analyze the impact of lipase pretreatment on the kitche grease digestion. Results showed that the optimized hydrolysis conditions were determined as enzyme dosage 1.15%，ratio of water to oil 0.9，pH 8.0，temperature 42.5 ℃. Under these conditions，the hydrolysis rate was predicted at 86.6% and the repeated experimental result was （88.1±2.2）%，which showed that the response surface model could predict the influence of four factors on the hydrolysis reaction well. For the results from anaerobic fermentation，the cumulative methane yield of the enzyme pretreated kitchen wastewater with grease was the highest with the value of 572.12 mL/g·COD，showed 55.10% and 14.56% increase than the wastewater with grease group（499.47 mL/g·COD） and the actual kitchen wastewater group（368.86 mL/g·COD） respectively. This indicated that grease had high methane production potential，and lipase pretreatment could obviously improve the methanogenesis efficiency. Further investigation demonstrated that enzyme pretreatment had little effect on pH variation，which showed the significant increase in volatile fatty acids（VFAs） and dehydrogenase activity during the early stage of anaerobic digestion. This manifested that pre-hydrolysis could promote substrate supply for the methane production and improve the methane yield efficiency.