Study On The Process Optimization Of Enzymatic Separation Recovery Of Carbon Source And Nitrogen Source From Food Waste And Its Residue Utilization

Food waste has the dual properties of pollution and resource.With the gradual improvement of garbage classification and food waste collection,the final disposal for minimization,decontamination and reutilization is very important.After sorting,impurity removal and three-phase separation,the organic components in the solid residue of food waste mainly include starch,protein and cellulose.Starch and protein are organic carbon and nitrogen sources with excellent bioconvertibility,thus their separation recovery is very pivotal for fine utilization of food waste.However,ultrasonic,hydrothermal and microwave methods are difficult to achieve the directional separation of organic components from food waste.Hence,in order to efficiently recycle carbon and nitrogen sources,this paper studied the performance of enzymatic extraction process on the separation treatment of food waste.On this basis,the breeding technology of Hermetia illucens was further used to treat the residue from the enzymatic treatment,achieving the sufficient consumption of food waste.The research results of this paper can provide useful ideas for the high-value utilization of food waste.The main results are as follows:(1)By amylase hydrolysis and isoelectric precipitation methods,the carbon source could be efficiently recycled from food-waste solid residue.Compared with single amylase treatment,the co-treatment of α-amylase and γ-amylase improved the extraction of carbon source and could reduce the enzyme amount used.Enzymatic temperature,p H and substrate mass concentration were key factors affecting the synergistic effect of the two amylases.The order of influences on the extraction efficiency of carbon source was substrate mass concentration > temperature > p H,and there was a significant interaction effect between substrate mass concentration and temperature.The optimal conditions for carbon source extraction were 57.0 ℃,p H 6.2,substrate mass concentration 190 g/L,enzyme mass fraction added 0.6%,enzyme mass ratio 3:1(α/γ),where the extraction efficiency of carbon source reached 76.9%.By isoelectric precipitation,the finally biochemical oxygen demand(BOD)concentration and BOD/N ratio in the recovered solution of carbon source reached76.8 g/L and 51.2,respectively.(2)Compared with alkaline and neutral proteases,acid protease was more favorable to the extraction of nitrogen source from food-waste solid residue.By direct enzymatic hydrolysis of acid protease,the extraction efficiency of nitrogen source and dissolved organic nitrogen concentration in extracting solution were respectively 44.8% and 5.9 g/L.By gradient amylase-protease hydrolysis,they were respectively increased to 62.7% and 7.4g/L.In addition,the concentration of soluble total sugar in the direct enzymatic extracting solution was 26.8 g/L,while that in the gradient enzymatic extracting solution was only 8.1g/L,decreasing by about 69.8%.After gradient enzymatic hydrolysis,the dissolution efficiency of starch and protein respectively reached 77.1% and 89.9%,and the reduction of solid organic matter reached 59.7%.The above results indicated that,compared with direct protease hydrolysis,gradient hydrolysis process of amylase-protease could further improve the extraction amount and purity of nitrogen source by effective pre-separation of carbon source,which had better separation and reduction performance.In the extracting solution of nitrogen source,small peptides and polypeptides with molecular weight less than 10000 accounted for 94.3%,while macromolecular proteins accounted for only 5.7%.The enzymatic hydrolysis kinetics analysis found that the critical protease concentration of gradient hydrolysis was 35.9% lower than that of direct hydrolysis,indicating the enzymatic hydrolysis of protein in food-waste solid residue was more likely to occur after starch separation.(3)The breeding technology of Hermetia illucens was used to further consume the residues after enzymatic separation treatment.The optimal inoculation ratio was selected as1500 larvae/kg-residue,based on the comprehensive consideration of growth index and organic matter transformation.At the optimal breeding condition,the average larval weight,survival rate and larval duration were 121 mg/larvae,96.8% and 288 h,respectively.The degradation and conversion efficiency of residues were respectively 63.0% and 40.6%.By the combined process of enzymatic separation and Hermetia illucens transformation,the total reduction efficiency of organic matter in food-waste solid residue reached 85.1%.The protein and fat contents of Hermetia illucens larvae were respectively 43.0% and 38.7%.The remaining insect sand after Hermetia illucens transformation achieved the application requirements of organic fertilizer,thus realizing sufficient utilization.The 16 S r RNA sequencing and microbial metabolic pathway prediction(PICRUSt)indicated that the gut microbiota of Hermetia illucens played an important role in the transformation of residue organic matter.