Study On The Food Waste Produces Bio-enzyme Which Promotes The Anaerobic Digestion Of Sludge

Anaerobic digestion is one of the treatment and disposal methods widely used for excess sludge,which can reduce and recycle solid waste.The excess sludge contains a large amount of macromolecular substances which are difficult to degrade,it limits the hydrolysis rate of anaerobic digestion.Therefore,excess sludge pretreatment is necessary to improve anaerobic digestion efficiency.The biological pretreatment method is simple in operation and has no secondary pollution,but the high price of the biological enzyme preparation limits its large-scale application.Therefore,there is an urgent need to develop a biological enzyme preparation with low economic cost and high energy treatment efficiency for pretreatment of excess sludge.Aspergillus oryzae is a fungus with high yield of protease and amylase.food waste is a cheap medium for Aspergillus oryzae because it is rich in organic matter such as protein and starch.In this paper,bio-enzyme was produced by using food waste as a medium for Aspergillus oryzae,which was used for biological pretreatment of excess sludge,and its effect on anaerobic digestion of sludge was studied.The main findings are as follows:?1?The condition optimization experiment of the culture of Aspergillus oryzae in the food waste showed that the Aspergillus oryzae was inoculated to the non-inactivated kitchen waste for solid-state fermentation,and the optimal culture time and optimum fermentation pH of the protease production were 84 h and 7.5,respectively.The optimum agitation speed of protease and amylase was 2 r·min^-1,and the optimum Ca²⁺concentration of protease production was 8.00 mmol·L^-1.The protease and amylase activities were produced at this time.They were 5641.13±276.58 U·g^-11 and 3141.36±389.55 mg·?mL·min?^-1,respectively.The content of protease and amylase in Aspergillus oryzae is 55%of its optimum fermentation medium?pig blood medium?,and its bio-enzyme production can be used as a biological pretreatment enzyme for excess sludge?hereinafter referred to as its For the"enzyme-enriched food waste"?.?2?The effect of the enzyme-enriched food waste on the pretreated sludge is directly proportional to the amount of the enzyme-enriched food waste.Using 30 g enzyme-enriched food waste to pre-treat the sludge,the VFAs and sCOD contents reached 4.60±0.25 g·L-1 and47.72±1.01 g·L^-1,respectively.The dissolved organic matter increased with the increase of pretreatment time of enzyme-enriched food waste.The content of VFAs was higher at 0¹2 h,and it could reach 7.62±0.04 g·L^-11 at 12 h.Moreover,the enzyme-enriched food waste pre-treatment sludge can produce flocculation and deflocculation in the sludge system,,the particle size gradually decreases in the mixed system while the pretreatment time increases.The results of anaerobic digestion showed that the cumulative methane production increased with the addition of enzyme-enriched food waste,and the methane yield of the pretreated sludge using 30 genzyme-enriched food waste reached 180.43±2.37 mL·?gVS?^-1.Pretreatment of sludge with enzyme-enriched food waste can improve the biodegradability of the system;reduce the viscosity of extracellular polymer?EPS?in the mixed system;accelerate the rupture of sludge microbial cell wall;accelerate the degradation of macromolecular proteins and starch,forming small molecules of amino acids and monosaccharides;thereby achieving the effect of pretreatment.?3?The anaerobic co-digestion of the enzyme-enriched food waste with the excess sludge can promote the methanogenesis process and increase the methane content.Cumulative methane production and average methane content were 308.46±19.47 mL·?gVS?^-1and 65.87%,respectively,and methane production increased by 31.91%.The modified Gompertz model can well fit the kinetics of anaerobic co-digestion and methanogenesis of enzyme-enriched food waste and excess sludge.The fitting coefficient R² of the model reaches 0.992.By steadily increasing the organic loading rate of the reaction system,the semi-continuous anaerobic digestion reaction of the enzyme-enriched food waste and excess sludge was achieved,and the OLR in the reaction system was increased to 43.82 g·?L·d?^-1,and the daily methane production was up to 1 L·d^-1.The protease and amylase activities also increased with the continuous operation of the reactor,and finally stabilized at 270.53 U·g^-1and 563.55 mg·?mL·min?^-1.