Saccharification Of Food Waste And Potential Investigation On Bioethanol And Biobutanol Fermentation

Severe environmental pollution and loss of resource will occur if food waste is not treated timely and effectively,because a large quantity of food waste is discharged annually.Food waste,which is rich in starch,protein,grease and other organic matters,exhibits great potential for biofuel production.However,it is not easy for the macromolecular materials to be degraded by microorganisms.In this study,starch of food waste was hydrolyzed by enzymatic method,and the changes of physicochemical characteristics of hydrolysates were studied to explore the mechanism of enzymatic hydrolysis.In addition,the hydrolysate was applied for bioethanol and biobutanol fermentation to the fermentation of bioethanol and biobutanol.Enzymatic hydrolysis was determined to be the optimum method for the saccharification of food waste than others.The optimal pH and the amount of enzyme dosage corresponding to alphaamylase and glucoamylase were 5.5,150 U/g-TS(Total Solid)and 4.0,150 U/g-TS,respectively.The results showed that the combined enzymatic hydrolysis of alpha-amylase and glucoamylase was superior to single enzyme,and the corresponding maximum sugar concentration was 204.20 g/L.Further study showed that the main component of reducing sugar in hydrolysate was glucose.The results of X-ray diffraction(XRD)and Fourier Transform infrared spectroscopy(FT-IR)showed that the enzymatic hydrolysis did not change the crystal type of starch,yet it improved the relative crystallinity and short-range order degree of starch.The integrity was broken with more fragmented pieces and looser structure,and average particle size of combined enzymatic hydrolysis was 41.23% lower than that of control,as revealed by Scanning electron microscope(SEM)and particle size distribution.The decrease of solid particle size resulted in the significant decrease of hydrolysate viscosity,which was beneficial to the improvement of mass transfer and heat transfer efficiency in the downstream fermentation process.Ethanol production from hydrolysate of food waste was studied.Results indicated that the ethanol production increased with the sugar concentration.The ethanol production and glucose conversion rate reached 69 g/L and 93%,with the optimal glucose concentration of 200 g/L.With addition of 0.5% tween-80,the ethanol production,productivity and glucose conversion rate were 79 g/L,3.57 g/L/h and 94.58%,respectively,which were 14.5%,42.8% and 1.7% higher than those of the control.The content of extracellular polysaccharide,conductivity of bacterial suspension and macromolecular spillage with addition of tween-80 increased by 25.95%,4.05% and 31.3%,respectively.These results indicated that tween-80 could significantly increase the permeability of cell membrane and accelerate the exchange of nutrients between the inner and outer membrane,which was the main reason for the increase of ethanol production.Further research of butanol production from food waste was conducted.The butanol and total solvent production with fermentation time of 60 h were 12.10 and 20.68 g/L,respectively,which were the maximum value in this study.Although acid crash can be avoided at low temperature of 25°C,it was not feasible for butanol fermentation to be conducted at such a temperature due to the low efficiency of fermentation.The utilization of substrate could be promoted up to 90% with 1 g/L yeast extract.The transition from acidogenic phase to solventogenic phase could be accelerated because of sodium butyrate.