Study On The Mechanism Of Biochemical Integrated Pretreatment Process Based On Corn Stover For Ethanol Production

In this paper,the research on the integrated process of microbial ensiling and hot-washing pretreatment of dry corn stover（DCS）for ethanol production was carried out.The enzymatic hydrolysis of steam exploded corn stover（ECS）was studied.The effects on cellulase hydrolysis by the enzyme dosage,substrate concentration and reaction time were investigated.The enzymatic hydrolysis process was optimized by response surface method.The optimum enzymolysis conditions were:reaction time56 h,enzyme dosage 15 FPU g^-1cellulose and substrate concentration 10%.Under the conditions,the cellulose hydrolysis rate was reached to 80.56%.The addition of PGE-4000（10 g/L）could promote the enzymatic hydrolysis.The cellulase dosage was reduced to 10 FPUg^-1cellulose,while cellulase hydrolysis rate was up to 82.12%.The influence of different fermentation modes was studied on cellulosic ethanol conversion efficiency.The results showed that the high substrate concentration（30%）fed-batch simultaneous saccharification and fermentation（FD-SSF）was the best way.The ethanol concentration was 59.16 g/L in the fermentation broth（72 h）,while ethanol conversion efficiency was reached to 77.34%.The effects of hot-washing treatment on the structure and properties of ECS（especially lignin）were studied.Hot-washing process had a significant effect on ESC’s physic-mechanical properties.The results of adsorption kinetics and adsorption isotherm showed that hot-washing process could increase the accessibility and affinity of the raw material to the cellulase without removing much of the insoluble lignin.The results of enzymatic hydrolysis showed that the cellulose hydrolysis rate was 85.37%without sulfuric acid or ethanol during hot-washing process.The ethanol concentration was 63.55 g/L in the fermentation broth（56 h）under high substrate concentration（30%）FD-SSF,while ethanol conversion efficiency was reached to83.07%.The advantages and disadvantages of aerobic and anaerobic treatment of DCS were investigated,so as to provide a new way for the pretreatment of DCS.The aerobic and anaerobic microorganisms were selected to study the effects of biological treatment on the structure and composition of DCS.Bacterial diversity and dominant microflora were analysied in microbial storage by high-throughput sequencing.The results showed that the aerobic treatment was able to degrade lignin,while the cellulose loss was 17.58%.After 4 week of anaerobic storage of DCS,the yield of lactic acid and acetic acid was reached to 4.32%and 2.90%,while the value of pH was reduced to 4.22.The cellulose was well preserved.The structure of DCS was loose,which was beneficial to the subsequent enzymatic hydrolysis and fermentation.Lactobacillus was the dominant bacteria with the highest abundance（34.51%）.The effects of the integrated process of microbial storage and hot-washing treatment on the structure and composition of DCS were investigated.The results showed that the ethanol concentration reached to 61.92%（56 h）in fermentation broth by high substrate concentration（30%）FD-SSF,while the ethanol conversion rate was up to 60.15%.Based on the above research,the integrated process of biochemical pretreatment could effectively improve the biodegradability and ethanol conversion of DCS.The study on the change of lignin by hot-washing under glass condensation temperature and the analysis of bacterial diversity in the process of microbial storage provided a theoretical basis for the feasibility of industrialization.