Effect Of Cellulase Addition On Anaerobic Digestion Of Corn Stovers

The total annual production of stovers is about 7.4×108ton in China, most of which are idle or burned. Using stovers as raw material for methane production is the most commonly used and effective treatment method, it is conducive to coordinated development of environment, ecology and resources. Hydrolysis acidification become the main rate limiting step in the process of anaerobic digestion due to the complex structure of lignocellulose, which would influence subsequent acidogenesis and methanogenesis. The effects of adding cellulase and bovine serum albumin to improve the hydrolysis reaction, increasing the gas production of anaerobic digestion process were investigated.With corn stovers as raw material, this study studied the effects of adding cellulase and bovine serum albumin directly to the system of anaerobic digestion, and the effects of cellulase and bovine serum albumin as a pre-treatment to the corn stovers during hydrolysis and anaerobic digestion. By examining the changes of material and gas production in the anaerobic digestion process, the relationship of gas production and glucose yields before and after pretreatment were studied, the mechanism and effects of cellulase and bovine serum albumin were also analyzed. The main conclusions of this study are as follows:Cellulase was added to the anaerobic system on the 1st,10th, and 20th d, respectively. The cumulative biogas production with cellulase addition increased by 18.66%,10.39% and 1.93%, respectively. Experimental results show that addition of cellulase at different times could promote anaerobic reaction, but adding cellulase in the beginning was more apparent. Adding cellulase effectively improved biomass hydrolysis during fermentation process, but showed weaker improvement on subsequent acidogenesis and methanogenesis. When adding bovine serum albumin and cellulase to anaerobic digestion system in the beginning, we found that the cumulative gas production increased by 8%, compared with the reaction system only adding cellulose. But the impact on the hydrolysis and acidification was more remarkable.During the study of enzyme pretreatment of corn stovers by cellulase, the effects of enzyme dosage, pretreatment time and substrate concentration were studied as the investigation index. The optimum conditions for the enzymatic pretreatment were enzyme dosage of 30 FPU/g, the pretreatment time 24 h, substrate concentration of 60 g/L. In this pretreatment conditions, the cumulative gas production reached 249.01 ml/g VS, the highest gas production rate was up to 23.77 ml/g VS·d. Compared with no enzymatic pretreatment group, the gas production peak appeared ahead of 3 d, the cumulative gas production increased by 36.9%. The bovine serum albumin as an assistant for the cellulose to pretreat corn stovers, and the results showed that bovine serum albumin could obviously improve the reducing sugar production after hydrolysis, when bovine serum albumin dosage was 0.08 g/g, reducing sugar production increased by 31.3%. Through the anaerobic digestion experiments of pretreated samples, we found that it had no effect on the accumulative gas production. This showed that the bovine serum albumin in the anaerobic digestion process only affected the enzyme activity during the hydrolysis phase, but no effect on enzyme activity of the subsequent acid production and methane production.