Breaking Biodegradation Barrier Of Maize Stover By Ozone

The agricultural residues in China are abundant but poorly exploited. Various pretreatment methods were developed to overcome the recalcitrance of biomass and make it possible to utilize crop straws efficiently. In this study, the ozonolysis pretreatment was used to improve the enzymatic hydrolysis of maize stover, provding a new method of biomass pretreatment.Firstly, the effect of sample particle size and the tissue difference of rind and pith on enzymatic hydrolysis was investigated. The result shows that particle size reduction of samples leads to the increase of specific surface area and enhances hydrolysis in a relatively low level. As the mesh of samples increases from 20/40 to 300,the enzymatic reducing sugar yield increases from 2.85% to 9.17%. The acid insoluble lignin(AIL) of rind is about 20%, slightly higher than the AIL of pith, which is about 17%. The enzymatic reducing sugar yield of pith is generally lower than rind, which are about 1.3%~6.0% and 4.7%~7.9%, respectively. These facts indicate that it is hard to significantly improve enzymatic hydrolysis by size reduction and rind and pith seperation.The ozone concentration distribution in the reactor was modelled after theoretical analysis of ozonolysis process. A kinetic model was got based on the curves of consumed ozone concentration. The effect of particle size and moisture on ozonolysis was investigated on this basis. The results of consumed ozone concentration curves, ozone consumption and delignification rate shows that both particle size and moisture have significant effect on ozonolysis, and there is an interation effect between the two factors. Further study revealed that water activity is responsible for the interation effect. It is concluded that the role of water in ozonolysis depends on water state. The sample of 300 mesh(the median diameter is about 75 mm) with the moisture content of 60% was ozonolysed for 90 min to reach the highest delignification rate of 80%. Besides, the strong linearity(R2=0.9679) between ozone consumption and lignin removal amount indicates that ozone mainly acts on lignin degradation.Then, the effect of ozonolysis on stover composition and hydrolysis efficiency was studied. The results show that ozonolysis significantly degrades lignin and partly solublize xylan while hardly affects cellulose. Ozonolysis markedly improves hydrolysis efficiency, and the trend of hydrolysis rate and delignification rate is parallel. Under the optimum condition(300 mesh sample with 60% moisture being ozonolyzed for 90 min), the cellulose hydrolysis rate reaches to 80%,which is 3 times higher than the raw samples(20%). Further analysis shows strong linearity(R2=0.9687) between lignin content and enzymatic reducing sugar yield, which means the lignin degradation is responsible for the improvement of hydrolysis rate. CLSM imaging shows that delignification enhances cellulase adsorption of sample partilces, which also proves the improvement of the enzymatic hydrolysis.Finally, the effect of ozonolysis degradation products on cellulase and fermentation bacteria was studied and the fermentation of ozonolysis sample was primarily evaluated. It is found that the degradation products show no inhibition on cellulase activity while inhibits the fermentation bacteria(Pediococcus acidilactici) to some extent. Overall, ozonolysis still enhances fermentation. Therefore, ozonolysis shows to be a promising pretreatment methods.