Study On Pretreatment And Different Saccharification Processes Of Rice Straw

Lignocellulose,which is mainly comprised of cellulose,hemicellulase,and lignin,is an important part of plants.Cellulose is a polymer of glucose,accounts for nearly 50%of the total proportion of plants.It is of great potential value.However,cellulose,as a skeletal tissue of plants,has a strong anti-degradation barrier.It is difficult for animals and microbes to efficiently release its huge mass.In this study,the rice straw with typical wood fiber structure was used as the material for research.The pretreatment technology of lignocellulose at medium temperature and atmospheric pressure and saccharification process of rice straw were investigated.The main results are as follows:Combined with the existing related research and the future trend of pretreatment,the target idea of pretreatment without reducing biomass particle size at medium temperature and atmospheric pressure was determined.Through the experiment,it was found that NaOH can effectively break the structure of rice and is more conducive to enzymatic hydrolysis and saccharification of cellulase.Through single factor and response surface experiments,a better pretreatment process was obtained:rice straw was placed in a 1.3%（w/v）concentration of NaOH solution,50℃for 30 h,then washed to neutral for further use.Meanwhile,the pretreatment of rice straw was analyzed by scanning electron microscope,infrared spectrum analysis and microbial culture experiment.All the results showed that pretreatment changed some key structures of rice straw.The pretreated rice straw could be hydrolyzed by cellulase and assimilated by microorganisms.Compared with the ability of enzyme production and the degradation ability of rice straw,Trichoderma richter was chosed for further saccharifying research.Through response surface optimization,the optimized cellulase producing medium,which using rice straw as the carbon source was obtained:rice straw 15 g,（NH₄）₂SO₄2 g,KH₂PO₄3 g,Mg SO₄·7H₂O 0.5 g,Tween-80 0.5 mL,FeSO₄·7H₂O 0.005 g,trace element solution 10 mL,H₂O 1000 mL.The FPA enzyme activity increased from 0.401 IU/mL to 0.612 IU/mL,increased by 52.6%.The optimized fermentation condition was 29℃,the initial pH 6,inoculum volume 5%,speed 150rmp for 8 d,and the enzyme activity was 1.121 IU/mL,increased by 83.2%.The crude enzyme hydrolysate produced by fermentation was used to the pretreated rice straw for hydrolysate and saccharification,and the specific sugar yield was 0.160-0.190 g/g.The results showed that there were differences between the optimal fermentation conditions and enzymatic hydrolysis conditions of Trichoderma reesei,which could be integrated by in-situ enzymatic hydrolysis to further improve the saccharification rate of rice straw.In liquid fermentation,in-situ enzymatic saccharification process was explored and optimized,and a better technological condition was obtained:30 g rice straw stalk per liter fermentation broth;The fermentation condition was:30℃,initial pH 6.5,48h,the enzymolysis conditions was:pH4.8,50℃for 24 h,and final sugar yield was 0.350 g/g.Based on the deficiency of low liquid loading of rice straw in liquid in-situ enzymatic saccharification process,a solid-state in situ enzymatic saccharification process was developed.The ratio of straw flour and wheat bran was 4:1,moisture content 60%,water initial pH 5.0,28℃for 48 h,enzymatic hydrolysis water pH 5.0,50℃for 24 h,enzymolysis water 10-50 mL（every 15g fermentation substance）.The final yield is between 0.320-0.360 g/g.The three saccharifying methods of direct saccharification of crude enzyme,in situ enzymatic saccharification and solid-state enzymatic saccharification were compared.It was found that crude sugar was first used for direct saccharification,and its yield was 0.160-0.196g/g,and the specific sugar yield of liquid in situ enzymatic saccharification was 0.320-0.350 g/g.The specific sugar yield of solid-phase in-situ enzymatic saccharification process is 0.320-0.360g/g.Due to the short fermentation time of in situ enzymatic hydrolysis process,adding a small amount of crude enzyme solution on this basis further enhanced the saccharification rate and increased the yield of sugar to 0.400-0.420 g/g.