Studies On The Pretreatment Of Rice Straw With Sodium Perborate And Performance Of Enzymatic Hydrolysis And Simultaneous Saccharification And Co-fermentation For Ethanol Production At High Loading Of Pretreated Rice Straw

With the rapid consumption of non-renewable energy and the emerging concern on global warming and environment protection,the development of green and environmentally friendly renewable energy is urgent.Rice straw(RS)is one of the most abundant lignocellulosic agricultural waste in the world.RS is mainly composed of three parts: cellulose,hemicellulose,and lignin.Lignin and hemicellulose form a solid binding layer,tightly surrounding cellulose,which hinders the contact between cellulose and cellulase.Therefore,the bioconversion of RS is normally conducted by pretreatment to remove its recalcitrance and enhance the enzymatic accessibility in the first step.Sodium perborate is a green bleach,widely used in medicine and pulp bleaching and other fields.The feasibility of pretreatment of RS with sodium perborate was studied in this paper and the mechanism of pretreatment with sodium perborate was preliminarily explored by Scanning electron microscopy(SEM),X-ray diffraction(XRD),and Fourier transform infrared spectroscopy(FT-IR).The performance of pretreated RS was evaluated by enzymatic hydrolysis and simultaneous saccharification and co-fermentation(SSc F).The effect of cellulase loadings on enzymatic hydrolysis and SSc F under high loading of substrate were studied and a high titer ethanol fermentation process was established.The effects of the concentration of sodium perborate,temperature and time on the pretreatment efficiency were studied,and the optimum pretreatment conditions were 8% sodium perborate at 80 ? for 4 h,leading to a lignin removal rate of 45.8%.The enzymatic hydrolysis efficiency of the pretreated RS reached 84.0% under the condition of 20 FPU/g of cellulase addition.The pretreated RS solid was fermented by SHY 07-1 with 4% substrate loading,leading to a maximum ethanol concentration of 15.3 g/L at 72 h,and the fermentation efficiency reached 92.0%.SEM,XRD and FT-IR characterization showed that the structure of RS was destroyed by sodium perborate and lignin was effectively removed,and the crystallinity was increased from 34.2% of untreated rice straw to 50.9% after pretreatment.The effects of different cellulase loadings(5,10,15,20 FPU/g RS)on enzymatic hydrolysis performance of pretreated RS at 10%(w/v),20%(w/v),and 30%(w/v)substrate concentrations were further investigated.With the increase of substrate concentrations,the concentration of glucose and xylose increased,while the enzymatic hydrolysis efficiency decreased.The cellulase loading significantly affected the concentration of glucose,xylose,and enzymatic hydrolysis efficiency.The concentration of glucose,xylose and enzymatic hydrolysis efficiency increased with the increasing cellulase loading.At a 20 FPU/g of cellulase addition and 30%(w/v)substrate concentration,130.3 g/L glucose and 43.2 g/L xylose were reached by enzymatic hydrolysis,and the enzymatic hydrolysis efficiency is 68.6%.The effect of different substrate concentrations on ethanol production by SSc F under 10%(w/v),20%(w/v)and 30%(w/v)substrate concentration was studied.With the increase of substrate concentration,the ethanol concentration and production efficiency increased while ethanol yield and fermentation efficiency decreased.To reduce cost,the effect of cellulase addition(5,10,15 FPU/g RS)on ethanol production at various substrate concentrations by SSc F was further investigated.With the increase of cellulase addition,the ethanol concentration,production efficiency,ethanol yield and fermentation efficiency increased.With the addition of 15 FPU/g RS cellulase at 30%(w/v)substrate concentration,92.4 g/L ethanol was reached by SSc F with a fermentation efficiency of 74.1%,a ethanol yield of 0.31 g/g and a production efficiency of 0.55 g/L/h.