The Saccharification Of Cellulose And Starch In Cassava Dregs For Butanol Fermentation

Due to the shortage of fuels and worsening greenhouse effect, the butanol fermentationindustry has flourished. The cassava dregs is the solid waste which is obtained by thecassava starch production or starch processing, the advantages of which are relatively highstarch and cellulose content, high output and low cost. It has been proved that it is feasibleand practical to produce butanol by using cassava dregs. This paper focused on the hydrolysisprocess of cassava dregs degraded by α-amylase, glucoamylase and cellulose and butanolfermentation course of hydrolysate decomposed by clostridium acetobutylicum.An analysis of process variables including enzyme laod，substrate concentration，enzymecombination, ways of enzyme addition effect to the hydrolysis process of cassava dregs byenzyme was carried out. When cassava dregs were separately hydrolyzed by α-amylase,glucoamylase and cellulose, of which the optimal enzyme loads were2500U/g starch，2000U/g starch，120U/g cellulose, respectively. When the hydrolysis was conducted byα-amylase and glucoamylase, of which the optimal enzyme loads were2500U/g starch，3000U/g starch, and the enzyme loads were also suitable for the situation of three enzymes.The glucose concentration in hydrolysate increased and the hydrolysis efficiency decreased,with the substrate concentration increasing. When the substrate concentration was12%, theglucose concentration of one step cassava dregs hydrolysis by three enzymes was81.3g/L,while the hydrolysis efficiency was less than50%. The glucose concentrations of hydrolysategenerated by single, two, three enzymes were sequentially increased. Two-step hydrolysis bythree enzymes could raise hydrolysis efficiency of cassava dregs, of which the preponderancewas avoiding the lag phase of two enzyme hydrolysis, solving the problem ofenzyme inactivation. Shearing action of homogenizer contributed to the increasing of glucoseconcentration hydrolysate which is up to121.5g/L.The procedure of optimizing culture was finished by steps of single factor optimization,Plackett-Burman and central composite design. The butanol concentration in fermentationbroth increased from7.01g/L to9.42g/L, i.e., the production increased by34.38%.When thesubstrate concentration is more than10%in butanol fermentation of cassava dregs hydrolysis,the butanol concentration kept around9.5g/L.A gas chromatography (GC) method together with a full evaporation headspace (FE-HS)sampling technique was developed for rapidly and simultaneously measuring volatileproducts for acetone-butanol-ethanol (ABE) fermentation. In this method, a small volume (< 50μL) of fermentation broth was directly injected into a sealed headspace sample vial (22mL)and the mass transfer of acetone-butanol-ethanol from liquid phase to vapor phase achievedequilibration at105°C for5min, the vaporous solvents were then determined by GC with aflame ionization detector. The results showed that the measurement precisions and accuracieswere excellent with present method, in which the relative standard deviations (RSD) ofethanol, acetone and butanol were1.7%,1.2%and0.76%, and their recovery was99.7±2.68%,100±1.78%and99.6±1.74%, respectively. The present method is simple, practical, automated,and suitable for application in the fermentation in related researches without any samplepretreatment.