| Prior to biological conversion of lignocellulosic biomass, natural barriers to efficient enzymatic hydrolysis must be overcome, and a few pretreatment technologies effectively accomplish this job with chemicals. Although several factors are postulated to impact enzymatic hydrolysis performance after pretreatment, we believe that these can be viewed in terms of two main aspects that control efficient deconstruction of cellulose and hemicellulose in biomass to sugars: enzyme adsorption and effectiveness. These two key factors are governed in one way or another by substrate and enzyme features and the local environment such as the presence of sugars and their oligomers and non catalytic additives. Thus, in a first of a kind study, we determined how leading pretreatment technologies of dilute acid, controlled pH, ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), flowthrough (FT), lime, and SO2 impacted important substrate features and cellulase adsorption/cellulase effectiveness for the deconstruction of cellulose in two important types of biomass: corn stover, an agriculture residue, and poplar, a woody biomass. In addition, the effect of selected physical parameters on cellulase adsorption/effectiveness was also determined. First, we gathered extensive data on the effect of enzyme type and loadings on cellulase effectiveness in terms of cellulose hydrolysis to glucose for each pretreatment. Then, enzyme adsorption parameters for these solids were evaluated based on the Langmuir equation and related to substrate features such as acetyl content, xylan/lignin removal, crystallinity, degree of polymerization of cellulose, and hydrophobicity. Then the relationship between cellulase adsorption capacity and hydrolysis rates/yields was determined. Acetyl content appeared to reduce cellulose accessibility and cellulase/other enzymes effectiveness, whereas xylan removal enhanced cellulose accessibility and enzymes effectiveness. In addition, because xylooligomers were shown to strongly inhibit cellulase/xylanase effectiveness, their rapid hydrolysis by adding beta-xylosidase was very important. On the other hand, lignin removal had a negligible effect on cellulose accessibility but a major impact on enzymes effectiveness and accessibility to xylan. Thus, delignification appeared not necessary for effective cellulose saccharification as long as xylan is removed. Other substrate features such as biomass crystallinity and cellulose degree of polymerization were related to other substrate features such as xylan/lignin removal, and consequently no clear effect of these on other key factors could be established. Furthermore, supporting this hypothesis, 24 hours hydrolysis rate data, measured at different cellulase loadings, was found to be directly related to cellulase adsorption capacity of pretreated solids despite the wide range of temperatures, types of chemicals, and pH levels applied for pretreatment. |
