Enhancing the Enzymatic Hydrolysis of Cellulosic Materials Using Simultaneous Ball Milling

Abstract

One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently, enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. alpha-Cellulose, employed as a model substrate, and SO2-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of alpha-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis of the carbohydrate moieties.

Biomass Size Reduction Machines for Enhancing Biogas Production

“…The effectiveness of the method depends on the lignin structure, the grinding elements, and the oscillation frequency of the shaker [1]. Mais [12] has tested its application to continuous process technology. The results of his work recommend biomass to be tempered with temperatures of 40-60°C and using grinding balls made of stainless steel.…”

Lignocellulosic Biomass Pretreatment

“…They found that there was a positive correlation between the amount saccharification of the substrate and the number of balls added to the reactor. At an enzyme loading of 10 FPU/g cellulose, 45°C, and 10% (w/v) solid concentration, an 85% conversion of the original substrate to monomeric glucose was observed (Mais et al, 2002). Higher yields were possible by increasing the enzyme loading or decreasing the substrate loading.…”

“…The resulting increase in surface area allows for more locations for catalytic breakdown of constituent sugars by enzymes. Mais et al (2002) conducted a study to evaluate the effectiveness of the simultaneous ball milling and hydrolysis of Douglas-fir wood chips in a ball milling reactor. They found that there was a positive correlation between the amount saccharification of the substrate and the number of balls added to the reactor.…”

“…Higher yields were possible by increasing the enzyme loading or decreasing the substrate loading. It is important to note that in this ball milling study, the biomass was first steam exploded with sulfur dioxide and delignified with an alkaline-peroxide solution before ball milling and enzymatic saccharification (Mais et al, 2002). Cost is most often the deterring factor in this type of pretreatment.…”

Degrees of polymerization (DP) and DP distribution of cellouronic acids prepared from alkali-treated celluloses and ball-milled native celluloses by TEMPO-mediated oxidation

“…Second, native celluloses and wood saw dust are ballmilled to convert the crystalline cellulose I regions in the native celluloses to disordered ones (Hermans and Weidninger 1946), and were subjected to TEMPOmediated oxidation to prepare CUAs with higher DP values. Recently, some new and effective ball-milling apparatuses have become commercially available, and efficiencies of enzymatic hydrolysis and chemical modifications of cellulose are improved by using ballmilled celluloses (Tassinai and Macy 1977;Ryu et al 1982;Endo et al 1999;Mais et al 2002;Qiu et al 2005). Because native celluloses have highly crystalline cellulose I structures, no water-soluble CUAs can be obtained by TEMPO-mediated oxidation even under harsh conditions (Isogai and Kato 1998).…”