Estimation of Treatment Time for Microbial Preprocessing of Biomass

Abstract

Biochemical conversion of lignocellulosic biomass to ethanol involves size reduction, preprocessing, pretreatment, enzyme hydrolysis, and fermentation. In recent years, microbial preprocessing has been gaining attention as a means to produce labile biomass for lessening the requirement of pretreatment severity. However, loss of sugars due to microbial consumption is a major consequence, suggesting its minimization through optimization of nutrients, temperature, and preprocessing time. In this work, we emphasized estimation of fungal preprocessing time, at which higher sugar yields can be achieved after preprocessing and enzyme hydrolysis. The estimation is based on the enzymatic activity profile obtained by treating switchgrass with Phanerochaete chrysosporium for 28 days. Enzyme assays were conducted once in every 7 days for 28 days, for activities of phenol oxidase, peroxidase, beta-glucosidase, beta-xylosidase, and cellobiohydrolase. We found no activity for phenol oxidase and peroxidase, but the greatest activities for cellulases on the seventh day. We then treated switchgrass for 7 days with P. chrysosporium and observed that the preprocessed switchgrass had higher glucan (39%), xylan (17.5%), and total sugar yields (25.5%) than the unpreprocessed switchgrass (34%, 37.5%, and 20.5%, respectively, p < 0.05). This verifies the utility of using enzyme assays for initial estimation of preprocessing time to enhance sugar yields.

The Confounding Effects of Particle Size and Substrate Bulk Density on Phanerochaete chrysosporium Pretreatment of Panicum virgatum

“…Phanerochaete chrysosporium is the most studied white-rot fungus used for biological pretreatment and is attractive because of its effectiveness as a pretreatment in as little as seven days (switchgrass) (Mahalazmi et al 2010) or 14 d (cotton stalks) (Shi et al 2009). The shorter incubation time could compensate for a decrease in pretreatment effectiveness compared with other species of white-rot fungi.…”

“…Sterilized airdried, green switchgrass (3 mm, 80% initial water content (w.b.)) was pretreated with P. chrysosporium for 7 d at 37 °C, and subsequent glucan digestion yielded approximately 5.5% of the theoretical yield (control with no P. chrysosporium yielded 8% of the theoretical yield) (Mahalazmi et al 2010).…”