Potential cost reduction of cellulosic biomass saccharification by fungal crude enzyme–commercial enzyme cocktail

A. Nanjundaswamy, B. Okeke
Auburn University Montgmery, US

Keywords: biomass enzymes, biofuel, switchgrass, gammagrass, saw dust

Summary:

One of the limitations for the commercial production of cellulosic ethanol is the high cost associated with enzymes for saccharification: enzymes for large-scale biomass saccharification cost at least $2-$3 per gallon of biofuel. With the objective of reducing enzyme cost, this study examined the production of ‘crude enzyme extract’ from two fungal strains and their supplementation with commercial enzymes for saccharification of three lignocellulosic feedstocks. Crude enzyme extracts of high-yielding Trichoderma sp. and Fusarium sp. were produced by submerged fermentation. Enzyme cocktails containing recommended dose of commercial enzyme (N), its 25% (N25) or 50% (N50) along with their supplementation of crude enzyme were used in the saccharification of acid-pretreated gammagrass, sawdust and switchgrass. C50N of both fungi resulted in the highest sugar yield in all three substrates. Trichoderma C50N yielded 5.0g/L glucose and 2g/L ethanol from acid-pretreated switchgrass indicating 80% conversion efficiency. Data from scale-up of enzyme production, switchgrass saccharification and ethanol fermentation will be discussed. Use of relatively inexpensive crude aqueous fungal enzyme extract can potentially reduce commercial enzyme usage in cellulosic ethanol production by at least one half contributing to the possibility of commercialization of cellulosic ethanol.