Thermochemical and Enzymatic Saccharification of Water Hyacinth Biomass into Fermentable Sugars

Abstract

Water hyacinth (WH) is a free-floating perennial aquatic plant that is considered a pest, due to its rapid grown rate and detrimental effects on environment and human health. It is nearly impossible to control WH growth, with mechanical extraction being the most acceptable control method; nevertheless, it is costly and labor-intensive. WH lignocellulosic biomass represents a desirable feedstock for the sustainable production of liquid fuels and chemical products. In this work, optimal conditions of thermochemical pretreatment for the release of reducing sugars (RS) from WH biomass were established: 0.15 mm of particle size, 50 g of dried solid/L of H2SO4 (3% w/v) and 20 min of heating time at 121 °C. Applying this pretreatment, a conversion of 84.12% of the hemicellulose fraction in the raw WH biomass into reducing sugars (277 ± 1.40 mg RS/g DWH) was reached. The resulting pretreated biomass of WH (PBWH) was enzymatically hydrolyzed by using six enzymatic complexes (all from Novozymes). Among them, NS22118 (beta-glucosidase) and Cellic® CTec2 (cellulase and hemicellulose complex) achieved higher saccharifications. By using NS22118 or a mixture of NS22118 and Cellic® CTec2, PBWH conversion into RS was complete. Monosaccharides released after pretreatment and enzymatic hydrolysis were mostly pentoses (arabinose and xylose) and hexoses (glucose), respectively.