Saccharification of lignocellulosic biomass using seawater and halotolerant cellulase with potential application in second-generation bioethanol production

Abstract

Global water scarcity at an alarming stage has triggered the interest of many environmentalists and global researchers. Use of freshwater in biomass-based industries would result in depletion of a precious natural resource, which is not sustainable in the long term. Thus, water management technologies are critical to the successful operation of an ethanol plant. Utilization of seawater-based systems and halotolerant enzymes can be a breakthrough in this context. The present study involves marine bacterial strains Bacillus oceanisediminis, Brevibacterium halotolerans, and Psychrobacter celer capable of producing halotolerant cellulases, isolated from Gopalpur, Odisha. The crude enzyme extracts and direct bacterial cultures were independently utilized for saccharification of pretreated rice straw, and the treated rice straw was characterized for the production of reducing sugars using high-performance liquid chromatography (HPLC). The possible bond breakage and formation during saccharification of cellulose was assessed using attenuated total reflectance with Fourier transform infrared (ATR-FTIR) spectroscopy. The relative fraction and size of crystallites in cellulose was evaluated by X-ray diffraction (XRD) study. The biomass saccharified using the crude cellulase from B. oceanisedimins was utilized for the production of bioethanol in freshwater and seawater-based media using Saccharomyces cerevisiae NCIM 3570 and Candida shehatae NCIM 3500. The maximum fermentation efficiency (45.74%) was recorded for saccharified rice straw in freshwater using a consortium of immobilized yeasts. The highest fermentation efficiency (36.69%) was recorded in the seawater system by immobilized S. cerevisiae.