Efficient pretreatment of sugarcane bagasse via dilute mixed alkali salts (K2CO3/K2SO3) soaking for enhancing its enzymatic saccharification

Strategies of pretreatment of feedstocks for optimized bioethanol production: distinct and integrated approaches

Bioethanol is recognized as a valuable substitute for renewable energy sources to meet the fuel and energy demand of the nation, considered an environmentally friendly resource obtained from agricultural residues such as sugarcane bagasse, rice straw, husk, wheat straw and corn stover. The energy demand is sustained using lignocellulosic biomass to produce bioethanol. Lignocellulosic biomass (LCBs) is the point of attention in replacing the dependence on fossil fuels. The recalcitrant structure of the lignocellulosic biomass is disrupted using effective pretreatment techniques that separate complex interlinked structures among cellulose, hemicellulose, and lignin. Pretreatment of biomass involves various physical, chemical, biological, and physiochemical protocols which are of importance, dependent upon their individual or combined dissolution effect. Physical pretreatment involves a reduction in the size of the biomass using mechanical, extrusion, irradiation, and sonification methods while chemical pretreatment involves the breaking of various bonds present in the LCB structure. This can be obtained by using an acidic, alkaline, ionic liquid, and organosolvent methods. Biological pretreatment is considered an environment-friendly and safe process involving various bacterial and fungal microorganisms. Distinct pretreatment methods, when combined and utilized in synchronization lead to more effective disruption of LCB, making biomass more accessible for further processing. These could be utilized in terms of their effectiveness for a particular type of cellulosic fiber and are namely steam explosion, liquid hot water, ammonia fibre explosion, CO2 explosion, and wet air oxidation methods. The present review encircles various distinct and integrated pretreatment processes developed till now and their advancement according to the current trend and future aspects to make lignocellulosic biomass available for further hydrolysis and fermentation.

Enhanced production of bacterial xylanase and its utility in saccharification of sugarcane bagasse

An investigation was carried out using sugarcane bagasse as the agricultural residue to study the optimization of xylanase production by solid-state fermentation. Maximum xylanase production (20.35 U/g substrate) was achieved by Bacillus substilis subsp. subtilis JJBS250 using 'one variable at a time approach' at pH 7.0, 40 °C after 48 h. After statistical optimization by response surface methodology (RSM) there was 4.82-fold improvement in xylanase production (98.16 U/g substrate). Further optimization of untreated and sodium carbonate pretreated sugarcane bagasse enzymatic hydrolysis was carried out using both bacterial (Bacillus substilis subsp. subtilis JJBS250) and fungal (Myceliophthora thermophila BJTLRMDU3) xylanases that showed high amount of reducing sugar liberation from untreated sugarcane bagasse (124.24 mg/g substrate) as compared to pretreated (76.23 mg/g substrate) biomass. Furthermore, biophysical characterization of untreated and sodium carbonate pretreated sugarcane bagasse using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), revealed the structural changes in the pretreated biomass.

An enhanced ionic liquid-tolerant immobilized cellulase system via hydrogel microsphere for improving in situ saccharification of biomass

A novel immobilized cellulase based on hydrogel microsphere was established to accommodate ionic liquid (IL)-involved in situ biomass saccharification. For immobilization, poly(N-isopropylacrylamide) (PNIPAM) was employed to immobilize cellulase, with immobilization yielded up to 95.6%. Besides, 1-ethyl-3-methyllimidazolium acetate ([EMIM]OAc) was found as an appropriate IL for in situ saccharification due to its relative enzymatic activity, which was as high as 167.5%. With utilization of immobilized cellulase in IL-pretreated in situ bagasse (BC) saccharification, relative enzymatic activity was 40.9%, which was higher than free cellulase under 5% (v/v) IL, and achieved 12.3%, which was found to be higher than free one in 25% (v/v) IL. Moreover, for estimating reusability, relative enzymatic activity on the 6th cycle retained over 85.2%. This novel immobilization system possessed a remarkable preservation to cellulase in hydrolysis contained interferences, e.g. IL, suggesting a noticeable practical potential in hydrolysis of cost-effective sustainable biomass materials.