• Energy Research

In the present work, alkali assisted microwave pretreatment (AAMP) of cotton plant residue (CPR) with high pressure reactor pretreatment was compared. Further, modeling of AAMP was attempted. AAMP, followed by enzymatic saccharification was evaluated and the critical parameters were identified to be exposure time, particle size and enzyme loading. The levels of these parameters were optimized using response surface methodology (RSM) to enhance sugar yield. AAMP of CPR (1mm average size) for 6 min at 300 W yielded solid fractions that on hydrolysis resulted in maximum reducing sugar yield of 0.495 g/g. The energy required for AAMP at 300 W for 6 min was 108 kJ whereas high pressure pretreatment (180°C, 100 rpm for 45 min) requires 5 times more energy i.e., 540 kJ. Physiochemical characterization of native and pretreated feedstock revealed differences between high pressure pretreatment and AAMP.

Harvesting of the micro alga Chlorococcum sp. R-AP13 through autoflocculation, chemical flocculants or by change in medium pH was evaluated. Surface charge of algal cells changed in response to the method used and affected flocculation efficiency. While aluminum sulfate and FeCl3 supported 87% and 92% efficiency, auto flocculation could recover 75% of biomass in 10min. Maximum efficiency (94%) was obtained with change in medium pH from 8.5 to 12.0 achieved through addition of 40mgl(-1) of NaOH. Since high concentrations of FeCl3 and AlSO4 were toxic to the cells, flocculation induced by pH change may be considered the most effective strategy. Residual medium after flocculation could be reused efficiently for algal cultivation, minimizing the demand for fresh water.

Abstract Production of bioethanol from lignocellulosic biomass is very challenging due to the heterogenous nature of the feedstock. An efficient pretreatment is necessary for maximizing the enzymatic hydrolysis efficiency and this in turn helps in reducing the total process economy. Conventional pretreatment using acid or alkali at high temperature and pressure is limited due to its high energy input. So there is a need for alternative heating techniques which not only reduce the energy input, but increases the total process efficiency. Microwave pretreatment may be a good alternative as it can reduce the pretreatment time at higher temperature. In the present study, a comparison of three types of microwave pretreatment such as microwave-acid, microwave-alkali and combined microwave-alkali-acid were tried using sugarcane bagasse as the lignocellulosic biomass. The enzymatic saccharification efficiency and lignin removal in each pretreatment method has been evaluated. Microwave treatment of sugarcane bagasse with 1% NaOH at 600 W for 4 min followed by enzymatic hydrolysis gave reducing sugar yield of 0.665 g/g dry biomass, while combined microwave-alkali-acid treatment with 1% NaOH followed by 1% sulfuric acid, the reducing sugar yield increased to 0.83 g/g dry biomass. Microwave-alkali treatment at 450 W for 5 min resulted almost 90% of lignin removal from the bagasse. The effect of pretreatment has been also evaluated by XRD, SEM and FTIR analysis. It was found that combined microwave-alkali-acid treatment for short duration enhanced the fermentable sugar yield.

Abstract Aspergillus unguis NII-08123, a filamentous fungus isolated from soil, was found to produce β-glucosidase (BGL) activity with high glucose tolerance. Cultivation of the fungus in different carbon sources resulted in the secretion of different isoforms of the enzyme. A low molecular weight isoform, which retained ~60 % activity in the presence of 1.5 M glucose, was purified to homogeneity and the purified enzyme exhibited a temperature and pH optima of 60 °C and 6, respectively. The K m and V max of the enzyme were 4.85 mM and 2.95 U/mg, respectively, for 4-nitrophenyl β-d-glucopyranoside. The glucose inhibition constant of the enzyme was 0.8 M, indicating high glucose tolerance, and this is the second-highest glucose tolerance ever reported from the Aspergillus nidulans group. The glucose-tolerant BGL from A. unguis, when supplemented to cellulase preparation from Penicillium, could improve biomass hydrolysis efficiency by 20 % in 12 h compared to the enzyme without additional beta glucosidase supplementation. The beta glucosidase from A. unguis is proposed as a highly potent “blend-in” for biomass saccharifying enzyme preparations.

Characterization of glucose tolerant beta glucosidase (GT-BGL) secreted by Aspergillus unguis NII 08123, determination of the gene and protein sequences of the enzyme and establishing its performance in blends for lignocellulose hydrolysis.Supplementation of A. unguis beta glucosidase (BGL) to cellulase released 1.6 times more sugar within 12 h during the hydrolysis of lignocellulosic biomass. The enzyme was determined to be similar to BGL-F from Emericella nidulans by MALDI-TOF analysis, and was found to be a GH3 family protein. Molecular Docking simulation studies showed that the enzyme has lesser affinity for glucose (- 5.7 kcal/mol) compared to its substrate cellobiose (- 7.5 kcal/mol). The residues present in the N-terminal domain are mostly involved in bond formation with both the substrate and the product, while the C-terminal domain contains the catalytic region. In-silico studies showed that its predicted structure is unlike that of previously reported BGLs, which might provide a clue to its exceptional catalytic activity.The GT-BGL from A. unguis NII 08123 was proven effective as a blend in for biomass hydrolyzing enzyme cocktails and the possible reasons for its glucose tolerance was determined through studies on its modeled structure.

Abstract The aim of this work was to evaluate cotton stalk (waste plant material after harvesting the cotton) as feedstock for bioethanol production. Different pretreatment strategies were tried using sodium hydroxide in a high pressure reactor equipped with a pitch blade turbine stirrer, followed by enzymatic hydrolysis using cellulases; the process optimization was carried out using Taguchi experimental design. Best results were achieved when the pretreatment was carried out at 180 °C for 45 min with mixing of substrate at 100 rpm. The sugar yield was evaluated based on pretreatment severity. The hydrolysis efficiency of pretreated cotton plant waste was very good (96%), showing the excellent efficiency of the method in removing the lignin. The material balance in each stage of the process was estimated and the total process efficiency was found to be 53% based on glucose conversion.

Alkali pretreatment of sugarcane tops was carried out with 3% NaOH for 60 min at 121 °C in a laboratory autoclave. The effect of solid loading, enzyme loading, incubation time and surfactant concentration on enzymatic saccharification was studied using a response surface method according to Box–Behnken design. Under optimized conditions 77.5% sugar was recovered from the pretreated biomass. This yield was seven times higher than that obtained with untreated sugarcane tops. A substantial amount of lignin (90%) was removed by this pretreatment method. Physicochemical characterization of native and alkali pretreated sugarcane tops were carried out by XRD, FTIR and SEM and the changes in the chemical composition were also monitored. The X-ray diffraction profile showed that the degree of crystallinity was higher for alkali pretreated biomass than that for native.

Mild alkaline pretreatment was evaluated as a strategy for effective lignin removal and hydrolysis of rice straw. The pretreatment efficiency of different NaOH concentrations (0.5, 1.0, 1.5 or 2.0% w/w) was assessed. Rice straw (RS) pretreated with 1.5% NaOH achieved better sugar yield compared to other concentrations used. A cellulose conversion efficiency of 91% (45.84 mg/ml glucose release) was attained from 1.5% NaOH pretreated rice straw (PRS), whereas 1% NaOH pretreated rice straw yielded 35.10 mg/ml of glucose corresponding to a cellulose conversion efficiency of 73.81%. The ethanol production from 1% and 1.5% NaOH pretreated RS hydrolysates was similar at ∼3.3% (w/v), corresponding to a fermentation efficiency of 86%. The non-detoxified hydrolysate was fermented using the novel yeast strain Saccharomyces cerevisiae RPP-03O without any additional supplementation of nutrients.