Location: Bioenergy ResearchTitle: Cellulosic ethanol production from green solvent-pretreated rice straw
|KUMAR, ADEPU - Sardar Patel Renewable Energy Research Institute|
|PARIKH, BHUMIKA - Sardar Patel Renewable Energy Research Institute|
|SHAH, EKTA - Sardar Patel Renewable Energy Research Institute|
Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2015
Publication Date: 4/28/2016
Citation: Kumar, A.K., Parikh, B.S., Shah, E., Liu, L.Z., Cotta, M.A. 2016. Cellulosic ethanol production from green solvent-pretreated rice straw. Biocatalysis and Agricultural Biotechnology. 7:14-23. doi: 10.1016/j.bcab.2016.04.008.
Interpretive Summary: Pretreatment of lignocellulosic biomass materials generally requires harsh conditions that can have negative environmental impacts due to the generation of toxic components and difficult recycling procedures. Recently developed “NAtural Deep Eutectic Solvents (NADES)” are green solvents consisting of bio-based ionic liquids and deep eutectic solvents from plant-based metabolites. NADES have a great potential in lignin separation from lignocellulosic biomass materials. ARS scientists in collaboration with scientists from Sardar Patel Renewable Energy Research Institute, India, investigated cellulosic ethanol production from NADES-pretreated rice straw using commercially available cellulase and ARS developed cellobiose-fermenting yeast strain Clavispora NRRL Y-50464. A successful cellulosic ethanol production process was accomplished using NADES reagents choline chloride/glycerol (CC-GLY), choline chloride/1,2-propane diol, and choline chloride/ethanediol. High ethanol production was obtained from CC-GLY treated rice straw within 36 h using this procedure. Results of this research demonstrated a potential environmentally friendly technology of NADES as an alternative method for lignocellulosic biomass pretreatment for cellulosic ethanol production. Outcomes in this research area will benefits international research and development efforts for clean and sustainable biofuels production.
Technical Abstract: Natural deep eutectic solvents (NADES) are recently developed “green solvents” consisted of bio-based ionic liquids and deep eutectic solvents mainly from plant based metabolites. NADES are biodegradable, non-toxic and environment-friendly. Conventional chemically synthesized ionic liquids have been tested for pretreatment of lignocellulosic materials but are toxic, expensive, and energy-intensive for recycling. We recently demonstrated higher level of lignin separation from rice straw using NADES pretreatment. In this study, we investigated cellulosic ethanol production from NADES-pretreated rice straw and the effects of NADES on performance of commercially available cellulase Cellic Ctec2 and cellobiose-fermenting yeast strain Clavispora NRRL Y-50464. NADES reagents at high concentrations (up to 30 %, v/v) of choline chloride/glycerol (CC-GLY), choline chloride/1,2-propane diol (CC-PD), choline chloride/ethanediol (CC-ED) showed no inhibition effect on Cellic Ctec2. However, the enzyme activity was nearly complete lost at low concentrations (> 5 %, v/v) of choline chloride/malic acid (CC-MA), choline chloride/malonic acid (CC-MAL), choline chloride/citric acid (CC-CA), choline chloride/tartaric acid (CC-TA), and choline chloride/lactic acid (CC-LA). NADES reagent CC-GLY and CC-PD at 10 % (v/v) did not affect growth rate, sugar consumption and ethanol production of Clavispora NRRL Y-50464. However, 10 % (v/v) CC-ED repressed and delayed the cell growth. Strain Y-50464 was sensitive and unable to grow on a medium containing all the other NADES reagents evaluated in this study. High levels of pH (< pH 3.0) in NADES inhibited enzyme activity of Cellic Ctec2 and growth of Clavispora strain NRRL Y-50464. When pH of the NADES reagents was neutralized or adjusted at pH 5, normal enzyme activity and cell growth were observed. Using choline chloride/glycerol (CC-GLY) treated rice straw, a maximum reducing sugars of 226.7 g/L was obtained with a saccharification efficiency of 87.1 % at 20 % solids loading and 12 FPU Cellic Ctec2. An ethanol production of 36.7 g/L was observed from 8 % of glucose within 36 h with a conversion efficiency of 90.1%. The NADES-pretreated rice straw efficiently removed lignin component from the feedstock and improved fermentation efficiency significantly. With selective NADES reagents such as CC-GLY, CC-PD, and CC-ED, cellulosic ethanol production can be accomplished using Cellic Ctec2 and strain NRRL Y-50464.