Rice Straw For Bioethanol Production Research Articles

Performance of combined hydrochemo-mechanical pretreatment of rice straw for bioethanol production

Pretreatment was an inevitable process in the biorefinery process of lignocellulosic biomass utilization. Generally, biomass was considered an essential carbon source that could be converted into several bio-based products such as biofuels and biochemicals. This study aimed to evaluate the performance of combined hydrochemo-mechanical pretreatment of rice straw for bioethanol production. Rice straw was pretreated with autoclave followed by ball-milling pretreatment. The hydrochemical pretreatment was performed in an autoclave with different concentrations of NaOH (1 and 10%) at 121 °C for two different durations (30, 60 min). The pretreated biomasses were then subjected to ball-milling pretreatment for size reduction and subsequently hydrolyzed via enzymatic and bioethanol fermentation. The obtained results indicated that the highest reducing sugars were 0.4513 kg reducing sugar/kg biomass obtained by 1% of NaOH at 121 °C, 30 min, which provided the highest energy efficiency and the lowest waste generation was 0.1423 kg reducing sugar/kWh and 0.2570 kg of waste/kg reducing sugar respectively. Moreover, the highest bioethanol yield was 0.0491 kg/kg biomass obtained from a similar condition. Additionally, the combined pretreatment suggested that it could be an alternative pretreatment for a lignocellulosic biorefinery in industrial applications.

Improvement of bioethanol production using a new fermentation system: The process analysis and micro-mechanisms study

Rice straw based bioethanol is a clean alternative energy source to alleviate the energy crisis and greenhouse gases emission. However, the efficient alkali pretreatment of rice straw for bioethanol production will generate several fermentation inhibitors, such as ferulic acid, which could inhibit bioethanol fermentation. Therefore, an adsorbent called Air Environment-Prepared Adsorbent at 250 ℃ (AEPA250) was prepared using the enzymatically hydrolyzed residue of rice straw to detoxify ferulic acid in this study for enhancing the subsequent bioethanol production. Analysis of the mass balance showed that ferulic acid detoxification by AEPA250 had a high removal efficiency of 94.393% with a low glucose and xylose loss of 2.532% and 8.219%, respectively. A higher 277.551 mg/L bioethanol concentration and 76.005% glucose consumption rate in the SSBP system were obtained compared to non-detoxified sample. Furthermore, proteomics analysis indicated that certain metabolic pathways of TCA cycle and ribosome pathway as well as various coded proteins of ACO1, MRP2, RPL24B, MRPL33, RPL32, RPL39, RPS17B, RPS19A, RPS26A and ATP5 contributed to ferulic acid detoxification in the SSBP system. The findings of this study may help develop efficient pretreatment methods, detoxification strategies and engineering yeast strains for improving bioethanol production in the future.

Ensiling pretreatment with two novel microbial consortia enhances bioethanol production in sterile rice straw

The present study extracts and enriches cellulolytic microbial consortia from yak (Bos grunniens) and evaluates their effects on the fermentation profile and bioethanol yield in rice straw silage. Two microbial consortia (CF and PY) with high cellulolytic activity were isolated and observed to be prone to utilize natural carbon sources. Two consortia were introduced with and without combined lactic acid bacteria (CLAB) to rice straw for up to 60 days of ensiling, and their application notably decreased the levels of structural carbohydrates and pH values of rice straw silages. Treatments that combining microbial consortia and CLAB resulted in the highest levels of lactic acid, water soluble carbohydrates, mono- and disaccharides, and lignocellulose degradation, with PY + CLAB group yielding the highest bioethanol production. The microbial consortia identified herein exhibit great potential for degrading fibrous substrates, and their combination with CLAB provides a feasible way to efficiently use rice straw for bioethanol production.

Enhancement of bioethanol production by a waste biomass-based adsorbent from enzymatic hydrolysis

Alkaline pretreatment is an efficient method to destroy the lignocellulose structure of rice straw for bioethanol production. This process generates various toxic compounds, such as ferulic acid, which could inhibit bioethanol production. In this study, a waste biomass-based adsorbent from the enzymatic hydrolysis of rice straw (AEPA250) was used for ferulic acid detoxification in the alkali-pretreated hydrolysate. The AEPA250 detoxification process was first optimized by response surface methodology to increase ferulic acid removal, while reducing glucose loss. This optimization of detoxification resulted in 99.268% ferulic acid removal coupled with 3.028% glucose loss. The fermentation processing parameters and bioethanol production for different fermentation systems were evaluated after adopting the optimal AEPA250 detoxification conditions to select the most suitable optimization method. The result revealed that optimized detoxified fermentation with AEPA250 filtration (ODF) system was more suitable for bioethanol production than optimized detoxified fermentation containing AEPA250 (ODFA) system followed by non-detoxified fermentation (NDF) system. A logistic model was applied to further compare the yeast growth kinetics of the ODF and NDF systems. The ODF system had a maximum specific growth rate (μmax) of 0.532 h−1, indicating that the ODF system possessed greater bioethanol fermentation potential. Metabonomics and transcriptomics analyses were used to identify differentially expressed metabolites and functional genes that contribute to detoxification by the ODF system. AEPA250 was produced by the enzymatic hydrolysis of biomass waste of rice straw in the bioethanol production process, and a self-sufficient bioethanol production system could be established by in-situ AEPA250 detoxification using the ODF system. These results pave the way for the realization of a cleaner bioethanol production process by reducing environmental waste production, exogenous adsorbent use, and the cost of enzymatic hydrolysis residue treatment.

Process optimization for chemical pretreatment of rice straw for bioethanol production

Pretreatment of rice straw was optimized by physical and chemical methods. Among all the pretreatment methods followed by saccharification, autoclaved ammonia pretreatment significantly enhanced the liberation of reducing sugars i.e. 233.76 ± 1.23 mg/g substrate as compared to other methods. Further statistical optimization by response surface methodology (RSM) including ammonia concentration, substrate concentration and autoclaving time, enhanced the saccharification rate by 1.9-fold i.e. 451.96 mg/g substrate at 5 % rice straw, 12 % ammonia and autoclave time of 30 min after saccharification of 6 h. Maximum liberation of reducing sugars (635.37 mg/g substrate) was attained under these optimized conditions at 60 °C after 48 h. Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscope analysis clearly confirmed the removal of lignin in pretreated biomass. Ammonia pretreated enzymatic hydrolysate was fermented by Saccharomyces cerevisiae at 30 °C, pH 7.0, 150 rpm and 20 % hydrolysate, resulted in 24.37 g/L bioethanol after 72 h.

Process development for sodium carbonate pretreatment and enzymatic saccharification of rice straw for bioethanol production

Optimization of pretreatment of rice straw was carried out with sodium carbonate. Initially, sodium carbonate pretreatment of rice straw followed by saccharification using partially purified cellulolytic enzymes of thermophilic mould Myceliophthora thermophila BJTLRMDU3 (20 U/g) at 60 °C and pH 5.0 after 6 h, released about 3-fold more reducing sugars with autoclaving (154.93 mg/g substrate) as compared to room temperature (51.01 mg/g substrate). Further optimization was carried out using statistical tools by response surface methodology (RSM) selecting three variables i.e., sodium carbonate concentration, substrate concentration and autoclaving time. Statistical optimization has resulted in enhanced liberation of reducing sugars i.e., 531.2 mg/g substrate using 5% rice straw, 1.25% sodium carbonate and autoclave time of 30 min after saccharification for 6 h. Furthermore, maximum liberation of reducing sugars (728.45 mg/g substrate) from pretreated rice straw was recorded after 48 h. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) data clearly confirmed the breakdown of cellulose and hemicellulose, removal of lignin and morphological changes in pretreated rice straw. Fermentation of enzymatic hydrolysate (20%) was carried out by Saccharomyces cerevisiae at 30 °C, pH 6.0, 150 rpm that resulted in 18.07 g/L ethanol after 72 h.

Assisted Single-Step Acid Pretreatment Process for Enhanced Delignification of Rice Straw for Bioethanol Production

Dilute acid pretreatment of lignocellulosic biomass at higher temperatures (>160 °C) solubilizes/removes hemicelluloses (xylan, arabinan, mannan, galactan) and acid-soluble lignin (ASL), but, it does not remove acid-insoluble lignin (AIL). During acid pretreatment, the condensation and redeposition of coalesced lignin over cellulose fibers reduces the access of cellulose to cellulases. For higher delignification, various multistage pretreatments are available, however, all these are energy/chemical intensive methods. Therefore, an effective pretreatment which provides increased cellulose accessibility by enhanced removal of hemicelluloses and lignin in a single-step would be preferred. Our investigation reports a novel assisted single-step acid pretreatment (ASAP) process for enhanced delignification of biomass under acidic conditions. Pretreatment of rice straw (particle size of 20 mm) with H2SO4 (0.75% v/v) + boric acid (1% w/v) + glycerol (0.5% v/v) (solid/liquid (S/L), 1:5) at 150 °C for 20 min remove...

CONVERSION OF RICE STRAW TO FERMENTABLE SUGARS AND BIOETHANOL BY MFEX PRETREATMENT AND SEQUENTIAL FERMENTATION

The global rise in energy consumption, predicted increase in energy demands, price fluctuations, depletion and drawbacks of fossil fuels have converged to create an urgent need to develop more sustainable energy systems based on renewable feedstocks. Lignocellulosic materials are attractive feedstocks for bioethanol production. Rice straw is a promising feedstock for sustained production of biofuel. Bioethanol from lignocellulosic biomass could be a promising technology though the process has several challenges such as efficient pretreatment methods for delignification of lignocellulosics. Pretreatment is a prerequisite step for increasing the enzymatic digestibility for conversion to biofuels in biorefineries. The merits of a new and promising pretreatment called Multipurpose Fiber Expansion (MFEX) method for pretreating rice straw for bioethanol production was studied, where rice straw was treated with steam and carbon dioxide in sequence to make use of the synergistic effects obtained under pressure and moderate temperature for a few minutes and then rapidly releasing the pressure. A total reducing sugars of 645mg/g dry treated rice straw was achieved within 24 hours hydrolysis using laboratory prepared cocktail cellulolytic and hemicellulolytic enzymes. Of this total, 400 mg/g was glucose, which was rapidly fermented within 24 hours by a genetically-engineered Klebsiella oxytoca P2 leading to bioethanol yield of 375 mg/g dry treated biomass. Biofuels provide a potential and promising green alternative to avoid the global environmental crises that arise from dependence on fossil fuels. Conversion of glucose as well as xylose to bioethanol needs some improved co-fermentation technologies, to make the whole process cost effective. Article DOI: https://dx.doi.org/10.20319/mijst.2017.32.356380 This work is licensed under the Creative Commons Attribution-Non-commercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Overexpression of CO2-responsive CCT protein, a key regulator of starch synthesis strikingly increases the glucose yield from rice straw for bioethanol production

Production of bioethanol from rice straw has attracted attention from the point of effective use of agricultural residue. Starch content is an important determinant for bioethanol production from rice straw. The overexpression of CO2-responsive CCT protein (CRCT), which is the positive regulator of starch synthesis in vegetative organs, notably increased the starch content in rice straw. To produce the bioethanol from rice straw, the dilute acid pretreatment is a general pretreatment method. Importantly, the glucose yields in liquid hydrolyzate after dilute acid pretreatment was markedly increased in the CRCT overexpression lines compared with non-transgenic rice. In addition, the overexpression of CRCT enhanced the biomass production. In contrast, CRCT did not affect on the glucose yields from cellulose in acid-insoluble residue obtained after dilute acid pretreatment. With respect to byproduct in liquid hydrolyzate which inhibits the fermentation, the formic acid content was increased, whereas the furfural, 5-hydroxymethylfurfural and acetic acid contents were unchanged by the overexpression of CRCT. These results demonstrate that genetic engineering of CRCT is an effective method to increase the bioethanol production from rice straw.

Improved physicochemical pretreatment and enzymatic hydrolysis of rice straw for bioethanol production by yeast fermentation

Lignocellulosic biomass such as agricultural and forest residues are considered as an alternative, inexpensive, renewable, and abundant source for fuel ethanol production. In the present study, three different pretreatment methods for rice straw were carried out to investigate the maximum lignin removal for subsequent bioethanol fermentation. The chemical pretreatments of rice straw were optimized under different pretreatment severity conditions in the range of 1.79-2.26. Steam explosion of rice straw at 170°C for 10min, sequentially treated with 2% (w/v) KOH (SEKOH) in autoclave at 121°C for 30min, resulted in 85±2% delignification with minimum sugar loss. Combined pretreatment of steam explosion and KOH at severity factor (SF 3.10) showed improved cellulose fraction of biomass. Furthermore, enzymatic hydrolysis at 30 FPU/g enzyme loading resulted in 664.0±5.39mg/g sugar yield with 82.60±1.7% saccharification efficiency. Consequently, the hydrolysate of SEKOH with 58.70±1.52g/L sugars when fermented with Saccharomyces cerevisiae OBC14 showed 26.12±1.24g/L ethanol, 0.44g/g ethanol yield with 87.03±1.6% fermentation efficiency.

Optimization of twin gear-based pretreatment of rice straw for bioethanol production

A laboratory twin-gear reactor (TGR) was investigated as a new means for the pretreatment of high solid lignocelluloses. Response surface methodology based on Box Behnken Design was used to optimize the enzymatic digestibility with respect to the pretreatment process variables: temperature of 50–90°C, NaOH concentration of 2–6% and no. of cycles of 30–60. The results revealed that the TGR-based pretreatment led to the significant structural alterations through increases in pore size, pore volume, cellulose crystallinity and surface area. SEM images also confirmed the surface modifications in the pretreated rice straw. A response surface quadratic model predicted 90% of the enzymatic digestibility, and it was confirmed experimentally and through the analysis of variance (ANOVA) as well. The TGR extrusion proved to be an effective means for exceedingly high solids lignocellulose.

Hydrotropic pretreatment on rice straw for bioethanol production

The aim of this study was to investigate the effect of hydrotrope as a pretreatment process on rice straw for bioethanol production. Sodium cumene sulfonate and sodium xylene sulfonate (Na–X) were used as hydrotropes to delignify rice straw. Effects of biomass loading, time, temperature and hydrotrope concentration were studied for both the hydrotropes. There was no loss of cellulose & hemicellulose in the hydrotrope solution. Sodium cumene sulfonate could remove more than 50% of lignin from rice straw with 5% biomass loading at 121 °C for 1 h. Reusability of aqueous hydrotrope solution was demonstrated. Enzymatic digestibility of the hydrotrope pretreated rice straw was studied and evaluated for subsequent bioethanol production. The use of the hydrotrope for biomass pretreatment has the potential to mitigate the environmental impact of chemical pretreatment.

Sodium Bicarbonate Pretreatment on Rice Straw for Bioethanol Production and Utilizing the Waste Water of this Process to Absorb CO2 in Biogas.

The concept of small scale biorefinery from lignocellulosic biomass demonstrated the efficiency of energy and environment through research works at a pilot plant of University of Technology, VNU-HCM. The concept focused on studying bioethanol production in which pretreatment is one of key steps to achieve the efficiency. The pretreatment using NaOH solution 1.0 wt % removed lignin effectively but it is not considered as an eco-friendly chemical. Therefore, this study aims to investigate the alkaline pretreatment using Sodium Bicarbonate (NaHCO3), which is argued to be more environment-friendly and quite cheap. A variety of different conditions were investigated to optimize the pretreatment, including concentration of Sodium Bicarbonate (2.0-8.0 wt%), rice straw content (2.5-10.0 wt%), reaction temperatures (from room temperature to 80oC) and soaking time (4h-32h). The optimized condition was also investigated in combination with ultrasound and stirrer. The results showed that sodium bicarbonate is of quite potential to be used in the rice straw pretreatment. In addition, the waste of water from pretreatment was utilized to absorb CO2 in Biogas which was obtained from Thai My Demonstration plant in Cu Chi District.

Evaluation of the life cycle of bioethanol produced from soft carbohydrate-rich and common rice straw in Japan with land-use change

This study evaluates the life cycle of ethanol produced from soft carbohydrate (SC)-rich rice straw (cv. Leafstar) and common rice straw (cv. Koshihikari) while considering land-use change to estimate CO2 emissions, energy balance (expressed as Net Energy Ratio, NER), and production costs. Three different pretreatment methods were considered: the DiSC (direct saccharification of culms), RT-CaCCO (room temperature-CaCCO) and CaCCO (calcium capturing by carbonation) processes. Although the reduction in CO2 emission was found to be 59%, 42% and −3.5% for the DiSC, RT-CaCCO and CaCCO processes, respectively, the CO2 emission reduction decreased significantly when land-use change was considered. This result clearly shows that the biomass (rice straw) should be obtained from paddy fields without land-use change. The NER values for the bioethanol produced by the DiSC, RT-CaCCO and CaCCO processes were estimated to be 2.7, 2.1 and 1.0, respectively, and the total costs were estimated to be 102, 134 and 151 Yen/L ethanol, respectively (US $1 = 100 Yen). The use of the SC-rich rice straw contributes to a reduction of the environmental load and costs for the pretreatment, enzyme production, and enzymatic hydrolysis processes. Therefore, the use of SC-rich rice straw for bioethanol production reduces the total cost of production, reduces CO2 emissions, and improves the NER. Our results suggest that the DiSC and RT-CaCCO pretreatment processes are promising pretreatment techniques and that SC-rich rice straw is a promising resource for bioethanol production.

Bioethanol Production from Indica IR.64 Rice Straw Biomass by Direct Saccharification and Fermentation

Lignocellulosic substances such as agricultural wastes are attractive feed stocks for bioethanol production. Indica IR.64 rice straw is one of abundant agricultural wastes in Indonesia and could be used to bioethanol production. It has several characteristics such as high content of cellulose and hemicelluloses that can be readily hydrolyzed into fermentable sugars. A simple process (the direct saccharification and fermentation process) to produce ethanol from rice straw was developed in order to establish an efficient bioethanol production. In this work, no harsh pre-treatment steps were applied and also use a simple one-vat reactor without the risk of losing liberated carbohydrate. The first step in using rice straw for bioethanol production is size reduction through milling and sieving process prior to enzymatic hydrolysis. Direct saccharification and fermentation (DSF) of Indica IR.64 rice straw was examined and compared with two type of control (systems devoid of yeast and enzyme). The experiment were carried out under anaerobic condition, where the cellulase crude enzyme and cellulosic substrates (rice straw) produced glucose from the cellulose and Saccharomyces cerevisiae directly assimilated the glucose to bioethanol. The faster rate of bioethanol production during DSF by S accharomyces cerevisiae was obtained within the first 12h. The maximum ethanol concentration, ethanol yield, and theoretical ethanol yield of untreated rice straw were 0.25 g/L, 10 and 14.88%, respectively. Nevertheless, the direct saccharification and fermentation shows the potential for lower cost and higher efficiency for bioethanol production.

Solid simultaneous saccharification and fermentation of rice straw for bioethanol production using nitrogen gas stripping

SSSF for ethanol production using N2 strippingwas mainly conducted by the synergy of hydrolytic enzymes and yeast cells.

Microwave Assisted Alkali Pretreatment of Rice Straw for Enhancing Enzymatic Digestibility

Rapid industrialization, increasing energy demand, and climate change are the conditions that forced the researchers to develop a clean, efficient, renewable, and sustainable source of energy which has a potential to replace fossil fuels. Ethanol is one of the attractive and suitable renewable energy resources. In present study, effectiveness of microwave pretreatment in combination with sodium hydroxide (NaOH) for increasing enzymatic hydrolysis of rice straw has been investigated and under optimum conditions obtained a maximum reducing sugar (1334.79 µg/mL) through microwave assisted NaOH pretreatment. Chemical composition analysis and scanning electron microscope (SEM) images showed that the removal of lignin, hemicellulose, and silicon content is more in microwave assisted NaOH pretreatment than the blank sample. X-ray diffraction (XRD) analysis revealed that the crystallinity index of rice straw treated with microwave assisted alkali (54.55%) is significantly high as compared to the blank (49.07%). Hence, the present study proves that microwave assisted alkali pretreatment can effectively enhance enzymatic digestibility of rice straw and it is feasible to convert rice straw for bioethanol production.

Long-term Field Storage Examination of Rice Straw for Bio-ethanol Production

Outdoor field storage of round-baled rice straw to suppress the cost of producing bio-ethanol from rice straw was investigated. Harvested rice straw was dried, collected, compressed and packed into round bales (rolls) by a round baler. Usually, the rolls are stored in a warehouse, or outdoors wrapped in a film coat. However, these storage costs push up the price of the bio-ethanol produced and reduce energy efficiency. To avoid this, outdoor field storage of rice straw rolls with or without film wrapping (wrapped rolls or non-wrapped rolls) was investigated in this study. The rolls were stored for about 9 months, from 19 December 2008 to 9 September 2009, taking into consideration the supply of rice straw for demonstrating a bio-ethanol pilot plant throughout the year. No significant increase of temperature in each roll was observed during the storage term, even though an increase was reported in previous studies. However, the straw should be stocked for other seasons, and it is important to grasp any problems during the storage period. In this study, no significant change was observed in the non-wrapped rolls throughout the term, suggesting that non-film wrapping round-baled rice straw can be stored in fields outdoors.