Bioconversion of Rice Straw into Ethanol: Fungi and Yeasts are the Backbone Microbiota of the Process (original) (raw)
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Cellulase production using different streams of wheat grain- and wheat straw-based ethanol processes
Journal of Industrial Microbiology & Biotechnology, 2011
Pretreatment is a necessary step in the biomass-to-ethanol conversion process. The side stream of the pretreatment step is the liquid fraction, also referred to as the hydrolyzate, which arises after the separation of the pretreated solid and is composed of valuable carbohydrates along with compounds that are potentially toxic to microbes (mainly furfural, acetic acid, and formic acid). The aim of our study was to utilize the liquid fraction from steam-exploded wheat straw as a carbon source for cellulase production by Trichoderma reesei RUT C30. Results showed that without detoxification, the fungus failed to utilize any dilution of the hydrolyzate; however, after a two-step detoxification process, it was able to grow on a fourfold dilution of the treated liquid fraction. Supplementation of the fourfold-diluted, treated liquid fraction with washed pretreated wheat straw or ground wheat grain led to enhanced cellulase (filter paper) activity. Produced enzymes were tested in hydrolysis of washed pretreated wheat straw. Supplementation with ground wheat grain provided a more efficient enzyme mixture for the hydrolysis by means of the near-doubled β-glucosidase activity obtained.
Journal of Food Science and Engineering, 2015
Effect of commercial cellulose enzymes was investigated by batch enzymatic hydrolysis at 15.0% (w/v) solid. It was found that the best commercial cellulose enzyme was Cellic ® CTec comparing to Accellerase 1000 TM and Accelerase 1500 TM. The Cellic ® CTec gave the highest reducing sugar concentration and rice straw conversion. Moreover, when the hydrolysate obtained from hydrolysis using Cellic ® CTec was fermented by Saccharomyces cerevisiae TISTR 5596, it would give the highest ethanol. In this study, the Cellic ® CTec was used for fed-batch prehydrolysis prior to ethanol production by simultaneous saccharification and fermentation (SSF) way at 20% (w/v) solid loading. It could produce 35.76 g/L or 4.6% (v/v) of ethanol concentration and 83.67 L/ton dry matter (DM) of yield.
Production of renewable fuels, especially bio-ethanol from lignocellulosic biomass, holds remarkable potential to meet the current energy demand as well as to mitigate greenhouse gas emissions for a sustainable environment. Present technologies to produce bioethanol largely depend on sugarcane and/or starch based grains and tubers (mainly corn, potatoes). This is partly due to ease of substrate handling and processing. On the other hand, use of sugarcane and food grains to produce bio-ethanol has caused significant stress on food prices and food security. Accordingly, the recent focus has been on lignocellulosic materials as a source for bio-ethanol. In fact, many countries are moving towards developing or have already developed technologies to exploit the potential of lignocellulosic materials for the production of bioethanol. This process of ethanol production generally involves hydrolysis of lignocellulosic biomass to fermentable sugars followed by fermentation of such sugars to ethanol. Achieving fermentable levels of sugars from lignocellulosic biomass requires relatively harsh pretreatment processes. The pretreatment process has pervasive impact on the overall operation because the process depends on the choice of lignocellulosic source, the size reduction via grinding, chemical treatment, acid hydrolysis, neutralization and fermentation. Recent advances in the process technologies have made it possible to use simultaneous saccharification and fermentation. In this process cellulase enzyme is the critical reagent as well as the cost determining factor. The advances in biotechnology as related to bioethanol have focused on engineering organisms that are capable of producing ethanol from cellulose, hemicellulose and lignocellulose. Such organisms are expected to be capable of not only degrading cellulose, hemicellulose and lignocellulose to fermentable sugars, but also are able to utilize both pentose and hexose sugars to produce ethanol at a relatively high yield. More recent and emerging approaches in bioethanol production are focused on reducing production costs. This approach uses consolidated bioprocessing schemes in which cellulase production, substrate hydrolysis, and fermentation are all accomplished in a single step. Countries, such as Nepal, that totally depend on the import of fossil fuels cannot ignore the potential of bioethanol derived from lignocellulosic biomass. Nepal is rich in biodiversity and posses variety of energy crops. Accordingly, developing policies and mechanisms that promote bioethanol will go a long-way in reducing the fuel crises in the countries lacking oil resources.
Production of Cellulase for Ethanol Fermentation from Pretreated Wheat Straw
Iranian Journal of Science and Technology, Transactions A: Science, 2016
Effect of different media compositions on cellulase production was observed using a strain of Trichoderma viride. Medium with yeast extract as nitrogen source was found the best from the other sources used. Then two modes of fermentation solid state and submerged were compared for the enhanced cellulase production. Better cellulase activity was observed in submerged fermentation than the solid state fermentation. Effect of mash size and agitation was also studied. Small mash size with agitation showed higher cellulase activity than the large size pretreated wheat straw. Bacillus cellulosilyticus was also used for the cellulase production. Trichoderma produced enhanced activities of cellulase enzyme (20.738 ± 0.006 IU). Scarification of pretreated wheat straw released maximum sugar up to 16.1 g/L, after hydrolysis in 48 h using indigenously produced enzyme. The optimum conditions for the saccharification of pretreated wheat straw were 5 and 30°C for pH and temperature, respectively in 48 h. The yield of ethanol was observed 10.4 g/L in saccharified wheat straw based medium.
Production of Biocellulosic Ethanol from Wheat Straw
Wheat straw is an abundant lignocellulosic feedstock in many parts of the world, and has been selected for producing ethanol in an economically feasible manner. It contains a mixture of sugars (hexoses and pentoses). Two-stage acid hydrolysis was carried out with concentrates of perchloric acid, using wheat straw. The hydrolysate was concentrated by vacuum evaporation to increase the concentration of fermentable sugars, and was detoxified by over-liming to decrease the concentration of fermentation inhibitors. After two-stage acid hydrolysis, the sugars and the inhibitors were measured. The ethanol yields obtained from by converting hexoses and pentoses in the hydrolysate with the co-culture of Saccharomyces cerevisiae and Pichia stipites were higher than the ethanol yields produced with a monoculture of S. cerevisiae. Various conditions for hysdrolysis and fermentation were investigated. The ethanol concentration was 11.42 g/l in 42 h of incubation, with a yield of 0.475 g/g, productivity of 0.272 g/l ·h, and fermentation efficiency of 92.955 %, using a co-culture of Saccharomyces cerevisiae and Pichia stipites.
3 Biotech, 2011
Cellulose is a major constituent of renewable lignocellulosic waste available in large quantities and is considered the most important reservoir of carbon for the production of glucose, for alternative fuel and as a chemical feedstock. Over the past decade, the emphasis has been on the enzymatic hydrolysis of cellulose to glucose and the efficiency of which depends on source of cellulosic substrate, its composition, structure, pretreatment process, and reactor design. In the present study, efforts were made to produce cellulase enzyme using rice straw. The produced enzyme was used for the hydrolysis of selected lignocellulosic substrate, i.e., sorghum straw. When rice straw was used as a substrate for cellulase production under solid state fermentation, the highest enzyme activity obtained was 30.7 FPU/gds, using T. reesei NCIM 992. 25 FPU/g of cellulase was added to differently treated (native, alkali treated, alkali treated followed by 3% acid treated and alkali treated followed by 3 and 5% acid treated) sorghum straw and hydrolysis was carried out at 50°C for 60 h. 42.5% hydrolysis was obtained after 36 h of incubation. Optimization of enzyme loading, substrate concentration, temperature, time and buffer yielded a maximum of 546.00 ± 0.55 mg/g sugars (54.60 ± 0.44 g/l) with an improved hydrolysis efficiency of 70 ± 0.45%. The enzymatic hydrolyzate can be used for fermentation of ethanol by yeasts.
Lignocellulosic ethanol production: current practices and recent developments
2011
Production of renewable fuels, especially bio-ethanol from lignocellulosic biomass, holds remarkable potential to meet the current energy demand as well as to mitigate greenhouse gas emissions for a sustainable environment. Present technologies to produce bioethanol largely depend on sugarcane and/or starch based grains and tubers (mainly corn, potatoes). This is partly due to ease of substrate handling and processing. On the other hand, use of sugarcane and food grains to produce bio-ethanol has caused significant stress on food prices and food security. Accordingly, the recent focus has been on lignocellulosic materials as a source for bio-ethanol. In fact, many countries are moving towards developing or have already developed technologies to exploit the potential of lignocellulosic materials for the production of bioethanol. This process of ethanol production generally involves hydrolysis of lignocellulosic biomass to fermentable sugars followed by fermentation of such sugars to ethanol. Achieving fermentable levels of sugars from lignocellulosic biomass requires relatively harsh pretreatment processes. The pretreatment process has pervasive impact on the overall operation because the process depends on the choice of lignocellulosic source, the size reduction via grinding, chemical treatment, acid hydrolysis, neutralization and fermentation. Recent advances in the process technologies have made it possible to use simultaneous saccharification and fermentation. In this process cellulase enzyme is the critical reagent as well as the cost determining factor. The advances in biotechnology as related to bioethanol have focused on engineering organisms that are capable of producing ethanol from cellulose, hemicellulose and lignocellulose. Such organisms are expected to be capable of not only degrading cellulose, hemicellulose and lignocellulose to fermentable sugars, but also are able to utilize both pentose and hexose sugars to produce ethanol at a relatively high yield. More recent and emerging approaches in bioethanol production are focused on reducing production costs. This approach uses consolidated bioprocessing schemes in which cellulase production, substrate hydrolysis, and fermentation are all accomplished in a single step. Countries, such as Nepal, that totally depend on the import of fossil fuels cannot ignore the potential of bioethanol derived from lignocellulosic biomass. Nepal is rich in biodiversity and posses variety of energy crops. Accordingly, developing policies and mechanisms that promote bioethanol will go a long-way in reducing the fuel crises in the countries lacking oil resources.