Environmental sustainability of bioethanol production from rice straw in India: A review

India is highly dependent on fossil fuels mainly coal, oil, and gasoline so as to fulfill its energy demands. But, excessive exploitation of fossil fuels, natural resource scarcity, day-by-day enhancement in oil prices, and emission of green house gases, all these conditions leads to the search for a renewable, sustainable source of energy. Bioethanol is a reliable, economical, and readily available resource of renewable energy, which can be used as a fuel for power generation. Rice is the main staple food of India, and rice crops generate a huge amount of rice straw as crop residue in the fields. Unsustainable use of rice straw and open burning of crop in the field produce threat to the environment by producing large amount of greenhouse gas (GHG) emission and also make farmer’s loose a very viable by-product. Rice straw can be used in bioethanol production and bring additional income and sustainable utilization. India is showing great interests toward the use of ethanol for supplementing its energy requirements. Conversion of rice straw into bioethanol not only overcome the nation’s dependency on foreign countries and saves lot of money spent on importing crude oil but also solves global warming issues.

Due to the world’s regular demand for rice as a predominant meals crop, the quantity of rice straw produced pressurizing the waste management techniques of the countries. Rice straw is a huge waste administration trouble in rice-producing countries such as China, India, Vietnam, Indonesia, Brazil, etc. Burning rice straw on the discipline is the most preferred option for farmers to get rid of the rice straw which creates an array of environmental issues. In addition to jeopardizing the surroundings by means of emitting a great quantity of greenhouse gases (GHGs), the inappropriate utilization of rice straw and open crop burning in the discipline additionally have a tendency to lose farmers a very worthwhile by-product. Benefits can be harnessed via utilising the ample rice straw as an uncooked cloth for precious product generation. This work critiques the huge elements of the use of rice straw as an imperative supply of easy energy. The paper emphasizes some essential background knowledge, such as the chemical, and bodily houses that decide the calibre of rice straw. The specific pretreatment techniques that can make rice straw equipped for hydrogen manufacturing have additionally been discussed. The cutting-edge thermochemical and biochemical methods for changing rice straw into hydrogen are vividly presented. Further analyzing the viability of producing hydrogen from rice straw in the context of modern agriculture turns into extra crucial. The existing assessment additionally mentioned the policies and modern state of affairs of hydrogen manufacturing globally and gives a forecast on the state of hydrogen as a clean fuel for a sustainable future

Exploring rice straw as substrate for hydrogen production: Critical challenges and opportunities

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.

Hydrotropic pretreatment on 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.

The study was carried out at Teaching and Research farm Adamawa State University Mubi, to evaluate the chemical composition of treated and untreated rice straw using urea. Rice straw as a crop residue is widely available in tropical countries and is used in an attempt to meet the energy requirements of growing ruminants. A major limitation to the use of rice straw is their high fiber content, low nitrogen and energy level. Therefore, treatment of rice straw with urea can lead to significant improvement in nutritional quality and greater utilization. The major objectives of the study was to Improve the nutritional value of rice straw using urea, to Evaluate the chemical composition of treated and untreated rice straw using urea. The dry matter, organic matter, crude protein, ether extract, Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF), and Ash values are 60.62, 84.01, 12.29,1.07, 62.78, 41.48 and 13.40 for the urea treated rice straw and 75.56, 87.11, 3.22, 0.63, 68.18, 40.70 and 12.34% for the untreated rice straw respectively. The treatment of rice straw with urea has significantly at (P<0.05) reduced its dry matter content by 75.56 to 61.02 % and increased the value of crude protein by 3.22% to 12.29%.It is concluded that urea appears to be as efficient as any other source of ammonia in the treatment of straw. Therefore, the findings of this study will be beneficial to farmers as it will provides improved simple method of formulating local animals’ feeds using simple material like rice straw.

As the staple food crop in Sri Lanka, paddy rice occupies around 34% (over 0.87 million hectares of land) of the total arable area in the country, corresponding to an average rice production of 3,774,344 t/year. Rice straw is the major biomass waste from rice cultivation, which approximates to an average of 2,830,758 t/year generation at a theoretical straw/grain ratio of 0.75. Open burning of rice straw in paddy fields is the common practice, which could result in an average GHG emissions of 92 kg CO2 eq/t of dry rice straw and other harmful airborne emissions. Application of rice straw into soil as an organic fertiliser is also an inefficient practice, compared to bioenergy generation using rice straw. The average composition of the Sri Lankan rice straw (i.e. 30.0 wt.% cellulose, 3.9 wt.% hemicellulose, 38.2% lignin, 16.1 wt.% wax, and 12.3 wt.% silica) shows the possibility to be used as a second-generation bioethanol feedstock. Existing studies indicate that bioethanol production from rice straw is more environmentally-benign, compared to alternative options, such as gasification for combined heat and power and dimethyl ether (DME) production. This study analyses the net energy indicators of a possible bioethanol production process from rice straw in Sri Lanka. Chemical process simulations using Aspen Plus software were utilised to evaluate the bioethanol production process from rice straw, with a plant output capacity of 1,000 litres/hr of dehydrated bioethanol (99.7 vol.% ethanol) that can be blended with gasoline as a commercial fuel (e.g. E10: 10% bioethanol+gasoline) without any vehicle engine modification. The cradle to gate bioethanol production process from waste rice straw, considered for net energy analysis consists of three major stages: 1. Rice straw preparation, 2. Rice straw transportation, and 3. Bioethanol conversion. The results show that the considered bioethanol production process has a positive net energy gain and increased renewability factor. Detailed analysis indicates that only around 8% of the total process energy consumption is utilised for the bioethanol dehydration operation that is favourable for converting any existing rice straw ethanol plant into commercial gasohol production plant. The sensitivity of bioethanol yield and process energy parameters for the net energy indicator results are further analysed and discussed. The findings from this study can support decision making for a future waste-to-biofuel plant using waste rice straw in Sri Lanka.Keywords: Rice straw, Bioethanol production, Net energy analysis, Process simulation, Waste-to-biofuel

In Egypt rice cultivation in the river Nile Delta produces large amounts of rice straw as residue. Assuming that about 20% were used for other purposes about 2.8 Mt were left on the fields for burning within a period of 30 days to get quickly rid of leftover debris. The resulting emissions give a significant contribution to the air pollution called the Black Cloud. A suitable technology for the use of rice straw is an important contribution to reduce air pollution and gives a significant contribution to use biomass as renewable energy in Egypt. Based on that fact rice straw was studied as possible feedstock for the BIOLIQ process. The BIOLIQ process which is under development at the Forschungszentrum Karlsruhe (Germany) is a two-step process for the production of chemicals, fuels or electricity from lignocellulosic biomass with high ash content. In the first step the biomass is liquefied by fast pyrolysis. The pyrolysis char and the pyrolysis liquid are mixed to form a slurry. In the second step the pumpable slurry is used to produce syngas in a pressurised entrained flow gasifier. After gas cleaning and conditioning the syngas is used for the production of fuels, chemicals and electricity as by-product. In this work rice straw is studied as a possible feedstock for fast pyrolysis and slurry preparation. First the Egyptian rice straw was chemically characterised. Ultimate analysis of rice straw showed an elemental composition of 47,8% C, 6,0 %H and 45,3% O, (daf). According to the elemental composition the HHV was calculated to be about 18,1 MJ/Kg (Dulong) up to 20,5 MJ/kg (Ebeling). Based on the experimental HHV 15,3 MJ/kg (rice straw dry, 18% ash) the HHV on a moisture and ash free basis was calculated to be 18,7 MJ/kg. According to the literature the lignin, hemicellulose and cellulose contents of rice straw were about 12%, 28% and 60%, respectively. The rice straw was chopped and sieved (2 mm sieve) and most of the straw dust was separated before use. The pyrolysis process was studied on laboratory and PDU (process demonstration unit) scale. During pyrolysis lignin gave the main contribution to the char formation. TGA pyrolysis experiments showed about 60% of volatiles, 20% fixed carbon and 20% of ash on the average (dry). These results were very close to the results of fast pyrolysis experiments in a PDU with a twin-screw reactor. The chlorine was focussed in the pyrolysis char up to a temperature of ∼500°C. If the pyrolysis temperature exceeded 500°C the chlorine was released and its concentration in the chars decreased. The outside of the rice straw stems was completely covered with silica forming a close protection layer. SEM-studies show that the pyrolysis took place only at the inner sides of the stems. Therefore rice straw had to be chopped very carefully in order to brake up short stem pieces and to split them up. Additionally the SEM pictures confirmed the volatility of chlorine at temperatures above 500°C. Condensate viscosity, char porosity and the particle size spectrum as well as slurry production techniques play an essential role for slurry preparation and result in practicable condensate/char-weight ratio variations between about 3 to 1.3 for worse and unfavourable situations. With a special colloid mixer, a robust tool well known for the preparation of a very homogeneous cement grout it was possible to prepare a pumpable char/tar mixture with a high mixing ratio of almost 50% by weight.

Amount, availability, and potential use of rice straw (agricultural residue) biomass as an energy resource in Japan

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

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.

Effect of water and rice straw management practices on yield and water productivity of irrigated lowland rice in the Central Plain of Thailand

As the staple food crop in Sri Lanka, paddy rice occupies around 34% (over 0.87 million hectares of land) of the total arable area in the country, corresponding to an average rice production of 3,774,344 t/year. Rice straw is the major biomass waste from rice cultivation, which approximates to an average of 2,830,758 t/year generation at a theoretical straw/grain ratio of 0.75. Open burning of rice straw in paddy fields is the common practice, which could result in an average GHG emissions of 92 kg CO2 eq/t of dry rice straw and other harmful airborne emissions. Application of rice straw into soil as an organic fertiliser is also an inefficient practice, compared to bioenergy generation using rice straw. The average composition of the Sri Lankan rice straw (i.e. 30.0 wt.% cellulose, 3.9 wt.% hemicellulose, 38.2% lignin, 16.1 wt.% wax, and 12.3 wt.% silica) shows the possibility to be used as a second-generation bioethanol feedstock. Existing studies indicate that bioethanol production from rice straw is more environmentally-benign, compared to alternative options, such as gasification for combined heat and power and dimethyl ether (DME) production. This study analyses the net energy indicators of a possible bioethanol production process from rice straw in Sri Lanka. Chemical process simulations using Aspen Plus software were utilised to evaluate the bioethanol production process from rice straw, with a plant output capacity of 1,000 litres/hr of dehydrated bioethanol (99.7 vol.% ethanol) that can be blended with gasoline as a commercial fuel (e.g. E10: 10% bioethanol+gasoline) without any vehicle engine modification. The cradle to gate bioethanol production process from waste rice straw, considered for net energy analysis consists of three major stages: 1. Rice straw preparation, 2. Rice straw transportation, and 3. Bioethanol conversion. The results show that the considered bioethanol production process has a positive net energy gain and increased renewability factor. Detailed analysis indicates that only around 8% of the total process energy consumption is utilised for the bioethanol dehydration operation that is favourable for converting any existing rice straw ethanol plant into commercial gasohol production plant. The sensitivity of bioethanol yield and process energy parameters for the net energy indicator results are further analysed and discussed. The findings from this study can support decision making for a future waste-to-biofuel plant using waste rice straw in Sri Lanka. Keywords: Rice straw, Bioethanol production, Net energy analysis, Process simulation, Waste-to-biofuel

Although using fossil fuels in energy sector has led to economic growth in different fields, it caused an increase in greenhouse gas emissions, in consequence, global warming and climate change. Biomass use is essential for energy production and environmental protection. Studies on biomass residues, biomass energy, and environmental impacts of straw to energy chain in Egypt as a case study were reviewed in this chapter. The studies showed that a significant amount of biomass wastes from the main sources of agricultural, municipal solid wastes, animal and sewage sludge, with a total energy potential of 416.9 PJ. The annual dry biomass wastes amount from crop residues is about 12.33 million tons, and 63.75% of these residues are generated from rice straw. Thus, the use of rice straw as a renewable fuel for energy generation could reduce fossil fuel consumption, CO2 emissions, and air pollution caused by open burning. Direct combustion recorded the highest technique for energy recovery from rice straw. Water washing of rice straw as a pretreatment method resulted in a reduction of undesirable inorganic compounds related to ash problems in consequence, improving the combustion behavior. On the other hand, anaerobic co-digestion of rice straw with sewage sludge showed a significant increase in the energy (six times) that could be obtained from solo sludge. The environmental impacts study indicated the largest share of the total energy consumed and GHG emissions was due to paddy production and transportation, respectively. The annual energy potential from power plant and anaerobic digestion plant was estimated at 4,193 GWh of electricity and 25,647 TJ of biogas energy, respectively. Thus, the use of rice straw as an energy source helps in reducing fossil fuel consumption and air pollution caused by open burning with about 3 Mt CO2-eq of GHG emissions.KeywordsBiomassEgyptEnvironmental impactsRice strawSustainable energy