Bioethanol production from agricultural wastes: An overview

Second-generation bioethanol can be produced from various lignocellulosic biomasses such as wood, agricultural or forest residues. Lignocellulosic biomass is inexpensive, renewable and abundant source for bioethanol production. The conversion of lignocellulosic biomass to bioethanol could be a promising technology though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosics. Proper pretreatment methods can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process. Conversion of glucose as well as xylose to bioethanol needs some new fermentation technologies to make the whole process inexpensive. The main goal of pretreatment is to increase the digestibility of maximum available sugars. Each pretreatment process has a specific effect on the cellulose, hemicellulose and lignin fraction; thus, different pretreatment methods and conditions should be chosen according to the process configuration selected for the subsequent hydrolysis and fermentation steps. The cost of ethanol production from lignocellulosic biomass in current technologies is relatively high. Additionally, low yield still remains as one of the main challenges. This paper reviews the various technologies for maximum conversion of cellulose and hemicelluloses fraction to ethanol, and it point outs several key properties that should be targeted for low cost and maximum yield.

Sustainable bio-ethanol production from agro-residues: A review

Due to rapid growth in population and industrialization, worldwide ethanol demand is increasing continuously. The abundant sources of lignocellulosic biomass (LB) from agricultural wastes are attractive feed stocks to become a sustainable source for bioethanol production. There are many crucial engineering steps involved in the bioethanol production route especially on the pretreatment which comprises of chemical, mechanical and biological approaches. In this study we reviewed the various pretreatment involved in biofuel production. By considering the all steps required which may incur costs then influence the price of bioethanol an effective pretreatment technology is required for minimizing the cost and concurrently minimizing other problem especially environmental pollution caused by the pretreatment process. Therefore, a compact step combining all or some of the steps and with additional application of green technology with ionic liquid (IL) will be beneficial to the future direct production of liquefied biofuel with chemical-mechanical-biological based techniques starting from the pretreatment study which therefore lessen cost incurred and process time.

The lignocellulosic substances such as agricultural wastes are promising feedstocks for bioethanol production. Because they are cost effective, renewable, abundant and not having primary value for food and feed. The current study suggests that improvements in polysaccharide hydrolysis of under-utilized biomass of carrot pomace may find practical use in its conversion to bioethanol by Saccharomyces cerevisiae and Pichia stipitis fermentation. Some important parameters for bioethanol production such as pretreatment procedures (CaO and activated charcoal treatments), nitrogen sources ((NH) 2 SO 4 , soy wheat, cheese whey), and pomace loading amount (15-120 g/L) were optimized in the study. The highest bioethanol production could be achived when the saccharification and fermentation conditions were optimized in order to increase monosaccharide yield and fermentation of both six-carbon and five-carbon monosaccharides. The bioethanol production was 1.9 –fold higher for S. cerevisiae and 4.6 –fold higher for P. stipitis when (NH 4 ) 2 SO 4 was added in addition to the trace nitrogen substances, vitamins and minerals present in carrot pomace. The highest bioethanol production values were obtained as 6.91 and 2.66 g/L in the presence of 120 g/L pomace loading, 1 g/L (NH) 2 SO 4 at the end of 72 hours incubation time at pH 6 by S. cerevisiae and P. stipitis , respectively.

The growth of the hospitality industry coupled with rapid population growth, urbanization and weak institutions and poor governance have undermined efforts to mitigate resultant negative environmental impacts. The general objective of this study was to examine the moderating effect of hotel star-rating on the relationship between green solid waste management practices and sustainability of hotels in solid waste disposal in Nakuru County, Kenya. The research used a cross-sectional mixed-methods survey design and targeted 259 hotels in Nakuru County. A sample size of 204 hotels was determined using Krejcie and Morgan formulae. Stratified random sampling was used for selecting hotel managers for the survey while purposive sampling was used for selecting the key informant interviewees. The data collection tools used in the study were a semi-structured questionnaire and in-depth interviews guide. A binary logistic regression model was used to evaluate the moderating effect of hotel star-rating on relationship between green waste management practices and sustainability in solid waste management in the hotel industry in Nakuru County. Results showed that hotel size, policies, staff capacity, and market access influence sustainable waste practices. A majority (94.1%) of Nakuru hotels are non-star rated, with only 5.9% star-rated, mainly 3-star (50%). Hotel star-rating did not significantly moderate the relationship between green solid waste practices and sustainability, with a marginal effect of -0.038 (p = 0.734). Star-rated hotels showed a slight, non-significant decrease in adopting sustainable waste practices, indicating star rating is not a key determinant of sustainability in Nakuru hotels. Star rating does not strongly influence the relationship between green waste practices and sustainability of hotel waste disposal practices. The study recommends that hotels should integrate green waste management into star ratings, develop policies, and train staff. Higher-star hotels should invest in advanced solutions while lower-star hotels adopt low-cost practices.

Lignocellulosic substances such as agricultural wastes are attractive feed stocks for bioethanol production. <em>Indica</em> 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 <em>Indica</em> 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 <em>Saccharomyces cerevisiae</em> directly assimilated the glucose to bioethanol. The faster rate of bioethanol production during DSF by <em>S</em><em>accharomyces cerevisiae</em> 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.

The growing interest on bioethanol has increased the pressure over new feedstock production and processing schemes. Conventional edible crops are no longer interesting as raw materials for the production of bioethanol because of their prices and ethical concerns; thus, new substrates must be used. Attending to these new necessities, lignocellulosic substrates, mainly agricultural and forest wastes, seem to be a very interesting option for bioethanol production. However, it is necessary to previously solve several limitations in their processing. These limitations are mainly related to the pretreatment used in the production process, because this stage is essential in order to make more accessible the substrates and increase the concentration of fermentable sugars after the enzymatic hydrolysis. The selection of the most adequate pretreatment and the best operation conditions for its implementation will lead to higher bioethanol yields, making the process cost-effective and more competitive with other liquid fuels. In this work, an overview of the biorefinery concept and the bioethanol production is presented.

Recent advances in CFD modeling of bioethanol production processes

Bioethanol production technology using lignocellulosic substrates has become a focus to overcome the limited supply of fossil fuels in the current century. Simultaneous saccharification requires an understanding of suitable efficient procedures in bioconversion row material into fermented sugar. In this study, the effect of pre-treated rice straws using ionic liquid on enzymatic saccharification by isolated actinomycetes was investigated. Ionic liquid to rice straw in a ratio (IL/RS) was set up 0 to 3 (g/g), and the remaining of the ionic liquids in pre-treated biomass was examined for their effect on the hydrolytic enzyme activity of the actinomycetes. Three actinomycetes were isolated from decomposed rice straw and were purified and screened for their cellulolytic and xylanolytic activity; one strain, namely ActRS-4, was selected as an optimum isolate for further hydrolysis examination. Both cellulase and xylanase activity exhibit a peak at a ratio IL/RS of 1 (g/g), the activity was 27.72 and 66.16 U/ml, respectively. The highest yield of sugar was also achieved at this IL/RS ratio for 8 days of incubation. The pretreatment indicates that it could promote an increase in the yield of glucose and xylose by 28% and 37% respectively. This study was promising to develop a one-pot conversion of lignocellulosic biomass into bioethanol using the biological process.

Bioethanol is one of the most promising and eco-friendly alternatives to fossil fuels, which is produced from renewable sources. Bioethanol can be produced from different kinds of raw materials. Conventional crops such as corn and sugarcane are unable to meet the global demand of bioethanol production due to their primary value of food and feed. Agricultural wastes are cost effective, renewable and abundant. To do this, very high gravity (VHG) fermentation which involves use of medium containing high sugar concentration(&gt;250g/L) must be implemented to achieve high ethanol concentration. However, VHG fermentation leads to significant stress for Saccharomyces cerevisiae due to osmotic pressure at the beginning of the fermentation and high ethanol content at the end. At this review, rice straw is the most abundant waste compared to the other major wastes and potentially produce 205 billion liters bioethanol per year, which is the highest among these four mentioned agricultural wastes.

Biomass co‐firing with coal is a near‐term option to displace fossil fuels and can facilitate the development of biomass conversion and the build‐out of biomass supply infrastructure. A GIS‐based modeling framework (EU‐28, Norway, and Switzerland) is used to quantify and localize biomass demand for co‐firing in coal power plants and agricultural and forest residue supply potentials; supply and demand are then matched based on minimizing the total biomass transport costs (field to gate). Key datasets (e.g., land cover, land use, and wood production) are available at 1,000 m or higher resolution, while some data (e.g., simulated yields) and assumptions (e.g., crop harvest index) have lower resolution and were resampled to allow modeling at 1,000 m resolution. Biomass demand for co‐firing is estimated at 184 PJ in 2020, corresponding to an emission reduction of 18 Mt CO2. In all countries except Italy and Spain, the sum of the forest and agricultural residues available at less than 300 km from a co‐firing plant exceeds the assessed biomass demand. The total cost of transporting residues to these plants is reduced if agricultural residues can be used, as transport distances are shorter. The total volume of forest residues less than 300 km from a co‐firing plant corresponds to about half of the assessed biomass demand. Almost 70% of the total biomass demand for co‐firing is found in Germany and Poland. The volumes of domestic forest residues in Germany (Poland) available within the cost range 2–5 (1.5–3.5) €/GJ biomass correspond to about 30% (70%) of the biomass demand. The volumes of domestic forest and agricultural residues in Germany (Poland) within the cost range 2–4 (below 2) €/GJ biomass exceed the biomass demand for co‐firing. Half of the biomass demand is located within 50 km from ports, indicating that long‐distance biomass transport by sea is in many instances an option.

Because of rapid growth in population and industrialization, worldwide ethanol demand is increasing continuously. The first-generation and second-generation biofuels are unable to meet the global demand of bioethanol production because of their primary value of food and feed. Therefore, algae are among the most potentially significant sources of sustainable biofuels in the future of renewable energy because of the accumulating high starch/cellulose and because they are widely distributed in nature. The focus of this paper is to review the production and recent advances in research and development in the algae bioethanol, including pretreatment, hydrolysis, and fermentation of algae biomass. Despite the many developments made in the recent years, commercialization of algal bioethanol remains challenging chiefly because of the techno-economic constraints. Technological breakthroughs in all major aspects must be overcome before it can be a successfully large-scale and commercialized product. Copyright © 2014 John Wiley & Sons, Ltd.

Rapid population growth is one of critical problems for most of Sub-Sahara African economic development. As a result of this, imbalances between population number and existing resource were intensified in developing countries including Ethiopia. Most of empirical studies show that rapid population growth was determined by different biological, social, economic and institutional factors. This study aimed to assess rapid rural population growth and its determinant factors in Wolaita zone. Relevant data were collected both from primary and secondary sources. Diverse types of data including demographic, socio-economic and policy-related data were obtained from 300 randomly selected rural households. Data were analysed using both descriptive and inferential statistics. Wolaita is characterized by a high population density and a fast population growth rate above 3 %. Population growth was indeed higher than annual national growth rate. The average household size in the study area was about 6.7 members per household. Age at first marriage, educational level, daily income and livelihood security of household heads, and contraceptive practice are consistently significant and principal factors of large household size. The population theory aspect of Malthusian, Utility Cost Theory and Mediating Theory principles mostly aligned with the study area realities. Therefore, this study points out that managing rapid population growth by implementing a strict population policy/strategy in the study area is important.

Every year, an abundance of agricultural wastes are produced after harvest, which are generally burned or discarded in the farmland. Agricultural wastes are an attractive lignocellulosic material for fermentable sugar production (glucose and xylose) since they are polysaccharide-rich resources. Unfortunately, the intimate associations between the main components of the cell wall create barriers for the enzymatic saccharification of cellulose and hemicellulose. Pretreatment plays a critical role in increasing enzymatic saccharification to obtain the glucose and xylose from pretreated agricultural wastes by different enzymes. The present review is a comprehensive evaluation to describe the advancements in pretreatment and enzymatic saccharification processes to produce the fermentable sugars from agricultural wastes. Using these agricultural wastes for the sugar production is ideal for developing bio-based chemicals while converting unwanted agricultural waste streams into valuable resources.

Bioethanol is a feasible alternative to fossil fuel, as it is considered to be clean, renewable, and green; it is obtained from biomass; and bioenergy crops have been proclaimed as one of the alternatives to fossil fuel. Wasted crop, which is defined as crop lost in distribution, is considered as feedstock to avoid conflicts between human food use and industrial use of crops. Agricultural wastes have been considered as best options to look for; agricultural waste such as fruit wastes could be a promising technology, though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosic materials. Worldwide, these fruit wastes are often simply dumped into landfills and oceans or used as animal feed; the recovery of wastes as renewable energy sources represents a sustainable option for the substitution of fossil energy in order to decrease expected environmental damages like global warming and acid rain. Fruit wastes have high levels of sugars like glucose, sucrose, and fructose that can be transformed to bioethanol through four processes of pretreatment, enzymatic hydrolysis, fermentation, and distillation.