biofuel

The concern about limited fossil resources has led researchers to use renewable and new energies. Bioethanol is one of the most important and widely used biofuels that can replace fossil fuels. Bioethanol can be produced from various agricultural products and waste, such as grains, molasses, fruit, lignocellulosic materials, and algae. Molasses, an amorphous sugar extracted from sugar cane and sugar beet, is considered one of the most essential raw materials of sugar base. Sugars are usually produced with Saccharomyces cerevisiae yeast and bio-ethanol. Starch-based materials, such as wheat and corn, must first be enzymatically hydrolyzed, and then bioethanol is obtained with the help of the fermentation process. Agricultural wastes such as cereal straw, sawdust, and black liquor are considered lignocellulosic raw materials. Lignocellulosic raw materials are first de-ligninized. Then, the enzymatic hydrolysis process is performed, and finally, with the help of fermentation, bioethanol is obtained. This review article first deals with the production status of this biofuel in the world's leading countries. Then, it briefly mentions the bioethanol production process from sugar, starch, and lignocellulosic raw materials and the challenges of each method. It also examines the types of yeasts and compares them and the effective parameters in the fermentation, pre-treatment, hydrolysis, and distillation processes.

Waste can be described as any type of material or object that has no other use and is to be thrown away. Perspective, the generation of waste materials is unavoidable in a consumption-based society, and it makes waste management a major challenge considering the huge amounts of waste produced globally. In fact, in 2014, about 2.6 billion tons of waste was generated in the European Union (EU), of which 41% was disposed of in landfills, 36% was recycled, 10% was used in excavation operations, 7% was treated in sewage treatment plants and the remaining of 6% was burned for creating energy or oxidation and stabilization of waste. Accordingly, in recent decades, humanity has changed its focus on traditional waste management from the concept of "collection and disposal" in favor of hierarchical management of waste to increase sustainability.Nevertheless, even when environmentally friendly practices such as recycling and reuse are carried out, many operations are "downcycling", meaning that the recycled product has less economic value than its original objective, and is not as valuable as the original product made from strong raw materials. In this way, the linear economy model based on the pyramidal hierarchy of waste materials, which is used today, also has limitations. Indeed, there are still opportunities to increase productivity in many industrial processes, but these gains are likely to be increasingly marginal and undifferentiated. Therefore, the future acceptance of the circular economy concept, as opposed to the current linear model, is a necessary paradigm shift. This new concept is increasingly considered a source of innovation in products, processes, and business models and opens up great opportunities that should be used by companies and organizations as competitive advantages in a dynamic market to be used globally. The processing of raw biomass to produce energy, fuel and chemicals through a combination of different applied technologies is considered a promising path to achieve sustainable waste management, with many environmental and economic benefits. The main processes related to energy recovery and biofuel production are considered under the concept of biorefineries. This waste biorefineries are facilities that integrate the necessary technologies to convert biomass feedstock and other waste into usable products, ensuring that the circular economy moves from theory to the real world. Existing waste streams can be converted to biofuels (waste-to-liquids, WtL) or energy (waste-to-energy, WtE) technologies, both of which are expected to be a key element in future waste management. In general, energy and biofuel production technologies from waste are classified into three main thermochemical, biological and chemical processes. Thermochemical technologies include processes of combustion/incineration, gasification, steam explosion, pyrolysis, hydrothermal liquefaction, and torrefaction; biological technologies include the processes of anaerobic digestion, fermentation, enzyme purification, and microbial electrolysis, and chemical technologies include hydrolysis, solvent extraction, transesterification, and supercritical conversion.

The present research is a descriptive-review study whose data was obtained through library studies and various sources were used to process the material. Considering the importance of biofuels as a source of renewable energy, we tried to use as much as possible the most relevant and up-to-date sources containing valuable points regarding the types of energy and biofuel production technologies from biomass. In this review article, the possibility of using the remaining post-processed waste as available and low-cost bio-renewable resources in waste bio-refineries has been investigated. Waste biorefineries are facilities that integrate the necessary technologies to convert biomass feedstock and other waste into usable products, ensuring that the circular economy moves from theory to the real world. Existing waste streams can be converted to biofuels (waste-to-liquids, WtL) or energy (waste-to-energy, WtE) technologies, both of which are expected to be a key element in future waste management. Accordingly, in this paper, we briefly study the current status of the main WtL and WtE technologies in order to use them as a tool for the management of residual post-processing wastes and by-products resulting from them, and finally about Future developments on the mentioned technical options are briefly discussed.

In this review research, the possibility of using the remaining waste after processing as abundant and low-cost bio-renewable resources in waste bio-refineries in the future was investigated. Existing waste streams have a complex and diverse composition according to their source, which require new logistics platforms of classification and valuation. With the exhaustion of the linear economy of "collection and disposal", new methods of waste management are inevitable in the long term. In this way, waste biorefineries that generate green energy and produce virtual products with high value and zero waste (no waste) in a "closed loop" and "up-cycling" approach are the "landfills" of the future. It is expected that they will be very important and vital in bringing sustainable waste management into the real world that will allow transformative economic growth under the concept of circular economy. However, from the technologies reviewed, it can be concluded that individual WtL and WtE processes are almost always limited in their scope and produce multiple unwanted products. In this regard, the gasification process is largely considered a technology with greater potential and scope in individual applications. However, even this process has drawbacks such as reactor design, feed system, and bitumen production that require costly post-treatment and/or further technical improvements. In contrast, the combination of several WtE and WtL processes in an integrated waste biorefinery allows reducing and eliminate the drawbacks of each process. For example, in gasification, some of the unwanted materials produced may be used and valued by further chemical processing, and even syngas can be upgraded. This new pyramid of waste valorization creates opportunities for specific technologies such as explosive depressurization and drying to become practical applications by reinforcing other well-established technologies in an integrated approach. Future research should primarily focus on establishing a hierarchy of processes to produce the highest value products, and then gradually progress to low-cost products and energy production. However, for this vision to become a reality, an increased effort by researchers is required with continued and sustained support from all potential stakeholders. More pilot or semi-pilot scale demonstration projects should be realized in the coming years, focusing on aspects such as energy balance and cost-benefit analysis that will ensure the viability of the proposed solutions

Microalgae are diverse group of simple organisms, which are incorporated in pharmaceutical, cosmic, nutritional and biodiesel productions. The amount of growth in microalgae is affected by physical and chemical conditions of growth environment. In commercial scale in order to achieve highest amount of biomass or biodiesel, it is necessary to use culture media with proper combination of materials. Therefore, in this study, effects of different values of temperature, light intensity, lighting period, saltiness and pH were tested by their effect on cell concentration, biomass, lipid and biodiesel production in desmodesmus microalgae. As a result, the best temperature for increase in cell concentration of microalgae was 25 degree of Celsius,  light intensity of 4500 lux, light period of 17 hours, saltiness of 5 ppm and pH of 8. The highest amount of biomass was achieved in light intensity of 3000 lux, 18 hours of lighting, saltiness of 5 ppm and pH of 9. The highest amount of lipid was produced at temperature of 26, light intensity of 4200 lux, lighting period of 16 hours, saltiness of 12 and pH of 9. Finally, the highest amount of biodiesel was produced at temperature of 26, light intensity of 4200, lighting period of  16 hours, saltiness of 11 and pH of 9.

Microbial lipids have a capacity to use in biofuels, pharmaceutical and nutrition industries. The production and application of these lipids are increasing in compare with vegetable oils. The production of microbial lipid by Yarrowia lipolytica CBS6303 from glucose and investigation of its fatty acids profile to determine its biofuel potential were the aims of this study. Maximum lipid production and dry weight were obtained 1.42 and 7 g/L after three days, respectively. The produced lipid by Y. lipolytica from glucose contains fatty acids that can be used as biofuel like oleic acid (34.71%), linoleic acid (19.45%), palmitic acid (17.05%), stearic acid (6.12%) and myristic acid (0.82%).

The limited availability, high cost and the adverse environmental impacts of fossil fuels, persuaded the researchers toward the use of renewable energies. Biofuels are considered as one of the main sources of renewable energies. Woody debris, agricultural waste, sugar cane, vegetables as well as oils of cereals and vegetables are among the primary sources for biofuels production. Biofuels are produced from living organisms or their metabolic byproducts (organic waste products or food). Lignocelluloses of plant cell wall are  interesting sources for production of sustainable biofuels. Theconversion of lignocellulose to biofuels using existing technologies is too expensive mainly because of the need for  chemical pretreatments and enzymatic hydrolysis required forcell wall deconstruction. Modification of cell wall composition by using biotechnological approaches resulted in the reduction of cell wall hardness in various plant species. These results are obtained by reducing the amount of lignin as well as changing the composition and structure of final polymer. In addition, in some cases the reduction of cell wall hardness has been achieved by altering the hemicellulose biosynthesis genes as well as the ectopic expression of microbial genes in the plants with the aim of breaking the connections between lignin and carbohydrates residues. So far, genetic engineering has been used to improve the enzymes involved in digestion of cellulose and lignocellulose sources and engineering metabolic pathways involved in the production of biofuels. Also, these transgenic plants often produced higher sugar yield and ethanol. Modification of the cell wall in transgenic plants can reduce the stiffness of the cell wall without negative impact on performance. This shows that cell wall modification can be resulted without affecting the cell wall integrity or plant performance. To better understanding of the cell walls structure, we need to modify the lignocellulosic components as well as to reduce the price of biofuels production. In this review we tried to give a comprehensive introduction of biofuels and to introduce different potent methods of genetic engineering for the efficient production of biofuels. We also tried to point out all the important points on the pathway that can be modify and improved by biotechnology engineering. Finally, by evaluation the ahead challenges, the appropriate methods are suggested.

Ethanol as a renewable biofule is an appropriate and viable alternative to the challenging fossil fuels. Bacillus subtilis, a gram positive bacterium, seems to be a promising choice since it has many useful features. For example B.subtilis ferments broad range of sugars derived from lignocellulosic hydrolysis. Transformation of this cellulytic bacterium to an ethanologenic one was accomplished via metabolic engineering techniques and Ethanol production operon of Z.mobilis was introduced to the B.subtilis. SR1 and SR21 strains expressed plasmid-borne ethanologenic genes of Z.mobilis but the genes had been integrated into the SR22 genomic DNA. Also lactate dehydrogenase gene had been knocked-out in SR21 and SR22 strains. Defect of cell growth in SR21 and SR22, suggests that NAD oxidation by lactate dehydrogenase is important for anaerobic growth. Considering the impact of Fe2 ion on alcohol dehydrogenase II activity, in further experiments Fe2 was added to the culture media and improvement in growth rates was seen. Final yield of ethanol production of SR1, SR21, and SR22 strains were 53.8%, 86.7%, and 83.9% respectively.

Greenhouse effect problems، environmental pollution، global increase in oil demand، and reduced fossil fuel resources have boosted research on the production of renewable energies such as bioenegries in recent years. Amongst various biofuels، biobutanol has been recently introduced as a replacement liquid fuel for gasoline and gas oil. Anaerobic bacteria such as Clostridium acetobutylicum are able to produce acetone، butanol، and ethanol using different sugar sources. This bacterium exhibits amylolytic activity and therefore is able to hydrolyzes starch to glucose and use it directly as carbon source. In this study، three substrates including glucose، treated starch and starch were used in different concentrations to produce butanol by Clostridium acetobutylicum PTCC 1492. For all three carbon sources، 60 g/ l of substrate was found as the optimum concentration. The results revealed that this bacterium is capable of producing butanol using all three carbon sources without any treatment. Butanol concentrations of 6. 45، 5. 81، and 4. 64 g/ l were obtained using non-treated starch، treated starch، and glucose as carbon sources، respectively. Discussion and The results suggested the possibility of using non-hydrolyzed starch as carbon source for butanol production. Also it was shown that non-treated starch produces more butanol compared to the treated starch.

Microalgae as a source of saturated and unsaturated fatty acids, pigments, pharmaceutical and food metabolites, has received more focus by biological researchers at last decades. The amount and composition of fatty acids produced by microalgae depended on biomass production and environmental factors such as changes in salinity, light and nutrient availability. In this study, the green microalgae Dunaliella bardawil isolated from Chabahar Bay was cultured under different salinities (35, 70 and 105 g/L) using Conway medium. All treatments with air pump at 25±2 ° C and 12L: 12D (h) photoperiod and aerated. Effect of different salinity on the growth rate, lipid production and fatty acid composition of algal biomass were examined. ANOVA results showed that the highest growth rate and lipid content in the salinity of 70 g/L was obtained which are 933 and 206 milligrams per liter, respectively. Maximum and minimum lipid content of D. bardawil measured, 24.5 and 19 percent, at 105 and 35 ppt, respectively. Due to reduced cell density in 105 grams of salt per liter of fat produced per unit volume decreased to 65mg/L. The results show that D. bardawil purification from Chabahar Bay with degree unsaturation between 95-73 has great potential for biodiesel production.

The production of bioethanol from lignocellulosic biomass could be considered as an appropriate and economic option to remove environmental disasters and improve energy security. In fact، lignocellulosic material is mainly composed of cellulose، hemicellulose and lignin. Lignin works as the adhering prevents the bioconversion of cellulose into sugars and ultimately to ethanol. To address the problem، various chemical، physical، physicochemical and biological methods have been suggested. Enjoying convenient operating conditions، production of non-hazardous wastes، and having no harmful side effects، make the biological methods a potentially proper option. Unfortunately، the biological methods are slower and less efficient in comparison with the other processes. In the present study، an attempt is made to resolve this problem in an enzymatic degradation of lignin of a rice straw sample. Several peroxidase enzymes were produced by a white rot fungus، and their effects on lignin removal from the biomass samples were investigated in shaking flasks. Lignin concentration and enzymes'' activity were measured by the acetyl bromide-soluble lignin spectrophotometric method and optical density method using special reagents، respectively. The results revealed that the enzymatic treatment could remove at least 30% of the lignin content of the lignocellulosic biomass. To achieve the maximum activity of the enzymes، The chemical composition of the culturing medium was optimized for the concentration of important metal ions including Cu2+، Mn2+ and Zn2+ through Box Behnken response surface methodology. The enzymes'' activity at the obtained optimal conditions increased four times for Manganese peroxidase، and lignin peroxidase.

Having considered that genetically modified organisms and their products are increasingly being used in the developing countries, observing biosafety rules and legislations as a tool to guarantee products` safety is recommended. Although biotechnology simulates the same mechanisms as the nature’s, however, some concerns about its potential risks and consequences when used inconsiderately have been raised. Therefore, it is undeniable that like other newtechnologies, biotechnological applications could carry some potential risks too. Having all taken into consideration, it could be concluded that exploiting new opportunities created by genetic engineering approaches is feasible provided that appropriate risk analysis and applying scientific methods for decreasing or preventing the risks involved, are performed. In this paper, the various aspects of bioethics and biosafety of introduction and application of genetically engineered microalgae are discussed. Also, the potential applications of these microorganisms and their bioproducts in social health and hygiene, bioremediation and green fuel production have been reviewed. The unique physiologic abilities turn microalgae as a prominent tool in reaching the goals of biotechnology in line with biosafety aspects.