Role Of Microbes In Biofuel Production

Microbes are the organisms not able to be seen from naked eye. They play various roles in our daily life used as in biofuel production, biofertilization etc.

Biofuel

Energy products such as alchohols, diesel, hydrogen, biogas produced by the help of microorganisms are called biofuels. Microorganisms help in fermentation process or provide essential enzymes and help in the production of biofuels. Due to increase in global energy demand and increase in global oil prices biofuel is an area of immense interest by microbiologists and biotechnologists.

Role of microbes in daily life:

• In Bioprocessors ( direct and indirect fermentation)
• As a source of biocatalyst (enzymes)
• Cell wall modification
• Feedstock preservation
• pretreatment
• Hydrolysis
• Fuel production (An array of conversion options)
• Other [energy saving & environmental roles
• Carbon recycling
• Micro-carbon sinks
• Waste treatment/Bioremediation

First-generation biofuels

Brazil uses sugar cane as an energy crop due to multiple reasons that are unique to this country:

• (1) Early investments ,immense research and industrial expertise.
• (2) Nature of sugar cane in which the product (sucrose) does not require processing of complex polymeric plant molecules.
• (3) Available vast areas of extremely fertile land with ample rain.
• (4) Availability of cheap labor.

Due to the high percent of sucrose in sugar cane syrup, extraction of sucrose from sugar cane is a relatively simple process.

Second Generation Biofuels

Scientists now are looking to harvest energy from weeds and other plants that grow naturally.(A process that has been termed cellulosic ethanol production).Currently, the emphasis is on using crop residues, e.g. stover, straws, hulls, stems, and stalks.The composition of these materials varies but, in general, the major polymers within lignocellulosic biomass is cellulose (35–50%),hemicellulose (20–35%), and lignin (10–25%). The presence of active cellulase systems (of all three enzymes) is widespread within the fungi, aerobic, and anaerobic bacteria.

Cellulase enzymes are either produced extracellularly, mainly in aerobic fungi, or produced as a complex structure called the cellulosome that is bound to the cell membrane in anaerobic bacteria (e.g. Clostridia), as well as members of the Neocallimastigales, anaerobic fungi present in the gut of rumens and other herbivores.

Currently, enzymes derived from the aerobic fungal genera Trichoderma and Aspergillus are most widely used in industrial settings.

Ethanol production:

• Saccharolytic microbes Fermentative microbes
• Hydrolytic enzymes
• Single species Complex of multiple enzymes (Cellulosome)

Fermentation

Ethanol is produced by microbial fermentation of the sugar.

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Microbial fermentation currently only works directly with sugars. Two major components of plants, starch and cellulose, are both made of sugars—and can, in principle, be converted to sugars for fermentation. Currently, only the sugar (e.g., sugar cane) and starch (e.g., corn) portions can be economically converted. There is much activity in the area of cellulosic ethanol, where the cellulose part of a plant is broken down to sugars and subsequently converted to ethanol.

Direct Fermentation

The production of ethanol where starting material is plants called direct fermentation. The first process is to identify the starting plant material. The second step is isolation followed by the development of bacterial and fungal strains. By using genetically engineered strains of bacteria or by yeasts these sugars are then converted into ethanol.

Indirect Fermentation

Another method for the production of ethanol is indirect fermentation. The starting material is pyrolyzed(burned) which produces Syngas. Syngas consists primarily of CO and carbondioxide. By using acetogenic bacteria these are than converted into ethanol.

Conversion of sugars to alcohols

The degradation of starch, cellulose and hemicellulose also yields hexoses and pentoses that can be fermented to produce ethanol. In this process multiple fermentation techniques are known that produces ethanol as an end product. For example; mixed acid fermentation by enteric bacteria and acid fermentation by some lactic bacteria

Biodiesel

Biodiesel is a form of diesel fuel derived from plants or animals. It is made by chemically reacting lipids such as animal fat (tallow), soybean oil,etc with an alcohol, producing a methyl, ethyl.

Biodiesel production

Algal biomass contains three main components: carbohydrates, proteins, and lipids. Bulk of the natural oil made by microalgae is in the form of tricylglyceride. Some algal species can production hydrogen gas under specialized growth conditions. The biomass from algae can also be burned similar to wood or anaerobically digested to produce methane biogas to generate heat and electricity.

Anaerobic digestion

Anaerobic digestion is a process by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels.

Many microorganisms affect digestion, including

• Acetic acid-forming bacteria (acetogens)
• Methane-forming archaea (methanogens
• These organisms speed up a number of chemical processes
• In converting the biomass to biogas.

BIOHYDROGEN AS BIOFUELS

Since hydrogen is oxidized to water it is the cleanest of all biofuels. It emits no carbon dioxide in the process .Hydrogen is the final product of fermentation and a side product in photosynthesis in many groups of microorganisms and a vast body of literature is available regarding the kinetics, structure, properties and behavior oh hydrogenase enzyme. There are three main focuses in the biohydrogen production research e.g. cyanobacteria and Green algae in biohydrogen production.

Biogas is a mixture of methane and carbon dioxide. It is produced under anaerobic conditions from the methanogenic decomposition of organic wastes. By a defined culture of fermentor and hydrogenotrophic(hydrogen-consuming) methanogen biogas production can be achieved. However, undefined cultures can also be used as inoculum for biogas production. The following image shows the production of biogas from microalgae.

Rather than the starting material stages most of the cost is in the production in biofuel production. So the approaches to lower cost are highly desirable. In consolidated biological processing the plant materials are converted into biofuels using microbial agents. This approach has been recognized as the most effective way of biofuel production more cost effective compared to first-generation biofuels that are currently commercially used.