Role of Microorganisms in Biofuel Production

 

Role of Microorganisms in

Biofuel Production

1.    Introduction:

 

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. Concerns over climate change have necessitated a rethinking of our transportation infrastructure. One possible alternative to carbon-polluting fossil fuels is biofuels produced by engineered microorganisms that use a renewable carbon source. Two biofuels, ethanol and biodiesel, have made inroads in displacing petroleum-based fuels, but their uptake has been limited by the amounts that can be used in conventional engines and by their cost. Advanced biofuels that mimic petroleum-based fuels are not limited by the amounts that can be used in existing transportation infrastructure but have had limited uptake due to costs. Several types of microbes such as whole cells of algae, fungi, yeast, and bacteria are employed to produce biofuel which include several steps such as aerobic and anaerobic fermentation, transesterification, etc. for biofuel production.

 

2.    Types of Biofuels:

 

Biofuel can be described as an inexhaustible, biodegradable fuel that is derived from biomass—that is, plant or algae material or animal waste. Biofuel is considered to be renewable energy since such feedstock material can be replenished readily. Major types of biofuels include:

 

       i.         
Bioethanol: Bioethanol is referred to as ethyl alcohol, its chemical structure comprises two carbon atoms linked with six hydrogen atoms and one atom of oxygen (C₂H₅OH). Bioethanol is mainly produced via microbial fermentation of carbohydrates. The Chemical composition of bioethanol can be shown as:

 

Methane (CH4)	40-75%
Carbon dioxide (CO2)	25-55%
Hydrogen sulphide (H2S)	0-3%
Ammonia (NH3)	0-1%
Water (H2O)	0-10%
Nitrogen (N2)	0-5%
Oxygen (O2)	0-2%
Hydrogen (H2)	0-1%

     ii.          Biogas: Biogas is a type of gas that is produced by the biological breakdown of organic matter with the help of microorganisms under anaerobic condition. Biogas consists mainly of methane and carbon dioxide. It can also include small amounts of hydrogen sulphide, siloxanes and some moisture. The relative quantities of these vary depending on the type of waste involved in the production of the resulting biogas. The primary composition of biogas includes:

 

 

 

3.    Production process of Biofuel:

 

a.      Biogas:

 

·       Biogas is a renewable source of energy which is produced by microbial decomposition of organic material under anaerobic conditions.

·       The raw materials include waste from animals and plants, including municipal waste.

·       The bacteria which produce the gaseous mixture are collectively known as methanogens. Methanobacterium is one such methanogen.

 

                                                    i.     Production process of Biogas:

 

Step 1: Pre-treatment and filling the digester:

 

Multiple types of organic matter, called substrates, go into the digester. These include liquid manure, renewable raw materials like corn or grass or waste produced by the food industry.

Step 2: The fermentation process:

 

The substrates are heated to various temperatures inside the fermentation and a series of microorganisms start breaking down the organic matter in the absence of light and oxygen .

 

Step 3: Producing biogas:

 

As a result of the fermentation, biogas with methane as the main ingredient is produced inside the fermenters. Besides methane and carbon dioxide, water and hydrogen sulfide are also formed.

 

Step 4: Pulling out the residues:

 

After fermentation, the residues called digestate are pulled out of the tank to be used as environment friendly, high quality fertilizer.

 

Step 5: Eliminating impurities:

 

The biogas goes through a cleanup process, in which water, hydrogen sulfide and impurities are removed to produce biomethane that can further be used to generate energy and heat.

                                            

      ii.     Microorganisms in Biogas production:

 

 

·       Hydrolytic and fermentative bacteria:

They remove the small amounts of O₂ present and create anaerobic conditions. Example: Thermoanaerobium brockii.

·       Syntrophic H₂ producing bacteria:

That oxidized NADH by reducing H⁺ to H_2, and thereby produce hydrogen. Example: Syntrophomonas wolfei.

·       Methanogenic bacteria:

Methanogens remove the H₂ produced by obligate H₂ producing bacteria, thereby lowering the H₂ partial pressure and enabling the latter to continue producing H_2. Example: Methanobacterium omelianskii.

·       Acetogenic bacteria:

Acetogenic bacteria also remove H₂ and enable the obligate H₂ producing bacteria to continue their function. Example:Clostridium aceticum.

 

b.     Bioethanol:

 

·       Bioethanol is a Colorless and clear liquid.

·       Used to substitute petrol fuel for road transport vehicles.

·       One of the widely used alternative automotive fuel in the world (Brazil & U.S.A are the largest ethanol producers)

·       Much more environmentally friendly

·       Lower toxicity level

 

Bioethanol is primarily composed of ethanol, a simple alcohol with the chemical formula C2H5OH. It also contains water and small amounts of other impurities, depending on the production process. These impurities can include:

·       2,3-butanediol

·       1,3-butanediol

·       Butanoic acid

·       Acetic acid

·       Glycerol Etc.

 

 

                                                    i.     Production process of Bioethanol:

 

·       Wheat/Grains/Corn/Sugar-cane can be used to produce ethanol. (Basically, any plants that composed largely of sugars)

·       The main method is  Sugar fermentation.

·       The other three methods are hydrolysis (extraction of sugars out of bio-mass wastes)

v concentrated acid hydrolysis

v enzymatic hydrolysis

v dilute acid hydrolysis

 

1.     Concentrated Acid Hydrolysis:

 

·       ~77% of sulfuric acid is added to the dried biomass to a 10% moisture content.

·       Acid to be added in the ratio of 1/25 acid :1 biomass under 50°C.

·       Dilute the acid to ~30% with water and reheat the mixture at100°C for an hour.

·       Gel will be produced and pressed to discharge the acid sugar mixture.

·       Separate the acid & sugar mixture by using a chromatographic column.

 

2.     Enzymatic Hydrolysis:

 

·       In bioethanol production, enzymatic hydrolysis is a critical step. It converts complex polysaccharides (such as cellulose and hemicelluloses) into simpler sugars.

·       These sugars serve as substrates for fermentation, ultimately yielding bioethanol.

·       Researchers continually explore new and effective enzymes to enhance the cost-effectiveness of the process.

 

3.     Dilute Acid Hydrolysis:

 

·       Oldest, simplest yet efficient method

·       Hydrolyze the bio-mass to sucrose

·       Hemi-cellulose undergoes hydrolysis with the addition of 7% of sulfuric acid under the temperature 190°C.

·       To generate the more resistant cellulose portion, 4% of sulfuric acid is added at the temperature of 215°C.

 

                                                  ii.     Microorganisms in Bioethanol Production:

 

·       The most employed microorganism for bioethanol production from sugar-containing feedstocks is Saccharomyces cerevisiae due to its capacity to degrade sucrose into hexoses (glucose and fructose).

·       The cells of S. cerevisiae require small amounts of oxygen for fatty acid and sterol synthesis during bioethanol production, so aeration is an important bioprocess parameter. S. cerevisiae does not tolerate higher sugar and salt concentrations in the medium or higher temperatures. Cane molasses media have the highest osmolarity as a consequence of medium sugar and salt concentrations, which negatively affects ethanol synthesis. Numerous studies have searched for S. cerevisiae strains with higher salt and temperature tolerance .

·       Yeast Schizosaccharomyces pombe is also used in bioethanol production since it tolerates high osmotic pressures (high salt concentrations) and high solid content .

·       In bioethanol production the possibility of using other microorganisms such as Zymomonas mobilis, Klebsiella oxytoca, Escherichia coli, Thermoanaerobacter ethanolicus, Pichia stipitis, Candida shehatae, Mucor indicus, etc. It is investigated that,  However, adequate alternative to S. cerevisiae still has not been found .

 

4.    Production influencing factors (Biogas):

 

Biogas production is a complex process influenced by several factors. Here's a quick rundown of the key ones:

 

·       Substrate: The type of organic matter you feed the digester significantly impacts biogas yield. Manure, food waste, and crop residues are all good options, but their biogas potential varies.

 

·       C/N Ratio: The carbon to nitrogen ratio (C/N) of the feedstock is crucial. Microbes need both carbon and nitrogen for growth. An ideal C/N ratio is typically between 20:1 and 30:1.

 

·       Temperature: The temperature inside the digester greatly affects the activity of microbes. There are three main temperature ranges used in biogas production:

 

§  Psychrophilic (cold): 15-25°C

§  Mesophilic (moderate): 30-40°C

§  Thermophilic (hot): 50-60°C

 

·       pH Level: The pH level of the digester should be slightly acidic, ideally between 6.5 and 7.5. If the pH falls too low or high, it can inhibit microbial activity.

 

Optimizing these factors is essential for maximizing biogas production from a digester system.

 

5.    Production influencing factors (Bioethanol):

 

Several factors can affect the production of bioethanol:

 

·         Feedstock: The type and quality of the biomass used (corn, sugarcane, switchgrass, etc.) significantly influence ethanol yield and production costs.

 

·         Fermentation Efficiency: The efficiency of the fermentation process, including the type of microorganisms (yeast or bacteria) and their ability to convert sugars into ethanol.

 

·         Pretreatment: Preprocessing steps like milling, grinding, or chemical treatments can affect the accessibility of cellulose and hemicellulose to enzymes, thus impacting ethanol yield.

 

·         Enzyme Activity: The effectiveness of enzymes in breaking down cellulose and hemicellulose into fermentable sugars.

 

·         Fermentation Conditions: Factors like temperature, pH, and nutrient availability during fermentation can affect the growth and activity of microorganisms.

 

·         Separation and Purification: The efficiency of separating

 

 

6.    Conclusion:

 

Microorganisms are major players in the production of biofuel. However, the product’s yield by native strains is not economical, thus making it necessary to develop and improve them through the approach of metabolic engineering and genetic engineering. Recent studies have focused on applying metabolic engineering to model strain development to optimize high productivity and energy value at a cheaper cost of production. In the nearest future, there is a high possibility that more unique metabolic pathways for biofuel production could emerge from database mining. Thus, the implementation of these pathways in industrial fermentation hosts may overcome any bottlenecks associated with the use of lignocellulosic biomass as a renewable fermentation feedstock. Metabolic engineers need to tap into the use of advanced technologies currently available such as the omics technologies and CRISPER/Cas9 system to design and generate novel strains of microbes with enhanced ability to produce biofuel from diverse substrates by insertion of relevant genes into the genome or deletion of obstructive ones.