Ethanol Production by Fermentation, Process, Applications, and Factors Affecting:
Introduction to Ethanol Production:
- Ethanol, also known as alcohol, is an organic chemical compound with the molecular formula C2H5OH.
- Alcohol in ambient conditions is a colorless clear liquid with a characteristic odor and is mixed with water in any proportion.
- Ethanol can produce in two ways Fermentation method and the Chemical synthesis method.
- 80% of ethanol is produced by the fermentation process and 20% by chemical synthesis.
- To produce ethanol number of micro-organisms are used like Yeast, bacteria, and fungi.
- Industrial production of ethanol is done by species like Saccharomyces cerevisiae, Schizosaccharomyces, Zymomonas mobilis, and Escherichia coli.
- Industrial production of ethanol can be carried out by submerged fermentation.
- Production of ethanol is completed in three steps upstream, fermentation, and downstream process.
- Ethanol is mostly produced from carbohydrates-based media using submerged fermentation, a variety of raw materials such as molasses-like cane and blackstrap molasses, beet molasses, and corn molasses are suitable for ethanol production.
- The optimum temperature used for the production of ethanol is between 30-40°C.
- The optimum pH is about 4-5.
- Various factors affect ethanol production like carbon and nitrogen source, Temperature, pH, Aeration and Agitation, Nutrient Concentration, Trace elements, etc.
Microorganisms used for Ethanol Production:
- Today, Ethanol fermentation technology plays a huge role in the Food, Energy, Pharma, and Medical industry.
- To produce ethanol various kinds of micro-organisms are used like Yeast, bacteria, and fungi.
- Ethanol is mainly produced by submerged fermentation using Saccharomyces cerevisiae from different sources of carbohydrates, such as molasses and sucrose-based media.
- Other species like Escherichia coli, Schizosaccharomyces, and Zymomonas mobilis are used for ethanol production.
- The main advantages of using this microorganism are: that it is easier to obtain and easy to handle its ease of handling. It gives maximum yield and can ferment a variety of cheap raw materials like molasses and starch.
Raw Materials used for Ethanol Production:
Although ethanol is mostly produced from carbohydrates or sucrose-based media using liquid fermentation, a variety of raw materials such as molasses-like cane and blackstrap molasses, beet molasses, and corn molasses are suitable for ethanol production.
Stages of Ethanol Fermentation:
Industrial fermentation of ethanol requires the three most important stages to complete product (ethanol) fermentation. These are the upstream process, and actual fermentation and the last one is downstream process.
1. Upstream process of fermentation:
- The upstream process includes the initial steps of a fermentation process.
- The upstream process of ethanol fermentation comprises initial tasks to screen and identification of suitable microorganisms, and their improvement, Substrate selection, and Culture media preparation to enhance productivity and yield.
- In the upstream process of ethanol fermentation, the medium should contain a carbon source, an energy source, a nitrogen source, and, micronutrients along with oxygen and water for the growth of microorganisms.
- The culture medium should be cheap and easily available, it should increase microorganisms’ growth, production, and desired product formation.
- To prevent contamination with undesired microorganisms, sterilization is essential. Sterilization of medium, air, and fermentor is done by either heat or membrane sterilization.
- Preparation of seed culture for ethanol production should be in the sufficient amount that is used in large fermentation vessels which helps in growing the microorganisms that are obtained from the pure stock culture.
2. Actual Fermentation Process:
- Fermentation is a process in which complex substances are converted into simple substances with the help of microorganisms.
- In this process, all the materials are added together in a bioreactor to produce the desired product.
- Maintaining optimal conditions required for lysine production like nutrients, are supplied for the growth and multiplication of microorganisms inside a bioreactor, Temp, pH, Oxygen concentration, etc.
- The fermentation is carried out at 30 to 40°C and is allowed for up to a few days.
- The number of trace elements and growth factors should be appropriate for the maximum growth of microorganisms.
3. Down-stream process:
- The downstream process of fermentation involves the recovery of products from the bioreactor through different processes like extraction, separation, purification, and packaging of the product.
- Here the fermentation broth is sent to an ultrafiltration system for the removal of cell debris and other suspended solids.
- Ethanol can be used in several ways.
- Ethanol is also present in alcoholic beverages and is also used as an antiseptic.
- In its pure form (anhydrous alcohol), it is widely used in industry, as a raw material for paints, solvents, aerosols, etc.
- In addition, it is used as a fuel mixed with gasoline or diesel.
- Hydrous ethanol (ethanol with about 5% water) is used in the production of food, cosmetics, flavorings, cleaning products, medicines, and vaccines.
- Mainly used in medical institutions for the purpose of prevention and treatment of illness.
- It is used for the purpose of disinfecting and cleaning furniture, miscellaneous goods, and houses.
- It is used to sterilize foods, improve their shelf life, and disinfect food processing factories and household cooking utensils.
Factors Affecting Ethanol Production:
- The optimum temperature used for the production of ethanol by submerged fermentation of Saccharomyces cerevisiae and other bacteria is between 30 to 40°C.
- Temperature can affect the growth of Saccharomyces cerevisiae activity. In the optimum temperature range, as the temperature increases the growth and metabolism of Saccharomyces cerevisiae accelerate, and the rate of the fermentation reaction increases.
- When the temperature exceeds the optimal temperature range as the temperature rises the Saccharomyces cerevisiae activity is quickly inactivated and the fermentation rate is reduced.
- Therefore, to ensure a normal fermentation process, it is necessary to maintain the optimum temperature.
- pH can affect the activity of microorganisms, enzymes, and fermentation rate.
- Based on the type of substrate and media and microorganisms the pH is vary.
- In defined media, the initial pH of the medium is usually adjusted to 4-5, while in the case of molasses, the pH must be neutral or slightly acidic.
- The pH of the medium is adjusted with NaOH, H2SO4, and HCl.
- In addition, pH will also affect the decomposition of nutrients in the medium. Therefore, the pH of the fermentation broth should be controlled.
- The supply of oxygen is a key factor for aerobic fermentation and therefore it requires oxygen.
- Aeration and agitation meet the oxygen demand of a fermentation process of L-lysine
- Agitation is important for heat transfer, adequate mixing, and mass transfer.
- Aeration and agitation both maintain the homogeneous environment of culture by continuous mixing.
- Therefore, a large amount of oxygen must be continuously added to the fermentation broth, and stirring can increase the solubility of oxygen in the fermentation broth.
- The concentration of dissolved oxygen increased with the increase in the speed of agitation.
- The concentration of various nutrients in the fermentation broth, especially the ratio of carbon to nitrogen, inorganic salts, and vitamins, will directly affect the growth of microorganisms and production rate.