Biological conversion

Digestion and fermentation

1. ENERGY TECHNOLOGY BIOLOGICAL CONVERSION CHEMICAL CONVERSION

2. Biomass origin - Resources – Biomass estimation. Thermo chemical conversion – Biological conversion, Chemical conversion Hydrolysis & hydrogenation, solvolysis, biocrude, biodiesel power generation gasifier, biogas, integrated gasification. UNIT 4-BIOMASS ENERGY

3. BIOMASS DIGESTION

4. DIGESTION Biomass digestion works by the action of anaerobic bacteria . These microorganisms usually live at the bottom of swamps or in other places where there is no air, consuming dead organic matter to produce, among other things, methane and hydrogen. We can put these bacteria to work for us. By feeding organic matter such as animal dung or human sewage into tanks – called digesters - and adding bacteria we can collect the emitted gas to use as an energy source.

5. DIGESTION This can be a very efficient means of extracting usable energy from such biomass – up to two-thirds of the fuel energy of the animal dung is recovered A large proportion of household biomass waste, such as kitchen scraps, lawn clippings and pruning, ends up at the local tip. Over a period of several decades, anaerobic bacteria are at work at the bottom of such tips, steadily decomposing the organic matter and emitting methane. The gas can be extracted and used by 'capping' a landfill site with an impervious layer of clay and then inserting perforated pipes that collect the gas and bring it to the surface.

6. PROCESS STAGES The four key stages of anaerobic digestion involve  HYDROLYSIS, ACIDOGENESIS,  ACETOGENESIS and METHANOGENESIS . The overall process can be described by the chemical reaction, where organic material such as glucose is biochemically digested into carbon dioxide (CO 2 ) and methane (CH 4 ) by the anaerobic microorganisms . C 6 H 12 O 6  → 3CO 2  + 3CH 4

7. HYDROLYSIS B iomass is made up of large organic polymers. For the bacteria in anaerobic digesters to access the energy potential of the material, these chains must first be broken down into their smaller constituent parts . The process of breaking these chains and dissolving the smaller molecules into solution is called hydrolysis . Therefore , through  hydrolysis the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids.

8. ACIDOGENESIS The biological process of acidogenesis results in further breakdown of the remaining components by acidogenic bacteria . Here , volatile fatty acids are created, along with ammonia, carbon dioxide, and hydrogen sulfide, as well as other byproducts. The process of acidogenesis is similar to the way milk sours.

9. ACETOGENESIS The third stage of anaerobic digestion is acetogenesis. Here , simple molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.

10. METHANOGENESIS The terminal stage of anaerobic digestion is the biological process of  methanogenesis. Here , methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the biogas emitted from the system. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8.

11. Types Biogas is comprised of about 60% methane, 40% carbon dioxide, and 0.2 to 0.4% of hydrogen sulfide . There are two major types of biogas designs promoted in India a ) Floating Drum b ) Fixed Dome

12. Types

13. BIOMASS DIGESTION- FIXED

14. Fixed Dome

15. ECONOMIC ADVANTAGES: Additional income  Autonomy in heat in a context of increase in the cost of fossil energies Diversification of outlets for crops Reduction of manure purchase thanks to valorization of digested sludge

16. Agronomic advantages Transformation of the liquid manure and the manure into a fertilizer, more easily assimilated by the plants, with reduction in the odours and the disease-causing agents Organic waste processing for competitive prices Insect elimination at the storage pit

17. ENVIRONMENTAL ADVANTAGES Biogas resulting by anaerobic digestion is a source of renewable energy because it replaces fossil energy Reduction of pollution due to nitrogen stripping Sustainable management of organic waste

18. Disadvantages of Anaerobic Digestion When carried out at a commercial scale on farms and at wastewater treatment works it requires a high level of investment in large tanks and other process vessels. If run inefficiently of Anaerobic Digestion can cause an odour nuisance. Does not convert as large a proportion of the carbon in the biomass to biogas as can be achieved using gasification.

19. INTRODUTION TO FERMENTATION Fermentation is a metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved ( Deficient ) muscle cells, as in the case of lactic acid fermentation. Fermentation, chemical process by which molecules such as glucose are broken down in absence of air (Anaerobically).

20. DEFINITION Fermentation is the chemical transformation of organic substances into simpler compounds by the action of enzymes , complex organic catalysts, which are produced by microorganisms such as molds, yeasts, or bacteria. Enzymes act by hydrolysis, a process of breaking down or complex organic molecules to form smaller compounds and nutrients.

21. FLOW CHART

22. AEROBIC FERMENTATION Aerobic fermentation means that oxygen is present. Wine, beer and acetic acid vinegar need oxygen in the “primary” or first stage of fermentation. When creating acetic vinegar, for example, exposing the surface of the vinegar to as much oxygen as possible, creates a healthy, flavorful vinegar with the correct pH.

23. ANAEROBIC FERMENTATION Anaerobic fermentation is a method cells use to extract energy from carbohydrates. when oxygen or other electron acceptors are not available in the surrounding environment. This differentiates it from anaerobic fermentation, which doesn’t use oxygen but does use electron-accepting molecules that come from outside of the cell.

24. ANAEROBIC FERMENTATION The process can follow glycolysis as the next step in the breakdown of glucose and other sugars to produce molecules of adenosine triphosphate (ATP) that create an energy source for the cell . And is able to produce nicotinamide adenine dinucleotide (NAD+)

25. ETHANOL FERMENTATION Ethanol fermentation converts two pyruvate molecules, the products of glycolysis, to two molecules of ethanol and two molecules of carbon dioxide. The reaction is a two-step process in which pyruvate is converted to acetaldehyde and carbon dioxide first, by the enzyme pyruvate decarboxylase.

26. ETHANOL FERMENTATION Yeast and certain bacteria perform ethanol fermentation where pyruvate (from glucose metabolism) is broken into ethanol and carbon dioxide. The net chemical equation for the production of ethanol from glucose is: Ethanol fermentation is used the production of beer, wineand bread.

27. ADVANTAGES Ethanol in this process is made using sugar (glucose) found in plants. This makes it a renewable source as it can be grown again. The process could be seen as carbon neutral because as the plant grows, it takes in carbon dioxide for photosynthesis. This therefore balances out the carbon dioxide released when it is fermented. High amounts of energy are not needed as sugar is fermented at temperatures of around 35°c to 40°c. Low cost process because of low temperature .

28. DISADVANTAGES When the ethanol concentration reaches about 15% the yeast dies and fermentation stops. The product obtained is not pure. 15% mixture must be concentrated and purified by distillation-extra cost Carbon dioxide is produced. It raises ethical questions as to weather we should use crops for ethanol when there are third world countries with no food .

29. Part A-Questions What do you mean by Digestion? What do you mean by fermentation process? List out the stages of digestion process. Sketch types digestion. Write advantages and disadvantages of Digestion and fermentation process.

30. Part B- Questions Explain Biochemical conversion methods. Explain with suitable sketch digestion process. Explain with suitable sketch fermentation process.