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

5. BIOMASS DIGESTION

7. 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.

8. 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.

9. 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 (CO2) and methane (CH4) by
the anaerobic microorganisms.
C6H12O6 → 3CO2 + 3CH4

10. HYDROLYSIS
• Biomass 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.

11. 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.

12. 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.

13. 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.

14. 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

15. Types

17. BIOMASS DIGESTION- FIXED

18. Fixed Dome

19. 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

20. 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

21. 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

22. 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.

23. 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).

24. 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.

25. FLOW CHART

26. 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.

27. 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.

28. 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+)

29. 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.

30. 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.

32. 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.

33. 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.

34. Part A-Questions
1. What do you mean by Digestion?
2. What do you mean by fermentation process?
3. List out the stages of digestion process.
4. Sketch types digestion.
5. Write advantages and disadvantages of
Digestion and fermentation process.

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