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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Bioenergy Page 1

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Energy is the capacity to do work. Bioenergy is the energy obtained from biological matter other than fossils.





Any biological matter that can be converted into energy or into a source of energy is called biomass.



Common Methods of Bioenergy Formation


  1. The process of converting biomass into energy is called bioconversion.
  2. There are various methods of bioconversion.



Form/Energy-source produced

Burning of wood, straw, covering of grains, etc.

Heat and Electricity

Carbonisation (heating of carbonrich plant or animal material like bones)


Hydrolysis and Fermentation

Ethanol or Ethyl alcohol

Pyrolysis (Chemical decomposition of organic matter produced by high temperature)

Charcoal, gas, liquid fuel (oil)

Bacterial action (Anaerobic)

Gases (Example: Methane)


Producer gas


Hydrocarbons similar to petrol



Raw Materials and Substrates


  1. The sources of biomass can be classified into two categories namely:
  • Organisms that are specially cultivated and/or harvested for the sake of their bioconversion. For example, under the social forestry programme, trees like Acacia (babul), Casuarina, Eucalyptus (nilgiri), Prosopis (subabul) etc. are cultivated for the sake of their quick-growing wood. Also, petrocrops i.e., plants that yield hydrocarbons are cultivated. Cultivation of bioenergy crops is called energy farms or energy plantations.
  • Biomass which are either byproducts or waste products of human activities, for example, Agro-industrial wastes, Forest residue, Crop residue, Animal wastes, Human wastes, Aquatic plants and urban solid wastes.



Producer Gas


  1. Producer gas is a mixture of carbon monoxide, hydrogen and oxygen, which is produced by incomplete combustion of a suitable biomass or coal.
  2. Raw material used is wood, charcoal, coke, peat or wastes.
  3. Producer gas is generated in a furnace called gasifier or generator. The raw material is treated in the gasifier by passing heated air at 650-1600 degrees centigrade. Oxygen in the air combines with carbon forming carbon monoxide. A cleaner filters the soot and ash from the hot gas. A cooler condenses the tar and other impurities. Presence of a valve results in mixing the gas with the air.
  4. Advantages of producer gas:
    • Producer gas is mainly used as an industrial fuel.
    • Producer gas is used in bus, truck, trolley, etc.
    • The design of the generator is simple.
  5. Disadvantages of producer gas:
    • For the production of producer gas, wood (which is scarcely available) is required.
    • The energy generated by the production of producer gas is not as powerful as that from petroleum.
    • CO, which is produced in the process, is poisonous.



Methane or Biogas


  1. The gas produced by the action of bacteria on biomass is called biogas. The main biomass used is cattle dung or gobar. Hence, biogas is also called gobar gas. Animal wastes, night soil and city wastes can also be used in the production of biogas.
  2. Composition of Biogas:
    Methane: 50
    - 75%
    Carbon dioxide: 30
    - 40%
    Hydrogen: Traces
    Nitrogen: Traces
    Hydrogen sulphide: Traces
  3. The process:

    Stage 1
    Anaerobic micro-organisms convert insoluble organic polymers into soluble monomers. This is carried out by certain hydrolytic enzymes secreted by these bacteria.

    The monomers are converted into soluble organic acids like acetic acid by the activity of bacteria.

    Stage 3
    The acetic acid is converted into methane and carbon dioxide gas by methanogenic bacteria.

    Stage 4
    This is a physical process of transition of the products from liquid to the gaseous phase.
  4. There are 2 basic designs of small biogas plants:
    Model 1:
    The Chinese Model
    This model maintains a constant volume, but variable pressure.

    Model 2:
    Indian Model
    This model maintains a constant pressure, but variable volume.



Advantages of Gas Plants


  • The burning of biogas does not pollute atmosphere.
  • Biogas is used as fuel in cooking and in small-scale industries.
  • The residues recovered from the biogas plant can be used as fertiliser.
  • Biogas improves sanitation. Thus, pathogens causing diseases to plants can also be controlled.
  • Biogas plants provide useful employment for rural people



Plants as Sources of Hydrocarbons


  1. Hydrocarbons are used as fuels and chemicals. Petrocrops are plants, which produce hydrocarbons.
  2. Euphorbias
    Latex of genus Euphorbia contains some photosynthetic products. 1/3rd of it is hydrocarbon, 1/5th protein and the remaining mostly water. Besides hydrocarbons, the terpenoids and hexoses present in latex are potential sources of gasoline. Plants belonging to families Asclepiadaceae and Apocynaceae are rich in hydrocarbons.
  3. Plants used for hydrocarbon production:
    Euphorbia lathyrces antiquorum
    Euphorbia tirucalli
    Calotropis gigantea
    Capaifera longsdorfi
  4. Sugarcane and Sugarbeet:
    • Molasses, sugarcane juice, sugarbeet, maize or sorghum starch and a limited quantity of cassava (tapioca) are used for the manufacture of fuel alcohol.
    • From sugarcane, the juice is extracted by mechanical expression. Similarly, from sugarbeet the juice is extracted by the process of diffusion. The bagasse, which is a byproduct of sugar production, contains lots of fibrous parts and it can also be used as the starting point for the production process.
    • In the next step, the hydrolysed juice is subjected to alcohol fermentation by the yeast, Saccharomyces cerevisiae.
      The process of fermentation takes place in huge fermenter vessels. Alcohol collects in the medium to a maximum concentration of 12
      - 16%.
    • After removing yeast, the medium is distilled and then dehydrated to obtain absolute alcohol. In this process, the yield of ethyl alcohol is about 50% of the fermentable sugar concentration.




 2C2H5OH + 2CO2



Melvin Calvin


  • U.S. Biochemist.
  • Life span±1911±1997.
  • Investigated the dark reaction of photo-synthesis at Lawrence Radiation Laboratory Berkely using radioactive carbon.
  • Discovered Calvin cycle for which he was awarded the Nobel Prize in 1961.
  • Also identified some plants belonging to family Euphorbiaceae which can convert a good amount of photosynthetic products into latex.


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