Biogas Production Technology

1. BIOGAS PRODUCTION
TECHNOLOGY
Dr. B. KARUNAI SELVI
ASSOCIATE PROFESSOR OF BOTANY
V.V.VANNIAPERUMAL COLLEGE FOR WOMEN
VIRUDHUNAGAR- 626 001
TAMIL NADU, INDIA
karunaiselvi@vvvcollege.org

2. BIOGAS
• Volta 1776 – Italian Physicist
• Demonstrated methane in the march gas
• It is also named as Klar-gas, refuse derived fuel (RDF),
gobar gas and Will-of-the wisp.
• It is produced by fermentation effected by anaerobic
bacteria called methanogens.

3. BIOGAS
• Under anaerobic conditions the organic materials are converted
through microbiological reactions into gases, [fuel] and organic
fertilizer (sludge).
• Methane is the main constituent of biogas.
• The mixture of gases is composed of
• Methane - 63%, Co2 - 30%, Nitrogen - 4%, Hydrogen-sulphide - 1%
and Traces of O2 and CO
• Biogas is used for cooking and lighting purposes in rural sector.
• It is devoid of smell and burns with a blue flame without smoke.

4. FEED STOCK FOR BIOGAS
• Biomass from aquatic and terrestrial origin
• Biomass from Animal Origin
• Cow dung
• Agricultural waste
• Organic waste
• Water
• Methanogens

5. METHANOGENS
• Methanogens are obligate anaerobes.
• They are mesophilic 21-45oC
• They have slow growth rate.
• They play a major role in breakdown of substrate into gas
from.
• They have co-enzyme M that reduces methyl group into
methane
• All the bacteria require H2 and formate for growth and
methane production.
• Methanogens are either autotrophs or utilize simple organic
compounds. eg. formate, acetate and methyl amine

6. METHANOGENS
Mechanism of methane production;-
• Specific co-enzymes are present in methanogens. They are
• M, hydroxy methyl coenzyme
• M, coenzyme F42O
• Coenzyme F430
• Component B
• Corrionoids,
• Methanofuran or Co2 → Reducing factor
• Methanopterin and formaldehyde → activating factor

7. Order 1: Methanobacteriales
• Family: Methanobacteriaceae
• eg. Methanobacterium thermoautotrophicum
Order 2: Methanococcales
• Family: Methanococcaceae
• eg. Methanococus voltae
Order 3 : Methanomicrobiales
• Family 1: Methanomicrobiaceae
• eg. Methanomicrobium mobile
• Family 2:Methanosarcinaceae
• eg. Methanosarcina barkeri
METHANOGENS

9. BIOGAS- CULTURE CONDITIONS
• Cellulolytic microorganisms are inoculated into the fermentor
to digest more cellulose.
• The bacteria capable of degrading hemicellulose are added
into the fermenter. Eg. Bacterioides ruminiocla.
• Sulphur bacteria in the feed stock are destroyed by heat shock.
• The pH of the medium is increased by adding lime.
• 25-45°C temperature is maintained in the fermenter.
• Generally, the C/N ratio 30:1 is preferred for the best growth
of methanogenic bacteria.

13. STAGES OF METHANOGENESIS
Solubilization
• The feed stock (cattle dung and other organic polymers) is
dissolved in water to make slurry.
• Polymers are hydrolysed into organic acids and alcohols by
hydrolytic fermentative bacteria – which are mostly
anaerobes.

14. Acidogenesis
• Simple organic material are converted into a acetate, H2 and CO2 ∙
Facultative anaerobic and H2 producing acidogenic bacteria
are participate in the reaction.
• Oxidation and reduction reactions are involved in the
conversion process
• These substances serve as food for the final stage
Action of acetogenic bacteria
• Fatty acid →.Acetate + H2 + CO2
• H2 + CO2 → acetate
STAGES OF METHANOGENESIS

15. Methanogensis
• Final stage of anaerobic digestion
• Methane producing bacteria are involved
• Acetate, H2 and CO2 are converted into methane CO2, water and
other products.
Methane producing bacteria
• Acetate + H2 + CO2 → Methane + H2 + CO2
• Acetate is a good substrate for methanogenic bacteria
STAGES OF METHANOGENESIS

16. CHEMICAL REACTIONS
Primary reaction;-
• Co + H2O → Co2 + H2
Secondary reaction
• Co2+4H2 → CH4 + 2H2O
Other reactions
Methane formation from different substrates;-
• 4CH3OH (methanol) → 3CH4+ Co2 + 2H2O
• 4H COOH (formate ) → CH4 + 3Co2+ 2H2O
• CH3 COOH (acetate) → 12 CH4 + 12 Co2

18. FACTORS AFFECTING METHANE
FORMATION
Slurry
• For proper solubilization the ratio between water and solid should be 1:1
Seeding
• Seeding of slurry with small amount of sludge
• Sludge contains acetogenic and methanogenic bacteria.
pH
• pH of the digest maintained between 6- 8
• acidic pH lowers methane formation

19. FACTORS AFFECTING METHANE
FORMATION
Temperature
• fluctuation in temperature reduces methane formation
• mesophilic digestion – temperature should be 30⁰C and 40⁰C ∙ thermophilic ones -
50⁰C and 60⁰C
Nitrogen Concentration
• Excess amount of N inhibits growth of bacteria.
• Lowers methane production
Carbon- nitrogen (C:N) ratio
• Improper c;n ration lowers methane production
• Maximum digestion occurs when C : N ratio is 30 : 1

20. FACTORS AFFECTING METHANE
FORMATION
Creation of anaerobic condition
• Methane production occur in anaerobic condition
• Digesters should be airtight.
• In India digesters are buried in soil.
Addition of algae
• Zygogonium sp. enhance biogas production
• The amount of biogas produced from alga was twice
• Duration of gas evolution increased with increasing the proportion of slurry.