BIOGAS PRODUCTION USING SMALL SCALE BIODIGESTER

1. Planning & Operating
Electricity Network with
Renewable Generation

2. 4. Biogas

3. Biogas Production Using
Small Scale Biodigester

4. What is Biodigester?
• Biodigester is a system that promotes
decomposition of organic matter.
• It produces biogas, generated through the
process of anaerobic digestion.
• Biogas generated can be used for cooking,
heating, electricity generation, and running a
vehicle.

5. Anaerobic Digestion
• Reduce
- Smell
- Greenhouse gas
- Pathogen level
• Produce biogas
• Improve fertilizer value of manure
• Protect water resources

6. Biogas
• Biogas is generated by the activity of anaerobic bacteria.
• Biogas is comprised of about 60% of methane, 40% of carbon
dioxide, and small amount of hydrogen sulfide, nitrogen, and
hydrogen.
• The heating value of biogas is about 60% of natural gas and
about 25% of propane.
• Biogas has corrosive nature and storage of biogas is not
practical.

7. Application of Biogas
• The technology of biodigester is widely used
in developing country such as China, Vietnam,
India, and Central and South America as well
as in developed country.
• Anaerobic digester can be used in remote
farm area to produce biogas from manure and
protect water resources.

8. Basic Designs of Digester
• Continuous-fed
• Batch-fed

9. Continuous-fed System
• Suited for large-scale manure substrate
bioreactor.
• Steady biogas production can be expected.
• May require auxiliary equipments.
• Requires high liquid content.
• Temperature, loading rate, and solid content
need to be carefully monitored.

10. Batch-fed System
• The simplest design.
• Low cost.
• The feedstock is loaded one batch at time.
• Irregular biogas production.
• Can operate on high solid content.
• Less susceptible to fluctuation of factors.
• Requires manual labor.

11. Bag Biodigester
• The idea is to make a small-scale, low-cost
biodigester plant so that anyone in the world
can make it and produce biogas.

12. Preparation
• Feed the bag with the effluent.
• Cut the garden hose to an adequate length and pull the bag
through the garden hose.
• Fold the bag against the surface of the garden hose.
• Attach the adapter to the garden hose over the bag.
• Connect the hose and the gas collector using adequate
adapters.

13. Operation
• The generator requires little maintenance
besides occasional stirring.
• When the batch is done, disconnect the
garden adapter and unload the effluent.
• For the next batch, apply about 10% of the
previous batch to activate the new batch.
• After loading the feedstock, connect the
adapter again and repeat the process.

14. Energy For The Future
Biogas
 versatile source of renewable energy: providing electricity and heat
 reduction of harmful methane emissions
 CO2 neutrality
 environmentally friendly way of preserving resources

15. Renewa
ble
Energy

16. Biomass
Benefits
Composition
Production
Definition

17. Factors effecting on the process
pH Value
Temperature
Retention time
Loading rate
Toxicity
C/N ratio
Slurry

18. MECHANISM OF THE OPERATION

19. Mechanism of the operation
Waste
collection
Dry
matter
tank
Screw
pump
The
digester
Gas
holder
Filtration
unit
Gas tank
Cogeneration
unit

20. • Easy visual control for daily
feeding input
• Or using inclined surface
Waste
collection

21. Can be constructed from concrete or galvanized steel plate
Dry
matter
tank

22. • Diameter >= 12”
• Length = 50’
• Used for handling liquids containing
solid in suspension with horizontal
transport
• Speed 30-60 rpm
• Capacity 15 L/s -11 m3 /s
Screw
pump

23. Floating drum planet
The
digester

24. Fixed dome planet
The digester

25. • Floating drum gasholder
• Fixed dome gasholder
• Plastic gasholder
• Separate gasholder
Gas holder

26. • Chemical absorption
• High pressure water scrubbing
• Pressure swing absorption
• Cryogenic separation
• Membrane separation
Filtration unit

27. Using propane gas cylinders
Gas
tank

28. Two type of cogeneration:
• Topping cycle
• Bottoming cycle
Cogeneration
unit

29. BIOGAS PLANT
Biogas plant is an airtight container that facilitates fermentation of
material under anaerobic condition.
Other names given to this device are ‘Biogas Digester’, ‘Biogas
Reactor’, ‘Methane Generator’ and ‘Methane Reactor
Recycling and treatment of organic wastes (biodegradable material)
through anaerobic digestion (fermentation) technology not only
provides biogas as a clean and convenient fuel but also an excellent and
enriched bio-manure.
The BGP also acts as mini bio-fertilizer factory; hence some people
refer it as ‘Biogas fertilizer plant’ or ‘Bio-manure plant’
Anaerobic digestion of organic matter produces a mixture of methane
(CH4) and carbon dioxide (CO2) gas that can be used as a fuel for
cooking, lighting, mechanical power and the generation of electricity, or
a replacement for other fuels.

30. CLASSIFICATION
Classification of biogas plants depends upon the plants design and mode of
working. One common way to classify them is
Batch type plant Continuous type plant
BIOGAS PLANT
Fixed Dome Biogas
Plant
Floating Gas Holder
Biogas Plant:

31. BATCH TYPE BIOGAS PLANT
a) Batch type biogas plants are appropriate where daily supplies of raw
waste materials are difficult to be obtained.
b) Batch type plant is charged at 50-60 day intervals
c) Once charged, it starts supplying the gas after 8-10 days and
continuous to do so for about 40-50 days till the process of digestion
is completed.Afterwards it is emptied and recharged.
d) Gas production in batch type is uneven.
e) Several digesters occupy more space.
f) This type of plants require large volume of digester, therefore, initial
cost becomes high.
g) Such plants are installed in european countries.
h) Donot suit the conditions in indian rural areas

32. OPERATIONAL PARAMETERS OF A BIOGAS
PLANT
Operation of a bio gas plant is affected by a no. of factors::-
A.Temperature
 Methane- forming bacteria works best in temp. ranges 20-55 C
 Digestion at higher temp. proceeds more rapidly than at lower temp.
 The gas production decreases sharply below 20 C and almost stops at
10 C
B. Pressure
 A minimum pressure of 6-10cm of water column i.e, 1.2 bar is ideal
for proper functioning.
 It should never be alllowed to exceed 40-50 cm of water column.
 Excess pressure inhibits release of gas from slurry and leakage in
masonry.

33. C. Solid to moisture ratio in the biomass
 If water content is too high, the mean slurry temp. and gas
production drops.
 If water content is too low, acids accumulate and hinder fermentation
process.
D.pH value
 In initial acid forming stage, pH value may be around 6 or less.
 During methane forming stage, pH value 6.5 to 7.5 is maintained.
E. Feeding rate
 Faster feeding rate will not help in increase gas production.
 At higher feeding rate the retention period will be less and
undigested Slurry may come out.
 So optimum feed rate should be maintained.

34. F. Carbon to nitrogen ratio
The optimum C/N ratio is 30:1 for maximum microbiological activity.
G. Seeding of biomass with bacteria
 To start and accelerate the fermentation process, a small amount of
digested slurry containing a methane forming bacteria is added to the
freshly charged plant. This process is known as seeding.
 Seeding helps to accelerate the starting of the digestion process.
H. Mixing or stirring
Mixing
 Maintains uniformity in substrate concentration,temp,other
environmentel factors
 Minimises formation of scum
 Prevents the deposition of solids at the bottom

35. I. Retention time
 Retention time should be optimum to obtain 70-80% complete
Digestion.

36. Fixed dome type of biogas plant

37. Raw materials required
Forms of biomass listed below may be used along with water.
•Animal dung
•Poultry wastes
•Plant wastes ( Husk, grass, weeds etc.)
•Human excreta
•Industrial wastes(Saw dust, wastes from food processing
industries)
•Domestic wastes (Vegetable peels, waste food materials)
Principle
Biogas is produced as a result of anaerobic decomposition of
biomass in the presence of water.

38. Construction
The biogas plant is a brick and cement structure having the following
five sections:
• Mixing tank present above the ground level.
• Inlet chamber: The mixing tank opens underground into a sloping
inlet chamber.
• Digester: The inlet chamber opens from below into the digester
which is a huge tank with a dome like ceiling. The ceiling of the
digester has an outlet with a valve for the supply of biogas.
• Outlet chamber: The digester opens from below into an outlet
chamber.
• Overflow tank: The outlet chamber opens from the top into a small
over flow tank

39. Working
 The various forms of biomass are mixed with an equal quantity of
water in the mixing tank. This forms the slurry.
 The slurry is fed into the digester through the inlet chamber.
 When the digester is partially filled with the slurry, the introduction
of slurry is stopped and the plant is left unused for about two
months.
 During these two months, anaerobic bacteria present in the slurry
decomposes or ferments the biomass in the presence of water.
 As a result of anaerobic decomposition, biogas is formed, which
starts collecting in the dome of the digester.
 As more and more biogas starts collecting, the pressure exerted by
the biogas forces the spent slurry into the outlet chamber.
 From the outlet chamber, the spent slurry overflows into the
overflow tank.
 The spent slurry is manually removed from the overflow tank and
used as manure for plants.
 The gas valve connected to a system of pipelines is opened when a
supply of biogas is required.

41. Floating gas holder type of biogas plant

42. The raw materials used and the principle involved are common to
both the types of biogas plants.
Construction
 The floating gas holder type of biogas plant has the following
chambers/ sections:
 Mixing Tank - present above the ground level.
 Digester tank - Deep underground well-like structure. It is divided
into two chambers by a partition wall in between.
 It has two long cement pipes:
i) Inlet pipe opening into the inlet chamber for introduction of slurry.
ii) Outlet pipe opening into the overflow tank for removal of spent
slurry.
 Gas holder - an inverted steel drum resting above the digester. The
drum can move up and down i.e., float over the digester. The gas
holder has an outlet at the top which could be connected to gas
stoves.
 Over flow tank - Present above the ground level.

43. Working
 Slurry (mixture of equal quantities of biomass and water) is
prepared in the mixing tank.
 The prepared slurry is fed into the inlet chamber of the digester
through the inlet pipe.
 The plant is left unused for about two months and introduction
of more slurry is stopped.
 During this period, anaerobic fermentation of biomass takes
place in the presence of water and produces biogas in the
digester.
 Biogas being lighter rises up and starts collecting in the gas
holder. The gas holder now starts moving up.
 The gas holder cannot rise up beyond a certain level. As more
and more gas starts collecting, more pressure begins to be
exerted on the slurry.

44. • The spent slurry is now forced into the outlet chamber from the top
of the inlet chamber.
•When the outlet chamber gets filled with the spent slurry, the excess is
forced out through the outlet pipe into the overflow tank.This is later
used as manure for plants.
•The gas valve of the gas outlet is opened to get a supply of biogas.
• Once the production of biogas begins, a continuous supply of gas can
be ensured by regular removal of spent slurry and introduction of fresh
slurry.

46. COMPARISON
SN.
FEATURE FLOATING DRUM FIXED DOME
1. COST More(due to steel drum) Less
2. CORROSION Yes (likely in steel drum) No
3. MAINTENANCE More
 Drum requires painting
 Flexible gas pipe
requires replacement
Less
 No steel part is used
 Gas pipe is fixed type
4. THERMAL
INSULATION
Bad Good(due to underground
construction)
5. SCUM
TROUBLES
Less likely More likely
6. GAS
PRODUCTION
PER UNIT
VOLUME OF
DIGESTER
High Low

47. 7. SCUM BRAKING By rotation of drum External stirrer is
required
8. LEAKAGE Less likely More likely
9. DANGER OF MIXING
WITH OXYGEN DUE
TO LEAKAGE,CRACKS
No More likely
10. GAS PRESSURE constant Variable
11. MASONRY
WORKMANSHIP
Average skill Specialized, skilled
masonry work
required