1. DIFFERENT TYPES OF
BIOGAS PLANTS

2. What is biogas?
Gas produced by the anaerobic digestion or fermentation of organic matter under anaerobic conditions.
Biogas = CH4 + CO2 + H2S + N2 + H2 etc
Typical biogas composition:
Methane, CH4 : 55-70%
Carbon dioxide, CO2 : %
Nitrogen, N2 : %
Hydrogen Sulphide, H2S : %
Hydrogen, H2 : %
Oxygen, O : %
pH-value : 6.5 to 7.5
Due Point : < - 80° C

3. Anaerobic Digestion CH4 + CO2 Complex Organic Carbon Hydrolysis
Monomers & Oligomers
Acidogenesis
Organic Acids
Acetogenesis
Acetate – H2 / CO2
Methanogenesis
CH4 + CO2

4. METHANE and CARBON DIOXIDE
LIQUEFACTION
PHASE
GASIFICATION
PHASE
COMPLEX
ORGANIC
MATTER
SIMPLE
ORGANICS
ACETATE
H2 / CO2
ACIDOGENS
METHANOGENS
METHANE and CARBON DIOXIDE
LOW ODOR EFFLUENT

5. Biogas Cycle Biomethane production Solar energy Photosynthesis
Animal husbandry
Crop harvesting
Industrial processing
Human consumption
Photosynthesis
CO2
H2O
Energy
crops
Biofertilizer
Electrical and/or thermal energy
Biogas
Natural gas pipeline
Organic wastes
Anaerobic digestion
CO2
Cleaning &
Upgrading
Energy crops

6. Factors affecting Biogas generation
pH concentration
Temperature
Total solid content of the feed material
Loading rate
Seeding
Uniform feeding
Diameter to depth ratio
Carbon to nitrogen ratio
Nutrients
Mixing or stirring or agitation of the digester
Retention time or rate of feeding
Type of feed stocks
Toxicity due end product
Pressure
Acid accumulation inside the digester.

7. Biogas potential in India
The annual estimated biogas generation potential based on available cattle dung is about 17,340 million m3.

8. Biogas plants in India Potential -12 million family type biogas plants
Achieved million family type biogas plants - 34% of the potential.
Functionality of the biogas plants is about 95.80%
Domestic biogas plants can supply few hours of electricity for domestic needs .i.e. More beneficial in rural areas.
Electricity can simply be produced by using Biogas generators of few kW capacity.
*APITCO Survey

9. Evolution of biogas technology in India
Experimentally introduced in the 1930's.
First research on Sewage Purification Station at Dadar in Bombay, undertaken by S.V. Desai and N.V. Joshi of the Soil Chemistry Division, Indian Agriculture Research Institute, New Delhi.
The early plants were very expensive, not cost effective, and not producing enough gas.
Some of the early models were also prone to burst, so the technology was not viable for dissemination.

10. In 1956, Jashu Bhai J Patel developed a design of floating drum biogas plant popularly known as Gobar Gas plant.
In 1961, Khadi and Village Industry Commission (KVIC) promoted Jashbhai Patel's design, which was later known as KVIC model.
Planning Research and Action Division (PRAD) based in Uttar Pradesh developed the 'Janata' fixed-dome plant - a modified chinese design.
Janata system is about 30% cheaper than a KVIC model.

11. Action for Food Production (AFPRO), New Delhi developed Deenbandhu model (an improved version of Janata model).
30 percent cheaper than Janata Model and 45 percent cheaper than KVIC model.
Presently, designs and models are galore in market.

12. Classification of biogas plant
Biogas plants may be classified in several ways:
Continous, semi-continuous and batch types (as per the process)
The dome and the drum type
Depend on shape of the digester (Horizontal or Vertical)
Depend on loading rate
Depend on HRT
Depend on construction material
Depend on feed material

13. Major Classification in
Biogas Plants

14. Biogas Digesters Biogas Digesters Conventional Biogas Plants High Rate
For
Insoluble wastes
(also called as High-strength wastes)
For
Soluble wastes
(also called as low-strength wastes)

15. Conventional biogas plants in India
Fixed dome type
Floating drum type
Bag type
Deenbandhu model with brick masonry
Deenbandhu ferrocement model
Pre-fabricated RCC fixed-dome
Janta biogas plant
KVIC floating metal drum type
KVIC type plant with ferrocement digester and fibre
glass reinforced plastic gas holder
Pragati model
Flexi Model

16. Characteristics of floating drum type
Consists of a deep well, and a floating drum (usually made of mild steel).
Drum rises as gas collects.
Constant gas pressure due to the drum weight. (The pressure is equivalent to the weight of gasholder over unit area)
Inlet is higher than the outlet tank, creating hydrostatic pressure which helps slurry to move through the system.
Maxing gas pressure attained cm water column.

17. Characteristics of fixed dome type
Invented in China in 1930’s.
Underground brick masonry compartment (fermentation chamber) with a dome on the top for gas at the storage.
Fermentation chamber and gas holder are combined as one unit.
Movement and weight of digested the slurry decides the gas pressure.
Variable gas pressure (0-90 cm water column)
Less expensive and requires less maintenance than floating drum type.

18. Components of biogas plant
Inlet pipe: The slurry is moved into the digester through the inlet pipe/tank.
Mixing tank: The feed material like dung is gathered in the mixing tank. Using sufficient water, the material is thoroughly mixed till a homogeneous slurry is formed.
Digester: Inside the digester, the slurry is fermented. Biogas is produced through bacterial action.
Gas holder or gas storage dome: The biogas thus formed gets collected in the gas holder. It holds the gas till the time it is transported for consumption.
Outlet pipe: The slurry is discharged into the outlet tank. This is done through the outlet pipe or the opening in the digester.
Gas Pipeline: The gas pipeline carries the gas to the utilization point like a stove or lamp

20. Fixed dome type biogas plant
( Janta biogas plant)

25. Deenbandhu biogas plant
Approved by GOI in 1986.
Design consists of two spheres of different diameters, joined at their bases.
Sphere shaped design - reduce the surface area of biogas plant - reduce cost.
The curvature in the bottom of the digester - nullify the earth pressure.
Structural strength of spherical structure is more than a rectangular structure.

26. Deenbandhu biogas plant
Mixing tank
Gas outlet pipe
Plinth level
Outlet tank cover
Displacement Chamber
Outlet Tank
Slurry Discharge Hole
Digester
Outlet gate
Gas storage Area
Inlet Pipe
Foundation
Initial slurry level
Deenbandhu biogas plant

27. Method of Emptying Deenbandhu
Open Gate Valve
Open Gate Valve
P.L
P.L
G.L
First step
First step
Second step
Second step
Stage I
Stage II

28. Contd.. Open Gate Valve Open Gate Valve P.L P.L First step First step
Second step
Second step
Stage III
Stage IV

29. KVIC Vs Deenbandhu KVIC type Deenbandhu model
Sr. No
KVIC type
Deenbandhu model 1.
This is floating gas holder type
This is fixed dome type masonry structure 2.
It is made above the ground level
It is under ground masonry structure 3.
Space above ground is used for
fitting of movable drum
The space above ground can
be used other beneficial
purpose 4.
Initial investment is low.
Initial investment is high. 5.
It requires some cost of
maintenance to maintain the
steel structure.
No. cost of maintenance 6.
Effect of low temperature during
winter is more.
Effect of low temperature is less

30. Contd.. KVIC type Deenbandhu model Gas is always produced at
Sr.No
KVIC type
Deenbandhu model 7
Gas is always produced at
constant pressure.
Gas pressure is variable. 8
Required less excavation
Required more excavation
comparatively. 9
Any skilled mason can construct
the plant.
It requires specially trained
mason to construct the plant 10
Well suitable for plain as well as for hilly areas where temperature variation goes to very low level.
Suitable for plain area 11
Suitable for Rocky area also.
It is not suitable for Rocky and
hard soil area.

31. Biogas Plant models available in India
Sr.no
Biogas Plants with movable gas holder
Fixed dome type
Digester and gas holder separate
Flexible bag plant 1
KVIC Design
Sichuan Model
Sulabh Model
Neoprene Bag Model 2.
IARI Design
Shanghai Model
Bardoli Model
Swasrik Biogas Plant 3.
PRAI design (Two Chambers)
Janata (Brick Masonry)
PAU Model
Red Mud Plastic Model 4.
Kamdhanu (baked clay) model
Bhagya Laxmi
Sangli Model

32. Biogas Plants with movable gas holder Fixed dome type
Contd…
Sr. No
Biogas Plants with movable gas holder
Fixed dome type
Digester and gas holder separate 5.
ASTRA Model
Kalinga (RCC)
CV Krishna Model(FRP Fixed Dome) 6.
JWALA Model
ASTRA (Chinese type) 7.
Ganesh Model
GAIC/ATRC (RCC segment) Model 8.
Khira model
AFPRO (Horizontal RCC pipe ) model 9.
FRP Model
Deen Bandhu Model 10
Ferrocement Digester Model, SERC Model, SPRERI Model.
Bharat Model

33. Flexible Balloon Digester
Originated in Taiwan, China, in the 1960s.
Rectify - problems experienced with brick and metal digesters.
Material - Neoprene coated nylon
- PVC
- RMP – Red mud plastic (produced from the residue from aluminum refineries)
The membrane digester is extremely light
Can be installed easily by excavating a shallow trench,
slightly deeper than the radius of the digester.
Simple construction, prefabricated, digester cost is low.

34. Flexible balloon biogas plant

35. What is meant by High rate digesters?
Refer to bioreactors in which the SRT (time for sludge biomass solids to pass through system) is separated from the HRT (time for liquid to pass through system).
Slow growing anaerobes can be maintained in the reactor at high concentrations, enabling high volumetric conversion rates.
Widely used for wastewater treatment
Retaining sludge in the reactor is immobilization onto support material (microorganisms sticking to surfaces, eg. filter material in the "anaerobic filter") or self-aggregation into pellets (microorganisms sticking to each other, eg. sludge granules). 

36. Contd…
Anaerobic fixed-film (sludge blankets) systems hold the bacteria in the digester for relatively long periods and provide for long SRTs and short HRTs.
The bacteria grow as fixed films of dendritic or “stringlike” masses on the supportive media or as clumps of solids within the openings or voids of the supportive media (such as gravel, plastic, and rock).
The openings make up approximately 50% or more of the media.
Soluble organic compounds are absorbed (diffuse into) by the bacteria, whereas insoluble organic compounds are adsorbed (attach) to the surface of the bacteria.
The flow of wastewater through fixed-film systems may be from the bottom to the top (upflow) or from the top to the bottom (downflow).

37. Types of High rate digesters (Fixed-film)
Baffled reactor
Expanded bed
Expanded granular sludge bed (EGSB)
Continuous stirred tank reactor (CSTR)
Fluidized-bed reactor
Fully packed upflow
Hybrid flow
Rotating biological contactor
Thin-film bioreactor
Upflow anaerobic sludge blanket (UASB)

38. What are sludge granules?
At the core of UASB and EGSB technology.
A sludge granule is an aggregate of microorganisms forming during wastewater treatment due to constant upflow hydraulic regime. 
The flow conditions creates a selective environment in which only those microorganisms, capable of attaching to each other, survive and proliferate.
Eventually the aggregates form into dense compact biofilms referred to as "granules“.
Due to their large particle size (generally ranging from 0.5 to 2 mm in diameter) , the granules resist washout from the reactor, permitting high hydraulic loads.

39. Contd..
Biofilms are compact allowing for high concentrations of active microorganisms i.e. high organic space loadings.
One gram of granular sludge organic matter (dry weight) can catalyze the conversion of 0.5 to 1  g of COD per day to methane.
i.e. on a daily basis granular sludge can process its own body weight of wastewater substrate.

40. Anaerobic sludge granules from a UASB reactor treating effluent

41. Granular Sludge
Granular sludge (1-3 mm)

42. The spaghetti theory of granulation
Pellet formation ("spaghetti balls")
Floccule formation via entanglement
disperse methanogens
Mature granules, with attachment of other anaerobic microorganisms onto the pellet.
The spaghetti theory of granulation

43. Inside a granule

44. Top applications of high rate anaerobic reactor systems
Breweries and beverage industry
Distilleries and fermentation industry
Food Industry
Pulp and paper.

45. Other Applications of high rate digesters
Sulfate reduction for the removal and recovery of heavy metals and sulfur
Denitrification for the removal of nitrates
Bioremediation for the breakdown of toxic priority pollutants to harmless products

46. USAB Upflow anaerobic sludge blanket
Developed by Dr. Gatze Lettinga & colleagues in1970's at the Wageningen University (The Netherlands).
Working :
Feed passes upwards through an anaerobic  sludge bed where the microorganisms in the sludge come into contact with substrates. 
Sludge bed is composed of microorganisms that naturally form granules (pellets) of 0.5 to 2 mm diameter
Sludge bed have a high sedimentation velocity i.e. resist wash-out from the system even at high hydraulic loads.
Resulting anaerobic degradation process is responsible for production of biogas.

47. Contd..
Upward motion of released gas bubbles causes hydraulic turbulence provides reactor mixing without any mechanical parts.
At the top of the reactor, the water phase is separated from sludge solids and gas in a three-phase separator (also known the gas-liquid-solids separator).
Three-phase-separator is commonly a gas cap with a settler situated above it.
Baffles are used to deflect gas to the gas-cap opening.

50. UASB reactor

51. Process flow diagram of UASB

52. UASB reactor

53. Expanded Granular Sludge Bed (EGSB) reactor
Variant UASB concept
Distinguishing feature - faster rate of upward-flow velocity
Increased flux permits partial expansion (fluidization) of the granular sludge bed, improving wastewater-sludge contact & enhancing segregation of small inactive suspended particle from the sludge bed.
Increased flow velocity is either accomplished by utilizing tall reactors, or by incorporating an effluent recycle (or both).
Appropriate for low strength soluble wastewaters (less than 1 to 2 g soluble COD/l) or for wastewaters that contain inert or poorly biodegradable suspended particles which should not be allowed to accumulate in the sludge bed.

54. Schematic diagram of EGSB reactor

55. EGSB

56. EGSB reactor
Sludge storage
Buffer tank
Conditioning tank
EGSB reactor

58. CSTR Continuous Stirred Tank Reactor
Also known as vat- or backmix reactor.
One or more fluid reagents are introduced into a tank reactor equipped with an impeller while the reactor effluent is removed.
Impeller stirs the reagents to ensure proper mixing.
Simply dividing the volume of the tank by the average volumetric flow rate through the tank gives the residence time, or the average amount of time a discrete quantity of reagent spends inside the tank.

59. Contd..
Behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR).
Run at steady state with continuous flow of reactants and products;
Feed assumes a uniform composition throughout the reactor.
Exit stream has the same composition as in the tank.

60. CSTR

61. CSRT

62. Inside view of CSTR

65. Baffled Anaerobic digester

66. Conventional biogas plants High rate anaerobic digesters
Sr.No
Conventional biogas plants
High rate anaerobic digesters 1.
Suitable for Insoluble wastes (such as particulate and colloidal organics) Also called high-strength wastes.
Suitable for treatment of soluble wastewater. Also called low-strength wastes 2.
Require lengthy digestion periods for hydrolysis and solubilization.
Wastewaters do not require hydrolysis and solubilization 3.
HRT of at least 10–20 days
Much faster rates of treatment are obtained. Have retention time of less than 8 hours. 4.
Suspended growth systems are being used for treatment.
Fixed-film systems are being used for treatment. 5.
SRT is the same as the HRT
Minimal HRT to reduce digester volume and capital costs. Maximal SRT is desired to achieve process stability and minimal sludge production.

67. One m3 of biogas is equivalent to
0.7 m3 of natural gas,
0.7 kg of fuel oil,
0.6 kg of kerosene,
0.4 kg of benzene,
3.5 kg of firewood,
12 kg of manure
4 kWh of electric energy,
1.5 kg of coal,
0.433 kg of LPG
1.6 kg of CO2

68. Size of plants, requirement of cattle dung and estimated cost
Quantity of cattle dung required daily
No. of cattle heads required
Estimated cost*
1 Cubic metre 25
2-3
Rs. 7000/-
2 cubic metre 50
4-6
Rs. 9000/-
3 cubic metre 75
7-9
Rs. 10,500/-
4 cubic metre
100
10-12
Rs. 12,500/-
*The cost is higher by 30 per cent and 50 per cent in hilly areas and North Eastern Region States, respectively.
MNRE

69. Biogas consumed for different applications
Use
Specification
Quantity of gas
consumed (m3 /hr)
Cooking
2" burner
0.33
4" burner
0.47
6" burner
0.64
per person per day
0.24 m3/day
Gas lighting mantle lamp of
100 Candle Power
0.13
Duel fuel engine
75-80% replacement
of diesel oil per B.H.P.
0.50
Electricity
1 kWh
0.21