DIFFERENT TYPES OF BIOGAS PLANTS

2. 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 : 25-40% Nitrogen, N2 : 0-2 % Hydrogen Sulphide, H2S : 0-3 % Hydrogen, H2 : 0-2 % Oxygen, O2 : 0-2 % pH-value : 6.5 to 7.5 Due Point : < - 80� C

3. Why should we go for biogas? Disposal and treatment of biological waste - a major challenge for the waste industry. Anaerobic fermentation - a superior alternative to composting. Limited domestic reserves and uncertain foreign supply of hydrocarbons. Provides clean combustible gas and high quality organic fertilizer for sustaining soil-fertility and also for Pisciculture. It has a typical calorific value of 21.48 MJ/m3 or 4,800 kcal/m3. Recognized renewable energy source Potential reduction of green house gas emissions.

7. 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.

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

9. Biogas plants in India Potential -12 million family type biogas plants Achieved - 4.12 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

10. 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.

11. 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.

12. 1984 - 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.

13. 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

15. Biogas Digesters

16. Conventional biogas plants in India Fixed dome type Floating drum type Bag type

17. 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 - 8-10 cm water column.

18. 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.

19. 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

26. 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.

27. Deenbandhu biogas plant

28. Method of Emptying Deenbandhu

29. Contd..

30. KVIC Vs Deenbandhu

31. Contd..

32. Biogas Plant models available in India

33. Contd�

34. 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.

35. Flexible balloon biogas plant

36. 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).�

37. 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).

38. 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)

39. 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.

40. 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.

41. Anaerobic sludge granules from a UASB reactor treating effluent

43. The spaghetti theory of granulation

44. Inside a granule

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

46. 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

47. USABUpflow 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.

48. 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.

52. Process flow diagram of UASB

53. UASB reactor

54. 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.

55. Schematic diagram of EGSB reactor

56. EGSB

59. CSTRContinuous 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.

60. 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.

61. CSTR

62. CSRT

66. Baffled Anaerobic digester

68. 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

69. Size of plants, requirement of cattle dung and estimated cost��

70. Biogas consumed for different applications