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BIOGAS TECHNOLOGY

1. Introduction: Properties of biogas

2. Justification for rural & other applications.

3. Feedstock for biogas: Aqueous organic wastes_ biodegradable

3.1. Microbial and biochemical aspects

3.2. Operating parameters for biogas production.

3.3 Kinetics and mechanism

3.4 Dry and wet fermentation.

3.5 Digesters for rural application

3.6 High rate digesters for industrial waste water treatment.

3.7. Textbooks and reference Materials

1. INTRODUCTION:

Production of a combustible gas by anaerobic digestion of

aqueous organic matter by mixed bacterial culture involving methane

producers is called ‘biomethanation’ and the product is called ‘biogas’

PROPERTIES OF BIOGAS:

Composition: 60 to 70 per cent Methane, 30 to 40 per cent carbon

dioxide, traces of hydrogen sulfide, ammonia and water vapor.

It is about 20% lighter than air (density is about 1.2 gm/liter).

Ignition temperature is between 650 and 750 C.

Calorific value is 18.7 to 26 MJ/ m3 (500 to 700 Btu/ ft3.)

Calorific value without CO2: is between 33.5 to35.3 MJ/ m3

Explosion limit: 5 to 14 % in air.

Removal of CO2: Scrubbing with limewater or ethanol amine solution.

Removal of H2S: Adsorption on a bed of iron sponge and wood

shavings.

Air to Methane ratio for complete combustion is 10 to 1 by volume.

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One cubic meter of biogas is equivalent to 1.613 liter kerosene or

2.309 kg of LPG or 0.213 kHz electricity.

Pressure & Temperature needed to liquefy: Biogas needs 500 psi, at

–83 oC & LPG Needs 160 psi, at ambient temperature.

Applications and Usage of biogas: 1. Cooking fuel-Design of Burner

2. Lighting Fuel-mantle lamp 3. Fuel for running I. C. Engines

4. Fuel for Power generation

(Refer: Chapter11, ‘Biogas Systems’— K.M.Mital)

2. JUSTIFICATION FOR RURAL & OTHER APPLICATIONS:

WHY Biomethanation in villages?

ENERGY RECOVERY, CLEAN BURNING

SUBSTITUTES FUELWOOD & DUNG CAKE AS

RURAL FUEL

HYGIENIC DISPOSAL OF ANIMAL WASTE

CONSERVATION OF MANURE VALUE

DUNG

WATER

BIOGAS

PLANT BIOGAS

PURIFY I. C. ENGINE +

PUMP OR

I. C. ENGINE +

GENERATOR

COOKING

LIGHTING

FUEL FOR

KILN

FURNACE

ETC.

TO

COMPOST PIT

(MANURE)

3

MILD CONDITIONS: 30o C, pH 6.8-7.2, FEED ONCE A

DAY

BURNER, MANTLE LAMP AVAILABLE; EASY GAS

PURIFICATION FEASIBLE

FOR RURAL FARM OR FAMILY SIZE PLANT,

SUBSIDY AVAILABLE.

DUAL FUEL ENGINE CAN PUMP WATER,

GENERATE POWER

BIOGAS TECHNOLOGY: SIMPLE & INDIGINOUS

3.1. Commonly Used Feedstocks for Biomethanation:

Animal Wastes, Crop Residues, Urban Wastes, Food & Agro-

Industry Wastes. (Mital, Ch. 7 To 10)

WET ORGANIC WASTE AS FEED FOR BIOGAS PLANT

ANIMAL WASTES: Excreta of cow, pig, chicken etc

MANURE, SLUDGE: Canteen and food processing waste, sewage

MUNICIPAL SOLID WASTE: After separation of non-degradable

WASTE STARCH & SUGAR SOLUTIONS: Fruit processing, brewery, press

mud from sugar factory etc

OTHER INDUSTRIAL EFFLUENTS (B O D): pulp factory waste liquor,

leather industry waste, coal washery wastewater etc.

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3.2 MICROBIOLOGIAL ASPECTS OF BIOMETHANATION

The biomethanation of organic matter in water is carried out in

absence of dissolved oxygen and oxygenated compounds like nitrate

and sulphate. The mixed groups of bacteria are naturally occurring in

the cow dung slurry and decomposition in three stages finally

produces a gas mixture of methane and carbon dioxide. Initially larger

molecules are hydrolysed to simpler molecules which in turn are

decomposed to volatile fatty acids like acetic acid, propionic acid etc.

by a second set of bacteria. Methane forming bacteria can convert

acetic acid, hydrogen and carbon dioxde and produce methane.

3.3 Operating parameters affecting the biogas production:

1. Temperature is an important parameter. Mesophilic methane

producing bacteria grow at an optimum temperature of 35oC the

gas production rate drops very much when temperature is less

than 10oC.

HYDRLYSIS OF BIOPOLYMERS TO MONOMERS

CONVERSION OF SUGARS, AMINO ACIDS, FATTY ACIDS TO

HYDROGEN, CO2, AMMONIA AND ACETIC, PROPIONICAND

BUTIRIC ACIDS

BIOMETHANATION: FROM ACID, H2 AND CO2 TO FORM CH4

CONVERSION OF H2, CO2, ACETIC ACID TO CH4 AND CO2

MIXTURE

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2. pH range of the waste water should be in the range of 6.8 to 7.8

as excess acid state hampers the methane producing bacteria

and the balance of nutrients is disturbed.

3. Ratio of carbon to nitrogen in the waste water influent or C/N

ratio is 30:1 and if nitrogen content in ammoniacal form is less

the bacterial growth is affected and the process slows down.

4. Proportion of solids to water: This is found to be not more than

10 per cent for optimum operation of digester to ensure

sufficient decomposition of ‘volatile solids’ and rate of

production of gas.

5. Retention time: The ratio of volume of slurry in the digester to

the volume fed into and removed from it per day is called

retention time. Thus a 20 liter digester is fed at 4 liters per day

so that the volume of digester is constant the retention time is 5

days. The required retention time is normally 30 days for

mesophilic (25-35oC) conditions.

6. Volumetric organic loading rate: This can be expressed as kg

Vs per volume per day based on the % weight of organic matter

added each day to the digester volume.

Digester loading rate %= (Per cent of organic matter in

feed)/(Retention Time) Loading rate range is 0.7 to25 kg VS/ m3

/ Day

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3.4. KINETICS OF ANAEROBIC FERMENTATION (Refer: Mital, 36):

Rate of substrate Utilization,

rs = Qmax * (Sx)/ (K+S) ---(1)

Where S is limiting substrate concentration

K is half life constant

X is concentration of bacterial cells

Qmax is maximum substrate utilization rate

For low substrate concentration, this equation is valid. For high

substrate concentration, it becomes as follows:

rs = Qmax*x ----(2)

The above model known as Monod model has limitations. For

complex substrates, kinetic parameters cannot be obtained for the

entire concentration range.

Chen and Hashimoto, Biotechnology Bio-engineering

Symposium 8, (1978) p 269-282 and Biotechnology

Bioengineering (1982) 24: 9-23

Volumetric methane rate in cubic meter gas per cubic meter of

digester volume

V = (Bo So / HRT)[1- K / (HRT*m-1+K)]

Bo = Ultimate methane yield in cubic meters methane (Varies from

0.2 to 0.5)

So = Influent volatile solids concentration in kgVS/m3

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(Loading rate range = 0.7 to 25 kg VS/m3 d)

HRT = Hydraulic retention time in days

K = Dimensionless kinetic parameter, for cattle dung, K= 0.8+

0.0016e0.06 So

m = Maximum specific growth rate of the microorganism in day-1

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3.5. RURAL DIGESTERS ACCEPTED BY MNES:

(Digesters for rural application)

1. KVIC (FLOATING DOME)

MASONRY CYLINDRICAL TANK

ON ONE SIDE INLET FOR SLURRY

OTHER SIDE OUTLET FOR SPENT SLURRY

GAS COLLECTS IN INVERTED ‘DRUM’ GAS HOLDER OVER

SLURRY

GAS HOLDER MOVES UP & DOWN DEPENDING ON

ACCUMULATION OF GAS /DISCHARGE OF GAS, GUIDED BY

CENTRAL GUIDE PIPE

GAS HOLDER (MILD STEEL): PAINTED ONCE A YEAR.

K V I C Mumbai

MEDIUM FAMILY SIZE BIOGAS PLANT HAVING GAS DELIVERY OF

3 M3 /DAY REQUIRES 12 HEAD OF CATTLE AND CAN SERVE A

FAMILY OF 12 PERSONS

TECHNICAL DETAILS OF A 3 M3 /DAY BIOGAS PLANT OF

FLOATING DRUM DESIGN

Name of the model KVIC Model

Size for 3m3 / day gas delivery

4.15m high, 1.6m dia, Volume 8.34m3 Inlet pipe 0.1m dia, 4m long Inlet tank 0.75m dia, 1m high Outlet pipe 0.1m dia, 1.1 m long

Retention period 30 to 50 days

Gas Holder 1.5 m dia, 1m high

Construction of gas holder MS sheet & angles, fabricated.

Constr. & layout, digester Brick, cement, digester below G. level

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2. JANATHA (FIXED DOME)

DIGESTER WELL BELOW GROUND LEVEL

FIXED DOME GAS HOLDER BUILT WITH BRICK & CEMENT

BIOGAS FORMED RISES PUSHES SLURRY DOWN

DISPLACED SLURRY LEVEL PROVIDES PRESSURE-UPTO THE POINT

OF ITS DISCHARGE/ USE

3. DEENABANDU (FIXED DOME, MINIMISES SURFACE AREA)

FIXED DOME PLANT, MINIMISES SURFACE AREA BY JOINING THE

SEGMENTS OF TWO SPHERES OF DIFFERENT DIAMETERS AT THEIR

BASES

FIXED MASONRY DOME REQUIRES SKILLED WORKMANSHIP AND

QUALITYMATERIALS TO ELIMINATE CHANCE OF LEAKAGE OF GAS

AFPRO, 25/1A,Institutional Area, D block, Panka Rd, Janakpury, N.Delhi.

BIOGAS

Janatha

Digeste

r

inlet

outlet

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4. PRAGATI

COMBINES FEATURES OF KVIC & DEENABANDU, MAHARASHSTRA

LOWER PART: SEMI-SPHERICAL IN SHAPE WITH A CONICAL BOTTOM

UPPER PART: FLOATING GAS HOLDER

POPULARISED IN MAHARASHTRA, UNDARP, PUNE

5. FERROCEMENT DIGESTER:

CAST SECTIONS, MADE FROM A REINFORCED (MORTAR+WIRE

MESH)- COATED WITH WATER PROOFING TAR

S E R I, ROORKEE

6. FRP DIGESTER:

FIBER REINFORCED PLASTIC MADE BY CONTACT MOULDING

PROCESS

7. UTKAL / KONARK DIGESTER

Reference: ‘Konark biogas plant-A user friendly model’ Mohanty,

P.K., and Choudury, A. K, (Orissa Energy Dev. Agency), Journal of

Environmental Policy and Studies 2(1); 15-21

Konark Biogas plant:

SPHERICAL IN SHAPE WITH GAS STORAGE CAPACITY OF 50%

CONSTRUCTION COST IS REDUCED AS IT MINIMIZES SURFACE AREA

BRICK MASONRY OR FERROCEMENT TECHNOLOGY

A PERFORATED BAFFLE WALL AT THE INLET PREVENTS SHORT

CIRCUITING PATH OF SLURRY (OPTIONAL)

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8. FLEXIBLE PORTABLE NEOPRENE RUBBER MODEL:

FOR HILLY AREAS, MINIMIZES TRANSPORT COST OF MATERIALS

BALLOON TYPE, INSTALLED ABOVE GL, MADE OF NEOPRENE

RUBBER

FOR FLOOD PRONE AREAS, UNDERGROUND MODELS NOT SUITABLE

SWASTHIK COMPANY OF PUNE DESIGN

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3.6. HIGH RATE DIGESTERS FOR WASTE WATER TREATMENT:

1. ANAEROBIC FILTER (UPFLOW and DOWNFLOW)

2. UPFLOW ANAEROBIC SLUDGE BLANKET DIGESTER(

UASB)

3. ANAEROBIC LIQUID FLUIDISED/ EXPANDED BED

DIGESTER

4. ANAEROBIC ROTATING DISC CONTACTING DIGESTER

5. ANAEROBIC MEMBRANE DIGESTER

6. ANAEROBIC CONTACT DIGESTER

Effluent Treatment & Disposal: I Ch. E, U.K., Symposium Series

No96, 1986., P 137-147, Application of anaerobic biotechnology to

waste treatment and energy production Anderson & Saw.

Energy & Environment Monitor, 12(1) 45- 51, ‘Biomethanation

Technologies in industrial water pollution Control’ A.Gangagni Rao,

Pune.

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HIGH RATE DIGESTERS FOR WASTE WATER TREATMENT:

1 ANAEROBIC FILTER (UPFLOW and DOWNFLOW)

ANAEROBIC FILTER CONTAINS A SOLID SUPPORT OR PACKING

MATERIAL IT WAS DEVELOPED BY YOUNG & MC CARTHY IN 1967

WASTEWATER FLOWS FROM BOTTOM UPWARDS THROUGH THE

PACKING, GAS SEPARATES, BACTERIA ARE RETAINED MOSTLY

IN SUSPENDED FORM,HRT RANGE OF 0.5 TO12 DAYS IS OBTAINED

SINCE SUSPENDED GROWTH TENDS TO COLLECT NEAR THE

BOTTOM OF THE REACTOR, ACTIVITY IS HIGHER THERE.

TYPICAL ORGANIC LOADING RATE OF 1 TO 40 KG COD/

M3/DAYAND A SRT OF 20 DAYS IS ACHIEVED.

AVOIDANCE OF PLUGGING DUE TO ACCUMULATION OF SOLIDS

IN THE PACKING MATERIAL AND ENSURING AN ADEQUATE

FLOW DISTRIBUTION IN THE BOTTOM OF THE REACTOR ARE

THE LIMITATIONS OF THIS.

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2. UPFLOW ANAEROBIC SLUDGE BLANKET DIGESTER (UASB)

UASB REACTOR IS BASED ON SUPERIOR SETTLING PROPERTIES

OF THE SLUDE

INFLUENT FED INTO THE REACTOR FROM BELOW LEAVES AT

THE TOP VIA AN INTERNAL BAFFLE SYSTEM FOR SEPARATION

OF THE GAS, SLUDGE AND THE LIQUID

GAS SEPARATED FROM SLUDGE, COLLECTED BENEATH PLATES

IN QUIET SETTLING ZONE, SLUDGE SEPARATES, SETTLES BACK

TOWRDS DIGESTION ZONE.

ORGANIC LOADING RATES OF 10 TO 30 KG COD /M3 DAY

REACTOR MIXING SHOULD BE ONLY BY THE GAS PRODUCTION

HRTRANGE OF 0.5 TO 7 DAYSS IS FEASIBLE WITH EXCEL.

SETTLING SLUDGE AND A SRT OF 20 DAYS(AT 35 0

C)

REF: TIDE,VOL9,NO4, DEC.1999,PAGE 232

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3. ANAEROBIC LIQUID FLUIDIZED/ EXPANDED BED DIGESTER

ACTIVE BIOMASS IS ATTACHED TO SURFACE OF SAND

PARTICLES THAT ARE KEPT IN SUSPENSION BY UPWARD

VELOCITY OF LIQUID FLOW

DEGREE OF BED EXPANSION IN EXPANDED BED IS 10-20% AND IN

FLUIDIZED BED IT IS 30-100%

BIOMASS RETENTION IN THE REACTOR IS EFFICIENT ,SRT OF 30

DAYS

PARTICLES PROVIDE LARGE SURFACE AREA FOR MICROBIAL

GROWTH AND BETTER MIXING COMPARED TO PACKED BED, HRT

RANGE OF 0.2 TO 5.0 DAY ACIEIVED.

TYPICAL RANGE OF LOADING RATE OF 1 TO 100 KG COD/M3 /DAY

REF: COMPREHENSIVE BIOTECHNOLOGY-MURRAY MOO YOUNG,

VOL4, PAGES1017-1027.

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4 ANAEROBIC ROTATING BIOLOGICAL DISC CONTACTOR

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5. ANAEROBIC MEMBRANE DIGESTER

SUSPENDED GROWTH REACTOR, COMBINED WITH A

SEPARATOR

EXTERNAL ULTRA / MICROFILTRATION MEMBRANE UNIT

FOR SOLID-LIQUID SEPARATION

PERMEATE BECOMES THE EFFLUENT AND THE BIOMASS

IS RETURNED TO THE REACTOR

MEMBRANE UNIT ROVIDES POSITIVE BIOMASS

RETENTION AND PARTICULATE FREE EFFLUENT

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6. ANAEROBIC CONTACT DIGESTER

BIOMASS SETTLED IN A SECOND TANK, RECYCLED TO

THE DIGESTER.

RECYCLE GIVES HIGHER SRT AND EFFICIENCY

MIXING IN THE FIRST TANK AND EFFICIENCY OF

SETTLING IN THE SECOND TANK IMPROVES

PERFORMANCE.

REQUIRE HRT OF 10 DAYS OR MORE.

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3.7. TEXT BOOKS AND REFERENCES

1. Biotechnology Volume 8, H.J.Rehm and G. Reed, 1986, Chapter 5, ‘Biomethanation Processes.’ Pp 207-267

2. K. M. Mital, Non-conventional Energy Systems, (1997), A P H

Wheeler Publishing, N. Delhi.

3. K. M. Mital, Biogas Systems: Principles and Applications,

(1996) New Age International Publishers (p) Ltd, N. Delhi.

Contents: 1.An Overview Of Biogas Technology 2. Microbiology Of

Anaerobic Digestion 3. Properties Of Biogas And Methods For Its

Purification 4. A Compendium Of Biogas Plant Design 5. Design,

Construction, Operation And Maintenance Of Biogas Plants 6.

Analysis Of Factors Affecting Biogas Yield 7. Biogas Yield From

Different Organic Wastes 8. Biogas Yield From Water Weeds 9.

Biogas Generation From Industrial Wastes 10. Biogas Recovery

From Sanitary Landfills 11. Applications And Usage Of Biogas 12.

Potential Of Biogas Plant Effluent As Enriched Fertilizer.13.

Approaches For Implementing Biogas Program Areas For Further

Research And Concluding Observations

4. Khandelwal K. C.and Mahdi, “Bio-gas Technology”, Tata McGraw-

Hill publ. Co. Ltd., New Delhi, 1986.

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5. ‘Biogas Production Technology: An Indian Perspective’, B.

Nagamani and K. Ramasamy (TNAU), Current Science, Vol7, No1,

pp 44-55 10th July, 1999

References:

1. Effluent Treatment & Disposal: I Ch. E, U.K., Symposium Series

No 96, 1986,

P 137-147, Application of anaerobic biotechnology to waste treatment

and energy production, Anderson & Saw.

2. ‘Anaerobic Rotating Biological Drum Contactor for the Treatment of

Dairy Wastes’, S. Satyanarayana, K. Thackar, S.N.Kaul,

S.D.Badrinath and N.G. Swarnkar, Indian Chemical Engineer, vol 29,

No 3, July-Sept, 1987

3. Energy Environment Monitor,12(1),45-51,‘Biomethanation

Technologies in Industrial Water Pollution Control’ A.Gangagni Rao,

Pune.

4. ‘Biogas production from sugar mill sludge by anaerobic digestion

and evaluation of bio-kinetic coefficients’, Tharamani. P, and

Elangovan. R. Indian journal of Environmental protection, 20, (10),

745-748, 2001