BiogasBiogas

Somporn Somporn JenkunawatJenkunawat

Biogas is gas produced from the fermentation of manure or organic matter by microorganisms in the anaerobic. Biogas is a mixture of gases such as methane (CH4), carbon dioxide (CO2) nitrogen gas (N2) and hydrogen sulfide (H2S), mainly composed of methane and combustible.

Biogas is produced from the wastewater treatment of Agricultural products and livestock plants by anaerobic digestion such as cassava, crude palm oil mill , fruit production factory swine farm, alcohol factory and so on.

Anaerobic Biological Digestion ProcessAnaerobic Biological Digestion Process

Bio-gas Bio-gas

Undigested

Solids & Water

Undigested

Solids & WaterAcetogenesisAcetogenesis

MethanogenesisMethanogenesis

HydrolysisHydrolysis

OrganicWaste

OrganicWaste

Organic MatterOrganic Matter

CH4 + CO2CH4 + CO2

beforebefore afterafter

Laboratory results on high solids digestionLaboratory results on high solids digestion

Properties of biogas as the fuel gas, depending on the amount of methane (CH4), which is igniting the gas in the atmosphere. The heating value of about 600 BTU / cubic foot (for methane gas to heat 1,000 BTU / cubic foot).

Pure methane gas is colorless, odorless when burned will give CO2, water and energy 5,000-6,000 Kcal/M3 at 15 oC. 735 cm of Hg pressure. While the H2S is mixed in will give smelly odor and corrosion. But when it is burned it smells less. The condensation point is -164.4 oC

Why Methane is suitable for renewable

energy source ?

The use of methane as an energy source.1. No blast occur.2. Have a slight odor so if leak will get the smell. 3. No toxic to human.4. Heat get could boil 18 liters of water in 9-10 minutes..

Factors influence on producing

biogas

1. Temperature 2. pH 3. Alkalinity 4. Nutrients 5. Inhibiting and Toxic Mate

rrrrr 6. Organic matter 7. Types of rrrrrr rrrrr

Effect of temperatureAnaerobic digestion is strongly influenced by temperature and can be grouped as: 1.Psychrophilic (0–20°C) 2.Mesophilic (20–42°C) 3.Thermophilic (42–75°C) Changes in temperature are well resisted by anaerobic bacteria, as long as they do not exceed the upper limit as defined by the temperature at which the decay rate begins to exceed the growth rate. However, an important characteristic of anaerobic bacteria is that their decay rate is very low at temperatures below 15°C.

Effect of pH and Alkalinity

The optimal pH range for methane producing bacteria is 6.8–7.2 while for acid-forming bacteria, a more acid pH is desirable .

In general, sodium bicarbonate is used for supplementing the alkalinity since it is the only chemical, which gently shifts the equilibrium to the desired value without disturbing the physical and chemical balance of the fragile microbial population .

Effect of nutrients

The bacteria in the anaerobic digestion process requires micronutrients and trace elements such as nitrogen, phosphorous, sulphur, potassium, calcium, magnesium, iron, nickel, cobalt, zinc, manganese and copper for optimum growth. . The required optimum C:N:P ratio for enhanced yield of methane has been reported to be 100:2.5:0.5.

Effect of organic loading rate

In anaerobic wastewater treatment, loading rate plays an important role. In the case of nonattached biomass reactors, where the hydraulic retention time is long, overloading results in biomass washout. This, in turn, leads to process failure. Fixed film, expanded and fluidized bed reactors can withstand higher organic loading rate.

Organic loads of anaerobic Organic loads of anaerobic digestersdigesters

Anaerobic lagoon Anaerobic lagoon 0.1 to 2 kilo 0.1 to 2 kilo COD/mCOD/m33/d/d

Anaerobic contact Anaerobic contact 1 to 5.5 kilo 1 to 5.5 kilo COD/mCOD/m33/d/d

Anaerobic filterAnaerobic filter 10 to 15 kilo 10 to 15 kilo COD/mCOD/m33/d /d

Fluidized bedFluidized bed 30 to 40 kilo 30 to 40 kilo COD/mCOD/m33/d/d

UASBUASB 15 to 25 kilo COD/m 15 to 25 kilo COD/m33/d/d Multiplate digesterMultiplate digester 9 to 15 kilo 9 to 15 kilo

COD/mCOD/m33/d/d IC reactorIC reactor 30 to 40 kilo COD/m30 to 40 kilo COD/m33/d/d

Inhibitor

The inhibitors commonly present in anaerobic digesters include:AmmoniaSulfideLight Metal ions

Aluminium Magnesium Calcium Potassium SodiumHeavy metal

Advantages• Get biogas

• Cost of construction is lower

• Daily expense is lower

• Eliminate chemical odor at least 90

percent• Using of biogas is

apart of reducing emission of greenhouse

Disadvantages

Need more area not suitable for factory that have limited area.

Microorganism for producing biogasThe production of biogas large molecular organic materials is decomposed into smaller molecule and turn to be inorganic matter and gases by bacteria in the anaerobic digester.

Anaerobic Digestion Process

11. Hydrolysis

Carbohydradtes Sim ple sugar + Alcohol

Proteins Pepti de + Amino acid

Fats Glycer ol + Fatty acid

Microorganisms : -Fat decomp osing microorganism, Cellulos

- e decomposing microorganis mand - Protein decomposing or

ganism

1. Liquefaction stage

12. Acid formation stage

r rr rrrr rrrrrrrr Organic acid + CO

2

Microorganism :Acid formers

2. Gasification stage

r rrrrrr rrrr rrr Organic acid

CO 2 + CH4

Microorganism : Methanogenic bacteria

Raw materials

Carbohydrate

Protein Fat

Propionic acid

Acetic acid

Acetica acid+inert organic residue

(digested sludge)

Butyric acid

CH4 + CO2

Reactions

Methanogenic Reactions

CH3COOH

CO2 + H2

CH4 + CO2

CH4

acetate carbondioxide

methane

methanecarbondioxide

hydrogen

acetoclasticmethanogenesis

autotrophicmethanogenesis

Changing of organic matter by anaerobic reaction

PROPINIC

ACID

COMPLEX

WASTE

OTHERINTERTMEDI

ATES

ACETICACID

CH4

15% 20

%

65%

17%

13%

35%

15%72

%

METHANEFERMENT

ATION

ACID FORMATIO

N

Compositionvolume (%) Methane

-4560

Carbon dioxide -4060

Nitrogen -25Oxygen -25Sulfide, disulfide, mercaptane

-010Ammonia -0110. .Hydrogen -002.Carbon monoxide -002.Other gases

-00106. .Temperature ,◦F

-100120

Specific gravity-102106. .

MoistureSat ur at edHigh heating value,BTU/M3

-400555

Doubling Time Cell Yield Cell Activity ksdays g VSS g-1 COD g COD g-1 VSS d-1 mM

Active Sludge (sugar)Aerobic Bacteria 0.030 0.40 57.8 0.25

Acidification (sugar)Fermentative Bacteria 0.125 0.14 39.6 ND

Acetogenesis (fatty acids)Acetogenic Bacteria 3.5 0.03 6.6 0.4

MethanogenesisAutotrophic (H2) 0.5 0.07 19.6 0.004Acetoclastic (acetate)Methanosarcina 1.5 0.04 11.6 5.0Methanosaete 7.0 0.02 5.0 0.3

More Details on the More Details on the Digestion ProcessDigestion Process

Volatile Solids (VS)

Volatile organic acids

Acid forming bacteria

Methane, carbon dioxide, water, trace gases

Methane formingbacteria

Odor

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1 . Rod shape of methanog en bacteria

1 .1 non sporulating- rod shaped cells

Methanobacterium solmgenii

Methanobacterium formicicum

Methanobacterium propionicum

-12. sporulating rod s haped cells

Methanobacterium omelianskii

Bacterial Shapes

2 Round shape of Met hanogen bacteria 21. Cell not sarcina

arrangement

Methanococcus vaniellii

Methanococcus mazei

22. Cell in sarcina arra ngement

Methanosarcina met hanica

Methabosarcina barkerii

Anaerobic Sludge Granules (SEM)

Acetate as Substrate (Methanosaeta)

Sucrose as Substrate (mixed culture)

1 Slow digestion or solid digestion

11. fined dome digester

12. floating drum digeste r or Indian digester

Biogas Plants

1 Slow digestion or solid digestion

13. plastic covered ditchor pppp pppp pppppppp

2 Fast digestion or wastewater treatment digester

21. Anaerobic Filter: AF

22. Upflow Anaerobic Sl udge Blanker: p ppp

Principles of microbial degradation of organic matter in the absence of oxygen and agglomeration, float up to the top with biogas. When contract with obstacles gas will rise while the microorganisms will fall to the bottom. This is suitable for wastewater with low suspended solids.

Upward-flow Anaerobic Sludge Blanket

influent

effluent

biogas

sludge bed

gas cap

settler

baffles

sludge granule

gas bubble

weir3 phaseseparator

Influent

EffluentRecycle

SludgeBed

Effluent settler

gascap

biogas

gasbubble

sludgegranule

Expanded Granular

Sludge Bed

rrrrr rrrrrr

The principle is to cover the pond with blanket to prevent the smell spreading and allows microorganisms to decompose organic substances in wastewater in the anaerobic condition. It takes at least 20 days, the investment is low but the amount of gas produced is less than other systems.

UASB - Internal Circulation (IC Reactor)

Brewery (Switzerland), 20 m height

UASB - Internal Circulation

Kraft Paper Mill Foul Condensates, Alabama