Biogas Somporn Jenkunawat

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 Process Bio-gas Undigested Solids & Water Acetogenesis Methanogenesis Hydrolysis Organic Waste Organic Matter CH4 + CO2

Laboratory results on high solids digestion before after Laboratory 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 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 Materials 6. Organic matter 7. Types of Biogas Plant

Effect of temperature Anaerobic digestion is strongly influenced by temperature and can be grouped as: Psychrophilic (0–20°C) Mesophilic (20–42°C) 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 digesters Anaerobic lagoon 0.1 to 2 kilo COD/m3/d Anaerobic contact 1 to 5.5 kilo COD/m3/d Anaerobic filter 10 to 15 kilo COD/m3/d Fluidized bed 30 to 40 kilo COD/m3/d UASB 15 to 25 kilo COD/m3/d Multiplate digester 9 to 15 kilo COD/m3/d IC reactor 30 to 40 kilo COD/m3/d

Inhibitor The inhibitors commonly present in anaerobic digesters include: Ammonia Sulfide Light Metal ions Aluminium Magnesium Calcium Potassium Sodium Heavy 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 biogas The 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

1. Liquefaction stage 1.1 Hydrolysis Carbohydradtes Simple sugar + Alcohol Proteins Peptide + Amino acid Fats Glycerol + Fatty acid Microorganisms : Fat-decomposing microorganism, Cellulose-decomposing microorganism and Protein-decomposing organism

1.2 Acid formation stage Complex organics Organic acid + CO2 Microorganism :Acid formers

2. Gasification stage Methane formers Organic acid CO2 + CH4 Microorganism : Methanogenic bacteria

Acetica acid+inert organic residue (digested sludge) Reactions Raw materials Carbohydrate Protein Fat Propionic acid Acetic acid Acetica acid+inert organic residue (digested sludge) Butyric acid CH4 + CO2

Methanogenic Reactions

Changing of organic matter by anaerobic reaction PROPINIC ACID COMPLEX WASTE OTHER INTERTMEDIATES ACETIC ACID CH4 15% 20% 65% 17% 13% 35% 72% METHANE FERMENTATION ACID FORMATION Changing of organic matter by anaerobic reaction

Composition volume (%) Methane 45-60 Carbon dioxide 40-60 Nitrogen 2-5 Oxygen 2-5 Sulfide, disulfide, mercaptane 0-1.0 Ammonia 0.1-1.0 Hydrogen 0-0.2 Carbon monoxide 0-0.2 Other gases 0.01-0.6 Temperature,◦F 100-120 Specific gravity 1.02-1.06 Moisture Saturated High heating value,BTU/M3 400-555

More Details on the Digestion Process Odor Acid forming bacteria Volatile Solids (VS) Volatile organic acids Methane forming bacteria Methane, carbon dioxide, water, trace gases

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Bacterial Shapes Rod shape of methanogen bacteria 1.1 non sporulating rod-shaped cells Methanobacterium solmgenii Methanobacterium formicicum Methanobacterium propionicum 1.2 sporulating rod-shaped cells Methanobacterium omelianskii

2. Round shape of Methanogen bacteria 2.1 Cell not sarcina arrangement Methanococcus vaniellii Methanococcus mazei 2.2 Cell in sarcina arrangement Methanosarcina methanica Methabosarcina barkerii

Anaerobic Sludge Granules (SEM) Acetate as Substrate (Methanosaeta) Sucrose as Substrate (mixed culture)

Biogas Plants 1. Slow digestion or solid digestion 1.1 fined dome digester 1.2 floating drum digester or Indian digester

1. Slow digestion or solid digestion 1.3 plastic covered ditch or plug flow digester

2. Fast digestion or wastewater treatment digester. 2 2. Fast digestion or wastewater treatment digester 2.1 Anaerobic Filter: AF

2.2 Upflow Anaerobic Sludge Blanker: UASB 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 weir 3 phase separator

Expanded Granular Sludge Bed Influent Effluent Recycle Sludge Bed settler gas cap biogas bubble sludge granule Expanded Granular Sludge Bed

Cover lagoon 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