Portable Biogas Plant

Portable biogas plants are small units designed for household and institutional purposes which generate energy from the biodegradable wastes. This will help in creating a hygienic environment and healthy surrounding for individual household as well as general public.

Making biogas at home entails the use of a long forgotten technology known as anaerobic digestion. Production of a combustible gas by anaerobic digestion of aqueous matter by mixed bacterial culture involving methane producers is called bio-methanation and the product is called biogas.

Design of Biogas Digesters

International Institute of Waste Management, Bhopal, has been able to develop prefabricated, portable biogas plants with a volume up to 5sqm. The time spent for transport and installation therefore is very low, no special manual skills are required for operation and maintenance. Mini biogas digester consists of one lower segment tank (digester) and another tank near it. The feedstock is put in the inlet, from where it is flushed into the main digester tank. In the digester tank, the organic waste is decomposed in different steps of anaerobic digestion producing biogas. The digester tank is connected to the sludge tank by a plastic pipe, through the outlet tank. For this biogas unit 3-5kg/day of waste is required. Recovered biogas can be utilized in a variety of ways. The biogas can be utilised for cooking as well as lighting purposes.

Advantages

• Energy recovery, Clean burning

• Substitutes wood and dung cake as rural fuel

• Hygienic disposal of waste

• Conservation of manure value

• Works in mild conditions i.e. 30oC and pH 6.8-7.2

• Easy gas purification feasible

• Subsidy available for rural farm and family size plants

• Pre-fabricated biogas plant is exempted from Sales Tax

• Simple and indigenous technology

Process

Step 1: Hydrolysis of biopolymers to monomers

Step 2: Conversion of sugars, amino acids, fatty acids to hydrogen, carbon dioxide, ammonia and acetic acids, propionic and butyric acids.

Steps 3: Conversion of hydrogen, carbon dioxide and acetic acid to methane and carbon dioxide mixture.

Properties

• Composition: 60-70% Methane, 30-40% Carbon dioxide and traces of hydrogen sulphide, ammonia and water vapour

• It is about 20% lighter than air (density is about 1.2gm/litre)

• Ignition temperature: Between 650-750°C

• Calorific value: 187.7 – 216 MJ/sqm (500-700 Btu/sqft)

• Removal of CO2 – Scrubbing with lime water or ethanol amine solution

• Removal of H2S – Adsorption on a bed of iron sponge or wood shavings

Do’s

• Biogas plant should be fed daily without fail for the proper operation of the plant.

• The bio-waste and water ratio should be equal for the proper functioning of the biogas plant.

• During regular operations of the plant, once a week the water content and moisture should be removed for proper flame in the stove.

• Slurry from the biogas plant should be diluted with water before using it as fertilizer.

Don’ts

• Overfeeding of the biogas plant should be avoided as it creates acidity and turns the plant non-functional.

• Under no circumstances chemicals, acid, lemon, big pieces of wastes, plastics, papers and tamarind feeding into

biogas plant should be allowed.