Project - Bio Gas

Biogas is a clean environment friendly fuel. Raw biogas contains about 55-65% methane (CH4), 30-45% carbon dioxide (CO2), trace of hydrogen sulfide (H2S) and fractions of water vapors, there is a great need to make biogas transportable. Compressing the gas in cylinders, this is possible only after removing its CO2, H2S and water vapor components.

Selection of feed stock
Bio gas is produced by anaerobic digestion of biological wastes such as cattle dung, Vegetable waste, sheep and poultry droppings, municipal solid waste, industrial waste water, agriculture waste, sea algae etc.

In our research project aimed at optimizing methane production from maize waste, sugar cane waste, black gram waste, vegetable waste and municipal wastes.

Methane production from organic substrates mainly depends on their content of substances that can be degraded to CH4 and CO2 composition and biodegradability are key factors for the methane yield from energy crops and animal manure Crude protein, Crude fat, Crude fiber, Cellulose, Hemi-cellulose, Starch and Sugar markedly influence methane formation.

Selection of Methanogens
Microorganisms, which produce methane under anaerobic conditions, are called methanogens.

We had some species of Methanogen bacteria. The process Biogas production uses these methanogens. We done many experiments on Agriculture waste (with out Cow dung, Poultry waste) Vegetable waste, household waste materials by using different aerobic, anaerobic (Methanogen) bacteria, the gas is produce. This will be done with in one or two days the enzymatic action of bacteria. This is a novel approach through our sector.

These methanogens are anaerobes, they are mesophilic, i.e. grow at 21--450c. Methanogens have Co-enzyme M that reduces methyl group into methane.

In our laboratory (SKS BIOPRODUCTS PVT LTD., GUDIVADA-Manufacturing of Biofertilizer and Probiotics) cultivate large amount of methanogens by the process of fermentation. These methanogens directly used as inoculum to carry out biogas production.

In this biogas producing methanogens besides Cellulolytic bacteria, Proteolytic bacteria and Acetogenic bacteria.

  • The Proteolytic bacterium degrades proteins into amino acids. A Cellulolytic bacterium degrades cellulose and other polysaccharides. Such microbes are called hydrolytic fermentative bacteria.
  • A second group of bacteria converts the sugars, aminoacids, methanol, glycerol and fatty acids into acetate, formate and propionate. These bacteria are called Acetogenic bacteria.
  • The acetate is converted into methane and carbondioxide. This reaction is carried out by a group of bacteria called Methanogen.
Construction of a modal biogas plant

Methane fermentation
Agricultural waste 70%, Municipal and other waste 30% is diluted to 50% by adding water to it. As a result the solid and liquid ratio becomes 1:1. This concentration favors the growth of Acetogenic and Methanogenic bacteria. The diluted feed stock is pumped into the fermentor (Biogas plant).

An amount of methanogenic, acetogenic and other degrading bacteria is taken from our lab and used as inoculum. This inoculum is pumped into the fermentor.

In our project, the culture conditions are modified suitably in the following ways to produce more biogas.

  • Cellulolytic microorganisms are inoculated into the fermentor to digest more cellulose.
  • Acetogenic bacteria are inoculated into the fermentor to produce more Acetate. It is useful for increasing the methane production.
  • 25-450c temperature is maintained in the fermentor.
  • Generally, the C/N ratio 30:1 is preferred for the best growth of methanogenic bacteria. So the C/N ratio is modified to 30:1 by adding specific wastes to the feed stock.
  • The feed stock is stirred well.
  • Pathogenic bacteria are killed by heat shock treatment at regular intervals of 60 days.
Purification of Biogas 
In the production of biogas presence of uncombustible gases like CO2, H2S and water vapor reduces its calorific value therefore necessary to remove these gases before compression.

CO2 scrubbing from biogas
A variety of processes are being used for removing CO2 from biogas. Several basic mechanisms are involved to achieve selective separation of gas constituents. These may include physical or chemical absorption, adsorption on a solid surface, membrane separation, cryogenic separation and chemical conversion.

Scrubbing of H2S
H2S is always present in biogas, although concentrations vary with the feedstock. It has to be removed in order to avoid corrosion in compressors, gas storage tanks and engines. H2S is poisonous and corrosive as well as environmentally hazardous since it is converted to sulfur dioxide by combustion. It also contaminates upgrading process. H2S can be removed either in the digester, from the crude biogas or in upgrading process. The most commonly used H2S removal process can be classified into two general categories namely: (1) dry oxidation process and (2) liquid phase oxidation process.

Biogas compression and storage
Biogas, containing mainly methane, could not be stored easily, as it does not liquefy under pressure at ambient temperature (critical temperature and pressure required are - 82.5 8C and 47.5 bar, respectively).

Compressing the biogas reduces the storage requirements, concentrates energy content and increases pressure to the level required overcoming resistance to gas flow. Compression is better in the scrubbed biogas.

Conclusions
The aim of this study is to explore the potential of biogas production in India from animal waste and its prospects in wider perspective. Presently, biogas is mainly used for cooking purpose and drive vehicles in India. To tap full potential of biogas, need emerges for its commercialization by making it transportable. Therefore biogas scrubbing and compression at high pressure for storage in cylinders are essential.

Different methods of scrubbing are reviewed and found that water scrubbing is simple, continuous and less expensive method for CO2 removal from biogas for Indian conditions. It simultaneously also removes H2S. After removal of CO2, biogas is enriched in methane and becomes equivalent to natural gas. It can be used for all such applications for which natural gas is being used viz. as a fuel for vehicles, CHP, electricity generation, etc.