Q.What is biogas? Write in brief about the production process.

Step 1. Define biogas. Biogas is a cheap, safe, renewable, non-conventional source of domestic and industrial fuel, produced by microbial fermentation; it is a gas mixture dominated by methane (roughly 50-60%) and carbon dioxide (roughly 30-40%), with some hydrogen sulphide and traces of other gases, making it highly inflammable.

Step 2. Describe the plant and feedstock. The commonly used KVIC or IARI biogas plant designs use a partly buried digester (concrete or steel) fed through a side charge pit with a slurry — typically cattle dung, a cellulose-rich waste, mixed with an equal proportion of water — with a gas holder above the digester collecting the gas produced.

Step 3. Describe the three-stage production process. Hydrolysis (solubilisation): anaerobic hydrolytic bacteria such as Clostridium and Pseudomonas break carbohydrates into simple sugars, proteins into amino acids, and lipids into fatty acids. Acidogenesis: facultative and obligate anaerobic bacteria convert these simple compounds into acids such as formic and acetic acid, plus hydrogen and CO2. Methanogenesis: strictly anaerobic methanogenic bacteria such as Methanobacterium and Methanococcus convert the acetate, hydrogen and CO2 into methane, CO2 and water.

Step 4. Note the benefits. The resulting biogas is used for cooking, lighting and small industry, burns with a smokeless blue flame, and the leftover sludge is used directly as fertiliser.

Defining biogas and walking through its three-stage anaerobic microbial production process

• Describing biogas production as a single undifferentiated fermentation step, instead of the three distinct microbial stages (hydrolysis, acidogenesis, methanogenesis).
• Omitting the approximate gas composition (mostly methane and CO2), which is what makes biogas usable as a fuel.