Q.Draw a diagrammatic sketch of biogas plant, and label its various components given below: Gas Holder, Sludge Chamber, Digester, Dung+water chamber.

A biogas plant is a simple, airtight system where organic waste like cattle dung is broken down by microbes in the absence of oxygen to produce methane-rich biogas. The process happens in a large underground tank called the digester. Here is how the labelled components fit together in a typical fixed-dome biogas plant:

• Dung+water chamber: This is the inlet tank where cattle dung is mixed with water to form a slurry. The slurry flows into the digester through an inlet pipe.
• Digester: The main underground tank where anaerobic bacteria decompose the slurry. It is a dome-shaped, brick-lined chamber that remains sealed to keep oxygen out.
• Gas Holder: The dome itself acts as the gas holder. As biogas collects at the top of the dome, it pushes the slurry level down, storing the gas under pressure.
• Sludge Chamber: The outlet tank on the opposite side. Spent slurry (digested sludge) overflows into this chamber and can be removed for use as fertiliser. …

Biogas production is a classic example of microbial fermentation — but instead of making alcohol or curd, we are harnessing the metabolic activity of methanogenic bacteria to produce a clean, combustible fuel. These bacteria thrive in oxygen-free (anaerobic) conditions and break down complex organic matter into simpler compounds, releasing methane and carbon dioxide as by-products. The NCERT textbook presents this as a practical, rural-friendly technology that solves two problems at once: waste management and energy generation.

The typical biogas plant, as described in the NCERT Class 12 Biology chapter on Microbes in Human Welfare, is a simple underground structure. It consists of a concrete tank or pit, divided into two main compartments by a partition wall. The design is elegant in its simplicity — no moving parts, no external power source, just gravity and microbial action.

Let us walk through the components you need to label in your diagrammatic sketch.

The Dung + Water Chamber is the inlet. This is where the slurry — a mixture of cattle dung and water in roughly equal proportions — is fed into the plant. The slurry flows by gravity into the main digestion tank. This chamber is usually a small opening at ground level, covered with a lid to prevent air from entering.

The Digester is the heart of the plant. It is a large, underground, brick-lined tank where the actual anaerobic fermentation happens. The slurry stays here for several days (typically 8–10 days at optimal temperature). Methanogenic bacteria, which are naturally present in cattle dung, break down the organic matter. The digester must be completely sealed from the air — oxygen kills the methane-producing bacteria. The NCERT emphasises that the temperature inside the digester should be maintained between 30–35°C for maximum gas production.

The Gas Holder sits directly above the digester. It is a dome-shaped or floating steel drum that collects the biogas as it rises from the slurry. In the floating-dome design, the gas holder moves up and down depending on the volume of gas accumulated. A pipe from the top of the gas holder carries the biogas to the point of use — typically a kitchen stove or a generator. The gas holder also acts as a seal, preventing air from entering the digester. …

Trace the slurry's own journey through the plant step by step, rather than describing the chambers by their spatial layout.

1. Cattle dung is mixed with water in the dung + water chamber (the inlet) to form a flowable slurry.
2. The slurry flows by gravity into the digester -- a sealed, underground, oxygen-free tank where methanogenic bacteria anaerobically ferment it over several days (ideally 30-35 deg C).
3. As fermentation proceeds, methane-rich biogas rises and collects under the gas holder (a floating dome) sitting above the slurry -- the dome rises as gas accumulates and can be piped off for use. …