Q.Study the given diagrams of Biogas plants – ‘A’ and ‘B’ and answer the questions that follow : [Diagram: Biogas Plant (A) – Slurry of dung; Biogas Plant (B) – Slurry of human excreta; each with Gas pipe, Gas holder, Sludge, Digester] Which one of the two biogas plants can be used for generating gas fuel and electricity and why ? Give suitable reasons in support of your answer.
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Start your 14-day free trial to unlock the full solution →Biogas Plant A (using dung/cattle-manure slurry) is the one used for generating both gas fuel and electricity — this is the classic Indian ‘gobar gas plant’, whose methanogenic bacteria give a consistent, high-methane biogas yield historically used both for cooking and for running generators.
Concept and Intuition
Biogas plants convert organic waste into methane-rich gas through anaerobic digestion by methanogenic bacteria. The two plants shown differ only in their feedstock: Plant A uses a slurry of dung (cattle manure), Plant B uses a slurry of human excreta. In India, the dung-based design is the well-established ‘gobar gas plant’ that has been used for decades in rural households and community setups — both as a cooking-fuel source and, at larger community scale, to run generators for electricity.
Step-by-Step Reasoning
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Identify the feedstock. Plant A is fed with cattle-dung slurry; Plant B with human-excreta slurry.
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Why cattle dung gives the more reliable biogas. Cattle dung naturally carries a large, stable population of methanogenic bacteria (already present in the cow's own gut flora) along with a feedstock composition (a favourable carbon-to-nitrogen ratio) that these bacteria digest efficiently and consistently. This gives a higher and more consistent yield of methane-rich biogas than human-excreta slurry, whose composition and microbial load are less standardised and more variable.
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Why this matters for electricity generation. Running a generator needs a steady, adequately methane-rich gas supply — an inconsistent feedstock gives inconsistent gas quality, which is unsuitable for reliable generator operation. The consistency of the dung-slurry plant's output is exactly why it is the design historically scaled up (as community/institutional biogas plants) to run generators for electricity, in addition to being piped directly to cookstoves as fuel. …
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