Question

A sudden drop in methane content with increased \(H_2S\) in biogas suggests dominance of

• A. Methanogens
• B. Sulphur oxidizers
• C. Sulphate reducers
• D. Nitrifiers

Hint:

Competition in anaerobic digesters: \[ \boxed{ \text{Sulphate reducers} \rightarrow H_2S \uparrow \rightarrow CH_4 \downarrow } \] An increase in \(H_2S\) generally indicates dominance of sulphate-reducing bacteria.

Answer 1

The Correct Option is C

Step 1: Recall the two microbial groups competing in a digester.
Anaerobic digesters host both methanogens, which produce methane, and sulphate reducing bacteria, which use sulphate instead of carbon dioxide as an electron acceptor.
Step 2: See what happens when sulphate reducers take over.
These two groups compete for the same substrates, and when sulphate reducers dominate, they consume the available hydrogen and organic acids before methanogens can use them.
Step 3: Read the gas composition change.
This shift shows up as falling methane output alongside rising hydrogen sulphide, since sulphate reduction produces $H_2S$ as its byproduct.
\[ \boxed{\text{Sulphate reducers}} \]