GATE CE 2025 Set 2 — Question 17
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Environmental Engineering → Wastewater Quantity & Sewerage → Design of Sewers
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Question
The bacteria mainly responsible for crown corrosion in a sewer is ______.
Correct answer
(C) Sulphur reducing bacteria
Solution
Crown corrosion in sewers is a result of the sulfur cycle. Under anaerobic conditions in the sewage, Sulphur reducing bacteria (SRB) like Desulfovibrio reduce sulfates to hydrogen sulfide (). This gas escapes to the sewer atmosphere and is subsequently oxidized to sulfuric acid () by sulfur-oxidizing bacteria (like Thiobacillus) on the moist crown of the pipe. The sulfuric acid then reacts with the concrete, causing corrosion. Among the given options, sulfur-reducing bacteria are the primary group involved in the initiation of this process.
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