Question

Crown corrosion of reinforced cement concrete sewer is caused by ______

• A. sulfur oxidizing bacteria
• B. iron oxidizing bacteria
• C. denitrifying bacteria
• D. fermentative bacteria

Answer 1

The Correct Option is A

Step 1: Understand crown corrosion. Crown corrosion in reinforced cement concrete sewers occurs due to the conversion of hydrogen sulfide gas (\( H_2S \)) to sulfuric acid (\( H_2SO_4 \)). This reaction is facilitated by sulfur oxidizing bacteria like Thiobacillus. 
Step 2: Role of sulfur oxidizing bacteria. In sewer systems, anaerobic bacteria produce \( H_2S \) in the wastewater. The \( H_2S \) gas rises to the crown (top) of the sewer and reacts with oxygen in the presence of sulfur oxidizing bacteria, producing \( H_2SO_4 \). The sulfuric acid corrodes the concrete at the crown of the sewer. 
Step 3: Analyze the options. (1) Sulfur oxidizing bacteria: Correct, as they produce \( H_2SO_4 \), causing crown corrosion. (2) Iron oxidizing bacteria: Incorrect, as they primarily oxidize iron and are not involved in this process. (3) Denitrifying bacteria: Incorrect, as they convert nitrates to nitrogen gas, unrelated to corrosion. (4) Fermentative bacteria: Incorrect, as they are involved in anaerobic fermentation processes, not corrosion.