What needs to be maintained to avoid the odour problem in tannery effluent treatment ?
- ALow pH
- BpH between 7 – 8
- CpH between 9·5 – 10Correct
- DHigh pH
Solution
Concept
Sulphide odour control in tannery effluent
Step-by-step solution
1. Tannery effluent contains sulphides. 2. At low pH sulphides are released as hydrogen sulphide gas, which causes odour. 3. Keeping the pH high (around 9.5–10) holds sulphide in the dissolved ionic form and prevents the odour.
Explanation
The sulphide equilibrium shifts towards HS⁻/S²⁻ at high pH, so H₂S is not liberated.
Why the other options are wrong
Low pH releases H₂S. The neutral range 7–8 still allows part of the sulphide to escape as H₂S. "High pH" with no limit is non-specific.
Shortcut
Sulphide waste: keep pH alkaline.
Common mistake
Choosing the neutral range because biological treatment likes pH 7–8.
Correct answer: C) pH between 9·5 – 10