Control of algal growth in service reservoirs and open storage: which chemical is typically dosed to suppress algae (with due care)?

Introduction / Context:
Algal blooms in open reservoirs and slow-moving basins can cause taste, odour, and filter-clogging problems. A common operational control is the careful application of algicides, notably copper sulphate, alongside preventive measures.

Given Data / Assumptions:

• Dose rates are low and must respect aquatic toxicity limits.
• Applied in quiescent waters; mixing ensured for uniform contact.

Concept / Approach:
Copper ions act as an algicide by disrupting cellular processes of algae and certain cyanobacteria. While chlorine (bleaching powder) is an oxidant and disinfectant, it is not typically the primary algicide for reservoir-wide control; alum and lime are for coagulation and pH/alkalinity adjustment.

Step-by-Step Solution:

Verification / Alternative check:
Utility manuals commonly recommend controlled CuSO4 application, often seasonally, with jar tests to determine dose.

Why Other Options Are Wrong:

• Bleaching powder mainly disinfects; persistent algae control is limited.
• Lime and alum modify pH/alkalinity and coagulate particles, not direct algicides.
• Hence copper sulphate is the appropriate choice.

Common Pitfalls:
Over-dosing copper leading to aquatic toxicity; failing to remove dead algae, causing taste and odour episodes.

Final Answer:
Copper sulphate