What type of feeder is recommended for large water treatment plants?

For plants with capacity over 20 MLD, gravimetric dry feeders or solution feeders are recommended for better accuracy and control (Clause 7.2).

What materials can be used for an alum solution tank?

RCC with acid-resistant lining, mild steel with rubber lining, or plastics like PVC, HDPE, or FRP are suitable options (Table 2).

What is the recommended detention time in a chemical solution tank?

A minimum detention period of 2 hours is recommended, though 3 to 4 hours is preferable for better dissolution (Clause 6.2.2).

What is the key difference between a volumetric and gravimetric feeder?

A volumetric feeder doses chemicals by a calibrated volume per unit time, while a gravimetric feeder doses by weight, offering higher accuracy (Clauses 5.2 & 5.3).

IS 9222

: 2000

Recommendations for handling and dosing devices for chemicals for water treatment, Part I: Coagulants

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This standard provides recommendations for the selection, handling, and operation of equipment used for dosing coagulants in water treatment plants. It covers both dry feeding and solution feeding systems, including guidance on storage, solution preparation, equipment types, and materials of construction to ensure accurate and reliable chemical application.

Recommendations for handling and dosing devices for chemicals for water treatment, Part I: Coagulants

Quick Reference Values

Recommended alum solution strength4 to 6 percent

Minimum detention period in solution tank2 hours

Recommended velocity in dosing lines0.6 to 1.5 m/s

Capacity of day storage/solution tankSufficient for one day's requirement

Accuracy of gravimetric feeders± 0.5 to 1 percent

Accuracy of volumetric feeders± 3 to 5 percent

Practical Notes

Careful selection of materials for tanks, pipes, and pumps is critical to prevent corrosion, especially when using acidic coagulants. Refer to Table 2 for material compatibility.

Regular calibration of dosing equipment is essential for maintaining correct coagulant dosage, which directly impacts treatment efficiency and operational cost.

Ensure proper design of solution tanks, including effective agitation, to prevent chemical stratification and maintain consistent solution strength.