Evaluating sodium bisulfite dechlorination by assay and residual chlorine

Can NaHSO₃ and sodium metabisulfite be dosed at equal commercial weights?

Incoming concentration determines how much active material is purchased. Residual chlorine in the effluent reflects process demand. Both need separate checks.

Set the endpoint from the dechlorination target

Confirm which salt is supplied. Use the same influent, contact time and residual chlorine method for the trial. Resample and reassess if the raw water’s oxidant demand changes.

Why does the dispatch titration not predict dechlorination on site?

Actual oxidant demand, storage and metering affect the result. Measure residual chlorine at the time of the trial. Membrane feed dechlorination: Check membrane supplier inlet limits. Track the residual chlorine endpoint in actual water. Process-water reduction: Compare remaining reducing capacity and downstream water quality as oxidant loading changes.

Checking Active ingredient and pH

Active ingredient (% by mass): State whether the result is expressed as NaHSO₃ or SO₂. pH (Dimensionless): Identify whether the test uses the as-received product or a specified concentration and state test temperature. Iron (mg/kg): Agree the requirement for the membrane system or the customer’s contamination controls.

What to record

• Product name
• Active quantity
• Initial residual chlorine
• Contact time
• Final residual chlorine

Technical references

• DuPont FilmTec: RO feedwater and residual chlorine control ↗

Products and processes