Dechlorinaton

[caneng2002]

I'm designing a small water treatment plant (150 m3/day) to remove Mn and Fe (very low levels in ground water source) using sodium hyplochlorite followed by greensand pressure filter.

To reactivate the filters I intend on using a 100 mg/L solution of NaOCl as per the green sand vendors recommendation.

My problem is ....to discharge the backwash water to the environment I need to have near non-detectable level of free residual chlorine (FRC).

I'm thinkg of using either ascorbic acid or sodium bisulphite to remove the removal the FRC but not sure on dosing rates?

Any suggestions?

 

[orenda1168]

Caneng2002:

You have a variety of choices for dechlorination, though either ascorbic acid (at 2.5 parts to each part of chlorine) and sodium ascorbate (at 2.8 parts to each part of chlorine) are the most expensive in terms of product cost and treating cost. I would suggest staying with sodium bisulfite (at 1.45 parts to each part of chlorine) which will be the most cost-effective.

Make sure that you exceed the stoichiometric value for sodium bisulfite shown above by a small percentage to cover variations in minute-to-minute chlorine concentrations.

Orenda