Chlorine Removal From Backwash Discharge

[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?

 

[bimr]

You backwashing batch volume is probably only going to be about 5 cu.m per filter run. Why don't you just put a small batch tank in to collect the backwash. You can use sulfite to remove the chlorine and then dump the tank volume. Us a small pump to recirculate the tank to mix it.

If you are worried about the chlorine, do you also have concerns regarding SS and Fe?

The amount of sulfite required is probably going to have to be determined empirically because of the other elements present in the water.