Hi, I just started at my new water treatment plant and I've come across something I can't explain and I'm hoping that someone can. We treat groundwater (which contains hydrogen sulfide [rotten egg smell]). We use two sedimentation tanks (where hydrogen peroxide is injected to remove the sulfides) and 2 parallel G.A.C. towers after the tanks. The effluent from the sediment tanks contains 0.00 ppm sulfides, however the effluent from the G.A.C.s contain slightly below 1 ppm sulfides (were only allowed 1 ppm to remain in compliance). I've asked around and this seems to be an anomaly to everyone. The only way i'm keeping the sulfides at bay is by largely increasing the hydrogen peroxide dosage. If anyone has any idea whats going on here, I'd greatly appreciate any insight. Thank you!
First of all, I would use the GAC towers in series. Much more efficient with respect to effluent quality as you can load the carbon in the first fitler to a maximum.
Check if the sulfides is not orginating from the GAC? It could be of low quality, contaminated...etc. From here it looks like the sulfides are originating from the GAC. Take several samples, chrush the activated carbon to a fine powder, and stirr it overnight. Measure the sulfides concentration in the aqueous phase. Use double distilled water (or at least a water source which is free of sulfides) and check the sulfide concentration before adding the crushed GAC.
Finally, before starting, make sure that you are using correctly your sulfides measuring kit and for interferences...one never knows :-)
Is it possible that your reaction time is not long enough, or that you have more naturally occurring iron than you are accounting for in your titration and it's killing the peroxide ?
Possibly there is some other solvent in the water that the GAC isn't effectively removing. I agree with the above statement that series is the way to go
Best of luck