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Chrome waste water treatment problem

I am having problems with our clarification tank. The chrome flock that flows into the tank does not always settle to the bottom. When this happens we have to stop treatment and siphon water away from the drain at the top of the tank. I was wondering if anyone has an suggestions on changes I could make to my pH or another suggestion. I now have a pH of 6.25 in the clarification tank.

Kevin Pike
- McAlester Oklahoma
2005

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Excess reducing agent can cause gassing in the clarifier. The bubbles can impinge on the floc, causing it to rise. Check your ORP and avoid overkill.

Paul Morkovsky
- Shiner, Texas, USA
2005

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2005

A pH of 6.25 is far too low. I'm surprised you can meet your permit limitations at that pH. Try a set point of 9 - 9.5.

You can also add some ferrous sulfate ⇦this on eBay or Amazon [affil links] and/or lime before the main pH elevation to bulk up the floc and make a better settling sludge.

Dave Wichern
Consultant - The Bronx, New York

Kevin, Right off the bat, your pH is too low. You can start with doing some jar tests of varies pH ranges. Seems any two systems may vary a little and the same system may vary daily for the optium pH. Start with a jar of your effluent and begin adjusting the pH, making very small adjustments when approaching pH 8.0 to 8.5. Observe the floc forming, the larger the better. Add your polymer and watch the settling rate. This works best if you can do more than one sample at a time so there will be a comparsion of the settling rate. I will usually do about six at a time to compare the different pH's. Usually a cloudy appearance means the pH is too high. Most polymer sales companies will do this for you so you will purchase their polymers.

Larry Brannock
- Cana, Virginia
2005