When running an industrial wastewater treatment system, the floc that forms can sometimes float. If your treatment system contains floating floc, you know it can be a challenge to eliminate. The floc actually contains the contaminants that are in your wastewater, so if it isn’t removed before the wastewater is discharged, you may be out of compliance with your discharge permit.
There are many things that cause floating floc. Some of the more common causes are described below, along with troubleshooting tips that you can use to help you determine what may be causing floating floc in your system.
Water flow that is too high
When the water flow rate is at or near the maximum flow rate that your clarifier was designed to handle, floc does not have time to settle in the clarifier like it should. This can cause the floc to float. If you have recently increased the flow rate, try decreasing it to see if the floc settles. If you have not increased the flow rate recently, you should investigate other causes.
Oxidants introduced into the Waste Stream
Oxidants like hydrogen Peroxide (H2O2) can cause floc to float. You can conduct a jar test to determine whether or not an oxidant is causing the floating floc. When you do so, look for the floc to be at the top of the beaker rather than the bottom. Sometimes it can take as long as 15 to 30 minutes to for floc to float. If you confirm that oxidants are causing the floc to float, you can add a reducing agent such as bisulfate or a proprietary metal precipitant to your waste stream. You should consult your wastewater treatment services vendor about the best procedure for adding reducing agents to your waste treatment program.
Floc that is too light and too large
In some cases, floc can become too fluffy and lightweight during treatment. There are several options for correcting this. You can try using a heavier coagulant, changing to a more compatible polymer, or altering how the polymer is dosed. Changing the polymer dosing method can be as simple as altering the dose rate. You can also change the polymer concentrations that are being used. For example, if you use an emulsion or dry polymer at 0.3% by volume, try 0.15% by volume instead. You may also want to consider changing where the polymer is dosed within the water treatment process. Sometimes dosing in the last reaction tank in addition to the clarifier can prevent floating floc.
The overdosing polymer can also lead to floating floc that will not settle. If your floc is very small and light (often called pin-floc), that is an indication that your polymer is being overdosed.You can conduct a jar test to determine the optimal polymer dose for your wastewater.
As anaerobic bacteria grow, they will outgas or release oxygen. This causes bubbles to rise to the surface of the water and for floc (or sediment) to float in large chunks, even when the system isn’t running. If you see bubbles and larger chunks of floc, biological outgassing is likely the culprit. To correct this problem, you will want to first flush out the clarifier with an air sparger, and then you can treat it with a biocide. The biocide will inhibit the bacteria growth.
If your wastewater treatment system has floating floc, it is always a good idea to consult your wastewater treatment services provider before attempting to correct it yourself. They can help you find a solution to the problem quickly and so you can avoid discharge permit compliance violations.