Industrial Wastewater Treatment – Removal of Floating Flocs

When running an industrial wastewater treatment system, the flocs that form can sometimes float. If your treatment system contains floating floc, you know it can be a challenge to remove. The floc actually contains the contaminants found in your wastewater, so if it is not removed before the wastewater is discharged, you may not be in compliance with your discharge permit.

There are many things that cause floating flocs. Some of the more common causes are outlined below, along with troubleshooting tips you can use to help you determine what may be causing the floating floc on your system.

Water flow too high

When the water flow rate is at or near the maximum flow rate your clarifier was designed for, the flocs do not have time to settle in the clarifier as they 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 the flow rate has not increased recently, you should investigate other causes.

Oxidizers introduced into the waste stream

Oxidants such as hydrogen peroxide (H2O2) can cause flocs to float. You can perform a jar test to determine whether or not an oxidant is causing the floating floc. When you do, look for the floc to be at the top of the beaker rather than the bottom. Sometimes it can take 15-30 minutes to get it up and floating. 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 service provider on the best procedure for adding reducing agents to your wastewater treatment program.

Floc that is too light and too big

In some cases, the flocs may become too fluffy and light during treatment. There are several options to correct this. You can try using a heavier coagulant, switch to a more compatible polymer, or alter the way the polymer is dosed. Changing the method of polymer dosing can be as simple as altering the dosing rate. You can also change the polymer concentrations that are being used. For example, if you are using a 0.3% by volume emulsion or dry polymer, try 0.15% by volume. You may also consider changing where the polymer is dosed within the water treatment process. Sometimes dosing in the last reaction tank in addition to clarification can prevent floc flotation.

polymer overdose

Polymer overdose can also lead to the formation of floating flocs that will not settle. If your floc is very small and light (often called a pin-floc), that is an indication that your polymer is overdosing.

biological degassing

As anaerobic bacteria grow, they will degas or release oxygen. This causes bubbles to rise to the surface of the water and flocs (or sediment) to float in large chunks, even when the system is not running. If you see bubbles and larger chunks of floc, biological outgassing is likely to blame. To correct this problem, you’ll want to first flush the clarifier with an air spray, and then you can treat it with a biocide. The biocide will inhibit the growth of bacteria.

If your wastewater treatment system has floating floc, it is always a good idea to consult your wastewater treatment service provider before attempting to correct it yourself. They can help you find a solution to the problem quickly and thus avoid download permission violations.