Antifoam for wastewater treatment plants

Why foam forms in the aeration basin

The air blown into the aeration basin forms bubbles that rise to the surface. In clean water those bubbles burst on their own. When the water carries substances that stabilize them, the bubbles pile up into a layer of foam that keeps growing as long as air goes in.

The most common causes are detergents and surfactants that arrive with domestic wastewater or with discharges from laundries, textile mills, food plants and cleaning product factories; grease and oil that pretreatment did not remove; and sudden load changes, such as a one-off industrial discharge or plant start-up, when there is not yet enough sludge to break down what comes in.

What problems foam causes

Foam that overflows carries sludge out of the basin and leaves it on channels, railings and walkways, where it gets slippery and smells. The plant loses biomass it needs for treatment.

If foam reaches the clarifier, it carries solids out with the treated water and raises the suspended solids in the discharge. Sometimes foam reaches the outfall and shows up in the river or channel, which brings complaints from neighbors and requests from the environmental authority.

How to tell what kind of foam your plant has

The color and texture of the foam tell you where it comes from. White, light foam that breaks easily almost always comes from surfactants that have not been broken down yet. It is typical of plant start-up, young sludge and discharges with a lot of detergent.

Brown, thick, greasy foam that builds up like a scum on the basin and the clarifier is usually biological. It is formed by filamentous bacteria that grow when sludge stays in the system for a long time or when a lot of grease comes in. This foam traps solids and does not break on its own.

Dark or black foam can point to parts of the basin with little oxygen or to sludge that is breaking down without air.

When an antifoam helps

An antifoam works well on white surfactant foam and on foam peaks that come with a discharge. It breaks the bubbles at the surface and keeps the foam from overflowing while the process settles.

With biological foam, an antifoam only helps for a while: the foam drops while it is dosed but comes back if the cause is not fixed. In those cases the sludge age has to be adjusted, the scum skimmed off so it does not return to the basin, and grease intake controlled. The antifoam keeps the plant running while those changes are made.

That is why, before recommending a dose, we ask what color the foam is, since when it appears and whether it matches a discharge.

Casdifoam D: use in wastewater treatment plants

CASDIFOAM D is a silicone emulsion that is diluted in water before dosing. It is applied with a dosing pump where the foam forms: sprayed over the surface of the aeration basin or at the basin inlet. It can also be sprayed in channels and at the outfall.

The dose is adjusted to use the smallest amount that keeps the foam under control. Going above that point does not improve the result and does raise the cost.

How we test it

To recommend a dose we work with a sample of your water. We ask for two to four liters of mixed liquor from the aeration basin, taken where the foam forms, in a clean, tightly closed container.

In the lab we bubble air through the sample in a graduated cylinder and measure the foam height without product and with CASDIFOAM D at several doses. With your plant's flow we work out the approximate monthly consumption. The plant trial is done with those figures.

CASDIFOAM D is a non-ionic silicone emulsion, stable in acid and alkaline conditions and at high temperature. It can be used as supplied or diluted in water; once diluted, use it within 24 hours.

Request a sample

Tell us about your plant: type of treatment, flow and when the foam appears. We will reply with instructions for sending a water sample and send you a sample of CASDIFOAM D.