Wastewater Foaming Problems

  • MDG
  • August 17, 2015

Identifying Causes of Foam

The cause of foaming should never be assumed. If there is foam in your plant, it is recommended to perform a microscopic evaluation of the foam and mixed liquor. As a general rule, if the organism is much more concentrated in the foam than the underlying MLSS, this can be associated with the foam. Dilution of the foam is necessary for microscopic evaluation, because foams are highly concentrated. There are many causes for foam and some of the foams look similar to the naked eye.

Methods of Foam Control

The best long-term strategy is to find and eliminate the root cause of the foam. Filamentous foams should not be trapped in the aeration tank or recycled back to the head of the plant. Wasting of filamentous foams to digesters can cause foaming in the digesters. Physical control of foams through sprays is difficult, but it has been done. For certain cases, such as filamentous foam, a chlorinated water spray has been successful. De-foaming chemicals are useful for surfactants that can’t be controlled at the source (common in industries such as paper mills). De-foamers do not eliminate the cause of foam, but can help keep foam from overflowing the basin. If it is possible, it is recommended to remove filamentous foams with a vac-truck and not let them accumulate on the surface of the aeration basin. At MDG, we believe we have found a culture that can outcompete filamentous bacteria for fats, oils, and grease.

Filamentous Foaming

There are three filaments that are known to cause foaming and these grow due to high amounts of fats, oils, and grease present in the wastewater. Septicity helps convert fats, oils, and grease to unsaturated forms, which are easier for these organisms to assimilate. These organisms are hydrophobic and at high nocardioform foamconcentrations they want to float to the surface. Filamentous foaming is a major cause of problems in wastewater treatment plants all over the world. Nocardioform and Microthrix parvicella foams are often controlled by lowering the sludge age. Chlorination of the RAS line is sometimes successful as well. Type 1863 grows at very young sludge ages (3-4 days or less).

Denitrification Scum/Foam

These foams/scums can look similar to filamentous foams in appearance. Denitrification is caused by anoxic conditions (no free dissolved oxygen), the presence of nitrate, and a carbon scum and foamsource (readily available BOD). Denitrification foams are common in the final clarifier and a major cause of effluent TSS violations. To eliminate denitrification, one of these variables needs to be addressed.

Surfactants and Others

Ideally, the source of surfactants are removed from the wastewater treatment plant to eliminate foaming. If this cannot be avoided, de-foaming chemicals or biological degradation (if possible) of the surfactant can help eliminate/reduce foaming. Surfactant foams are more common in the winter months when the biochemical reactions and metabolism of the bacteria are slower. Increasing the MLSS and sludge age is commonly recommended. Other foams, such as zooglea, nutrient deficiency, dead, bug foams, and excessive solids recycling foams involve addressing the root cause of the problem.


There are many potential causes of foam. One should never assume the cause of a foam and make operational changes until the foam has been properly identified. Long term control of foaming problems involves removing the cause of the foam at the source. There are different control strategies for different types of foams and improper control strategies (such as summary augchlorinating a zooglea foam) can make the problem worse. We encourage you to send us samples to help determine the cause and recommended control strategies if foaming issues develop in your plant.