Wastewater Foaming Problems

Identifying Causes of Foam

The cause of foaming should never be assumed. Foaming problems can be diagnosed through microscopic evaluation. 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. Because foams are highly concentrated, dilution of the foam is necessary for microscopic evaluation. There are many causes for foam and some of the foams look similar to the naked eye. If there is foam in your plant, it is recommended to perform a microscopic evaluation of the mixed liquor and the foam.

Methods of Foam Control

The best long-term strategy is to find the root cause of the foam and eliminate this. 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 has been done. For certain cases, like 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 may possibly outcompete filamentous bacteria for fats, oils, and grease. We are interested in developing case studies to prove this theory.

Types of Foam/Scum and Physical Description

Cause of Foam / Physical Description
Start-up Foam / White, billowy
Filamentous/ type 1863 / White, billowy
Beggiatoa (scum) / White scum found in septic conditions in fixed film processes
Surfactant / White, soap-suds like. Often see “rainbow” reflection in sunlight
Slime-Polysaccharide (zooglea) / Sticky, viscous. Higher abundance of zooglea in foam than underlying MLSS. Elevated polysaccharide observed in reverse India ink stain
Slime-Polysaccharide (nutrient deficiency) / Sticky, viscous. Elevated polysaccharide observed in reverse India ink stain
Excessive Fines Recycle (from anaerobic processes) / Volcano, pumice-like appearance. High inert solids content in foam
Denitrification / Dark scum, often with rising bubbles
Nocardioform or Microthrix parvicella filaments / Dark brown foam or scum
“Dead bug” foam / Dark brown

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 concentrations, 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/ and 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 source (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 address

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. We are interested in pursuing case studies to show impacts of bioaugmentation products on surfactant foams. Other foams, such as zooglea, nutrient deficiency, dead, bug foams, and excessive solids recycling foams involve addressing the root cause of the problem.

Summary

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 chlorinating 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. We also successful case studies in which we demonstrated accelerated recovery from a surfactant related upset and also reduced Nocardioform foaming with bioaugmentation products.

Reference

  • 3rd Edition Manual on Causes and Control of Activated Sludge Bulking, Foaming, and Other Solids Separation Problems. David Jenkins, Michael G. Richard, Glen T. Daigger, 2003
  • All photos courtesy of Microbial Discovery Group, 2014