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