Foam Producing Filamentous Bacteria

The two most commonly occurring foam-producing filamentous bacteria in the activated sludge process in North America are Microthrix parvicella (Figure 20.4) and Nocardioforms (Figure 20.5). Foam production by Microthrix parvicella and Nocar-dioforms occurs through different biological processes. Microthrix parvicella is hydrophobic and captures air and gas bubbles that result in the production of foam. Foam production from Nocardioforms is the result of (1) the secretion of lipids by living cells that coat the floc particles and capture air and gas bubbles and (2) the release of biosurfactants (e.g., ionized ammonia) that lower the surface tension of the activated sludge.

The undesired growth of each foam-producing filamentous bacteria can be associated with specific operational conditions (Table 20.3). By monitoring and regulating these conditions, the undesired growth of these organisms and their production of foam can be controlled.

Because foam-producing filamentous bacteria are present in large numbers in the foam, the foam represents a source of "reseeding" of the activated sludge with filamentous bacteria. Therefore, treatment of the foam also should be addressed when attempting to control the growth of foam-producing filamentous bacteria (Table 20.4).

FIGURE 20.4 Microthrix parvicella.
FIGURE 20.5 Nocardioforms.
TABLE 20.3 Operational Conditions Associated with the Undesired Growth of Foam-producing Filamentous Bacteria

Operational Condition

Filamentous Bacterium

Microthrix parvicella

Nocardioforms

High MCRT (>10 days)

X

Fats, oils, and grease

X

X

High pH (>8)

X

Low DO and High MCRT

X

Low F/M (<0.05)

X

X

Low nitrogen or phosphorus

X

Low pH (<6.5)

X

Readily degradable cBOD

X

Slowly degradable cBOD

X

X

Winter proliferation

X

TABLE 20.4 Operational Measures Available for the Control of Filamentous Organisms in Foam

Collapse the foam with the application of cationic polymer.

Collapse the foam with the application of final effluent through lawn sprinklers.

Collapse the foam with non-petroleum-based defoaming agent.

Digest the foam with application of bacterial cultures that contain lipase enzymes.

Physically remove the foam.

Treat the foam with 10-15% sodium hypochlorite solution and spray the foam with final effluent approximately 2-3 hours after sodium hypochlorite treatment.

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