What causes foaming in aeration basins, and how can it be mitigated?

• A. Foaming Is Caused By Excess Stirring And Should Be Mitigated By Increasing Aeration
• B. Foaming Is Often Caused By Incompatible Surface-Active Compounds Or Filamentous Organisms; Mitigate By Balancing Nutrients, Reducing Shear, Or Using Anti-Foam If Allowed
• C. Foaming Is Caused By Low Temperature And Should Be Warmed
• D. Foaming Is A Sign Of Too Little Oxygen And Should Be Increased By Air Flow

Answer: (B)

Foaming in aeration basins is driven by surface-active compounds and certain filamentous organisms that produce sticky extracellular polymers. These substances reduce surface tension and create stable bubbles at the air–water interface, leading to persistent, frothy foam on the basin surface. The best way to address this is to target both the chemical and biological factors: balance nutrients so the growth of foam-forming organisms and excessive polymer production is minimized; reduce mechanical shear and energy input, since aggressive mixing can keep foam formed and stable; and, if allowed by the plant’s policies, use an anti-foam agent to suppress the foam while the underlying causes are being corrected.

Increasing aeration or stirring often worsens foaming by introducing more air and energy into the system, and low temperatures or simply increasing oxygen alone are not the primary drivers of foam formation.