The Role of Dispersed Nocardioform Filaments in Activated Sludge Foaming: Fid-Bau Portal

The Role of Dispersed Nocardioform Filaments in Activated Sludge Foaming

Narayanan, B. / de Leon, C. / Radke, C.J. / Jenkins, D.

Activated sludge foaming caused by filamentous microorganisms is a major wastewater treatment plant operating problem. This paper presents the results of an investigation of the role of dispersed nocardioforms in activated sludge foaming. Dispersed nocardioforms had a greater propensity for foaming than floc‐bound nocardioforms. The mode of effluent withdrawal from an aeration basin plays a major role in determining the relative proportion of dispersed and floc‐bound nocardioforms in the activated sludge. Reactors with “trapping” features (sub‐surface mixed liquor withdrawal) had significantly higher dispersed nocardioform populations than reactors with “non‐trapping” features (surface mixed liquor withdrawal). High dispersed nocardioform filament concentrations were correlated with a high propensity for foaming. Cationic polymer and poly‐aluminum chloride reduced foaming by flocculating dispersed nocardioforms, thereby converting them to floc‐bound nocardioforms. Low non‐ionic surfactant concentrations changed the relative proportions of dispersed and floc‐bound nocardioforms by deflocculating floc‐bound filaments and converting them to the dispersed growth form. This could act as a trigger for initiating the rapid‐onset nocardioform foaming events observed at activated sludge plants.