Foaming estimation tests in activated sludge systems

Persistent biological foaming phenomena in activated sludge systems due to excess of filamentous microorganisms with hydrophobic properties, such as GALO, Microthrix parvicella and others, are frequently reported everywhere. Nevertheless, even if the number of plants affected by this trouble is high, presently there are no suitable general methods to evaluate properly the phenomenon. This paper reports on the results of a series of foam tests (Scum Index, Foam Rating), of hydrophobicity measurements of activated sludge (mixed liquor and foam) and measurements of extension of aeration tank covered by foam surfaces. The data obtained by using the above indicated methods are clearly correlated with the capability of activated sludge to produce foam. Nevertheless a different coherence between foam test measurement data and foam coverage of aeration tanks was encountered in comparison to that between hydrophobicity measurement data and foam coverage of aeration tanks due to the hydraulic regime of surface.