Journal
WATER RESEARCH
Volume 45, Issue 5, Pages 2146-2154Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2010.12.026
Keywords
Activated sludge; Bacillus subtilis; Foaming; Mycolata; Surface scum; Surfactants
Funding
- Australian Research Council [LP0774913]
- Melbourne Water
- South East Water
- Australian Postgraduate Award PhD Scholarships
- La Trobe University
- Australian Research Council [LP0774913] Funding Source: Australian Research Council
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Screening pure cultures of 65 mycolic acid producing bacteria (Mycolata) isolated mainly from activated sludge with a laboratory based foaming test revealed that not all foamed under the conditions used. However, for most, the data were generally consistent with the flotation theory as an explanation for foaming. Thus a stable foam required three components, air bubbles, surfactants and hydrophobic cells. With non-hydrophobic cells, an unstable foam was generated, and in the absence of surfactants, cells formed a greasy surface scum. Addition of surfactant converted a scumming population into one forming a stable foam. The ability to generate a foam depended on a threshold cell number, which varied between individual isolates and reduced markedly in the presence of surfactant. Consequently, the concept of a universal threshold applicable to all foaming Mycolata is not supported by these data. The role of surfactants in foaming is poorly understood, but evidence is presented for the first time that surfactin synthesised by Bacillus subtilis may be important. (C) 2010 Elsevier Ltd. All rights reserved.
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