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Vitamin supplementation is advertised in wastewater treatment to compensate for a deficiency of growth factors and thereby increase sludge activity and purification efficiency. Addition of vitamins of the B-complex was tested with activated sludge from 5 plants and compared to municipal sludge. Auxotrophy of bacteria isolates turned out to be compensated in most cases by vitamin producers in the activated sludge biocenoses.

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Non-filamentous hydrophobic scum bacteria were isolated from scumming wastewater treatment plants (WWTP) by means of adhesion to hydrocarbons. They were characterized with respect to taxonomy, substrate preferences, cell surface hydrophobicity, and emulsification capability. Their role during flotation events is discussed. Rhodococci are selected by hydrolysable substrates and contribute to flotation both by cell surface hydrophobicity and emulsifying activity at long mean cell residence times (MCRT). Saprophytic Acinetobacter strains are able to promote flotation by hydrophobicity and producing emulsifying agents under conditions when hydrophobic substrates are predominant. Hydrogenophaga and Acidovorax species as well as members of the Cytophaga/Flavobacterium group are prone to proliferate under low loading conditions and contribute to flotation mainly by emulsification.