Actinomycete Scum Problems in Australian Activated Sludge Plants

The formation of extensive, biological foams or scums on the liquid surfaces of domestic activated sludge plants in Australia was investigated. A survey of the problem in Queensland and Australia was carried out; the dominant organisms in the foam were isolated and identified; their physiology was investigated and the intrinsic reasons for foam formation were explored in the laboratory. Foaming in activated sludge plants was found to be a significant problem in Australia. Greater than 90% of plants in Queensland have experienced biological foaming episodes, whilst in 38% of the plants the problem was continuously present. Nocardia amarae and a newly described actinomycete Nocardia pinensis were the dominant organisms isolated from the foam. Plants that contained N . pinensis in the scum were found to be operated at long sludge ages. Although technical problems were experienced with chemostat methodology when applied to N. amarae , a limited amount of information about their physiology was obtained. The cells of N. amarae were found to be hydrophobic and a surfactant(s) was produced in culture. These are properties which suggest an explanation for the mechanism of foam formation based upon adsorptive bubble separation theory.