In this paper almost twenty years of experience with sludge bulking and foaming/scumming problems in extended aeration and BNR plants in Johannesburg is summarised. Various reasons for these problems are proposed and remedial measures discussed. A general hypothesis for bulking and scumming in BNR and other plants is proposed and design features to minimise these problems recommended. Practical experience with a full scale plant incorporating some of these features is described.

Activated sludge, biological nutrient removal, bulking, carousel, foam, Microthrix parvicella, Nocardia, scum, wastewater treatment
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© IWA Publishing 1996
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