Scum formation in a nutrient removing activated sludge plant

Abstract

Under certain conditions air emrainment is identified as a major contributing cause to scum build-up at the Johannesburg Nor­ thern Works. Under normal operating conditions the relative proportions of filamentous organisms in the MLSS and scum re­ mained unchanged and neither Microthrix parllicella nor Nocardia were found to predominate. Introduction of sludge recycl­ ing in the primary clarifiers caused scum to consist almost entirely of Microthrix parvicella. It is suggested that bubble strength may be promoted by the biological production of chemicals that promote film stability and that bubbles collapse when these film strengtheners are removed by syndets.

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