Causes and control of low F/M bulking in long sludge age nutrient removal activated sludge systems

Doctoral Thesis


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University of Cape Town

A problem plaguing the greater proportion of nutrient removal activated sludge systems treating municipal sewage, is the prolific growth of :filamentous organisms (bulking), which inhibits the rate of sludge settling in the clarifier (secondary settling) stage of treatment and reduces plant throughput. To find the causes of :filament proliferation, a four-stage investigation was conducted: (1) A review of literature indicated that the promoted method for control of bulking in carbonaceous removal systems (the selector reactor) does not control bulking in nutrient removal systems. (2) From a laboratory-scale experimental programme it was concluded that low F /M filaments proliferate when sludge is subjected to alternating anoxic-aerobic conditions with nitrite present. (3) A review of the biochemistry of respiration led to the formulation of a biochemical model for facultative organism respiration, an important aspect of which is a series of mechanisms that give rise to inhibition of aerobic respiration following anoxic conditions. Inhibition of respiration was measured in activated sludge with aerobic batch test procedures. ( 4) Application of the biochemical model to filaments and floe-formers allowed the formulation of a biochemical/microbiological (bulking) model to describe the prolific growth of filamentous organisms. The model was tested and verified at laboratory-scale.

Includes bibliography.