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Investigations were conducted into a possible relationship between oxygen tension and activated sludge settling characteristics. Using seqage as substrate, two parallel activated sludge units were operated at different oxygen tensions effectively simulating operation at conventional and saturation levels of dissolved oxygen. Under controlled mixing conditions, settling characteristics were monitored at several sludge ages. At the same time preliminary comparisons were made between the two systems in terms of sludge production, sludge activity, nitrifying ability, floc size and appearance several other physical characteristics.

Results indicated a greater uniformity of operation at the higher oxygen tension along with a somewhat better effluent quality. However, no improvement in settling characteristics was noted at the higher level of dissolved oxygen.

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