Loss of Head in Activated Sludge Aeration Channels

This paper involves the consideration of no new hydraulic theory or formulas. The problem implied in the title includes an analysis of flow conditions that differ from those encountered in- the-usual channel problems, because the introduction of diffused air tends to retard velocity.

The presentation is semi-hypothetical, and the various functional values expressed are, strictly speaking, relative only. As such they are susceptible to direct application and use on the basis of any value of n that may be selected. The assumption is made that a roughness coefficient of n = 0.013, in Rutter's formulas, is reasonably applicable for all practical purposes to channels constructed in a manner similar to that described herein, and for unaerated sewage.

The purpose of the studies was to determine the extent to which flow is retarded when diffused compressed air is introduced into a flowing mixture of sewage and activated sludge, the total suspended matters in the mixture varying inappreciably from a normal value of 3 000 ppm. Numerous previous experiments have led the writer to conclude that this solids content does not change the hydraulic properties of the mixture from those of water alone. The tests indicate definitely that: (a) Resistance to flow increases because of diffused air; (b) as the velocity of flow decreases, the resistance increases; and (c) the use of higher values of n is necessary because of increased resistance. The subject has been treated sufficiently herein to enable readers to comprehend the nature of the problem and the applicability of the results to problems of design.