Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Chemical Engineering


Professor K.L. Murphy


This dissertation examines the degree of nitrification which can be accomplished in combined and separate activated sludge systems over a temperature range of 5º to 25ºC and a system solids residence time range of 4 to 10 days under both steady and non-steady operating conditions.

Treating municipal sewage under steady flow conditions, it was found that the rate of nitrification was independent of the concentration of filterable TKN or ammonia. Temperature and solids retention time significantly affected filterable TKN removal. The degree of nitrification obtained in both combined and separate sludge systems was comparable.

The parallel pilot plant systems were subjected to a number of non-steady influent conditions. The responses to a pulse change in influent pH and a step-down in temperature indicated that the separate sludge system had a greater capacity to withstand such conditions. Transfer function models, together with time series models, were developed to describe the dynamic responses of the nitrifying systems to changes in influent flow, and organic carbon and inorganic nitrogen concentration. The observed and model results indicated greater effluent filterable TKN variation can be expected from nitrifying systems operated under variable flow and concentration inputs than for variable concentration inputs alone.

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