| Summary: | Includes bibliographical references. === In 1978 Ekama and Marais put forward a general model for the activated sludge process based on an energy requirement
for adsorption of the nutrient onto the organisms. They briefly outlined an alternative bi-substrate hypothesis in which the energy requirement for adsorption fell away.
No evidence in support of this alternative hypothesis was presented. The objective of this thesis was to investigate which of the two hypotheses gave the better description
of the activated sludge process kinetics. When the adsorption hypothesis was replaced by the bi-substrate hypothesis in the general model and applied to the completely mixed
activated sludge process and their predictions compared with experimental data, it was not possible to establish conclusively which hypothesis is to be preferred. As a
consequence it was decided to test the two models under extreme conditions. The contact stabilization process was selected as the one presenting a most severe test of
the predictive power of any hypothesis on activated sludge kinetics, and most likely therefore to establish the superiority of one hypothesis over the other. In order
to obtain experimental data against which the hypotheses could be evaluated a series of laboratory scale tests on the contact stabilization process were conducted
under time invariant and cyclic flow and load conditions at two temperatures,
12°C and 20°C. From a comparison of the experimentally observed and theoretically
predicted data it was concluded that an additional factor had to be taken into account before a valid comparison could be made
- whereas the general activated sludge theory accepted a rapid and complete enmeshment of influent particulate COD, in the contact reactor the experimental data indicated incomplete enmeshment in the short contact time available. When allowance was made for partial enmeshment in the predicted response of the system it was concluded that the bi-substrate hypothesis was superior to the adsorption one.
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