In current design practice the components of the complete mix activated sludge system are designed as individual units with little or no appreciation for the process interactions which occur between system components. To achieve acceptable process efficiency and to realize cost effectiveness a unified design approach is necessary. This research effort was initiated to define the characteristics of the economic optimum complete mix activated sludge configuration while considering system interactions.

A computer program was developed for the completion of the process design and the economic analysis of the aeration basins, the settling basins, and the return sludge pumping facilities for the complete mix activated sludge system. The process design was formulated subject to constraints on the following:

  1. effluent suspended solids
  2. effluent substrate concentration
  3. underflow solids concentration
  4. maximum and minimum mixed liquor suspended solids concentration
  5. maximum and minimum values for settling basin depth

Recognizing the importance of the final settling basin to the overall economics and performance of the activated sludge process emphasis was placed on settling basin design. Settling basin surface area requirements for thickening were identified using the settling flux approach. To ensure comparison of systems capable of producing equivalent effluent qualities settling basin performance was evaluated using a model reported in the literature. The model selected shows sensitivity to settling basin detention time, overflow rate and mixed liquor suspended solids concentration.

Using the optimization routine, simulations were performed to identify the optimum system configuration as defined by this model. The optimum system aeration basin hydraulic detention times were found to be higher than those typically used, while the optimum system mixed liquor suspended solids concentrations were found to be lower than those typically used. Optimum system settling basin hydraulic detention times and depths were found to exceed conventional detention times and depths in current usage. Although the optimization routine developed in this research may not have wide spread applicability, the results are felt to be significant in identifying optimum system trends.


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Graduation Date





Dietz, John D.


Master of Science (M.S.)


College of Engineering




141 p.




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