Comparison of Oxygen Transfer Parameters Determined from the Steady State Oxygen Uptake Rate and the Non-Steady-State Changing Power Level Methods

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test.