ON-LINE ESTIMATION OF OXYGEN UPTAKE RATE FOR THE ACTIVATED SLUDGE PROCESS (CONTROL, SIMULATION, TRANSFER)

The purpose of this study was to develop a technique for on-line estimation of oxygen uptake rate (OUR) and to investigate the use of OUR in monitoring and control of the activated sludge process. A mathematical expression for the relationship between the plant specific oxygen transfer coefficient (K) and air flow rate was necessary for the estimation of OUR. Three different least squares methods, a direct linear method, a discrete linear method, and a non-linear method, were investigated as estimation techniques for K. Data from a full-scale, instrumented wastewater treatment plant were collected in order to evaluate the usefulness of each of the three methods. It was found that the direct linear method with data smoothing, although mathematically less rigorous than the other two methods, yielded a satisfactory estimate and was preferred over the non-linear method because of its computational simplicity. Difficulties were encountered with the discrete linear method because of disturbances in flow rate at the plant due to the on-off operation of several influent pumps. A comparison between the measured and estimated OUR showed similar trends indicating that the estimated OUR could be used in control. The use of OUR for control purposes was investigated by means of computer simulations using an existing mathematical model modified to simulate conditions at the full-scale plant. Control strategies, using OUR estimates, for air flow rate and step feed manipulation were developed and demonstrated to be effective. Because OUR is a better indicator of sludge activity than dissolved oxygen, the estimated OUR may also be used to monitor process conditions and obtain an estimate of the active fraction in the sludge. The latter may enable improved control strategies for sludge age to be developed