Comparison of oxygen transfer parameters from four testing methods in three activated sludge processes

In this investigation, the mass transfer of oxygen was determined using four different testing methods in three activated sludge processes, as per the guidelines established by the American Society of Civil Engineers (ASCE 1997). The testing methods applied included the steady-state oxygen uptake rate (OUR), the non-steady-state changing power level (CPL), the non-steady-state hydrogen peroxide addition (HPA) and the off-gas methods. The analysis indicated that steady-state OUR and off-gas methods resulted in comparable estimates of oxygen transfer parameters, with somewhat higher variations observed in the data from the off-gas method. The application of HPA and CPL methods produced variable results under the same process conditions and these testing methods affected the process. Based on the comparative evaluation conducted in these controlled experiments, the validity of HPA and CPL tests to measure the oxygen transfer under process conditions is questionable. Overall, the off-gas method appears to be superior, as it does not require steady-state process conditions. However, under suitable conditions the steady-state OUR method may be an economical option to study oxygen transfer under process conditions.