Evaluation of different analytical methods for tracer studies in aeration lanes of activated sludge plants

There are many different methods available for analysing the results of tracer studies on the aeration lanes of activated sludge plants. If the results are to be used for modelling then it is necessary to calculate the number of tanks in series to allow the dispersion within the tanks to be accurately modelled. Two methods for this are presented in this paper and both are based on Levenspielʹs work. The WRc method calculates the number of tanks in series but provides information on short-circuiting only by visual inspection of the residence time distribution (RTD) curve. The Martin method produces information on mean residence time and number of tanks in series for a number of separate flow “strands” through the tank. In this way, “short-circuiting” can be parameterised in a manner consistent with mathematical models of the activated sludge process. Other methods for analysing RTD curves, whilst giving useful information on the flow regime within the tanks, are not suitable for use in dynamic models of wastewater treatment.