CHARACTERIZATION OF MIXING PATTERNS IN AN ANAEROBIC DIGESTER BY MEANSOF TRACER CURVE ANALYSIS

A range of methods for analysing tracer response curves was evaluated for determining mixing patterns in a pilot-scale contact process anaer obic digester. The methods considered included point indices, analytic al models such as the dispersion model, and combined models describing different hydraulic zones. In addition, a computer simulation model w as developed to quantify the mixing zones and the interaction between them. The methods were compared for (i) ease of use, (ii) accuracy, (i ii) consistency, and (iv) application over a wide range of operating c onditions. The ease of use of the point indices was offset by their in consistency and inaccuracy in several cases. Combined models were sens itive to small changes in the form of the tracer response curve. The r esults from the simulation model showed a consistent pattern with chan ging operational conditions. A further development of the model was pr oposed to enable rapid analysis of tracer curves which would promote i ts use among design engineers.