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Residence Time Distribution modelling to characterise the hydraulic efficiency of reactor networks

The understanding of the hydraulic behaviour of any reactor is essential in order to optimise the efficiency of the process for which it has been designed. This research project is aiming to build a mathematical model to interpret the Residence Time Distributions (RTDs) which are generated by means of tracer studies carried out on reactor networks, particularly within the field of Wastewater Treatment plants.

Fluid Dynamics 1

The project has progressed through a series of experiments on laboratory scale reactors with well understood hydraulic characteristics to produce RTD data sets which were then be used to validate and calibrate the mathematical model. The mathematical model has been formulated on the basis of tank-in-series theory. The laboratory tests have been carried out using Rhodamine WT as the tracer and the respective concentrations are analysed using the Self-Contained Underwater Fluorescence Apparatus (SCUFA). The initial experiments have been carried out using a single mixed tank reactor with the tracer injected in as a pulse input, step input and step-step input.

The reactor was configured in a variety of ways to create known dead zones and short –circuits. The work then progressed to looking at various combinations of multiple tanks in series and in parallel to refine the mathematical model and develop it further. The model was finally tested at full scale Wastewater Treatment plants on activated sludge processes in an attempt to characterise the hydraulic performance of the reactors and in turn, possibly identify the source of any associated treatment problems with the processes. After some calibration experiments to determine how much of the Rhodamine was absorbed by the organic matter (bacteria) in the process, the model was successfully applied to the RTD results from the full-scale trials, identifying some flaws in the original tank designs that promoted sever short-circuiting and dead zones. It was also tested in a drill mixing process for the oil industry in Libya and was again successful as it could identify those tanks where mixing was inefficient and short-circuiting was prevailing (Figure - RTD modeling of a 3 tank in series Activated Sludge treatment process).

Project coordinator: Prof. Laurence Gill