Interpreting Residence Time Distributions in Water Treatment Systems

This thesis establishes residence time distribution (RTD) as a key tool for the investigation of water treatment systems. RTD software for tracer data modelling and interpretation is developed and validated for problem solving purposes in water treatment systems. The technique focuses on the systematic interpretation of RTD data using a tanks-in-series based model and an indicator, flushing time (tf ). This approach removes the subjectivity often associated with RTD interpretation and is tested extensively using experimental and numerical data. The influence of design elements, intended to enhance hydraulic efficiency, is also addressed. For this purpose, both numerical modelling (Mike 21) and the proposed approach are employed. Results reveal that the interpretive provides valuable information, facilitating a greater understanding of the hydraulic effects of changes to geometry and inlet/outlet configuration than other techniques alone. The approach was shown to be particularly successful at interpreting RTD curves from stormwater treatment systems due to their susceptibility to stagnation. However, it was shown to have limited applicability in systems with complex flow characteristics (such as large bioreactor vessels) or those susceptible to extensive short-circuiting. The approach was also found to be unsuitable for evaluating the impact of deviations from ideal flow on pollutant removal in systems governed by complex biokinetic reactions