The dispersion model was used to study mixing levels in a full scale aeration tank. The effect of air flow rate, water flow rate and diffuser type was investigated. The peak time technique proved satisfactory in predicting the theoretical tracer response curve generated using the dispersion model. The dispersion model adequately described the longitudinal mixing that occurred in a full scale aeration tank equipped with fine and coarse bubble air diffusers. Response curves from two tanks-in-series were also obtained. / Thesis / Master of Engineering (ME)