Application of residence time distributions to stormwater treatment systems

Abstract

Statistical measurements and qualitative assessments made by applying standard residence time distribution theory to non-steady-flow systems are of limited utility. A method is developed to enable non-steady-flow systems to be brought into the realm of steady-flow systems, so that residence time distribution (RTD) theory can be employed in a straight forward manner to characterize the non-ideal flows in these systems. Constructed wetland effluent concentrations resulting from impulse tracer inputs to the systems are considered. In addition to representing the concentrations with standard RTD functions, the concentrations are represented as functions of the cumulative discharge volume. This method provides the ability to easily analyze and compare data from steady and non-steady-flow systems, and thus to infer the degree of non-ideality of unsteady systems.