Experimental Analysis and Modeling of a Stormwater Perlite Filter

This paper presents the study of a mixed porous media, composed of expanded perlite (EP) and nonwoven needle punched geotextile, used to remove suspended solids (SS) in urban runoff before it is infiltrated. Several laboratory procedures were designed to quantify the most important variables that characterize the performance of this filter media: SS removal efficiency (R) and the variation in time of filtration rate (Q). Different grain size distributions of EP, diverse SS concentrations, and different hydraulic and geometric conditions were tested in order to determine the most effective filter media in terms of the maximization of R and Q. A dimensionless parameter, the "global performance index" (GPI), was developed to reach this objective. Measured data were also used to build a dimensional model to represent the performance of the filter media mathematically. The theory, assumptions, derivation and performance of this model are presented, and then compared to an existent empirical model. The dimensional model better reproduces the observations, becoming a useful tool for the design, operation and evaluation of commercial porous media filters.