Solids removal in storm-water filters modeled using a power equation

Storm-water filters and biofilters are limited by physical clogging. Several models have been proposed to predict the flow rate through the media throughout its lifespan. Urbonas (1999) modeled flow rate through a downflow sand filter as a function of the suspended solids loading on the media surface using a power equation. This paper confirms this equation in describing the flow rate through mixed-media downflow filters at a laboratory scale but with unique coefficients for different media. Confounding effects of influent solids concentration and filter surface diameter on the relationship between flow rate and suspended solids loading were seen, indicating that other factors are important in describing that relationship. Maintenance issues also were investigated, with the results showing that removal of about 5-10% of the surface of the media had little long-term impact on flow rate recovery.