Laboratory Column Experiment on Particle Trapping Capabilities of Various Biofilter Mixtures

Stormwater biofilters are widely used in urban areas to reduce runoff volume, peak flows and stormwater discharges and impacts to receiving waters. However, the performance of these systems in urban areas is affected by premature clogging of filtration media by incoming sediment, which in turn can decrease the life span of the device. Capture of fine particulates and eventual clogging is one of the most common causes of failure in stormwater infiltration devices. This presentation will describe a series of controlled laboratory column tests conducted to determine particle trapping capabilities of sand-peat media mixtures, Tuscaloosa surface and subsurface soils, using challenge water made up of a wide range of particle sizes.

The test sediment in the challenge water was based on a mixture of fine ground silica particulates, medium sand, and coarse sand, mixed with Black Warrior River water to result in a wide range of particle sizes. The mixture added to the water resulted in a generally uniform particle size distribution ranging from about 20 μm to 2,000 μm. The purpose of this challenge water mixture was to have significant amounts of each size range of material so performance by particle size range could be observed and evaluated, not to create a mixture similar to stormwater. The influent (dirty) water samples and the treated effluent water samples obtained from the laboratory column tests were analyzed in several separate particle size ranges so the results can be applied to actual particle size distributions.

The results indicated that significant particulate trapping occurred for most lab columns with little difference for the different column media mixtures. However, columns with local area soils had increased discharges of very small particle sizes compared to the influent water due to washing of the fines from the local soil media.