Considerations in selecting a (bio)filtration media to optimize lifespan and pollutant removal

Many research studies have been published regarding the treatment efficiency of bioretention for a wide variety of pollutants found in urban stormwater runoff. However, limited information is available on predicting the treatability of these pollutants between media and between sites. Predicting the treatment ability of bioretention/infiltration/filtration media is a function of both soil and water chemistry. This paper begins that meta-analysis of pollutant removal as a function of chemistry. The results presented here are from a single project evaluating candidate bioretention media to meet numeric effluent limits and are based on a limited number of samples. As additional data becomes available in the spring, the analysis will be expanded. The preliminary results indicate that the media that appear to have the best removal ability for a wide range of metallic pollutants are those that have both cation exchange ability and comparatively high organic matter content. For metals, this also may require a lower media pH because of the generally increased solubility of metals at lower pHs. Lower pHs and higher organic matter contents, however, must be evaluated further if phosphorus removal is also desired since phosphorus is removed better at higher pHs and lower organic matter contents. These results also highlight the trade-offs in pollutant capture versus export when using ion-exchange media.