A Novel Bioretention Media Made from Native Soil

Most bioretention media are sand based. Sand is expensive and is a non-renewable natural resource. To replace sand in bioretention media will not only reduce the construction cost, but also reduce the carbon footprint. Additionally, the use of sand-based media presents challenges for landscape architects in terms of plant variety and aesthetics. This leads to designers and landscape architects to avoid sand-based media or reduce the proportion of sand in the media, which makes the bioretention system underperform during storms. In order to address these concerns while still adhering to hydrology and pollutants removal requirements, we have developed a granule media made from excavated soil. The process involves drying the native soil to around 40% of its weight, crushing and screening it into particles smaller than 2 mm, and using an environmentally friendly adhesive to pelletize the fine particles using disk granule machines. The resulting granules can be soaked in water for years without dispersing. The media has a porosity of over 40% and an infiltration rate ranging from 200 mm to 2000 mm per hour, depending on the size of caithe granules. We have tested popular plants in this media and found that their health is not significantly different from plants grown in regular soil. The media also exhibits impressive removal rates for COD, TP, NH3-N, and TN, ranging from 20% to 90% depending on the configuration. Detailed findings from both lab and field studies will be presented in the paper.