Biofiltration units (e.g. bioswales and rain gardens) are depressed landscape areas that are designed to receive and filter stormwater runoff. They are applicable in residential and commercial environments with grass, shrubs and perennials plants. The top soils are usually covered with shredded hardwood bark and mulch. The benefits of biofiltration applications include decreased surface runoff, increased groundwater recharge, and pollutant treatment through a variety of processes.
The use of the biofiltration as a BMP (Best Management Practices) for treating stormwater runoff has been advocated for in many parts of the world. However, results from many installed units show that biofiltration application for water quality improvements has not always been positive due to inappropriate design and poor maintenance. This is evident in the limited and inconsistency in available data for biofiltration application performance from different studies.
It is against this background that this study was undertaken to evaluate the performance of the rain garden and the bioswales (biofiltration swales) constructed on the campus of Youngstown State University to treat stormwater runoff from a parking facility. Stormwater samples were taken from biofiltration inlets, outlets and along the biofiltration units after rain events over a period of ten months. Samples were analyzed for a variety of water quality parameters including nutrients (ammonia-nitrogen, total phosphorus and nitrate-nitrogen), metals, oil and grease, conductivity as well as pH. Parameters were analyzed according to the American Standard Methods. Laboratory results were then analyzed using SPSS statistical software (repeated measures) to compare concentration changes along the biofiltration units.
Results from the study indicated that the biofiltration units on Youngstown State University campus is efficient in removing 81.3% total suspended solids (TSS) , 39.1% total phosphorus (TP), 58.1% ammonia (NH3-N), 7.4% reduction in conductivity and 28.5% reduction in chemical oxygen demand.