Pollutant removal performance of field scale dual-mode biofilters for stormwater, greywater, and groundwater treatment

Abstract To extend the application of stormwater biofilters (known also as bioretention systems or raingarden) under varied climate conditions, the concept of dual-mode biofilters (i.e., a biofilter that treats two sources of water) has recently emerged. However, studies of these systems have been limited to the laboratory-scale, and validation of the new concept at the field-scale is paramount. This paper presents results from the first field study on two full-scale dual-mode biofilters that operate under different climate conditions and operational regimes. The first, a dual-mode stormwater-greywater biofilter located in Jurong, China, received stormwater and greywater in various combinations. The second, a dual-mode stormwater-groundwater biofilter in Kfar-Sava, Israel, treats stormwater in the wet season and contaminated groundwater in the dry season. It was observed that the stormwater-greywater (Jurong) biofilter was able to provide effective treatment for the majority of pollutants regardless of time of the year, water source, or operational mode (stormwater-only, greywater-only or mixed). Higher levels of greywater nitrogen (total nitrogen ~5.5 mg/L, about two times that in local stormwater) and carbon (e.g., BOD5 110 mg/L about ten times that in stormwater) were also found to positively impact nitrogen removal. The stormwater-groundwater (Kfar-Sava) biofilter was able to effectively treat stormwater, with up to 73% removal of total nitrogen, however, when groundwater containing high levels of nitrate (up to 150 mg/L, compared to