Pathogen and indicator microorganism removal in field scale stormwater biofilters

Knowledge of pathogen removal in stormwater biofilters has predominately been extrapolated from bacterial indicators; indeed, the removal of actual pathogens in these systems has not yet been studied. Furthermore, there is no knowledge on as to how the pathogen removal capacity varies in biofilters with different design parameters (e.g. media composition, inclusion of submerged zone). Hence, this study presents the performance of two field biofilter cells (with different designs) dosed with semi synthetic stormwater in removing ten faecal microorganisms, including: indicators and pathogenic bacteria, protozoa and virus. A net reduction in concentrations was observed for all pathogens and indicators, but the removal performance varied between bacteria, protozoa and viruses. Interestingly, the behaviour of the chosen bacterial pathogens was comparable to the bacterial indicators, whereas protozoan and viral pathogen removal were lower than their corresponding indicators. Biofilters containing a submerged zone generally had higher removal.