Viral pathogens in urban stormwater runoff: Occurrence and removal via vegetated biochar-amended biofilters

Abstract

Urban runoff is one of the greatest sources of microbial pollution to surface waters. Biofilters can limit the impact of stormwater runoff on surface water quality by diverting runoff from receiving waters. However, our understanding of how biofilter design choices, including the addition of vegetation and geomedia, may impact the removal of pathogens is lacking. In this study, we characterized viruses (adenovirus, enterovirus, norovirus GII, crAssphage) in San Francisco Bay area urban runoff and assessed the removal of lab-cultured viruses (MS2, adenovirus 2, coxsackievirus B5) from biochar-amended biofilter mesocosms during challenge testing. We quantified viruses using (RT-)qPCR and F+ coliphage plaque assays. We found that all the pathogenic viruses targeted were found at low concentrations (adenovirus: all positive samples were <limit of quantification, enterovirus: <limit of quantification-1.9 × 10² gc/L, norovirus GII: <limit of quantification-1.2 × 10² gc/L) in San Francisco Bay area urban runoff and the presence of norovirus GII in runoff was associated with developed land use and decreased precipitation. Biofilters had variable success in removing adenovirus, enterovirus, and MS2 from runoff in laboratory-scale column experiments. In addition, there was no significant difference in the removal of each virus in vegetated versus non-vegetated biofilters, with the exception of MS2 which had slightly higher removal in vegetated biofilters (0.40 log₁₀ units, Welch's t-test, p = 0.004). When comparing removal of human viruses and viral indicators, adenovirus and enterovirus were removed more efficiently (log_10-removal adenovirus = 3.2; log₁₀-removal enterovirus = 1.1) than indicator virus MS2 (log₁₀-removal by RT-qPCR = 0.36, log₁₀-removal by plaque assay = 0.36). These results provide evidence that MS2 may be a conservative indicator for human virus removal in biofiltration systems, but more work is needed to examine this relationship. Results from this study can help inform design choices regarding biofilters intended to improve water quality and our understanding of virus attenuation in biofiltration systems.

Keywords: Abbreviations; Adenovirus = AdV; Enterovirus = EV; Low impact development = LID; MS2; Norovirus GII = NV GII; PV = pore volume; adenovirus; biofilter; enterovirus; norovirus GII; pathogen; stormwater; urban runoff; vegetation.