Fecal indicator bacteria and virus removal in stormwater biofilters: Effects of biochar, media saturation, and field conditioning

Abstract

Stormwater biofilters are used to attenuate the flow and volume of runoff and reduce pollutant loading to aquatic systems. However, the capacity of biofilters to remove microbial contaminants remains inadequate. While biochar has demonstrated promise as an amendment to improve microbial removal in laboratory-scale biofilters, it is uncertain if the results are generalizable to the field. To assess biochar performance in a simulated field setting, sand and biochar-amended sand biofilters were periodically dosed with natural stormwater over a 61-week conditioning phase. Impact of media saturation was assessed by maintaining biofilters with and without a saturated zone. Biochar-amended biofilters demonstrated improved Escherichia coli removal over sand biofilters during the first 31 weeks of conditioning though media type did not impact E. coli removal during the last 30 weeks of conditioning. Presence of a saturated zone was not a significant factor influencing E. coli removal across the entire conditioning phase. Following conditioning, biofilters underwent challenge tests using stormwater spiked with wastewater to assess their capacity to remove wastewater-derived E. coli, enterococci, and male-specific (F+) coliphage. In challenge tests, biochar-amended biofilters demonstrated enhanced removal of all fecal indicators relative to sand biofilters. Additionally, saturated biofilters demonstrated greater removal of fecal indicators than unsaturated biofilters for both media types. Discrepant conclusions from the conditioning phase and challenge tests may be due to variable influent chemistry, dissimilar transport of E. coli indigenous to stormwater and those indigenous to wastewater, and differences in E. coli removal mechanisms between tests. Mobilization tests conducted following challenge tests showed minimal (<2.5%) observable mobilization of fecal indicators, regardless of media type and presence of a saturated zone. While our results emphasize the challenge of translating biochar’s performance from the laboratory to the field, findings of this study inform biofilter design to remove microbial contaminants from urban stormwater.

Biochar-augmented biofilters to improve pollutant removal from stormwater – can they improve receiving water quality?

“…Of these, 14 met our inclusion criteria, and data were extracted from those papers. 44,54,[60][61][62][63][64][65][66][67][68][69][70][71] In total, 243 log 10 removal values were extracted from the 14 papers, and these data were used to assess trends in the removal performance. We plotted log 10 removal for the biochar-augmented biofilters for each tested contaminant and compared those with the log 10 removal of control experiments containing no biochar ( Fig.…”

Urban stormwater characterization, control, and treatment

“…Inactivation of bacteria by CuO was also shown, suggesting that CuO‐modified WTR can increase both adsorption and inactivation of E. coli in stormwater. The removal of fecal indicator bacteria by large sand biofilters augmented with biochar was tested by Kranner, Afrooz, Fitzgerald, and Boehm (2019). The effect of including a saturated zone was also tested.…”

Predicting Solute Transport Through Green Stormwater Infrastructure With Unsteady Transit Time Distribution Theory

“…The water quality benefits attributable to GSI are often quantified based on the fraction of storm water pollutants (measured on a concentration or mass basis) removed during laboratory or field challenge experiments (Bedan & Clausen, 2009; A. P. Davis et al., 2009; Feng et al., 2012; Hatt et al., 2009; Kranner et al. 2019; L. Li & Davis, 2014; Y. Li et al., 2012; Parker et al., 2017; Ulrich et al., 2017). Much of this research has focused on the link between system design and pollutant removal, for example how the choice of plant species and the presence or absence of a submerged zone influences the removal of nutrients (e.g., H. Kim et al., 2003; Payne et al., 2018; Read et al., 2008; Read et al., 2009; Rycewicz‐Borecki et al., 2017) and how media amendments influence the removal of microbial contaminants and heavy metals (e.g., Y. Li et al., 2016; Mohanty & Boehm, 2014; L. Zhang et al., 2010).…”

“…The water quality benefits attributable to GSI are often quantified based on the fraction of storm water pollutants (measured on a concentration or mass basis) removed during laboratory or field challenge experiments (Bedan & Clausen, 2009; A. P. Davis et al, 2009;Feng et al, 2012;Hatt et al, 2009;Kranner et al 2019;L. Li & Davis, 2014;Y.…”