Field Studies of Microbial Removal from Stormwater by Bioretention Cells with Fly-Ash Amendment

Abstract

Abstract:Microbial pollution in stormwater is a concern in urban areas across the U.S. and is a leading cause of water-quality impairment in the United States. This issue may be addressed through the use of best management practices (BMPs) and target limits for pathogenic indicator species. Bioretention is a commonly used low impact development strategy that addresses this growing pollution problem at the source. Bioretention removal efficiencies have been well studied when considering nutrients and heavy metals, but field-scale treatment data are limited for microbial indicators. The primary objective of this study was to quantify microbial removal by installed bioretention cells with fly-ash amended soils. Three bioretention cells in Grove, Oklahoma were monitored over one and a half years and the removal microbial efficiency was quantified. Overall, removal rates for E. coli, enterococci, and coliphage were highly variable, with mean and standard deviations for removals for each site respectively: E. coli 87%, 35%, and 43%; enterococci 97%, 95%, and 80%; and coliphage 38%, 75%, and 32%. The site with negative removal efficiency appears to have some groundwater intrusion during storm events. Based on this relatively limited data set, these fly-ash amended bioretention cells performed 49% better than those with a sand-only filter media layer currently reported in the literature. Based on this initial field study, it appears that fly-ash amended bioretention cells may be a viable option for enhanced microbial removal from stormwater runoff.

Scientific Evidence behind the Ecosystem Services Provided by Sustainable Urban Drainage Systems

“…However, bioretention performance can fluctuate [80] and can even increase the concentrations of pollutants [81] and nutrients [53]. Operativity can improve with age [82] and some modifications [83]; fly ash amendments improved microbial removal in bioretention cells [84] and are an effective option for phosphorus removal [85], as a retrofitted upflow filter [86]. Bioretention acts as both a nitrogen source and sink (by infiltration and plant uptake mainly) [87].…”

Field Scale Demonstration of Fly Ash Amended Bioretention Cells for Stormwater Phosphorus Removal: A Review of 12 Years of Work

“…However, both cells were still meeting hydraulic design standards and providing pollution retention. Youngblood et al [51] in concert with Vogel et al [4] quantified E. coli, enterococci and coliphage effluent removal in three of these BRC. They found that, while removal was highly variable, fly ash amended bioretention in these cells performed 49% better than those with a pure sand filter media layer reported in the literature.…”

Urban Stormwater Characterization, Control and Treatment

“…removal. In the only field-scale study, E. coli removal by fly ash-amended bioretention cells amended exhibited highly variable but generally positive removal efficiencies, but additional testing would be required to determine if observed rates were better than non-amended media (Youngblood et al, 2017). In column studies, the effect of biochar (Afrooz and Boeh, 2017) and Cu 2+ -activated zeolite (Chandrasena et al, 2017) media amendments on FIB were tested.…”