Abstract
This study sought to evaluate how dissolved organic carbon (DOC) affects attenuation of trace organic contaminants (TOrCs) in biochar-amended stormwater biofilters. It was hypothesized that (1) DOC-augmented runoff would demonstrate enhanced TOrC biodegradation and (2) biochar-amended sand bearing DOC-cultivated biofilms would achieve enhanced TOrC attenuation due to sorptive retention and biodegradation. Microcosm and column experiments were conducted utilizing actual runoff, DOC from straw and compost, and a suite of TOrCs. Biodegradation of TOrCs in runoff was more enhanced by compost DOC than straw DOC (particularly for atrazine, prometon, benzotriazole, and fipronil). 16S rRNA gene quantification and sequencing revealed that growth-induced microbial community changes were, among replicates, most consistent for compost-augmented microcosms and least consistent for raw runoff microcosms. Compost DOC most robustly enhanced utilization of TOrCs as carbon substrates, possibly due to higher residual nutrient levels upon TOrC exposure. Sand columns containing just 0.5 wt % biochar maintained sorptive TOrC retention in the presence of compost-DOC-cultivated biofilms, and TOrC removal was further enhanced by biological activity. Overall, these results suggest that coamendment with biochar and compost may robustly enhance TOrC attenuation in stormwater biofilters, a finding of significance for efforts to mitigate the impacts of runoff on water quality.
Highlights
Stormwater runoff has degraded urban water quality by transporting contaminants to receiving waters.[1]
Removal of trace organic contaminants (TOrCs) in Low impact development (LID) systems is poorly understood despite their broad presence in urban runoff.[4]
Many toxic stormwater TOrCs such as urban-use pesticides,[5−7] flame retardants,[8] and chemicals from vehicle fluids[9] are relatively mobile, allowing them to pass through LID systems.[10]
Summary
Stormwater runoff has degraded urban water quality by transporting contaminants to receiving waters.[1]. Microcosms were diluted to 125 mL with autoclaved synthetic stormwater (composition in Table S3), and a sodium azide (NaN3) solution (5 mL of 4 g/L in DI water, 154 mg/L final concentration) was added to control microcosms to inhibit biological activity (biotic microcosms diluted with 5 mL autoclaved DI water) These dilutions allowed sufficient volume for numerous sampling events and reduced the DOC to more representative levels (i.e., less than 50 mg/L, Table S5). Due to constraints on sample analysis, DNA extraction and sequencing was carried out for three representative biotic microcosms from each condition (nine total), and the column seeding solutions (Figure S4). Quantitative PCR (qPCR) of overall bacterial 16S rRNA genes was conducted to qualitatively compare gene copy numbers among samples (Method S4)
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