Improved contaminant removal in vegetated stormwater biofilters amended with biochar

The potential for carbonaceous sorbents to improve contaminant removal (particularly for trace organic contaminants, TOrCs) in stormwater biofilters was evaluated in intermittently dosed, vegetated columns simulating scaled-down treatment systems. Columns amended with biochar or granular activated carbon (GAC) were evaluated relative to performance benchmarks set by columns representing unamended treatment systems (i.e., sand filters and vegetated biofilters). Biochar amendment (6.7 wt%, 33 vol%) strongly improved TOrC removal, despite potential fouling due to the presence of an upper compost-amended layer. Biochar-amended biofilter columns maintained greater than 99% TOrC removal throughout five months of dosing with TOrC-spiked creek water (equivalent to approximately 1.3 years of runoff volume), relative to less than 50% removal of most TOrCs by unamended biofilter columns. GAC amendment (6.7 wt%, 12.5 vol%) also improved TOrC removal, though less effectively than biochar (>70% removal), because the biochar's lower density (i.e., higher volume composition) and smaller particles improved performance. These results indicate that full-scale biochar-amended biofilters could potentially remove TOrCs effectively for several years, as treatment depths up to five times greater than the 10 cm experimental depth may be feasible for full-scale systems. Further, contaminant removal survey experiments conducted after 6 months of operation revealed that biochar amendment improved removal of total organic carbon, total nitrogen, nitrate, and total dissolved phosphorus in biofilters by greater than 60%. The findings of this study demonstrate the potential of biochar amendment to broadly improve contaminant removal in biofilters, motivating and informing the application of full-scale biochar-amended biofilters for improved water quality.