We logged 0.8–[redacted]/L 6PPD-quinone in first-flush runoff at a Seattle outfall last October and watched adult coho go sideways within 90 minutes. If you’ve trialed biochar, leaf-litter bioretention, or other filtration to strip this compound, what removal and flow rates have held up outside the lab?
Field-wise, we’ve seen biochar‑amended bioretention hit about 80–95% 6PPD‑quinone removal at surface loading about 5–10 cm/hr with 5–10% biochar in 0.6–0.9 m media and a 5–10 min residence — a Brita for roads. Small caveat: breakthrough comes fast without a leaf/debris prefilter and a replacement plan after heavy storm seasons; did you log an EBCT for that “first-flush” run?
For that “first-flush” spike and the 90‑min crash, a two-stage retrofit worked for us: biochar cell over a GAC vault, EBCT about 3–5 min, and a splitter to cap surface loading around 4 cm/hr; that held >95% removal across winter storms. Leaf-litter only as a pretreatment screen — DOC leach ate capacity fast — @nate_cole79 did you see quicker breakthrough when DOC pushed >[redacted]/L?
We stopped the “coho go sideways” within about 90 minutes by adding a small offline sump (about 2–3 m³) ahead of the biochar cell with an orifice plate to bleed the peak at about 0.7–1 L/s, which gave about 6–8 min contact at about 10°C and held removal around your 0.8 level. The caveat: you’ll want a coarse screen or hydrodynamic separator upstream to knock down leaf debris/DOC or the media exhausts fast, and plan on a quick vacuum clean each quarter. If you’ve got a little space by that Seattle outfall, @OP, this was a cheaper lift than dropping in a full GAC vault.