STORMWATER METALS REMOVAL TESTING AT SEATTLE-TACOMA INTERNATIONAL AIRPORT
Abstract:The Port of Seattle tested four filtration media in controlled laboratory experiments to determine their effectiveness for concurrent metals removal and toxicity abatement in synthetic stormwater. Media tested included commercially available leaf compost (CSF®) media, a zeolite/perlite mix, and a polyamine sponge, as well as the recently developed citric acid modified soybean hull media. Up to three replicates per medium were tested using synthetic water at three different levels of zinc (concentrations ranging from 100–200 ppb, 250–500 ppb, and 800–1700+ ppb). These levels represent typical ranges of zinc in urban runoff. Dissolved zinc fractions averaged 82% over the concentrations tested. Toxicity was assessed using acute C. dubia (48 hr) bioassays. The commercially available media were tested in OEM Stormfilter™ cartridges, while the soybean hulls were tested in a specially developed wedge cell representing a section (pie slice) of the standard Stormfilter™ cartridge.
The CSF® media removed up to 75% of the zinc and reduced toxicity significantly for influent concentrations of up to about 300 ppb zinc. Variations of the CSF® media (“extra fine” and reduced flow rates) improved zinc removal modestly compared to the standard version. The soybean hull material removed 80% to 99% of the zinc over all influent concentrations though it reduced pH to toxic levels. After pH adjustment, the effluent from the soybean material was non-toxic over all concentrations tested (survival was 100% in pH-adjusted effluent samples). Augmenting the soybean material with leaf compost media or activated carbon effectively buffered effluent pH to circum-neutral ranges. Other media tested removed modest amounts of zinc and were capable of sufficiently reducing toxicity only in the lowest concentrations tested, while some media appeared to generate toxicity. Based on these screening level results, the standard CSF® and soybean hull media have been selected for onsite stormwater treatment BMP testing at the Seattle-Tacoma International airport.
Document Type: Research Article
Publication date: 2002-01-01
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