This project aimed to provide sustainable design suggestions for urban stormwater remediation at Washington State Ferry terminals. Researchers conducted laboratory and field-scale column tests to recommend specific types of plant filtration media for copper and zinc adsorption.
In the Pacific Northwest, elevated soluble zinc and copper concentrations originating from urban stormwater runoff pose a significant threat to native salmon and steelhead populations. In response to urbanization, existing stormwater infrastructure needs to be upgraded to treat non-point source pollution, including soluble metals, before they enter receiving waters. Media filtration best management practices provide the flexibility and small treatment footprint needed to retrofit areas where space is limited, such as ferry terminal staging areas, and dry plant matter has shown promise as an available, effective, and reasonably priced filtration medium.
A previous study evaluated the use of plant matter in raw form, thermally treated (torrefied), and carbonized. Laboratory column tests indicated that the most efficient adsorption for both copper and zinc was non-torrefied wood (Douglas fir), followed in order by pea gravel, torrefied wood, and charcoal (lodgepole pine). However, it was not understood why the raw crumble® particles worked better than the biochar. Therefore, this project conducted more comprehensive experiments to explore the relationship between the physicochemical properties of a wide range of wood crumbles and biochars and their copper and zinc adsorption.
The researchers extended the species of wood materials investigated by performing laboratory studies on Douglas-fir crumbles®, poplar crumbles®, tanoak crumbles®, lodgepole pine crumbles®, ultra-char of poplar®, ultra-char of alder®, and ultra-char of Douglas fir®.
On the basis of the results of both column tests and batch experiments on all samples, tanoak crumbles appeared to be the optimal option for both copper and zinc. By themselves, the laboratory column tests indicated that the most efficient adsorption medium was poplar char, followed in order by tanoak crumbles, poplar crumbles, Douglas fir char, Douglas fir crumbles, lodgepole pine crumbles, and alder crumbles. In addition, both column experiments and batch adsorption tests indicated that the surface areas of the wood crumbles and ultra-char of different wood crumbles are highly related to each substance\’s ability to adsorb copper and zinc. Media with larger surface areas showed greater adsorption of heavy metals.
Authors:
Indranil Chowdhury
Yuhao Tian
Mehnaz Shams
Michael Wolcott
WSU Department of Civil and Environmental Engineering
Jim Dooley, Forest Concepts, LLC
Sponsor: WSDOT
WSDOT Technical Monitor: Tom Bertucci
WSDOT Project Manager: Lu Saechao