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TREATMENT OF URBAN STORMWATER FOR DISSOLVED POLLUTANTS: A COMPARATIVE STUDY OF THREE NATURAL ORGANIC MEDIA
Ray*, A. B., I Wojtenko**, AND R Field*. TREATMENT OF URBAN STORMWATER FOR DISSOLVED POLLUTANTS: A COMPARATIVE STUDY OF THREE NATURAL ORGANIC MEDIA. DOI: 10.1002/rem.200, J.A. Simon (ed.), Remediation Journal. John Wiley & Sons, Ltd., Indianapolis, IN, 15(4):89-100, (2005).
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The feasibility of using hard and soft wood tree mulch and processed jute fiber, as filter media, for treating mixtures of dissolved pollutants (toxic organic compounds and heavy metals) in urban stormwater (SW) runoff was evaluated. Copper (Cu), cadmium (Cd), chromium (Cr+6), lead (Pb), and zinc (Zn) were studied as examples of heavy metals while benzo[a]pyrene (B[a]P), naphthalene (NP), fluoranthene (FA), 1,3 dichloro benzene (DCB), and butylbenzylphthalate (BBP) represented the organic compounds. Both jute and mulch combined with sand were used without any modification of their particle sizes. Actual SW runoff samples were spiked with predetermined concentrations of all ten pollutants. Each medium removed close to 100% of all the organic compounds within the concentration range studied. Although the removal efficiencies for metals in all three filter media (hard and soft wood mulches and jute fiber) were similar, the percentages of metals removed depended on the metal species and varied from 10 to 100 %. Flow rates of the influent varied both with the media type and the media to sand ratios. The flow rate decreased as the proportion of sand in the mixture was increased. The increased retention time resulted in a higher removal of the organic pollutants but appeared to have an opposite effect on metals removal. Equations relating percent of pollutants removed with flow rate were developed for each medium. Sorption capacities of the medium for each of the pollutants were also determined. Of the two wood mulches, the hardwood mulch sorbed a higher percentage of the pollutants than the softwood mulch. The sorption capacity of jute fiber, on an equal weight basis, was found to be 40 % higher than that of the hardwood mulch. Both of the organic media, on a mole basis, sorbed the pollutants in an identical sequence: for metals,
Cr+6 >Cu, Zn>Cd>Pb; for organics, NP>DCB>FA>B[a]P>BBP.