POLLUTANT ASSOCIATIONS WITH PARTICULATES IN STORMWATER

ISSN： 1938-6478

Source： Proceedings of the Water Environment Federation, Vol.2005, Iss.11, 2005-01, pp. : 4973-4999

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Abstract

Many studies have identified metals in urban runoff as a major contributor to the degradation of urban streams and rivers. Metals of most concern are copper, cadmium, chromium, lead, mercury, and zinc. Metals in urban runoff can occur as dissolved, colloidal and particulate-bound species. Therefore, it is important to measure all forms of heavy metals, especially the particulate and filterable fractions, when determining their fate and effects.The objectives of these tests were to determine the associations of heavy metals and nutrients with different-sized particulates using cascade sieves and filters. Sequential extraction experiments were also conducted to examine the treatability and other characteristics of the filterable (<0.45 μm) portion of the heavy metals using Chelex-100 resin, UV-light exposure, and Anodic Stripping Voltammetry (ASV).A decrease in concentration with sequential removal of particulates was obtained for total solids, turbidity, chemical oxygen demand and total phosphorus. Total solids, turbidity and total phosphorus were reduced by more than 50% with removal of particulates. Heavy metals were generally found more in the filterable fraction and not greatly removed by reduction in particulates. Less than 50% of Zn, Cu, Cd or Pb were associated with particulate fraction.The use of ASV was also developed to measure the ionic forms of heavy metals in the filterable (<0.45 μm) fractions. Good sensitivity was obtained by using Square Wave Stripping Voltammetry with a 5 minute deposition time. The use of ASV with samples exposed to the Chelex-100 ion exchange resin were unsuccessful. Colloidal analysis showed that most of the Zn, Cd and Pb were not present in the free ionic form, but were bound to colloidal or organic matter whose bonds could be broken by exposure to ultraviolet light. Only Cu occurred in mostly the ionic form.