Adsorptive infiltration of metals in urban drainage - media characteristics

Urban pavement drainage often contains significant quantities of anthropoge nic metal elements, including Cd, Cu, Pb and Zn that exceed surface water d ischarge standards. In many urban areas low rainfall pH, results in predomi nately dissolved metal element mass. Such partitioning has critical implica tions for the selection of in-situ treatment. One such category of treatmen t is engineered infiltration systems. To be effective, such systems must ad sorb dissolved metal elements to their fixed media while also acting as fil ters for particulate-bound fractions. One such strategy is called a partial exfiltration trench (PET). The PET contains oxide-coated sand (OCS); an am photeric media of high surface area (5-15 m(2)/g) as compared to uncoated s ilica sand (0.01-0.05 m(2)/g). OCS was generated through heating a mixture of silica sand and ferric nitrate solution to dryness. This paper presents results of both media characterization and bench scale PET simulations. Med ia tested were OCS and plain silica sand. Media testing was carried out unt il capacity was exhausted, using both synthetic and actual stormwater loadi ngs. Testing was conducted for pH levels of 6.5 and 8.0. Results indicated that OCS had greater capacity than silica sand for all dissolved fractions. As the pH was raised from 6.5 to 8.0, OCS capacity was improved. A PET con figuration with porous pavement resulted in the highest in-situ treatment c apacity for metal element bearing storm water. (C) 1999 Elsevier Science B. V. All rights reserved.