Laboratory comparison of four iron-based filter materials for water treatment of trace element contaminants

Abstract

A laboratory investigation provided preliminary comparison of trace element contaminant water treatment capabilities for four iron-based filter materials. The iron-based filter materials tested were zero-valent iron (ZVI), porous iron composite (PIC), sulfur modified iron (SMI), and iron oxide/hydroxide (IOH). Two types of trace element contaminant solutions were tested, one combined As, Cr, and Se (added as AsO4(3-), CrO4(2-), and SeO4(2-), respectively), while the second combined Cd2+, Cu2+, and Pb2+. The laboratory investigation included saturated falling-head hydraulic conductivity tests, contaminant removal-desorption/dissolution batch tests, and low-to-high flow rate saturated solute transport column tests. Hydraulic conductivity test results indicate that all four iron-based filter materials have sufficient water flow capacity as indicated by saturated hydraulic conductivity values greater than 1 x 10(-2) cm/s. Essentially, 100% of each trace element (As, Cd, Cr, Cu, Pb, and Se) was removed by SMI during the contaminant removal portion of the batch tests and during the column tests, while IOH exhibited good removal of each trace element except Se. Results from the contaminant removal portion of the batch tests and from the column tests showed ZVI and PIC were effective in treating Cd, Cr, Cu, and Pb. With the exception of Se adsorption/precipitation onto IOH, the desorption/dissolution portion of the batch tests showed that once As, Cd, Cr, Cu, Pb, or Se are adsorbed/precipitated onto ZVI, PIC, SMI, or IOH particle surfaces, these trace elements are then not readily desorbed or dissolved back into solution.