WP4 Metals in the Environment: Chemistry and Fate Issues
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(SUN-1117-766217) Partitioning of Hg, Se, and As in a pilot-scale constructed wetland for wastewater treatment.

Sundberg, S¹, Hassan, S², Rodgers, Jr., J¹, ¹ Clemson University, Clemson, SC, USA² University of Georgia, Athens, GA, USA

ABSTRACT- Constructed wetland treatment systems (CWTS) designed to treat constituents of flue gas desulfurization wastewater have the ability to concentrate, transfer, and transform Hg, Se, and As. This results in the distribution of these elements in different forms among environmental media, including sediment, detritus, and macrophytes. The objective of this research was to investigate partitioning of Hg, Se, and As in a pilot-scale constructed wetland by measuring the concentrations in sediment, detritus, on root and submerged shoot surfaces of macrophytes, and within roots, submerged shoots, emerged shoots, and seeds of macrophytes collected from the CWTS. Since determining total concentrations of these constituents in the sediment cannot provide some essential information about mobility, bioavailability, and potential impacts, operationally-defined species of Hg, Se, and As associated with sediment in the CWTS were characterized using sequential fractionation procedures. Detritus contained the greatest concentrations of these elements, with an overall increase in Hg and Se and decrease in As from the wastewater inflow to outflow in the constructed wetland. Sediment concentrations of Hg, Se, and As were one to two orders of magnitude less than detritus. Sediment-associated Hg was primarily in its elemental form, whereas As was largely contained in the sediment fraction consisting of crystalline lattice structures of primary minerals and silicates. Selenium was more evenly distributed among sediment fractions. Significantly more Hg, Se, and As was accumulated by macrophyte tissues than adsorbed to macrophyte surfaces exposed to water. Mercury, Se, and As concentrated in the root tissues, with minimal translocation to the aerial portions of the plant. Negligible concentrations of these constituents were found in the seeds. The observed partitioning of Hg, Se, and As in this CWTS will play an important role in designing the full-scale constructed wetland treatment system.

Key words: constructed wetlands, elements, partitioning, sediment