Conditioning of Heavy Metal-Polluted River Sediments by Helophytes

Abstract

ABSTRACT Aquatic sediments in industrial regions are often polluted by heavy metals. When removed by dredging, the sediments become an environmental risk. Because of the high costs and the deficient sustainability of landfill disposal, we intend to develop a remediation process for cleaning heavy metal-contaminated sediments by solid-bed bioleaching. Unfortunately, freshly dredged sediments are often impermeable to water. Therefore, they have to be conditioned to improve their hydrodynamic properties and make them suitable for solid-bed leaching. The treatment basin of 5.9 m × 7.5 m of a pilot-scale plant for sediment conditioning was filled with 0.5 m freshly dredged sediment, which originated from a trap in the Weisse Elster River near Leipzig, Germany, and was contaminated with Zn, Cr, Pb, Cu, Ni, and Cd. The sediment was planted with the helophytes Phragmites australis, Phalaris arundinacea, and Agrostis stolonifera. The vegetation evaporated large amounts of water and transported oxygen into the sediment. During conditioning the anoxic, black, muddy-pasty sediment changed to the oxic state and turned into a grayish brown, crumbly, soil-like material. Furthermore, the sediment turned acidic, its buffer capacity decreased, and, because of pore and particle enlargements, it became easily permeable to water. The plants on the sediment incorporated heavy metals in their biomass, especially Zn, Ni, Cd, and Co, but not enough for sediment remediation by phytoextraction.