HR: 12:05h
AN: B12A-08    [Abstracts]
TI: Effect of Wetland Plants on the Reduction of Hexavalent Chromium in Sediments
AU: Zazo, J A
EM: juan.zazo@uam.es
AF: Universidad Autonoma de Madrid, Departamento de Ingenieria Quimica, Madrid, 28049, Spain
AU: Paull, J
EM: jpaull@Princeton.EDU
AF: Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States
AU: * Jaffe, P R
EM: jaffe@princeton.edu
AF: Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ 08544, United States
AB: The effect of wetland plants (Typha latifolia and Carex lurida) on the reduction of Cr(VI) to Cr(III) at relatively low initial Cr(VI) concentrations (< 5 mg/L) was studied. Experiments were carried out using tubular microcosms operated in a greenhouse under plug flow conditions. Cr(VI) reduction was enhanced significantly by the presence of plants. This is explained by a decrease of the redox potential promoted by the root exudates released by the roots of the plants. Using these root exudates as their carbon source, and in the absence of nitrates, sulfate-reducing bacteria are able to reduce sulfate, building up the concentration of acid volatile sulfide (AVS), which in turn reduce Cr(VI) to Cr(III). Moreover, evapotranspiration induced by plants also contributes to enhance the removal of Cr(VI) by concentrating the species in the sediment porewater and therefore affecting the reaction kinetics. The effect of diurnal cycles on the Cr(VI) reduction rate has also been also studied. The diurnal cycle influences both root exudates released by plants as well as evapotranspiration. Higher levels of dissolved organic carbon in the pore water and evapotranspiration, occurring from around noon to 3 pm, correspond to a higher sulphate reduction rate and a lower redox potential in the sediments. This promotes a higher Cr(VI) removal during the day hours. Finally the Cr(VI) reduction dynamics were fitted to a kinetic equation that depends on the AVS and Cr(VI) concentration.
DE: 0418 Bioremediation
DE: 0461 Metals
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0488 Sulfur cycling
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting