Ligand-Enhanced Electron Utilization for Trichloroethylene Degradation by ^·OH during Sediment Oxygenation

The potential of oxygenating Fe(II)-bearing sediments for hydroxyl radical (^·OH) production and contaminant degradation has been proposed recently. Here, we further show that specific ligands can largely enhance contaminant degradation during sediment oxygenation due to increased utilization efficiency of sediment electrons. With the addition of 0-2 mM sodium ethylene diamine tetraacetate (EDTA) or sodium tripolyphosphate (TPP) in sediment suspension (50 g/L, pH 7.0), trichloroethylene (TCE, 15 μM) degradation increased from 13% without ligand to a maximum of 80% with 2 mM TPP and was much higher with TPP than EDTA because EDTA competes for ^·OH. Electron utilization efficiency for ^·OH production increased with increased ligand concentration and was enhanced by up to 6-7 times with 2 mM EDTA or TPP. Electron transfer from sediment to dissolved Fe(III)-ligand is mainly accountable for the enhanced electron utilization efficiency by the ligands with low adsorption affinity (i.e., EDTA), and additional variation of sediment surface Fe(II) coordination is mainly responsible for the enhancement by the ligands with high adsorption affinity (i.e., TPP). Output of this study provides guidance and optional strategies for enhancing contaminant degradation during sediment oxygenation.