Degradation of drinking water disinfection byproducts by synthetic goethite and magnetite

Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface. Fe(II), a potent reductant when associated with iron oxide surfaces, can mediate the reduction of halogenated organic compounds. Batch experiments were performed to investigate the kinetics and pathways of the degradation of selected chlorinated disinfection byproducts (DBFs) by Fe(II) in the presence of synthetic goethite and magnetite. Trichloronitromethane was degraded via reduction, while trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldyde hydrate were transformed via both hydrolysis and reduction. Chloroform and trichloroacetic acid were unreactive. Observed pseudo-first-order reductive dehalogenation rates were influenced by DBP chemical structure and identity of the reductant. Fe(II) bound to iron minerals had greater reactivity than either aqueous Fe(II) or structural Fe(II) present in magnetite. For DBPs of structure Cl₃C-R, reductive dehalogenation rate constants normalized by the surface density of Fe(II) on both goethite and magnetite correlated with the electronegativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1- trichloropropanone.