Steel wool and carbonyl iron powder activation of persulphate for the degradation of pollutants

Abstract

Commercial zerovalent iron (ZVI) – as steel wool and carbonyl iron powder – activation of persulphate (PS) has been demonstrated to be effective in the degradation of four important water pollutants, namely, orange G (OG), salicylic acid (SA), phenol (Ph), and 1-naphthylamine (1NA) in the presence or absence of methanol (MeOH). The addition of MeOH mimics the presence of industrial solvents and/or feedstuff in real industrial wastewater. The alcohol had a more retarding effect on the degradation of an aromatic pollutant relatively resistant to oxidation such as SA due to the presence of an electron-withdrawing group compared to a pollutant such as 1NA that has an electron-donating group. The azo bond in OG constituted a structural weakness leading to a comparatively more effective degradation of the aromatic moieties. Fe2+ was not only less effective than the commercial ZVI in activating PS; it was also more significantly retarded in its activity by MeOH. In addition, the surfaces of the ZVI were not oxidised, an advantage over ZVI nanoparticles, and they required no prior pretreatment indicating the probable suitability of waste iron filings for PS activation. As an activator of PS, ZVI is optimised at a size range of 0.1 μm < d < 100 μm. It was also demonstrated that the poor optimisation of PS concentration not only increases oxidant consumption or treatment time but also results in the persistence of undesirable aromatic degradation by-products. These results are important for the development of low-cost and effective industrial wastewater treatment schemes.