Tri-protonated ferrate: A novel electro-synthesised pre-oxidant/coagulant for NOM and DBP precursors removal in drinking water production

The generation of tri-protonated form of ferrate (H3FeVIO4+) in acidic media offers unique opportunities for drinking water treatment. Compared to the more conventional deprotonated ferrate form (FeVIO42 ), H3FeVIO4+ is an extremely strong oxidant rendering it both an effective pre-oxidant and coagulant for water treatment applications. In this work, the treatment performance of H3FeVIO4+ at removing natural organic matter (NOM) and disinfection by-product (DBP) precursors was evaluated and compared against FeVIO42 and the most commonlyused iron-based coagulant: ferric chloride (FeCl3) when treating the water from two drinking water reservoirs in Australia. Results demonstrate that FeVIO42 and H3FeVIO4+ react with organic matter in intrinsically different ways, influencing the removal of dissolved organic carbon (DOC) and the formation potentials of carbonaceousDBPs upon subsequent disinfection with chlorine or chloramine. H3FeVIO4+ dosing achieved the highest DOC removal observed: 77 % for water from site A and 60 % for water from B, both significantly superior to FeVIO42 (water A: 22 % and water B:18 %) and FeCl3 (water A: 40 % and water B: 41 %) dosing. Moreover, H3FeVIO4+ preoxidation of water A and subsequent chlorination reduced trihalomethanes (THMs), iodo-trihalomethanes (ITHMs), haloketones (HKs) and chloral hydrate (CH) precursors by 81 %, 92 %, 53 % and 61 %, respectively, whereas for water B the THMs, I-THMs, HKs and CH precursors were reduced by 60 %, 52 %, 20 % and 58 %, respectively, heavily outperforming the performance of FeVIO42 and FeCl3 in the removal of all measured DBPs. Finally, the formation of bromate was not observed when either ferrate(VI) forms were applied, thus rendering H3FeVIO4+ an interesting alternative pre-oxidant/coagulant, even for high bromide-containing waters (such as water B: 240 mu g L 1).