One-step Ferrate(VI) treatment as a core process for alternative drinking water treatment

Traditional water treatment plants adopt multiple treatments to sequentially treat raw water for producing potable water. Besides complex treatment design and operation, they typically require a large space to accommodate different reactors. Furthermore, emerging issues (e.g. poor removal of persistent micro-pollutants) challenge the conventional treatment train. In this study, bench-scale tests were performed with real surface waters to evaluate ferrate(VI) treatment as a key alternative process for traditional water treatment. Of note, most earlier investigations on ferrate(VI) for water treatment utilized ferrate(VI) merely for pre- or post-treatment or simply as a disinfecting agent. Fundamentally different from the previous efforts, this study aimed to assess whether one-step ferrate(VI) addition, coupled with sedimentation, provided a comprehensive treatment, better than or equivalent to conventional surface water treatment. Results show that ferrate(VI) could simultaneously and effectively remove turbidity, degrade natural organic matter (NOM), and inactivate bacterial indicators in one single dose. The treatment performance relied heavily on ferrate(VI) dose and pH. Generally, higher ferrate(VI) dose improved the treatment results, except that it might re-suspend particles at a high dose at an alkaline condition. Lower pH favored coagulation due to reduction of zeta potentials on particle surface and promotion of their aggregation and enhanced the degradation of NOM because of higher Fe(VI) reactivity toward reductive moieties. In contrast, higher pH benefited the disinfection efficiency due to better stability and greater exposure of ferrate(VI). This study demonstrates that ferrate(VI) treatment can serve as a core treatment process in alternative water treatment designs for addressing various challenges.