A novel process involving the in-situ electrochemical generation of ferrate and permanganate oxidants, in circumneutral conditions, from low concentration aqueous iron (Fe2+) and manganese (Mn2+), is investigated for the treatment of ubiquitous and recalcitrant micro-pollutants, atrazine and perfluorooctane sulfonate (PFOS). The present study first investigated the electro-generation of both ferrate and permanganate in the absence of pollutants, in order to reveal the effect of current density (10, 40 and 80 mA cm-2) and initial Fe2+ and Mn2+ concentrations (9-182 µM) on oxidant generation. Subsequently, the efficacy of both electro-oxidation (EO), and the simultaneous electro-oxidation and ferrate/permanganate generation and oxidation, on atrazine and PFOS degradation was investigated, as a potential treatment technology for small system applications.

Ferrate and permanganate synthesis was clearly observed but was largely unaffected by current density, indicating mass transport limitations. In contrast, synthesis was affected by the initial iron/manganese concentrations, with 0.4-18.4 µM ferrate generated from initial Fe2+ concentrations of 9-179 µM, and 0.09-0.84 µM permanganate generated from initial Mn2+ concentrations of 55-182 µM, respectively.

When operating under simultaneous EO and ferrate/permanganate oxidation, atrazine degradation exceeded that of the EO-only process. Depending on the current density and initial iron/manganese concentration, an atrazine removal of 33-75%, 35-82% and 36-77% was yielded during EO, EO-ferrate and EO-permanganate processes, respectively, and characterised by pseudo-first-order kinetics. Under the same conditions, PFOS was observed to decrease by 22-35% and 34-65% during the EO and EO-ferrate processes, respectively, with no increased degradation during the EO-permanganate process. Unlike atrazine, PFOS degradation was observed to follow mixed-order (zero and first) reaction kinetics.

The effect of natural organic matter (NOM) on atrazine and PFOS degradation was also investigated. Ferrate was observed to be significantly scavenged by resorcinol, a representative small molecular weight NOM compound, resulting in decreased atrazine removal. The use of a real-water lyophilised NOM, however, yielded increased PFOS removal due to physical adsorption by hydrophobic interactions.