Ferrate(VI) Reaction with Effluent Organic Matter (EfOM) in Secondary Effluent for Water Reuse

Ferrate(VI) (Fe(VI)) has been recognized as an alternative treatment agent for water reuse. Although the studies on ferrate(VI) for wastewater treatment early began in the 1970s, the aqueous chemistry of ferrate(VI) remains undeveloped. A key challenge is to understand the interactions between Fe(VI) and effluent organic matter (EfOM) in biologically treated municipal wastewater (i.e. secondary effluent). In this study, bench-scale tests were performed to preliminarily evaluate Fe(VI) removal and transformation of EfOM in secondary effluent for water reuse. Results showed that Fe(VI) was very effective for the removal of UV254, but slightly alleviated chemical oxygen demand (COD) under the tested conditions (initial pH = 7.54; no pH adjustment; and Fe(VI) = 0.0-15.0 mg/L). Molecular weight (MW) fractionation revealed that high (> 10 k Da) and medium (10-1 k Da) MW EfOM molecules were decomposed into low MW compounds (< 1 k Da) at a low Fe(VI) dose (1.0 mg/L), causing an increased low MW fraction. As Fe(VI) dose further increased, UV254 of all the MW groups were somewhat reduced. Fe(VI) treatment exhibited a better removal performance than the control treatment with Fe(III) coagulation alone, because Fe(VI) oxidation and coagulation both potentially contributed to the EfOM removal. Particularly, Fe(VI) oxidation appeared to play a more essential role in the EfOM transformation.