Tertiary treatment of Berlin WWTP effluents with ferrate (Fe(VI))

New and higher standards in the EU water framework directive necessitate advanced treatment of secondary effluents for reduction of trace organic compounds (TrOCs) and nutrients before the discharge into receiving surface waters. Due to its dual function as oxidant and coagulant, ferrate is considered as a promising alternative for tertiary treatment. The oxidation of selected TrOCs and simultaneous flocculation of phosphates by ferrate was tested in batch experiments with secondary effluent from Berlin Ruhleben. The concentrations of carbamazepine (CBZ) and diclofenac were reduced by >90% with ferrate dosages of 6 mg/L as Fe. CBZ was transformed to 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one, which is known as the major product from the reaction of CBZ with ozone. In contrast to ozonation, no further transformation of this product was observed. The concentration of ibuprofen was not reduced by ferrate treatment. For efficient removal of 60-100 μg/L phosphate-P to values <20 μg/L, ferrate dosages of 3-4 mg/L as Fe were sufficient.