Exhaustive depletion of recalcitrant chromium fractions in a real wastewater

This paper reports investigations on electrochemical removal of Cr(III) from a real wastewater sample from a 4 × 104 m3 d−1 purification plant located in the leather district of Arzignano (Italy). A crucial point evaluated is the relation between Cr(III) abatement and the reduction of total organic carbon and chemical oxygen demand. Here we present the results of different abatement approaches including advanced oxidation processes (AOPs) and electrocoagulation applied separately or in series. Neither of these methods show satisfactory results when applied alone. In particular, AOPs are completely inefficient owing to the formation of Cr(VI), which is more soluble than Cr(III). Almost total depletion (99.7%) of the recalcitrant fraction of Cr(III) is successfully achieved by combining ozonization and electrocoagulation processes. The results are consistent with the abatement of Cr in its hexavalent form by fast precipitation as NH4Fe(CrO4)2.