Purification of Cr(VI)-containing wastewater by membrane-free electrodeionization

ABSTRACT In this study, a membrane-free electrodeionization (MFEDI) technology was demonstrated first time for the removal of hexavalent chromium (Cr(VI))-containing wastewater. Two packing configurations, namely, layered semimixed packing MFEDI (LSMP-MFEDI), and fully mixed packing MFEDI (FMP-MFEDI), were comprehensively investigated for Cr(VI)-containing wastewater treatment. During the treatment stage, the treatment capacity of FMP-MFEDI (132 h) was twice that of LSMP-MFEDI (60 h), with the effluent conductivity under 1 μS/cm. The enhancement is primarily due to the initial adsorption of dichromate(Cr 2 O 7 2- ) by quaternary amine groups, which promotes the co-adsorption activity of tertiary amines. More importantly, during the electroregeneration stage, FMP-MFEDI (229.7 mg/L) exhibited higher regenerated average Cr(VI) concentrations than LSMP-MFEDI (170.5 mg/L), along with a reduced energy consumption (0.19 kWh/g for FMP-MFEDI, 0.25 kWh/g for LSMP-MFEDI) and an increased water recovery rates (95.6% for FMP-MFEDI, 94.1% for LSMP-MFEDI). Such an enhanced electroregeneration performance in FMP-MFEDI was because that the strong-base and weak-base anion-exchange resins fully interact to form a “contact face”, which comprises both tertiary and quaternary amine functional groups. The tertiary groups promoted the release of Cr 2 O 7 2- from the quaternary groups, thereby showing a synergistic effect in electro-releasing the adsorbed Cr 2 O 7 2- . This provides abundant localized ion-depletion regions, consequently enhancing the electroregeneration property.