Poly(vinylidene fluoride) membrane supported nano zero-valent iron for metronidazole removal: Influences of calcium and bicarbonate ions

• Effects of Ca2+ and HCO3− on metronidazole removal by PSN were probed.
• Differing impacts of Ca2+ and HCO3− under varying conditions were depicted.
• Results proved the feasibility of using PSN for pretreating antibiotic wastewaters.

This study examined the influences of calcium and bicarbonate ions on the performance of poly(vinylidene fluoride)-supported nano zero-valent iron (PSN) for metronidazole (MNZ) removal. The presence of Ca2+ and HCO3−, whether in their individual or collective forms with low or high levels, exerted differing degrees of inhibitions to MNZ removal by PSN, but these inhibitions were insignificant. Adding some other inorganic ions (i.e., NH4+, SO42−, Mg2+, PO43−, and NO3−) into MNZ solutions also caused suppressive effects and their inhibitive ability generally followed the order: NH4+ > SO42− > Mg2+ > PO43− > NO3−. Humic acid (HA) was found to introduce relatively larger inhibition to MNZ removal by PSN, whether in its single presence in MNZ solutions or in its coexistence forms with Ca2+ or HCO3− in MNZ solutions. The interaction of Ca2+, HCO3− and HA with iron (oxy)hydroxides on PSN surface might contribute to these adverse impacts on PSN‒MNZ reaction system. It was noteworthy that, even with 20 mg/L HA in MNZ solutions where high levels of Ca2+ and HCO3− were introduced, the MNZ removal by PSN was still above 73.37%. Results reported herein indicated the potential of using PSN to pretreat antibiotic wastewaters in complex environmental conditions.