Persulfate enhanced ciprofloxacin removal from water by laser-induced graphene-based electroconductive ultrafiltration membrane†

Abstract

The ineffective removal of emerging pollutants by conventional treatment plants has necessitated the use of advanced treatment techniques such as electroconductive membranes. High-pressure-driven nanofiltration (NF) and reverse osmosis (RO) can provide ∼50–99% removal of emerging contaminants but are energy-extensive processes, require pre-disposal treatment, and are more susceptible to fouling. On the other hand, microfiltration (MF)/ultrafiltration (UF) cannot remove emerging contaminants and shows only minor removal. Electrochemical interaction with charged surfaces and incorporation of an advanced oxidation process (AOP) can help in removing emerging contaminants. Here, we have shown electroconductive laser-induced graphene-based filters and UF electroconductive membranes for emerging contaminant ciprofloxacin (CIP) removal with the combination of persulfate-AOP in crossflow filtration mode. The effects of applied voltages, initial solution pH, and the addition of different persulfate and ferrous sulfate concentrations were investigated for CIP removal. In all crossflow filtration tests at 2.5 V, ∼90% CIP removal in the permeate was observed, which is comparable to that of conventional NF. The synergistic effect of CIP-electroconductive membrane interaction, regeneration of ferrous ions at the cathode, and generation of reactive radicals are the major reasons for the removal of CIP. The use of CIP-spiked synthetic wastewater showed comparable removal even at the lower concentration of 500 μg L⁻¹. Degradation pathways for the electro-persulfate–ferrous and electro-persulfate systems were also proposed with the first time reporting of a by-product with m/z = 160. The study results show that the synergistic effect of electroconductive membrane separation and AOPs can help tackle emerging contaminants, including pharmaceuticals.