Water treatment intensification using a monophasic hybrid process coupling nanofiltration and ozone/hydrogen peroxide advanced oxidation

Abstract

This study assesses the feasibility of designing a hybrid ozonation / nanofiltration membrane process that can simultaneously oxidize and reject contaminants while exhibiting reduced membrane fouling. An innovative monophasic configuration, in which a pre-ozonated water was mixed at the membrane cell inlet to the water to be treated doped with H2O2 (at equimolar concentrations of H2O2 and O3), was implemented, allowing to avoid an ozone-enriched gas flow in the membrane cell. Thus, two commercial polymer membranes, NP10 (polyethersulfone) and NF270 (polyamide), were assessed in a cross-flow configuration despite their low-ozone compatibility compared with ceramic membranes. Ozone removal yields>90% were obtained whatever the studied water matrix. Fast ozone decomposition initiation reactions with H2O2 and with some moieties of the natural organic matter were responsible for a low ozone lifetime in the liquid bulk, allowing to protect the membranes from ozone and radicals. Deethylatrazine (DEA) was used as a radical tracer, allowing to determine Rct values with orders of magnitude of 10-6 and 10-7 in drinking water and a river water sample, respectively. The concentrations of two pharmaceuticals, carbamazepine and sulfamethoxazole, in the permeate and the retentate were lower than the detection limit in drinking water when the PES membrane was tested. During treatment of the river water sample, membrane fouling dropped by a factor two while there was no alteration of both the PES and PA membranes. Finally, thanks to synergistic effects induced by contaminant oxidation and rejection, dissolved organic content and DEA were both removed at around 70% when PA membrane, exhibiting a tighter microstructure than PES, was used.