Heterogenous fenton catalysis in filter media for effective removal of pharmaceuticals and personal care products in water

Abstract

The growing consumption and discharge of pharmaceuticals and personal care products (PPCPs) has become one of major global environmental concerns, owing to their eco-toxicity and persistence in the environment. Conventional water and wastewater treatment methods are incapable of effectively removing PPCPs micropollutants from water. The heterogeneous Fenton (H-Fenton) process has shown its promise as a solution for advanced oxidation and water purification. This study presents the innovative material approach that integrates H-Fenton catalysis with various filter media for the degradation of PPCPs during the filtration process. By embedding iron-molybdenum (Fe-Mo) bimetallic catalysts into montmorillonite-based ceramic membranes (MMTCM), alumina ceramic membranes (CM), and alumina ceramic beads (ACBeads), the research resolved challenges such as low catalytic efficiency, sluggish Fe(II) regeneration, and poor catalyst immobilization, of the H-Fenton process for efficient removal of PPCPs from water. First, Fe-Mo bimetal oxides (FeMoO) were added in montmorillonite to fabricate catalytic ceramic membrane FeMoMMTCM for continuous Fenton reactions during water filtration. The catalyst that uniformly distributed across the membrane provided abundant Fe(II) sites for enhanced H2O2 activation and ‧OH radical production. The FeMoMMTCM/H2O2 system achieved a 98.6% removal of naproxen (NPX) in 3.4 mins, greatly outperforming FeMoMMTCM filtration alone without H2O2 (17.5%) and FeMoO-less MMTCM/H2O2 (21.1%). The catalytic membrane filtration was able to remove 70% of organic pollutants from the actual secondary wastewater effluent. The superior performance is attributed to the synergistic Mo(VI)/Mo(IV) and Fe(II)/Fe(III) redox cycles for sustained Fenton reactions. Additionally, it also shows the economic feasibility of the approach with the use of low-cost montmorillonite and low-temperature sintering. Next, a commercial CM was coated with a hybrid Fe-Mo bimetal oxide catalyst to form the catalytic membrane FeMo/NM88B@CM for H-Fenton reaction. A catalytic layer (~24 µm thickness) was coated on the CM surface, providing numerous active sites for H2O2 activation. The FeMo/NM88B@CM/H2O2 system achieved 98.5% removal of moxifloxacin (MOX) in 3.1 mins, outperforming both FeMo/NM88B@CM filtration (16.8%) and CM/H2O2 system (16.2%). The system also performed exceptionally well in treatment of actual secondary effluent, removing more than 60% of residual organics while mitigating the membrane fouling problem. It is considered that H2O2-induced Mo(VI)/Mo(IV) cycle of the Fe-Mo bimetallic catalyst played a crucial role in driving the Fe(II)/Fe(III) redox cycle for continuous regeneration of Fe(II) and long-term H-Fenton oxidation of PPCPs in water. Lastly, a bimetallic catalyst of NH2-MIL-88B(Fe)/MoO3 was synthesized on the ACBeads surface to integrate catalytic Fenton oxidation and media filtration into a system for high-rate water treatment. The FeMo@ABs/H2O2 system achieved a remarkable 96.2% removal of bisphenol A (BPA), surpassing the 21.5% removal by FeMo@ACBeads filtration without H2O2 dosing and the 20.9% removal by bare ACBeads with H2O2 dosing. The superior catalytic performance is attributed to the FeMo bimetallic catalyst coated on ACBeads, where the active Mo(IV)/Mo(V) cycle facilitates the Fe(II)/Fe(III) cycle for Fe(II) regeneration and H-Fenton reactions. The study provides an approach of catalyst synthesis and immobilization on ACBeads and similar low-cost media to achieve continuous H-Fenton oxidation of PPCPs micropollutants during the low-cost filtration process for water purification.