Novel ultrafiltration flat sheet mixed matrix membranes for arsenic and lead removal and fouling mitigation

Abstract

The aim of this work is to develop novel, efficient and environmental friendly water treatment technology with low cost and low energy consumption for adsorptive removal of selected heavy metals such as arsenic (As) and lead (Pb) from aqueous system as well as membrane fouling mitigation. In order to overcome the shortages of adsorption and membrane technology, porous asymmetric nanocomposite flat sheet ultrafiltration (UF) mixed matrix membranes (MMMs) incorporated with hydrophilic metal oxide nanoparticle adsorbents were prepared through the phase inversion process. Prior to the fabrication and characterization of MMMs, metal oxide nanoparticles, i.e. Fe-Mn binary oxide (FMBO) with high As adsorption capacity and hydrous manganese dioxide (HMO) with high Pb adsorption capacity were synthesized and used as inorganic fillers and adsorbents in flat sheet polyethersulfone (PES)-based MMMs. The effects of impregnating inorganic metal oxide nanoparticles on the PES-based MMMs morphology, pure water flux, adsorption capacity, surface pattern formation and membrane fouling mitigation were studied by varying the loading of the metal oxide nanoparticles. Both flat sheet PES/HMO and PES/FMBO MMMs were characterized using scanning electron microscope (SEM), contact angle goniometer, atomic force microscope (AFM) and Fourier transforms infrared (FTIR) spectrometer. The best performing membranes prepared from the FMBO/PES ratio of 1.5: 1 demonstrated the pure water flux as high as 94.6 L/m2.h.bar and maximum As(III) uptake capacity of around 73.5 mg/g. On the other hand the experimental results showed that with increasing HMO:PES weight ratio from zero to 2.0 times, the membrane water flux was increased from 39.4 to 573.2 L/m2.hr.bar (more than 14 times) and the optimized membranes fabricated from the HMO/PES ratio of 2.0 : 1 showed the highest Pb(II) adsorption capacity i.e. 204.1 mg/g. The continuous UF experiments showed that the optimized MMMs could achieve promising results by removing selected heavy metals from water samples by producing permeate of high quality to meet the maximum contaminant As level set by World Health Organization (WHO), i.e.<10 µg/L As and <15 µg/L Pb. Furthermore, the adsorptive performance of MMMs could be easily regenerated using alkaline and acidic solution. This work also contributed to the novel membrane design with present simple method to control nano-sized pattern formation (alignment of macromolecular nodules) on the polymeric membrane surface. Unlike the lithographical method, the proposed method allows the control of smaller nano-sized patterns of a large membrane area at a lower cost and further shows promising results in reducing membrane fouling due to the protein adsorption. Antifouling property of PES membrane was improved with increasing HMO:PES weight ratio from zero to 1.5 and most importantly, the initial pure water flux of the membranes could be nearly completely recovered by a simple deionized water washing.