Abstract
The health risk of organic micro pollutants in water is yet to be comprehensively established. However, the persistence of these pollutants in the environment as a result of continuous discharge even at trace concentrations is considered to pose major environmental concerns. Advance treatment methods such as membrane-assisted processes (MAPs) are potential technologies capable of removing a wide range of these organic micropollutants (OMPs) detected in water. In this study, investigation of surface-coated ultrafiltration (UF) poly(vinylidene fluoride) (PVDF) hollow fibre membrane for the removal of organic micropollutants (OMPs) in water was performed. Coating of PVDF membranes with poly(1-phenylethene-1,2-diyl)/polystyrene and pluronics F68 solutions through physical adsorption was carried out in two modes: “dipping” and “spraying”. Surface characterization of coated membranes showed that the coating layer potentially influenced the surface properties suitable for improved solute-membrane interaction. Characterization of the pore size and distribution through Scanning electron microscopy (SEM) images analysis showed that polystyrene coating in sprayed and dipped coating procedure, exhibited more reduction in pore size (19−31%) and closer pore size distribution than the pluronics F68 dip coating (6%). The average roughness (Ra) and maximum peak-to-valley distance (Rmax) measured using the Atomic Force microscopy (AFM) recorded more roughness and irregularity in surface topography in the polystyrene coated membranes compared to the pluronics F68 coating with the dipped polystyrene coating method attaining more roughness (Ra – 0.393 µm). Contact Angle (CA) measurements showed that the dipped Polystyrene coated membrane achieved the highest increase in hydrophobicity (29%) while the dipped pluronics F68 coating achieved a 10% increase. Correlation between the changes in surface roughness and hydrophobicity was evident in the study. Generally, the polystyrene material impacted the membrane surface the most, and the dipped coating procedure recorded the highest surface modification impacts. The performances of the coated membranes in the rejection of the model organic micropollutants, caffeine (hydrophilic) and carbamazepine (hydrophobic) spiked (as single and mixed components) in various water matrices i.e. deionized water, surface water and synthetic wastewater (at concentration range of 300 -1000 μg/L) correlated with the coating materials and methods used. The dip-coated membranes using polystyrene material, achieved better removal of recalcitrant hydrophobic carbamazepine compared to the spray-coated membrane in deionised water, but not in other water matrices. Whereas for both methods of coating, removal of caffeine was relatively insignificant in deionised water but reasonably higher in surface water and synthetic wastewater. From these results, it is inferred that hydrophobic interactions and size exclusion might be the major removal mechanisms involved in rejection by the coated membranes and the colloidal and particulate matter in surface water and fouling in membrane bioreactor system facilitated sorption removal mechanism. The membrane coating enhanced reduction of the pore size, decreasing the membrane permeability and providing more sites for possible solute-membrane interactions. it is demonstrated that physical adsorption of functional polymers is a simple and efficient way to modify the surface properties of polymeric membranes for water filtration application.