Characterization of electrospun polystyrene membrane for treatment of biodiesel's water-washing effluent using atomic force microscopy

The application of atomic force microscopy (AFM) for characterization of electrospun microporous membranes was assessed. The surface roughness, pore size and its distribution, nodule size as well as fiber diameter were analyzed for an electrospun polystyrene membrane before (M1) and after surface modification via contact-heating (CH) method (M2). It was found that thermal modification has improved the overall surface morphology and topography, exhibiting a decrease in mean pore size and nodule size, lowering roughness parameters, which led to more uniform and circular pore geometry, and higher hydrophobicity. As a result, separation performance was improved when the membranes were used for the treatment of biodiesel's wash water effluent. It was also observed that both membranes were effective in treating the highly polluting saponified wastewater. In particular, the application of M1 resulted in the reduction rates of 58, 26, 92, 95 and 50%, respectively, for COD, BOD, TS, TDS and TSS. More promising reduction rates were achieved with M2, where those of COD, BOD, TS, TDS and TSS were at 75%, 55%, 92%, 96% and 30%, respectively. The multi-objective separation mechanism of electrospun membranes (screening, depth filtration and adsorption), could be the cause of their superior separation performance.