Membrane fouling by nanofibres and organic contaminants – Mechanisms and mitigation via periodic cleaning strategies

Abstract

The fouling of water filtration membranes by nano/microplastic fragments can result in the decline of the water flux across membranes, however, the impact of other types of nano/microplastics on filtration processes, such as nano/micro fibres, has not been well characterised. The flexibility and high aspect ratio of nano/micro fibres could favor their adsorption onto filtration membranes, hence the presence of such fibres in water streams constitutes a potential threat to membrane units. In this work, the fouling of ultrafiltration membranes by a mixed system of poly(ethylene terephthalate) nanofibres and organic contaminants commonly found in textile industry effluents was investigated before mitigation strategies based on periodic gas scouring were developed. The nanofibres were prepared by electrospinning and cryo-sectioning using a freezing agent containing the organic contaminants of interest, poly(ethylene glycol) and poly(vinyl alcohol). Results showed that the organic contaminants induced a water flux decline across the membranes of 50% in less than an hour due to internal pore blocking whereas the adsorption of pure fibres as loose entanglements contributed to less than 10% of the permeation loss observed due to low pore coverage. Although applying periodic gas scouring was not efficient to dislodge the organic contaminants from the pores, this cleaning procedure removed up to 75% of the nanofibres from the surface of the membranes due to the shear forces generated by the gas bubbles. Hence, this study suggests that ultrafiltration membranes and gas scouring procedures could be successfully applied to control and limit the presence of fibres present in complex water streams.