Revealing key meso-particles responsible for irreversible membrane fouling in an integrated oxidation-coagulation ultrafiltration system: Fouling behavior and interfacial interaction mechanism

Abstract

This study applied a ferrate in-situ oxidation-coagulation ultrafiltration integrated system in drinking water treatment, illustrating the influence of meso-particles on membrane fouling behavior by oxidation-coagulation regulating. Under neutral conditions, the meso-particles between 20 and 100 nm were the mainly components at initial oxidation phase. Subsequently small molecules gathered to meso-particles of 200–500 nm under the flocculation, and 40 % of micro-particles aggregates were detected finally. According to the statistical correlation between multiscale particles and membrane flux and resistance, wherein meso-particle especially in range of 20–100 nm principally contributed to the irreversible fouling while the correlation coefficients above 0.9, and reversible fouling related to the synergy of meso- and micro-particles. Additionally, the fouling behavior of meso-particles on the membrane surface and the structural evolution of the fouling layer were illustrated based on the interfacial interaction, UV–vis reflectance spectroscopy and molecular dynamics simulation. The changes in hydrophilicity and charge of the meso-particle (20–100 nm) increased the attractive interaction with the membrane, causing severe membrane fouling. As flocculation progressed, the polynuclear Fe-hydroxide interacted with HA molecular fragments, and aggregated to meso-particles in range of 200–500 nm, which had smaller molecular gap and more tight structure than micro-particle (500–1000 nm), due to the HA molecular fragments were more strongly bound on the polynuclear Fe-hydroxide compared to iron hydroxide cluster. The stable and compact structure induced the meso-particles deposited on membrane surface and hardly be physically cleaned. The investigation of meso-particle on membrane fouling was provided new insight into the membrane separation process.