Biological membrane fouling control with the integrated and separated processes of MIEX and UF

Abstract

In this work, three different processes including ultrafiltration (UF), separated magnetic ion exchange resin (MIEX)-UF and integrated MIEX/UF were employed to investigate the introduction of MIEX on biological membrane fouling control in synthetic bacteria solutions. Independent UF was firstly performed using extracellular polymeric substances (EPS)- free live bacteria, live bacteria, or dead bacteria as feed, and the operation time when TMP reached 35 kPa was 105, 75 or 55 min respectively. The most severe fouling with dead bacteria was attributed to EPS and some endocellular components which favored the adhesion of bacteria on membrane surface. The introduction of MIEX helped to alleviate membrane fouling, and the alleviation effect for EPS-free live bacteria feed was the least significant. It was inferred that the organic substances could be firstly adsorbed by the anion-exchange resin and then promote the adhesion of bacteria. This was supported by direct adsorption tests with MIEX where the removal efficiencies followed the order of dead bacteria > live bacteria > EPS-free live bacteria. The integrated process worked better than the separated one in both single cycle and multi cycle filtration tests, and this was mainly attributed to the dynamic resin layer, which worked in several manners, including acting as a physical barrier, enhancing adsorption/adhesion of foulants and suppressing reproduction of the bacteria. Regeneration of MIEX was also conducted with aqueous NaCl or NaHCO3. The removal efficiency was much more stable in the latter case, which could still reach 33% after five cycles (~83% of the initial capacity).