Pre-coating of outside-inside capillary UF membranes with iron hydroxide particles to limit non-backwashable fouling during seawater algal blooms

Abstract

This research is structured on two hypotheses in which the first one is that pre-coating method using iron hydroxide particles in combination with ultrafiltration (UF) is able to control the non-backwashable (nBW) fouling in outside-inside UF membrane system caused by transparent exopolymer particles produced by marine algae species, Chaetoceros affinis. The initial assumption is that the success of the pre-coating method strongly depends on the uniform coverage of pre-coat material along the membrane surface that forms a protective layer. The second hypothesis is based on the presumption that a sequestering agent can avoid the growth of the iron hydroxide nanoparticles over time. Pre-coating experiments were performed with 6, 1, and 0.15 mg Fe3+/L coagulant equivalent dose to synthetic seawater spiked with algal organic matter to assess its effect to membrane backwashability, especially the nBW fouling development. The results showed that all of the applied dosages for pre-coating were able to reduce the nBW fouling rate. Based on the observations, coating with 1 mg Fe3+/L equivalent dose was the optimum dose to control the nBW fouling. It immediately stabilizes the fouling resistance from the first filtration cycle onwards. When a lower dose was applied, the stabilization occurred at lower rate. However, the success of pre-coating did not seem to be only attributed to a physical mechanism, (protective layer) but there is another mechanism that helps to control the nBW fouling. Results from SEM images supported this hypothesis by showing that the membrane surface was not fully covered by the iron hydroxide particles. It was an indication that there must be another mechanisms occurring in the pre-coating process.