Effects of Pore Size and Surface Modification on the Alumina Microfiltration Membrane Fouling in MBR with Backwashing

Abstract

The effects of pore size and surface modification on the fouling and cleaning properties in membrane bioreactor (MBR) with backwashing were studied using porous alumina microfiltration membranes with pore sizes of 0.2, 0.5, 0.7, and 1.5 μm. The surface modifications were conducted using silane coupling agents, 3-Aminopropyltrimethoxysilane (APTMS) for a positively charged surface, Chlorotrimethylsilane (TMS) for a weak hydrophobic surface, and Trichlorooctadecylsilane (ODS) for the strong hydrophobic surface. The two-stage fouling behaviors were typically observed and elucidated by shifting the fouling mechanism from adsorption to cake formation during operation. The fouling properties were characterized by the filtration resistance of cake layer Rc, the filtration resistance caused by adsorption Ra, which were determined from the difference in the filtration resistance for the filtration direction and the backwash direction, and Transition Point (TP) which divides the fouling stages. From the effect of pore size, the membrane having 0.2 μm, which was the smallest pore size in this study, showed the highest anti-fouling performance. This result was elucidated by pore blocking caused by particulate foulants having particle sizes close to the membrane pore size. The effect of the surface modification was mainly found in the adsorption properties of foulants. The TMS-modified membrane, which had a weak hydrophobic pore surface, showed the highest anti-fouling performance, which would be provided by blocking the further accumulation of foulants by the adsorption layer formed in the initial stage of the operation. From the cleaning properties of the fouled membranes by physical and chemical cleanings, the unmodified membrane, which has a hydrophilic surface, showed the best cleaning properties. The decrease in the absolute value of the zeta potential due to fouling was observed as a general trend and the adsorption of foulants in MBR was one of the causes of the decrease.

Keywords

• MBR
• Filtration resistance
• Zeta potential
• Surface modification
• Fouling