## 2 Materials and Methods  
The alumina supports were extruded using two different Al\({}_{2}\)O\({}_{3}\) powders (based on the average particle size). The \(\alpha\)-Al\({}_{2}\)O\({}_{3}\) powder with small-sized particles (average particle size: 4.8 \(\mu\)m, AM-210, purchased from Sumitomo Chemical Co., Tokyo, Japan) is referred to as S-Al\({}_{2}\)O\({}_{3}\) and the one with large-sized particles (average particle size: 15.66 \(\mu\)m, 400 mesh, purchased from Kramer Industries, Inc., Piscataway, NJ, USA) is referred to as L-Al\({}_{2}\)O\({}_{3}\). These powders were first dry-mixed. Methylcellulose (Sigma-Aldrich, St. Louis, MI, USA) was used as a binder (10 wt%) and deionised (DI) water was used as a solvent (20 wt%); both were added to the powder mixture. The mixture was aged at room temperature for 48 h and extruded using a double-screw extruder (KTE-50S, Kosentech, Sungnam, Korea). The extruded alumina support layer had cylindrical-tube-type dimensions (outer diameter: 24 mm; length: 150 mm) and 30 inner holes (inner diameter: 2 mm). After extrusion, the specimens were dried at ambient temperature for 24 h. The dried specimens were calcined at 400 \({}^{\circ}\)C for 4 h to burn off the binder and then sintered at 1500 \({}^{\circ}\)C for 2 h.  
According to the composition shown in Table 1, alumina powder (avg. particle size: 0.27 \(\mu\)m, AKP-30, purchased from Sumitomo Chemical Co. Ltd., Tokyo, Japan) was ball-milled with 2-propanol (Sigma-Aldrich, St. Louis, MI, USA), DI water, and an organic binder (polyvinyl alcohol, M.W. 500, Junsei Chemical, Tokyo, Japan) to prepare the microfiltration membrane. Darvan-CN (M/S, R.T. Vanderbilt Co., Norwalk, CT, USA) was added as a dispersant. Next, multichannel tubular supports, masked from the outside, were dip-coated with a conventional tabletop dip-coater (EF-4300, E-flex, Bucheon, Korea) for 60 s at a withdrawal speed of 1 mm/s. After drying at room temperature for 24 h, the samples were sintered at 1300 \({}^{\circ}\)C for 1 h with a heating and cooling rate of 3 \({}^{\circ}\)C/min. Alumina microfiltration membranes were surface-modified using the SiO\({}_{2}\) sol-gel process, as described in our previous study [20; 21]. A mixture of ethanol/DI water was prepared; then, 0.1 M tetraethyl orthosilicate (TEOS) was dissolved in this mixture by stirring to obtain the SiO\({}_{2}\) sol solution. The solution's pH was adjusted to 9.0 by adding 1.0 M NH\({}_{4}\)OH. The pristine alumina microfiltration membranes were submerged in the SiO\({}_{2}\) sol solution at ambient temperature for 10 min. This process was conducted under a vacuum to form a uniform silica layer. Next, the membranes were washed with ethanol and dried in an oven at 100 \({}^{\circ}\)C. Finally, the SiO\({}_{2}\)-modified membranes were calcined at 200 \({}^{\circ}\)C for 6 h. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Slurry Composition**} \\ \hline
**Powder** & **Solvents** & **Binder** \\ \hline AKP-30 & H\({}_{2}\)O & IPA & PVA \\
8 wt\% & 57 wt\% & 33 wt\% & 2 wt\% \\ \hline Darvan-CN added as a dispersant. & & & \\ \end{tabular}
\end{table} 
Table 1: Slurry composition for dip-coating of alumina on multichannel cylindrical-tube-type support layer. Humic acid (HA) was used as a model foulant to analyse the fouling behaviour. The membrane fouling test was conducted in four steps. In step 1, a stable baseline flux (\(J_{0}\)) was obtained by the pure water permeation of the membranes for 2 h. In step 2, membrane fouling was observed by the continuous supply of HA (10 ppm solution, pH 6.5, Sigma-Aldrich, St. Louis, MI, USA) as a foulant for 1 h (\(J\)). In step 3, backwashing was conducted for 10 min with a sodium dodecyl sulphate (10 mM solution, pH 11, Sigma-Aldrich, St. Louis, MI, USA). In step 4, the membranes were again subjected to permeation with the DI water to obtain a stable flux (\(J_{1}\)). All tests were conducted at 25 \({}^{\circ}\)C and repeated three times.