Evaluation of structural/performance variation between α-Al₂O₃ and polyvinylidene fluoride membranes under long-term clean-in-place treatment used for water treatment

The objective of this study was to compare the structural stabilities of alumina (α-Al₂O₃) and polyvinylidene fluoride (PVDF) membranes against harsh clean in place (CIP) and fouling conditions. Fouling propagation and flux recovery were examined for five CIP cycles by using an acid and an oxidant as cleaning chemicals. Furthermore, variations in the surface characteristics of pristine, fouled, and chemically cleaned α-Al₂O₃ and PVDF membranes were examined by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle measurement, and Fourier transform infrared spectroscopy (FTIR), and the increase in the normalized pressure and variation in rejection efficacy of foulants were evaluated. Additionally, the fouling propensity and reversibility were determined on the basis of fouling indices, the resistance-in-series model, and total fouling analysis. The results showed that the α-Al₂O₃ membrane was less susceptible to fouling compared with the PVDF membrane and exhibited a less structural deterioration. Moreover, foulant deposition/adsorption on the ceramic membrane was confined to the surface and could be efficiently removed through hydraulic cleaning. Owing to less variation in its hydrophilic nature and electrostatic attraction, the filtration pressure increase was less compared with that for the PVDF membrane. In particular, α-Al₂O₃ showed 12 % lower residual fouling, a high and stable rejection efficiency, recoverable fouling resistance of 61.17 %–66.07 %, a quantitatively unchanged irreversible fouling resistance, and relative decreases from 25.49 %–16.24 % at the end of the experiment.