Performance of a ceramic ultrafiltration membrane system in pretreatment to seawater desalination

Pretreatment to reverse osmosis (RO) seawater desalination historically has been achieved using organic (polymer) ultra- and micro-filter (UF/MF) membranes. Newly developed inorganic (ceramic) membranes offer unique advantages over the currently employed membranes, and were recently introduced for the purpose. In this work, we investigate the performance of a zirconium dioxide ceramic membrane with 0.05 μm pore diameter to clarify raw seawater under different operating conditions. The influences of cross-flow velocity (2.7–4.9 m s−1), temperature (15–55 °C), transmembrane pressure (TMP) 0.1–0.2 MPa, and seawater pH (5.5–9.5) on permeate flux and rejection were assessed. The results show that the zirconium dioxide membrane at cross-flow velocity of 3.7–4.2 m s−1, TMP of 0.14–0.18 MPa, temperature of 25–30 °C and seawater pH of 8.0–9.0 exhibited a high flux of 420–450 L m−2 h−1 with turbidity and CODMn rejection of 99.0–99.5% and 32–35%, respectively. This work also introduces a new experimental procedure to determine different filtration resistance (Rm, Rsads, Rpads, Rcp, Rpb and Rcr) components, which helps the analysis of performance characteristics and the better understanding of interactions between the membrane and foulants. The present results show that the effect of concentration polarization was dominant in the ultrafiltration of raw seawater, and various fouling components contribute to the total in the order of Rcp > Rsr > Rm > Rsads > Rpads > Rirr. Further, reversible fouling was much more significant than irreversible fouling. The experimental method also showed interrelation between the reversible and irreversible resistances, whereby part of Rsr is transformed into Rirr within 20 min of filtration. The results of this study indicate that zirconium dioxide ultrafiltration pretreatment before RO desalination can achieve consistent permeate quality and low fouling potential at high permeate fluxes.