Purification of bilge water by hybrid ultrafiltration and photocatalytic processes

Investigations have been performed on the purification of bilge water by a combination of ultrafiltration and photocatalytic processes. The separation of oil from bilge water obtained from Szczecin-Swinoujscie harbour was performed on a laboratory-scale ultrafiltration pilot plant with tubular membranes made from poly(vinyl chloride) (PVC), polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF). The examined membranes with MWCO of 70 kD for PVC and PAN and 100 kD for PVDF produced a permeate with an oil content less than 15 ppm. Rejection of chemical oxygen demand (COD) was in the range 92-96% for the ultrafiltration treatment. The permeate is generally of acceptable quality for direct discharge into the Baltic Sea district in accordance with present legislation. Further treatment of UF permeate has been performed by heterogeneous photocatalytic oxidation in order to remove the residual oil. The photocatalytic process was carried out using titanium dioxide based catalyst. The complete decomposition of oil was achieved after 2 h of UV illumination using a K-TiO2 photocatalyst with content amounting to 0.8 g/dm(3) and after 3 h of UV illumination using 0.8 g/dm3 of KOH/TiO2 photocatalyst. The photocatalytic process was found to be very effective for the permeate reclamation. (C) 1998 Elsevier Science B.V. All rights reserved.