Treatment of bilge water using a combination of ultrafiltration and reverse osmosis

The objective of this work was to investigate the possibility of bilge water treatment in the integrated ultrafiltration/reverse osmosis (UF/RO) system. The studies were carried out with a model oily wastewater and bilge water collected from a ship. The influence of transmembrane pressure on the permeate flux, degree of the retention of organic (including oil) and inorganic compounds was investigated. During the ultrafiltration process of bilge water the effect of feed concentration on the permeate flux and degree of oil retention was also studied. The studies on the two stage treatment of bilge water combining UF and RO have demonstrated a high effectiveness of purification. The permeate from the first stage of bilge water treatment had the oil content below 10 ppm and was free of suspended solids whereas almost all turbidity was removed. The second stage of the treatment resulted in the removal of TOC in more than 70% and in 90% of all cations examined (Na+, K+, Mg2+, Ca2+, Zn2+, Mn2+, Al3+, Li+), P2O5 and the sulphate anion. The obtained RO permeate was free of oil. The permeates obtained in the UF and RO processes comply with the regulations concerning the effluents discharged into the environment.