Bilge water separation by membrane distillation

Oily wastewaters constitute a dangerous pollution to the natural environment; hence, new methods of their treatment are constantly being developed, Bilge water generated on ships is an important pollutant for marine environment. In addition to oil, these wastewaters often contain a variety of harmful constituents, such as surfactants and heavy metals. In this work membrane distillation was used for the treatment of bilge water, resulting in almost the complete separation of pollutants. However, the organic matter present in bilge water can cause the wetting of hydrophobic membranes. Polypropylene membranes were applied and their good resistance for wetting was confirmed during long-term studies of separation of bilge water with different compositions. It was observed that a significant amount of precipitate containing CaCO3 was formed on the membrane surfaces as a result of feed heating, resulting in decline of the permeate flux. The initial module efficiency was restored using a periodic rinsing of the membranes with a diluted HCl solution. Tested bilge water contained a significant amount of SO4-2 ions (592-1388 mg/L). The formation of precipitate also containing CaSO4 was observed after the feed was concentrated to 2.72 g SO4-2/L. As a result of deposit precipitation, the concentration of SO4-2 ions was decreased to 1.52 g/L, which allowed to continue the bilge water separation process without the permeate flux decline.