Separation of saline oily wastewater by membrane distillation

Membrane distillation was used for the treatment of saline oily wastewaters collected from harbour deoiling installation. The turbidity of these wastewaters was in the range 63-87 NTU, salt concentration was 6-11 g/L and the oil content in the feed was below 40 mg/L. Two types of commercial polypropylene capillary membranes were applied for the process study. The intensive membrane fouling during the wastewater separation was observed. Modules rinsed with water removed the organic deposits formed. However, the CaCO3 scale was accumulated on the membrane surfaces during 1500 h of the process, resulting in a permeate flux decline by more than 40%. The initial yield of modules was recovered by membrane rinsing with 5 wt% HCl solution. The long-term studies demonstrated that the separated oily wastewaters did not cause wetting of the applied membrane. The degree of retention amounted to 98% for the inorganic compounds and more than 99% for the organic compounds.