(555d) Improved Emulsion Breaking for Treatment of Bilge Water by Induced-Air Flotation

Disposal of bilge water from ship engine room has been one of the serious environmental issues the maritime industry today is concerned about. Emulsified oil-in-water poses problem in bilge water treatment because of the high stability of the emulsions causing difficulties in separation by conventional gravitational processes. Hence, an alternative technique to pre-treat emulsified bilge water from ship engine room was developed: induced-air flotation with poly(aluminium chloride) as destabilizing agent. The removal of oil and grease and turbidity from synthetic bilge water samples by this technique was carried out with test fluid prepared by mixing industrial diesel oil, heavy fuel oil, surfactant, iron oxide and distilled water. The pH of the test fluid was adjusted to 9, the typical pH of bilge water, to stabilize the emulsion. Experiments were carried out in an induced-air flotation system to evaluate the individual and combined effects of PAC dosage, air flow rate, and settling time in removal efficiencies for oil and grease and supernatant turbidity. It was observed that the PAC concentration, compared to air flow rate and settling time, has a greater influence on the removal efficiency. Although different treatment conditions were used, the results showed excellent removal efficiencies (close to 99%) attained at 0.3 ml/L PAC dosage, 9 L/min air flow rate and 40 min settling time. Using this set of conditions, the treated water had a residual oil and grease concentration that was less than 10 ppm, a value which satisfies current maritime regulations. The PAC could not be too high, otherwise, the water tend to become cloudy, resulting in poor removal efficiency. It is believed that this kind of improved emulsion breaking appears to have a great potential as pre-treatment for treating emulsified bilge water on board.