6.6 Coalescing bed-type oily water separators This design of separator produces an effluent quality of better than 20 mg/litre. Figures of 15 mg/litre with 25% oil concentration and 6 mg/litre with 5%0 oil concentration have been recorded during tests on board ship When fitted with a clean water discharge valve which closes when the oil discharge valves are open, the separator can function adequately when handling 100% oil as for instance when the bilge water has been stripped off and only the oil is left6.6 Coalescing bed-type oily water separators • This design of separator produces an effluent quality of better than 20 mg/litre. Figures of 15 mg/litre with 25% oil concentration and 6 mg/litre with 5% oil concentration have been recorded during tests on board ship. • When fitted with a clean water discharge valve which closes when the oil discharge valves are open, the separator can function adequately when handling 100% oil as for instance when the bilge water has been stripped off and only the oil is left