Water that is cleared for discharge from a marine vessel is one that contains less than 15 parts per million of oil. The oil water separator system uses the gravity system which can achieve 100 parts per million. It also uses some form of filter in order to further break down the parts per million.
A complete unit of oil water separator system is first filled with clean water. Next, the oil water mixture is then pumped via a separator inlet pipe towards the coarse separating unit or compartment. In this section, the oil which has a lower density will separate and rise and be contained in the oil collection space. The remaining oil and water mixture will now flow down to the fine separating compartment and then will move slowly in between the catch plates. More oil will then separate from the underside of the catch plates and will travel outwards until it will feel free to rise to the oil collecting area. The water which is almost 100 percent oil free will then pass into the central pipe and will leave the separator compartment. The purity of the oil and water mixture is at 100 parts per million. An automatic valve will then release the separated oil towards a storage tank. Air will then be released from unit via a vent valve. In the upper as well as the lower parts of the separator unit, electric and steam heating coils are provided. The type of heating coil will be dependent on the type of oil that will be separated from water. Where you will ensure greater purity from the water, it will have to pass through a filter unit.
The untreated wastewater will then flow in turn to two filter stages and the oil will be removed as it passes to some oil collecting spaces. The first stage of the filter process will remove the physical impurities present in the mixture and will then promote a fine separation of the oily mixture. The next stage of filter will use coalesce insets in order to achieve a final de-oiling of the substance. The method of coalescence refers to the breakdown of surface tension on the oil droplets found in the oil and water mixture which causes these to join and increase in size. The oil collected in the collecting area is then drained separately, usually once a week. The filter inserts on the other hand will require changing from time to time. Its useful life is usually dependent on the operating conditions inside the vessel.