Purpose: Type approval of an oily water separator/ bilge separator is the process by which a recognised authority (flag Administration, IMO/classification) tests and approves a particular model-typical of oil filtering equipment to confirm it meets the MARPOL Annex I and MEPC performance criteria (i.e. discharging effluent containing less than 15 ppm oil-in-water). It permits only approved models to be installed and used on ships, ensuring that the vessel's oily water discharge complies with the discharge standards and that the management/monitoring arrangement is effective.

Criteria (MEPC 107(49), and previously MEPC 60(33), the revised guidelines):

• The system (separator + 15 ppm filter + oil content monitor/alarm/automatic stopping) must achieve the specified output effluent quality (oil content not exceeding 15 ppm and, where it is the approved type, automatic control).
• It must be tested with representative emulsions/bilge water and demonstrate satisfactory performance over the required flow rates, in the appropriate temperature/viscosity range, and after dosing.
• It must be robust, not cause coagulation issues, and its parts are standardised and maintainable; the system must shut down/divert automatically when the oil content exceeds 15 ppm (the automatic stopping device/valve and the monitoring/reco have to respond promptly), and produce an alarm.
• The separated oil must be manageable, and the system must not allow unapproved bypasses; it must be reliably connected and suitable for the service.
• The 15 ppm monitor/alarm/recorder (if fitted) also requires type approval so the discharge is monitored and recorded.

Why it is important: Only type-approved equipment meets MARPOL, so ships can legally discharge treated oily water (subject to the required distance, discharge conditions and record in the Oil Record Book). Type approval ensures the equipment used in the fleet is effective, thereby preventing operational pollution and providing a uniform standard that PSC can verify; it also satisfies the flag/authority's requirements for the IOPPC and the discharge within the 15 ppm rule.

MEPC 60(33) (1992) was an earlier guideline for approval of OWS/15 ppm equipment; it set basic requirements that the processed effluent contain less than 15 ppm and that the separator be tested on shore with the appropriate test program - the first approach required the oil content to be less than 15 ppm, with a specific test method, but limitations:

• It used a defined reference oil and standard test oil; performance variables (emulsion type, temperature, dosing) were not fully covered; and it relied on a single set of conditions.
• It did not effectively control systems that could be bypassed or that relied on gravity separation only.

MEPC 107(49) (2003/2004) updated and enhanced the requirements, introducing:

• A more rigorous test programme: the separator must be tested with different oil-in-water emulsions (stable emulsions), at several flow rates and temperatures, and pass with an oil content limit under 15 ppm; the automatic stopping device/alarm/valve performance is verified.
• A 5 ppm "alarm" or stricter requirement for the discharge (MEPC 107 requires the OWS to stop/divert automatically when the oil content exceeds 15 ppm; the 15ppm monitor/alarm/recorder), and it tightened the requirement so the equipment cannot be easily manipulated.
• Requirement for the automatic stopping unit and the oil content monitor/ alarm system to be type-approved together, and the whole combination tested.
• The need for the separator to be tested and the component (filters) to be certified; the revised guideline increased the reliability and the efficacy of the 15 ppm discharge, and required the recording and automatic operation so that discharges meet the Annex I discharge criteria.
• It also tightened the definition of the oil content monitor, the alarm, and the auto-stop, which operate on the <15 ppm and <5 ppm (for some) to enforce compliance.

In summary, MEPC 107(49) imposed a more stringent, repeatable and realistic test (multiple emulsified/dosed bilge water types, temperature/flow), required automatic stopping and better monitoring/teles with an alarm + recorder, reducing the risk of discharging over 15 ppm and ensuring verifiable compliance at port inspections.