Getting to the Root of Oily Water Separator Challenges

Screen Shot 2020-11-09 at 12.00.38 PMDischarging oil overboard illegally remains a concern for any vessel operator and almost every marine engineer is familiar with or has at least heard about the “magic pipe.” Oil discharges have resulted in significant fines and imprisonment, making the treatment of bilge water an essential part of any engine room operation. Annex 1 of MARPOL says that any direct discharge of oil or oily water mixture into the sea is prohibited. The regulation goes on to explain how an oily water mixture must be treated onboard  before being discharged.

If bilge water is required to be treated and oily water separators are required on all vessels >400 GT, what causes the system to malfunction?

Oily Water Separators (OWS) treat bilge water for compliance with MARPOL Annex 1, but many vessels cite challenges with keeping them in good working order, increasing the risk of a nightmare oily water discharge scenario. Many systems on the market rely on a centrifugal process and/or filters, both of which require significant long-term maintenance and investment. Centrifuges operate under high pressure and high temperature, both of which are harsh on the system components, including the oil content meter, and overtime the costly filters must be replaced

What breaks down OWS systems performance? Emulsified oils are one of the main causes of OWS’ not performing optimally, so frequently, in fact, that it is specifically noted in MARPOL regulation MEPC 107(49) that emulsions must be dealt with by the OWS. Emulsified oils are microscopic, yet can wreak havoc on mechanical parts and systems. Several of the most common OWS systems address emulsions by filtering out the emulsified oils. These filters must be incredibly fine to catch the microscopic emulsions, which are <100 nm in size, and thus easily clogged, resulting in improper function and even complete loss of effectiveness.

Chemistry provides a reliable solution

The Marinfloc CD OWS system deals with emulsions differently, with no fine filters or centrifugal components. Marinfloc CD systems are designed to address emulsions with flocculation, a process widely used in wastewater treatment on land. Flocculation is a chemical process in which a chemical agent is introduced to the wastewater (in this case the oily water on board) to suspend the target compound in the form of flakes (or flocks) on the surface. The target compound is suspended in a liquid, not dissolved, and the resulting “flocks” are easily removed, resulting in separation of the target compound from the wastewater. Flocculation is reliable and cost effective. The only consumable cost is the cost of the flocculant agents, which can be readily sourced in the marketplace. The average cost for 1,000 liters of treated bilgewater is approximately $3.50 USD. The Marinfloc CD system is certified by all major classification societies and has a certificate for 5 ppm by DNV-GL, well below the MARPOL requirement of 15ppm, while also meeting the lower levels set by most green initiatives.

For technical specs or more information on the chemical flocculation process, please contact To see how it works, check out this video.


11-10-2020 at 6:00