Oily Water Separator Survey

Hi Guys

My name is Gavin, I’m currently completing a Master of Applied Science (Marine Engineering) with the University of Tasmania, Australia. As part of my course, I’m carrying out a research project that analyses the performance of oily water separators (OWS) across the maritime industry. The aim of the research is to find out if poorly designed supporting systems are negatively effecting OWS performance. To determine this, I’ve created a 5-10 minute survey aimed at the people who operate these systems (i.e. seagoing engineers). I’d like to get as many engineers as possible to take the survey, so i thought i’d post a link to the survey on this forum, if allowed. The survey itself will provide information that will rank current OWS types against other provided technical data. This information should then reveal ways of improving OWS system design.

The inspiration behind my research has come from my time spent working as a marine engineer for the last 7 years, mostly in the Oil & Gas industry. During this time, I’ve experienced a number of OWS systems that were poorly designed, sometimes making them almost unusable. This in turn placed undue pressure on the engineers that operated them. For the majority of these cases, slight changes to the system during installation would have prevented these issues.

The survey is completely anonymous and no personal information is taken or requested. My target audience is seagoing engineers, of which I need a minimum of 300 responses to give this project weight. If any engineers on here have a spare 10 minutes to complete the survey it would really be appreciated. The more industry professionals that take the survey, the more accurate the research will be, which will hopefully lead to less stress for the people that use these systems. Whenever we hear about OWS violations, it’s usually the seafarers that are blamed. The survey has the potential to shed light on what the actual issues are.

Link to the survey – https://www.surveymonkey.com/r/M2LLFB5

If you have any questions or need clarification on anything, please feel free to ask me here or by emailing me at gavinh@utas.edu.au.

Here’s a link to an article that also explains the survey - https://www.maritimeprofessional.com/news/improving-oily-water-separators-357052

Thanks for reading!


OK, i took the survey … all 84 questions … (not really) they were good questions and no motive other than ows so kudos to gavin’s effort.
I don’t know that 300 engineers are going to do this but he did have some good questions, the one on what sort of tank you’re pulling from sometimes threw me.
A lot of us will shun something like this but I’d bet if more G captain people responded to some of the better surveys like this one it may affect the kind of readership and quantity of readers attracted to our forum.
The other response of course was …""don’t know just waited till mid ocean and pumped overboard on the mid-watch!! ha hahha


Agree @jimrr. This seems like a worthwhile subject matter. Good of you to bump it as only 9 survey takers so far. I’m sure there are more in this community who have some input to offer and people generally have some time on their hands right now.

TBH I had a difficult time choosing a system type I’ve used that I felt was the “best”. I’ve found them all to be somewhat mediocre.

I think there are a few drivers for this, but the primary one besides OWS equipment design is engine room piping design philosophy. Everyone knows OWS run better and longer between cleaning when they are having to process less oil to begin with. Having proper drain segregation so that equipment containing oil is bunded with either pluggable drains for full containment, or drains leading to a waste oil tank rather than draining to the bilge. Even additional containment areas under equip like engines so that oil/fuel leaks from crankcase doors and fuel galleries drain to waste oil tanks, but water leaks/drains from intercoolers and JW pumps drain to bilge water tanks. A clean bilge leads to a clean bilge water tank leads to an efficiently running OWS.

Tank design can help as well, with bilge settling tank decanting to a second tank for OWS suction. Where I’ve seen the most opportunity for contamination is in decanting water from a waste oil tank into the bilge settling tank. This is done obviously to reduce the amount of waste oil/contaminated water that has to be offloaded at cost to shore. This can usually be avoided best by the above mentioned drain segregation in the first place.

Final note on OWS design, in my experience most OWS are rated for a similar throughput gal/hr. I’d rather see a larger, more robust, easier to clean/flush unit even if it has a low throughput. Equipment running properly and efficiently gets used. Equipment requiring constant maintenance and still not running efficiently is more susceptible to getting bypassed.


I took the survey. Hope the input helps.

1 Like

well, doing ANYTHING with that stuff is not desirable, even for a machine! but I think the easiest way to different results is to heat the input. water doesn’t change much with temp. increase but oil sure does. (in a ows)
Otherwise, like I say, keep the thing clean, keep the contaminates out of the engine room and let it do it’s work …(clean it a lot & use HOT water to flush it) Otherwise, i don’t see much on the horizon changing it for now.

1 Like

Took the survey. I think the most effective change that could be implemented is getting rid of the ridiculous 15 ppm limit and going to a volume based regulation that is more reasonable and effective. A small amount of water at 500 ppm is reasonable and wouldn’t cause any environmental issues. The current limit basically invites bypassing, as has been proven over and over again around the world.

1 Like

Wouldn’t work for ocean going ships as the main engine air cooler can pull tons (literally) of water out of the charge air per day. This water is virtually pure but has to be processed like any other water produced in the engine room.

Perhaps an either/or compliance option? I don’t see why your idea shouldn’t be an allowable option. The deck Dept on tankers is allowed up to 50ppm (IIRC) and there’s other stipulations regarding ship’s speed, etc. That shit looks like a chocolate milkshake going over the side so if that’s ok with the USCG, then there should be some room for compromise regarding ER limits.

Well, that would be an example of another change that could be made. That water should be able to be contained and pumped overboard unprocessed.
The intent of the law (no more giant oil slicks and environmental damage) should be the end goal. 15 PPM makes that a lot harder to accomplish. So, the equipment gets bypassed and more damage results than if the limit was just set at a level that makes the engineering easier.
Volume wise, most oil and gas boats could keep under a reasonable limit especially with good engine room design.

Be glad you haven’t had to try and meet a 5 ppm limit yet!!!

On another note, has anyone had any experience (good/bad/otherwise) with centrifugal OWS? I haven’t actually operated one myself and was always curious. I always assumed you’d be dealing with too many potential different specific gravities with the various oil weights for it to be effective?

I’ve used them a couple of times. We would circulate the bilge through the OWS for a few days prior to discharging overboard to remove as much oil as possible, and by doing this we could consistently get the levels down to 0-1ppm. Maintenance load was no more than a normal LO purifier.

If it was up to me, all 5ppm units would have to centrifugal, but i’m sure the people in charge of the budgets would have something to say about that!

Thanks to everyone that’s taken the survey so far - it really is appreciated!

The last 4 vessels I’ve worked on have all had 5ppm units installed. 3 of them were just your normal, run-of-the-mill gravity-type OWS that had their PPM limits reduced from 15ppm to 5ppm with no further modifications. They had all been certified by class, so i suppose they must have somehow passed under perfect laboratory test conditions, but they weren’t fit for purpose when installed on-board. Even the addition of some basic form of pre-treatment, like a settling tank and/or heating, would have helped.

The IMO & other national authorities have been mostly silent when it comes to OWS use for years now, unless they’re trying to make an example of a company/seafarer found to have made an illegal discharge. To me this seems like an unfair situation - The rules and legislation governing OWS design & installation are quite basic, and yet the seafarers that use this equipment are expected to abide by the IMO rules even when provided with poorly operating yet legal equipment. Hopefully this project might be one way of getting things to improve.

I’ve used a GEA centrifuge type OWS before. It was my favorite by far. We’d run it pretty much continuously, just switching the overboard to recirc when we were in waters that we couldn’t discharge. The only issue that I recall having was after someone dumped a bunch of soap into the system. The OWS OCM didn’t have any issues, but the white box OCM went nuts. The soap was foaming between the OWS and white box. We were able to play around with the throughput and backpressure to get it to stop.

The GEA OWS was the same size as our aux lube oil purifiers and about half of the parts were interchangeable which was helpful for spares.

1 Like

Disclaimer: these comments are based on one guys experience which was only on gravimetric and coalescing type OWS’s and older ships or carelessly designed ship - so perhaps these centrifugal separators if they are working so well will negate some of what follows…

Shedding light on the “problems” is not really an issue as you yourself have experienced.

See you are getting close to the answer right there.

Don’t get me wrong I wish you well shining a light on the problems.

The biggest problem is getting shipowners and the technical employees they hire ashore to realize this is not an OWS problem it is a system problem. That is to say achieving the goals of MARPOL is a “process” and so involves a system not a single piece of equipment.

This guy here came close to getting it right.

He’s going in the right direction system-wise but I found his section on “Human Factors” pretty much insulting to shipboard engineers. However, I did of course agree with this section:

It could be concluded that human factors issues are related to ship’s crews alone, but it is important to emphasize that this is not the case in OWS system operation and design. As an example, it is noted that Naval Architectural and Marine Engineering design curriculums completely ignore the existence of systems that serve the public. As such, a graduate Naval Architect or Marine Engineers will not have any education on the design of such systems. This has resulted in generally very poorly designed OWS systems aboard ships. Consequently, training on OWS and associated systems should extend from the designers through the shipyards through the engine room crews.

The majority of my working life was at sea and I’m sure my attitudes changed over time but I never saw it as an imposition to follow the law and not put oil in the ocean. Which is why I bristled at the authors twisted argument to prove engineers are taking the route of least resistance or need “extra” motivation.

Now this is an older paper, I finished up my at sea experiences on a very old ship and I don’t track ME/NArch training programs BUT I suspect looking at this as a process may not have gained wide spread acceptance just yet among owners and designers.

If regulatory bodies define an illegal discharge and snake oil salesman tells an owner this piece of equipment does that they don’t seem to want to make investment in tanks, heaters, filters, additional process steps etc. Just buy the one item, have it suck directly from the bilge and argue with the crew later about how it works and then blame them for when it does not perform or meet the goals.

I think there is a pot full of problems with IMO but in this specific case I’m going to give them the benefit of the doubt and believe they came to the limits according to some scientific thought process and probably some compromise between factions wanting higher and lower limits. What is the right limit is a separate discussion so I’m against adjusting the limits because its hard to meet with an out of the box OWS. Also because even on an ancient ship we were able to reliably operate a plant that could meet the limits. Took years of adding a tank here, pump there, filter here, drain segregation etc. but it can be done.

Legitimate questions can be asked as to what’s worth it and how enforcement could be used to level the playing field between those doing it right and those that only demonstrate they have the equipment aboard and an ORB that “proves” they’re golden. Subjected to PSC’s all around the world and its mostly a tick the box type inspection no real understanding of the process either. Understandable a PSC could take days if they got into details. But the questions or rather lack of questions really tell me they have bought the OWS is the only thing that matters hook, line and sinker. So is there motivation to do it the right way or not?

But hey back to IMO, how about when they made a new rule that OCM’s had to read emulsions as well as oil particles? The operational problems you bemoan were valid then as well. People standing on their heads to get these plants to work and then come out with that. Can’t make it over the existing bar so raise it higher? How about recognizing what is going on and assisting flag states with solutions then.

Of course tweaking design of OWS’s and OCM’s should continue - build a better mousetrap and they will beat a path to your door. But if that is the length and breadth of ones view I don’t think much is going to change for shipboard engineers.

1 Like

I think from a global standpoint you’ve identified a root problem around the shoreside/shipboard OWS vs System problem. The OWS is definitely seen by management as the end-all piece of equipment…its required, its been provided, you have no excuse for it not processing, you have no excuse for needing to pump tanks to shore (caveat later below…)

On the human factors section of that paper (any idea on the publish date by the way?) I agree with that section you highlighted. I don’t recall any hands on OWS training at the academy, and frankly I recall reflecting not long after graduation at how the OWS was operated on the training ship and thinking that they were definitely bypassing it.

Regarding the desire to follow the law and not put oil in the ocean, you are certainly not alone in feeling that this is NOT a burden or imposition. I have never had any desire to break the law or harm the environment. But unfortunately experience tells me that is not as universal an opinion as we’d like. And despite the origins of the “magic pipe” cases we see in the papers every so often, this is not just an FOC ship issue.

I have seen at two different US based companies I’ve worked for with US officers and crew no less than three incidents regarding improper OWS operation and discharge to sea.

  • The first was due to arrogance on the part of a senior officer. The system wasn’t set up to easily keep oil residues out of the bilge tanks and the separators needed constant cleaning. He thought he was smarter than the system, had no qualms about polluting, and felt that since he worked for the government that the rules didn’t apply anyway, so he tricked the OCM with potable. (Officer directly responsible was eventually promoted; Gov’t Employee)

  • The second was a case of perceived pressure from management and actual pressure from the C/E to not want to have to pay for slops to go ashore. Again, due to other maintenance deficiencies there was far more water and oil to process than normal. He thought it would reflect poorly on him if he had to pump out. (C/E retired, Officer directly responsible was eventually promoted; Gov’t Employees)

  • The third was again a case of perceived management pressure to avoid the cost of pumping to shore, actual pressure from a person with undue authority and a complete lack of respect for the law, and an unwillingness to stand up for oneself. (Those responsible were fired; Private Sector)

I’ve never understood the pressure from shore issue myself. Whenever I’ve been in a position where the OWS needed new filters or coalescer media and the parts hadn’t arrived due to supply chain problems, I never had any push back at all about getting slop tanks to transport to shore. It is an explainable cost. If management had a problem with my spending I could always point out that I’d attempted to order enough filter material for spares but someone on shore cut my order quantity. I would never be able to explain breaking the law.

Perceived pressure offshore is real though, to some more than to others. In times of uncertain employment, having the integrity to do things right and the willingness to be fired for it is certainly not a given, though it is necessary. Improvements to the whole bilge processing system is a great goal.


Hi shipengr,

I’m aiming to have the results published by October, providing things don’t get too crazy with this virus. Thanks very much for your comment, your thoughts are appreciated.

1 Like

Not sure on the dates. It was a SNAME paper but for some reason no date on my re-print of that. I think it might have been a NY MET section paper. The earliest I made written reference to it was in 2006 so sometime around then possibly.

At the time we were in the middle of trying to upgrade the processing of oily water on our old ship and some of the concepts overlapped with ideas we had to improve things.

We adopted the tall thin bilge holding tank to improve settling. That tank included electric heating and temp control, aeration bubbler piping in the bottom (with timer control). Some other feature of the “process” were a big bag filter as OWS pre-filter, a 2nd 3 way valve after the OCM/OWS controlled one for testing and “warm up”, an OWS post filter of the X-ORB type. A set of detailed procedures to process the water and an incinerator rounded out the system.

Could bore you with more details but PM me if you are undertaking mods and looking for info.

But more to the examples you gave - the cooperation and funding for our mods were appreciated (though we had to fight for that) but more importantly if we were pushed against the wall (long port stay or short voyages) we were always backed up by town if we needed to pump slops off. That was rare but there was no negative consequences for requesting that.

I agree with everything you say. Couldn’t have put it better myself. We all know that operating an OWS with a trickle of clean water going to the oil sensing unit will keep the process going without the 3-way valve opening and diverting the discharge water back to the holding tank. At the same time the sampling line from the discharge pipe is observed. The result is that say three m3 of bilge water was discharged averaging 100 ppm. Yes the unit is designed to control for maximum 15 ppm discharge. If you try to obtain this then be prepared for many hours nursing it. I have spoken frankly to many surveyors about this and they know the problem all to well.