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Oily Water Separation On Board Ships. 5

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Lis

Lis

Marine/Ocean
Oct 23, 2002
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I am carrying out a research project into new methods for separating oil and water, as found in machinery space bilges on board ships.

I am currently researching technologies used shore-side and evaluating their potential for use at sea. I am particularly interested in ozonation, UV exposure, biotechnologies, electrocoagulation, chemical additives, ultrafiltration and dissolved air flotation.

If anybody has any information or experience with any of these, or any other technologies, and would be willing to answer a few specific questions in this area, could you please let me know by replying to this thread.

Many thanks,

Lisa Wooderson.
 
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The problem we seem to have with current separating techniques is that they cannot process all the different types of contaminant and also the fact that the blige water often forms a stable suspension.

The sort of contaminant we usually find are monocyclic hydrocarbons, low and high MW polycyclic hydrocarbons and also low and high MW petroleum hydros (by the way, I am not really chemically minded and got these ...cyclic names from a colleague who is - I just know we use various fuel and lube oils and this is what they break down into, according to him). Combined with this there are sometimes traces of metal from wear and corrosion and also, often sewage and cleaning agents (the detergents in these chemicals and oils are causing the emulsions and hence poor gravimetric separation).

With regards to UF, I am not sure of the effect of sewage and chemical attack on the membranes...do you know if anything like this has been investigated? I presume it has but am failing to find any data on it - I have read several papers detailing tests but never anything that is appropriate to ship board waste water..have you come across anything like this?
 
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Almost forgot...

You mentioned that you have knowledge/experience with bio-treatments:

I have been reading up a lot about this today and what I have managed to ascertain so far is that some treatments work in 2 stages - initially breaking down oil into smaller globules and then dispersing the molecules to be broken down into CO2 and H2O. I assume that this is effective for surface oil, but what would be the effect on emulsified oils? Would the emulsion need to be broken first or will bio-treatments do this as well?
 
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UF membranes came be made from a variety of materials that can be resistant to oils and certain chemicals although solvents might hurt them.
UF performance would not be affected by emulsification.
Also, biological performance is improved the more emulsified/dissolved the food (oil in this case) is dissolved in the water.
 
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Centrifugation? Reclaim oil and resell at port?

Activated Carbon Adsorption? Unload used carbon for custom regeneration and reload with freshly activated carbon?

Just some ideas. There must be well established technologies with application history? eg: cruise ships in sensitive environments like Alaska Glacier Bay or the Gallapago's or the Caribiean, etc? Maybe EPA or a marine organization has more info.

Interesting. Good luck!
 
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rbcoulter - thanks for that it is most useful and has really set things into motion this end now!!

DeltaCascade - thanks for your ideas too. I don't know what your specialisation is but just in case you are interested in what we do...The reason we don't use centrifugal separation is really a case of volume: where for removing water from fuel or lube oil centrifuges are extremely effective and efficient because of the small quantity of water removed from the oil, when dealing with bilge water, the opposite is true. There is a large volume of water and small globules and quantities (sometimes emulsified) of oil to be removed. It is for this reason centrifugal separation is not deemed to be particularly appropriate for this application ON SHIPS...but I think it may be shore side.
All ships are governed by the same regulations and the ppm oil in water that we are allowed to pump over the side does vary depending on area. These regs are becoming more stringent and are up for review again in 2003. The current technology is based around coalescing plates and gravimetric separation, although some companies are starting to experiment with ceramic UF systems..The main problems associated with the common shipboard OWS (coalescers and gravity based) are that they cannot break emulsions (resulting in oil passing overboard) and they are adversely affected by solvents and sewage.
I work on cruise ships myself and have worked with a combination of plate coalescers, coalescing beds and gravity tanks. Such OWSs often struggle to produce an effluent of less than 15ppm (majority of areas require this) and, with more stringent rules coming in, we are trying to develop systems to take the oil content down to <1ppm.
Regarding carbon adsorption, I do not really know how effective that is in these cases...but I am about to go find out now that you have mentioned it!! Thanks again and I hope you found this interesting!!!

Lisa.
 
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I used to work in the area of separations (centrifuges). I recall that the navy was working on a system that involved a strainer (to get the chunks out), followed by a 10 to 30 micron filter (there was debate on what was good enough), then a liquid centrifuge (to get the contamination down to 75 to 300 ppm and remove any &quot;free&quot; hydrocarbons) and then a polish step. The polish material could either be throw-aways like filters or carbon or re-newable membrane systems. The system configuration could be tailored to ship size and tour duration. For example, a coast gaurd vessel with short tours might use only throw away filters, but a carrier might use the full system with a membrane because they wanted to reduce consumables.

Hope that helps.
 
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Yeah. Also, crushed walnut shells are used as media for water filtration in the oil industry quite successfully ... down to 1-2 ppm oil in produced water. The media is intermittently backwashed and oil is separated in backwash tank; more economical than &quot;throw-away&quot; cartridge filters for large applications, but likely less economical in marine vs land applications. Likely similarly, for pre-coat filters.

Searching EPA's web site for &quot;bilge&quot; came up with what appears to be a state of the art process that is being developed, or at least trialed. Excerpts follow:

Combined Centrifugal Separator/Membrane Ultrafiltration System for Shipboard Treatment of Bilge and Ballast Water
(Project Amount: $225,000)

The objective of this project is to develop a bilge water treatment process by combining a centrifugal separator pretreatment step to remove solids and large oil droplets, and a novel, fouling-resistant composite ultrafiltration membrane-polishing step to remove the remaining emulsified and dissolved oil and produce dischargeable water that meets the new regulations.

...Further reading at EPA's site shows discussion of the new ceramic membranes that you mentioned.

You are probaly also aware of dissolved air flotation. Bio-digestion processes don't seem to be there yet, even with imnmobilized bacteria?...

Best of luck with your project :)
 
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Thanks both of you for all this info! I have also come across a lot of info about this ceramic membrane system that the RN and USN trialled...it looks pretty good but I am wondering if they found any shipboard vibration problems with the inherent fragility of the ceramics..I read that they were planning to continue ship board trials for this purpose but no amount of digging has so far revealed any results of this...have you come across anything?

I also have a local contact working for a membrane technology firm now so I am hoping to find out some more details from him shortly..keep you posted!!

Thanks again!!

Lis.
 
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I used to work several years in the marine OWS field.
As you mention the currently used separation technic is based on gravity separation followed by coalescence.
These machines have to produce an effluent with less than 15 ppm oil, while the influent which is bilge water is a complex mixture and might contain (sea water, heavy fuel oil, IFO, gas oil, lubricants, detergents, particulatte matter etc).

Specifications, as well as testing procedures for this type of equipment are issued by the International Maritime Organization (IMO). To my knoweledje revised specifications are expedted in the next few years, but I don't think that the limit of 15 ppm is going to change.
The flowrate of this equipment is generally from 1 to 10 m3/h.
Activated Carbon filtration could be a good option for final treatment.
 
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The regs for OWSs are changing from 2005. The 15 ppm limit will remain but all new OWSs fitted will require emulsion breaking capabilities as well as heavy fuel oil removal capabilities. The price of these as well as running costs will be substantially more than the current industry norm.

In some other forum, biotreatment was mentioned. This is really a no go area on board a ship, although, technically possible. Mostly due to retention periods and complex nature of bilge water.



 
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You consistantly mention emulsions causing problems. Hence to remove any oil you have to increase the droplet size. Currently there are two types of fibrous coalescing media available which may assist you here.

One is PECT-F by which is usually installed upstream of any hydrocyclones while the other is The Mare's Tail ( If you want I can e-mail you a recent paper on The Mare's Tail.

If you are pumping this bilge water overboard then there may be enough pressure to allow effective operation of hydrocyclones. These units can handle large volumes of water but require at least 3barg driving pressure (more if available). Since the water is already emulsified I'd have no problems pumping the water up to pressure then passing it through PECT-F/Mare's Tail and a hydrocyclone. However since the regulations are circa 15ppm you may require some further treatment, probably your membranes or ultrafiltration may be suitable.

Hydrocyclones typically produce a reject stream of 3-5% volume of the inlet i.e. Q(reject) = 0.03 x Q(Inlet). This stream will not be entirely oil, so you'll have to have an idea of how to deal with this concentrated stream - maybe blending it in with the centrifuge feed for the fuel oil.

One further issue that I'd raise is that the tests for overboard water do not always exclude dissolved hydrocarbons. Consequently any mechanical separation (platepack, centrifuges, hydrocyclones) may be working at their optimum but you still do not achieve 15ppm overboard. They will only remove dispersed oil.

I hope that this is of use to you.
 
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The engineers on our vessels are having trouble with adequately maintaining the 15ppm via the coalescer type OWS, although it is only 3 years old. I have sailed for 30 years and had the same problems. Has anyone had any experience with ULTRAFILTRATION onboard ships? If so, any contacts please?
 
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Lis, a combination of organo-clay and activated carbon is commonly used to remove oils from water. The clay can break emulsions if they are formed as a result of mechanical action. In fact organo-clay has been used by the Navy for use on submarines. E-mail biomininc.com for further information.

 
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Dear Ms. Lisa Wooderson,

I am a former Naval Officer and chief engineer. If you are still searching for a solution for treating bilge water, ballast water, etc., please email me. I will forward a few white papers to you that may give you some insight into treating low flowrates, such as pumping the bilges and very high flowrates such as ballast water.

Sincerly,
Todd

toddforet@usa.net
 
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Lis,

Ozonation and hydrogen peroxide treatments , followed by filtration have been found effective in oxidizing both single, double and triple bonds H-C including aromatic hydrocarbon. As long as bromate formation is not a problem they are good treatment solutions. They are use to disinfect ballast water in ships before dumping into sea.

209larry
 
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