Acronym’s decoded:

OWS – Oily Water Separator

PPM – Parts Per Million

IMO – International Maritime Organisation

USCG – US Coast Guard

MCA – Maritime and Coastguard Agency

OCM – Oil Control Monitor

OMS – Oil Monitoring System

Recent events have shown that some crews continue to by-pass oily water separators and perform illegal overboard discharge, which has resulted in fines into the millions and even the possibility of imprisonment.  Operators must become more vigilant and ensure they adhere to industry environmental rules. AtZ have a wealth of experience to assist operators in developing efficient OWS Systems.

To ensure minimal environmental impact on our seas, bilge water on board ships must meet industry standards before discharge is permissible. Various environmental agencies globally (IMO, USCG and MCA) have issued regulations which ship operators must follow to reduce oil pollution and to protect our marine environment.

Marpol Regulations

How is oil in water measured? The IMO MARPOL standard of measurement of oil, which was adopted in 1977 and measures oil in water content in ppm (parts per million) and describes the concentration level of oil within water. One ppm is therefore equivalent to 1 millilitre of oil per 1000 litres of water, 0.001%.

The IMO states that no bilge water can be discharged into the sea that has an oil content that exceeds 15ppm for more than 10 seconds. Any bilge water that cannot be discharged in compliance with this regulation must then be retained on board until it can be discharged at a suitable reception facility. Accurate records for oil discharge must be maintained and kept on board.

It is now mandatory for vessels over 400 gross tonnes (250 gross tonnes for oil tankers) to be fitted with oil in water monitoring devices to ensure these standards are met. Non-compliance with these regulations can leave organisations facing severe fines and penalties, and not only has an environmental impact on our seas but also means organisations can face costly interruptions to operating schedules. Monitoring records, certification and equipment calibration checks must be kept on board and produced upon request.

Marpol 73/78 Annex 1, summarised:

  • An International Oil Pollution Prevention Certificate shall be issued (and is required), after an initial or renewal survey for nearly every vessel.
  • There will be annual interval surveys of the vessel structure, equipment, systems, fittings, arrangements and material described in Annex 1
  • There will be an annual survey which is a general inspection of the structure, equipment, systems, fittings, arrangements and material described in Annex 1
  • Surveys of ships as regards the enforcement of the provisions of this Annex shall be carried out by officers of the Administration (Marpol). The Administration may, however, entrust the surveys either to surveyors nominated for the purpose or to organizations recognized by it.

Failure to produce this documentation can result in a delay in the vessels onward movements.

MARPOL – The International Convention for the Prevention of Pollution from ships was introduced in November 1973 by the International Maritime Organisation and covers the prevention of pollution from ships into our seas. Annex 1 is the prohibition of any discharge into the sea of oil or oily mixtures from ships and states that it is mandatory for vessels to be fitted with an oil in water monitor, for continuous oil content analysis to ensure no water is discharged which exceeds the mandated discharge limit of 15ppm oil-in-water.

The Technology

The oily water separator (OWS) is a vital piece of engine room equipment. It is used to ensure that water is discharged overboard within legal limits. The OWS must be maintained in full working order and operated according to MARPOL regulations.

Persons using the equipment must be fully familiar with how it operates. The OWS is frequently inspected at port state inspections. There should also be an OWS operation manual on board and relevant staff should be familiar with the manual, and should have practised with the equipment. Please refer to MARPOL Annex 1 for more information. The USCG are particularly vigilant that crews can demonstrate a working knowledge of the OWS system, they will often board ships to carry out unscheduled checks.

Bilge water suitable for discharge is defined as that which contains less than 15 parts per million of oil. Oil/water ‘Separator Units’ using the gravity system (Static Separation) can struggle to achieve <15ppm and may utilise some form of secondary ‘Filter Unit’.

Oily water separators utilise several different technologies, such as: Static Separation, Centrifugal Separation and Chemical Process Separation.

The most common OWS (Static) consist of three segments:

Static Separator unit

This unit consists of catch plates which are inside a coarse separating compartment and an oil collecting chamber.

Here the oil having a density which is lower than that of the water, makes the former rise into the oil collecting compartment and the rest of the non-flowing oil mixture settle down into fine settling compartment after passing between the catch plates.

After a period of time the oil in the water coalesces on the underside of the oleophilic plate eventually forming droplets before coalescing into liquid oil which floats off the plates and collect in the oil collecting chamber. The oil content of water which passes through this unit is normally 100 parts per million of oil or less.

A control valve (pneumatic or electronic) releases the separated oil in to the designated OWS sludge tank.

A Heater may be incorporated in this unit to increase the process efficiency.

The Filter unit

This is a separate unit usually seen on MPEC 107 (49) complainant systems, whose input comes from the discharge of the Separator unit. The unit consists of three stages – filter stage, coalescer stage and collecting chamber.

The impurities and particles are separated by the filter and are settled at the bottom for removal.

In the second stage, the coalescer induces the coalescence process, in which oil droplets are joined together by breaking down the surface tension between them.

These large oil molecules rise above the mixture into the collecting chamber and are removed when required.

The output from this unit should be less than 15 ppm to fulfil legal discharge criteria. If the oil content in water is more than 15 ppm then maintenance work such as filter cleaning or renewal of filters is to be done as required.

Wavestream by Wave International Bilge Water Filtration and Polishing Systems can be fitted to any OWS to improve its efficiency.

Oil Content Monitor and Control Unit

This unit functions together in two parts – monitoring and controlling.

The ppm of oil is continuously monitored by the Oil Content Monitor (OCM); if the ppm is above 15 it will alarm and feed data to the control unit.

The control unit continuously monitors the output signal of the OCM and if an alarm arises, it will prevent the oily water going overboard by activating, typically, a 3 way solenoid valve.

The 3 way valve inlet is from the OWS discharge, where one outlet is to overboard and a second outlet is to re-circulation. When the OCM is in alarm, the 3 way valve discharges the oily mixture back to the bilge.

AtZ are an approved supplier, calibration and service provider of Deckma Hamburg Oil in Water monitoring devices, and can supply a complete range of spare parts for most oily water separators.

Helping to protect the environment

Installing a Deckma Hamburg oil monitoring solution onto your vessel ensures that you have a continuous overview of the oil particles contained in your residual water – which is the most important prerequisite to effectively protect the environment.

All Deckma Hamburg bilge alarm monitors are in accordance to the IMO Resolution  MPEC 107, (49), and certified by the US Coast Guard, the German See-Berufsgenossenschaft, and by the competent Canadian, Chinese, Russian and Scandinavian authorities.

Deckma Hamburg offer a range of OMS solutions suitable for a range of application needs.

Product in focus: OMD-2008 EV FC ACU Deckma Safeguard

According to MEPC.107(49) the 15ppm Bilge Alarm has to be provided with a representative sample, i.e. the operator of the instrument is responsible to maintain a proper sample flow through the instrument. The recommended sample flow rate for Deckma instruments is approximately 2 litres per Minute. At this flow rate, with a common setup of separator and 15ppm Bilge Alarm, it is easily possible to reliably operate the instrument, and to ensure the required short reaction time to changes in the oil content of the effluent water.

However, generally the instrument does not know about the sample stream flow rate. If circumstances lead to interruptions of the sample flow, or if the sample flow is stopped completely, the portion of the sample that is in the sample glass tube will be measured continuously. The instrument will display the same measurement result for a long time, but it may fail to adequately react to changes in the overboard discharge water oil content.

All Deckma MPEC 107 (49) OMD series instruments have a dedicated input to connect a flow switch to monitor the sample flow rate.

The LATEST EVFC versions of the OMD-2008 instrument come with a flow sensor that measures the sample flow rate, and automatically sets the instrument into alarm condition if a sufficient flow rate is not maintained. The OMD-2008 EVFC is designed to make manipulation and tinkering with the instrument setup much more difficult to achieve.

Additionally for the OMD-2008 EVFC instruments, an automatic cleaning unit (ACU) is available. This system quickly and regularly cleans the sample glass tube without having to open the Measuring Cell. With the ACU, maintenance of the system becomes very easy, ensuring high reliability and reduced maintenance workload.

AtZ Marine engineering expertise

Our team of marine engineers have extensive experience and knowledge, ensuring ships are compliant with bilge water discharge regulations.

We have been working with some of the world’s leading cruise ship and shipping/cargo operators since 1998, providing a trusted and reliable service which ensures critical operations are never interrupted.

AtZ will survey, commission and install your equipment to ensure the correct solution is delivered for your application. On the completion of install the AtZ service team will then log your unit(s) and advise an appropriate calibration and service schedule, along with recommend on-board spares holding to minimise downtime.

AtZ hold a stock of service exchange units for ships operating to tight schedules, ensuring regulatory compliance at all times.

We pride ourselves on our 24/7 support, and are on call to support our customers in dock or at sea globally 365 days a year. Our team is on standby to travel to your vessel whether for planned maintenance or emergency repairs.

AtZ will also be holding a technical talk session at London International Shipping Week, focusing reducing the environmental impact on our seas from international shipping oil pollution. AtZ will be joined by trusted partners, Deckma Hamburg GmbH, Wave International, and ACM Composite Bearings to deliver a session looking at technologies to monitor and eliminate oil from bilge tanks and stern tube seal arrangements. Tuesday 12th September 2017,  09.00am – 12.30pm, university of Greenwich, Hamilton house. For further details and to register, please visit click HERE.

About AtZ:

ATZ provide equipment sales, support and consultation services to the marine, power generation and petrochemical sectors and were established in 1998, becoming the sole UK agent for Deckma Hamburg, the oil-in-water monitoring specialists. The organisation then expanded its portfolio by becoming the sole UK agent for AEGIR-Marine and ACM Bearings, along with innovative brands such as, ABCON, Wavestream and Tribomar.

Written by Louise Woolley, with thanks to Clive Wilson, AtZ Project Engineer and Dave Newell, Director for their technical input into the article.

Media Enquiries

Louise Woolley   

AtZ Marketing Manager

+44 (0) 2380 455447


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