Understanding MARPOL and oil pollution from ships

Malcolm Latarche

Malcolm Latarche · 12 October 2017


Although the contamination of the seas by oil appears to have slipped down the agenda with most attention today being paid to air pollution and species transfer, it was oil and grease that were the first concerns when the MARPOL Convention was first formulated.

The driving factor behind MARPOL in the early days were numerous pollution incidents mostly involving oil spills but the rules do as well cover smaller scale operational pollution and in most jurisdictions these are treated as being more serious in terms of criminal negligence than accidental loss of cargo or bunkers as a result of grounding or collision. Operational pollution by oil and related substances is covered in ANNEX I of MARPOL as well as the US EPA’s VGP introduced in 2008. The major part of ANNEX I is actually concerned with construction and cargo operations of oil tankers over 150gt and the parts which affect other vessel types over 400gt is confined to a very few operational matters as well as the form and issuing of the International Oil Pollution Prevention Certificate (needed in most ports to obtain customs clearance) and the need for ships to have and maintain an oil record book.

The first demand as regards the operational waste oil from machinery is that the ship must be fitted with adequate holding tank capacity for any waste that cannot be dealt with by way of discharge or incineration. Most ships generate large amounts of oily waste (waste contaminated with oil) and waste oils (such as spent lubes or sludge from fuel and lube treatment systems).

As well as the oil in the bilge water there will be grease, detergents and cleaning fluids along with contaminants that may have been removed from fuel and lube treatment systems, some of these may present more of a hazard to the marine environment than oil does. Prior to the introduction of regulations, all of this waste would generally have been disposed of at sea. Today all vessels above 400gt are required to filter the waste so as to reduce the oil content to a maximum of 15ppm (Canadian rules on the Great Lakes have a maximum of 5ppm) before discharging it at sea. Some classification societies also demand a higher standard of 5ppm to comply with their voluntary clean design notations.

The resultant waste must be retained on board for disposal ashore. The filtering is done by a bilge or oily water separator – a piece of equipment that has gained an unenviable reputation in recent years. As well as the separator, all vessels subject to the regulation must also be fitted with an oil content monitor (OCM) and bilge alarm to detect if the treated bilge water being discharged meets the discharge requirements. Separators used on board ships are not generally unique pieces of equipment design specifically for marine use but will be versions of separators used in many industries ashore.

It is generally accepted that separators have not performed as well at sea as they do in applications ashore. There are many reasons for this including the fact that the waste products are less easy to deal with, the conditions at sea with constant movement in many planes affecting operation and the fact that installed systems often lack the capacity to meet the demands placed on them.

As a consequence, they require constant monitoring and frequent cleaning and overhaul which has made them unpopular with many seafarers. This coupled with the operators’ desire to reduce the cost of disposing of treated waste ashore has led to several instances where the separator has been by-passed and waste discharged illegally overboard.

These are the so-called ‘magic pipe’ incidents that lead to regularly reported prosecutions by port state control regimes and heavy fines and imprisonments especially in the US.

The regulations may lay down a maximum limit of oil but they leave the means of achieving this open. As a consequence, several technologies are used across the diverse range of separators available and crew members may find themselves having to operate and service unfamiliar those that use membranes, flocculation or absorption filters means valuable time must be spent searching out manuals and attempting to make sense of them.

Early separators were mostly of the gravity separation type that employ plate or filter coalescing technology to separate oil and water. The bilge water is usually heated gently to improve separation with the oil gradually settling out above the water content. The oil is then pumped to the holding tank and the water discharged to sea after passing through the OCM. Without further refinements, gravity separators can have difficulty in meeting the 15ppm standard especially when the bilge water contains emulsified oils which do not separate easily.

Centrifugal separators also work using the different densities of oil and water but with the centrifuge greatly multiplying the gravity effect as the centrifuge accelerates. This type of separator is more efficient and can generally deal with emulsified oils. Many crew members are familiar with this type of equipment which is also used for preparing fuels and lubes before use by removing sludge and homogenising the fuel or lube. They are more compact than gravity type separators but have the disadvantage of requiring power to operate the centrifuge and because of their moving parts often have a higher maintenance requirement.

One way for separator performance to be improved is to add a polishing device into the circuit. Several makers’ current systems include a polishing stage but for older vessels, adding a polishing unit between separator and monitor will improve the performance sufficient to prevent alarms sounding constantly.

Other technologies are also used for cleaning bilge water including absorption and adsorption, flocculation, biological and membrane separation. Absorption and adsorption are very similar physicochemical processes and for the purpose of this guide can be considered together.

In both cases, the bilge water is forced through the sorption media in a reactor or contactor vessel and the oil is removed. When the sorption material has reached its full capacity it is removed and replaced with fresh material. Some sorption materials can be regenerated on board but others will need to be delivered to shore. Popular absorption materials include bentonite and zeolite used as substrates or in cartridges. Typically 100m3 of bilge water will require 10kg of media. Flocculation and coagulation make use of an emulsion breaking chemical to treat emulsions after any free oil has been separated. The chemical breaks down the emulsion and the released oil comes together to form flocks which can then be skimmed off leaving the remaining water to go through further filtration stages. This method tends to produce large amounts of sludge and requires an outlay on the chemical reagent.

Biological treatment employs microbacteria in a bioreactor to literally consume the organic chemicals in the oil converting it to carbon dioxide and water. It is a slow but effective treatment for oil and emulsions as well as also removing some of the other solvents often found in bilge water. Capital outlay can be high but operating costs are low. Care must be taken to avoid overload on the microrganisms and maintaining operating temperature within the safe range to avoid destroying them.

Membrane technology, ultrafine filtration and reverse osmosis are all physical means of preventing oil and other large molecules from remaining with the water that can pass through the filter barrier. They are efficient but require attention to prevent blocking of the filter or membrane.

Avoiding problems with separators begins long before the device is switched on and involves a proper plan for managing waste streams and doing as much as possible to prevent emulsions forming especially if they are chemical emulsions resulting from the use of cleaning chemicals and detergents. So called primary emulsions in which larger drops of oil are dispersed in water generally separate through gravity within 24 hours.

Secondary emulsions caused by turbulent conditions where oil droplets are very fine become stable and will not separate easily. Solid material should also be prevented from contaminating the bilge as much as possible. Not only does it promote emulsification it also creates false alarm situations and shuts down the separator requiring crew intervention to restart the separation process. Filters and removal of solids before treatment will allow the separator to operate more effectively and for longer.

Oil-in-water monitors may be fooled by suspended solids such as rust and scale which are quite innocuous but they may not detect the presence of some chemicals which could be toxic to marine life when discharged into the sea. The monitor is a crucial component of separators and is often not an in-house product of the separator maker.

Sealing the leaks

Lubricant leak from propeller shaft and rudder bearings are a common cause of pollution and have attracted attention in recent years. Until around 50 years ago, many ships were fitted with propeller shaft bearings made from lignum vitae an extremely dense timber with a high degree of natural lubricity but these were abandoned in favour of metal bearings and mineral oil lubricants.

Now, as environmental regulations tighten, water-lubricated propeller shaft bearings are becoming a popular alternative to oil-lubricated bearings for commercial vessels. This was already happening before the US EPA revised the VGP in 2013 but that action is likely to accelerate take up of water lubricated bearings and new seal types and also a greater use of new approved lubricants.

Conventional seals inevitably leak over time due to wear and damage but water-lubricated bearings avoid oils and grease lubricants altogether. Seawater is pumped into the bearing and it simply discharges to the sea. It lubricates and dissipates heat from shaft friction and most manufacturers of water lubricated seals say their products provide equal performance to conventional seals.

US VGP spurs new lube need

Under the new VGP introduced in the US in 2013 the list of permitted substances and the quantity each ship above 300gt will be allowed to discharge was reduced – quite dramatically in some cases. One of the changes under the VGP affects lubricants in any equipment or system that has an oil-to-sea interface. In essence, that affects all propulsion systems and also deck machinery where run-off over the ship’s side could occur.

Previously under the earlier 2008 VGP, operators were free to use any lubricant they wished but from December 2013 the rules require environmentally acceptable lubricants (EALs) unless doing so would be ‘technically unfeasible’. EALs are defined as biodegradable, which rules out all mineral-based lubricants and even some synthetic alternatives. The exact definition of an EAL is contained in an EPA document, EPA 800-R-11-002 November 2011, which can be accessed via the organisation’s website. Operators have to apply for a VGP before a vessel enters US waters and to do so they need to identify all oil-to-sea interfaces and lubricants involved.

Although ship operators can expect product makers to advertise compliant products there are some labelling schemes that may give added assurance. In general, any product carrying endorsement by the following is likely to be approved.

  • Blue Angel
  • European Ecolabel
  • Nordic Swan
  • Swedish Standards SS 155434 and 155470 Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) requirements, and
  • EPA’s Design for the Environment (DfE)

EPA does not consider on-deck equipment that comes into contact with rain, splashed with waves, wave-generated spray, or subject to icing to be a form of immersion, and therefore not an oil-to-sea interface. Vessel operators are not required to use EALs in on-deck machinery that is not subject to immersion. However, discharges from deck machinery are subject to other discharge requirements, such as those for Deck Washdown and Runoff (Section 2.2.1 of the VGP), which recommends the use of EALs.

Among the most obvious systems that are considered oil-to-sea interfaces are the stern tube, rudder bearings, CP propellers, thrusters, and fin stabilisers. In addition, winches, cranes, hatch covers, and even crane wires and the like must be considered. The ship will be required to document all lubricants and any reason why the use of an EAL would be technically unfeasible.

Most major oil companies and some specialist suppliers have formulated compliant products that are readily available although with a premium price tag. However, these products are not necessarily compatible with some makes of seals, especially conventional rubber seals. This is a known problem and most combinations of lubricants and seals have been tested for compatibility over normal dry docking cycles of two to three years.

In selecting an EAL, operators must therefore seek advice from the seal manufacturer and great care must be exercised if the vessel makes use of enhanced or extended dry docking strategies. Inspections with regard to EALs would involve visual sheen tests and inspections of deck runoff.

Some checking will be carried out by state authorities, with California and Florida expected to be quite active. The ‘unless technically infeasible’ proviso can allow some temporary relief if the ship has seals that are incompatible with any EALs, in which case it can continue to use mineral oil until the next planned docking, when the seals are to be replaced, or if the equipment manufacturer has no recommended seal-EAL combination for its product. Some pre-lubricated wire ropes are also included in the exemption.

If the use of an EAL in an oil-to-sea interface is claimed to be technically infeasible, the ship must carry documentation to that effect. Supporting documentation written by the manufacturer or owner must not be more than one year old and must confirm the factual situation. Any such claims may be investigated by the US authorities, with severe penalties if they are found to be falsely declared.

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