What makes the Baltic Sea polluted? Waste and sewage from ships

John Nurminen Foundation and Traficom have launched a project whose goal is to identify the most harmful and dangerous chemical emissions into the Baltic Sea related to washing the tanks of chemical tankers in Finnish ports. At the same time, it is intended to find solutions to reduce permitted emissions.

Many people outside the industry would rub their eyes. Do we still leave dangerous substances from ships in the Baltic Sea? Nowadays, when the conversation turns to ship waste and wastewater, I often come across two completely opposite points of view. Others, usually people in the shipping industry, say that nowadays no waste or waste water gets into the sea from ships – decades ago it used to be the other way around. Others believe that the situation is still as bad as it was 50 years ago, when some kind of waste, wastewater or even polluting substances carried as cargo were discharged into the sea from ships.

The truth is of course somewhere in the middle. A lot has been achieved in waste matters, but there is still a lot to be done and tasks to be done. In this article, I go through the waste handling of ships in the Baltic Sea. The situation is from this year, and this text, fortunately, quickly becomes outdated as things develop.

Shipping must do its part

The most significant cause of eutrophication in the Baltic Sea is agriculture. It has been calculated that almost half of the phosphorus flowing into the Baltic Sea in Finland comes from agriculture, and a third of the nitrogen. Shipping’s share of the Baltic Sea eutrophication has been calculated to be only a few percent (Source). However, this does not mean that shipping should not do its part, even though agriculture is a bigger polluter.

Many types of solid waste are generated on board, such as food waste, packaging materials, materials used for cargo support, glass and other recyclable waste, paper and metal, as well as hazardous waste, such as paints and solvents. Even decades ago, it was common for ships to dispose of their waste simply by throwing it overboard. Sorting, handling and handing over waste to the port generate costs that were often considered extra in the operating environment at the time. On the other hand, burning waste on board has been around for a long time and is still a significant way of disposing of waste.

Nowadays, it is forbidden to throw all solid waste into the sea, with the exception of small exceptions, which can be left in the sea far from the shore. These exceptions include food waste and waste from animals transported on board. Solid waste is sorted and handed over to ports during port calls, unless it is incinerated on board. Problem waste, such as separation waste (sludge) and used lubricating oil from the cleaning of ships’ fuel, must be left in ports.

In the Baltic Sea, passenger ships are already leaving their black waters in ports

A lot of different types of waste water are generated on board. Black water is toilet waste water, and gray water is produced in showers and sinks and in ship kitchens. Both eutrophicate waterways, and especially large passenger ships generate large amounts of waste water.

According to international regulations, black sewage can be discharged into the sea untreated at a distance of 12 nautical miles from the coast and treated at a distance of three nautical miles.

In the Baltic Sea, however, the situation is different and all passenger ships must treat their toilet waste water or leave it in harbor reception facilities. Although this became mandatory only last year, shipping companies operating between Finland and Estonia/Sweden have been doing this for decades. It should be noted that this regulation does not apply to cargo ships.

The regulations do not apply to grey waters

There are no international regulations regarding grey water. On the other hand, it is understandable that attention has been focused on black waters in the past, but grey water emissions from large ships are nevertheless considerable. In addition, there is a lot of kitchen waste in greywater, i.e. in practice it’s just pure eutrophication waste.

Although oil accidents on ships are fortunately rare, almost every year we read about oily waste water left behind by ships. Oily bilge water accumulates on the bottom of ship’s engine rooms, the oil content of which is usually very low. In recent years, more and more attention has been paid to illegal bilge water discharges in the Baltic Sea, but it has been difficult to hold shipping companies accountable. Most ships have equipment that separates oil from water. This purified water can be released into the sea. If there is no equipment, the oily bilge water must be delivered to the ports.

Ballast waters carry alien species

The stability and manoeuvrability of the ship is affected by the weight of the cargo on board. When there is no cargo or there is less than usual, the ship usually takes ballast water from the local water area instead of the cargo. It is also often used as a stabilizer in a loaded ship. In large cargo ships, very large quantities of ballast water are needed. Ballast water contains plants, organisms and bacteria that migrate to new habitats and can spread there without restriction and destroy the local population. These alien species can cause considerable economic losses to power plants, water intakes and fisheries. Once a species has settled in a certain area, it is practically impossible to eradicate it.

The only way to combat alien species is to prevent their spread, i.e. in practice only take ballast water that is from the same area where it is released, or clean the ballast water. In 2024 the order to install ballast water purification systems on all ships will finally come into force. Technically, they are often very different systems, for example based on ultraviolet light or chemicals.

Using antifouling paints is a choice


The ship’s economic progress is also greatly influenced by the surface of the ship’s bottom. Microorganisms that stick to the bottom slow down the vehicle and increase fuel consumption. Throughout the ages, the hulls have been protected with various anti-sticking agents such as, for example, antifouling paints. It is often a matter of choice, antifouling agents reduce fuel consumption but are harmful to the marine environment.

Emissions from sulphur scrubbers are new pollutants

A new type of waste water caused by ships into the sea is the emissions from scrubbers that reduce the sulphur content of exhaust gases. There are two types of scrubbers, closed loop and open loop systems. In closed-loop systems, the waste coming from exhaust gas cleaning is delivered to land, but open-loop systems leave the waste in the sea. In addition to sulfur, it often also contains other harmful heavy metals. Most of the scrubbers used in the Baltic Sea are open circulation systems.

Cargo residues and washing waters to ports

A wide variety of cargoes are transported in the cargo hold of ships, and some of them are completely harmless to the environment and others are very harmful or even toxic. When changing the type of cargo, the residues of the previous cargo must be completely removed before new loading. According to the regulations, harmful cargo residues and washing waters must be left in the port’s reception systems. Harmless washing waters and cargo residues can be left 12 nautical miles from the coast if the port does not have adequate reception systems. In addition to the above, engine cooling waters, if seawater is used for engine cooling, can cause harmful environmental effects.

The “no special fee” system encourages proper waste treatment

As you can see, unfortunately, there is still a lot of waste from ships going into the sea. In order to reduce illegal emissions in the Baltic Sea, so-called “no special fee” – a system whose idea is that a ship coming to the port pays a waste fee anyway when leaving oily waste, black water and solid garbage. Thus, the vessel does not save a penny by leaving the waste in the sea on the way to the port. However, the system does not cover, for example, hold’s wash water or scrubber wastewater.

At the moment, ports are obliged to accept all the waste that ships want to leave, but they can charge the reception as they wish. The most significant current developments, such as the John Nurminen Foundation and Traficom’s project mentioned at the beginning, have focused on expanding the “no special fee” system also to waste or wastewater that is not illegal to discharge into the sea. In other words, that the ships would also leave all the wash water and grey water from the cargo holds in the ports, and above all that the ships would know what can be left in which port.

From the news I’ve heard from the field, the steps towards leaving all waste in ports have made good progress, but there is still work to be done to ensure that all ships leave all their waste and sewage ashore and that ports receive and process it properly.

This blog has been published previously in Finnish in Navigator Magazine in December 2022.

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