Ship-generated nutrient discharges on the Baltic Sea

Céline Vaneeckhaute,
Canada Research Chair in Resource Recovery and Bioproducts Engineering

BioEngine Research Team and Laboratory on Green Process Engineering and Biorefineries (BioEngine)

Associate Professor,
Department of Chemical Engineering, Faculty of Science and Engineering, Université Laval,
Québec, QC, Canada

Nutrient discharges into the Baltic Sea and the resulting phenomenon of eutrophication have caused environmental issues in the area for decades. Eutrophication is characterized by the proliferation of harmful algae blooms and low-oxygen (hypoxic) waters, all affecting ecosystem diversity, aquaculture activities and tourism, to name a few. The increase in maritime transportation and the resulting increased production of ship-generated wastes contribute to the devastating environmental impact on maritime ecosystems worldwide. Due to its important ecological and socio-economic character, the Baltic Sea has been designated as Particularly Sensitive Sea Area (PSSA) by the International Maritime Organization (IMO) in 2005. This involves the application of strict discharge regulations provided by the International Convention for the Prevention of Pollution from Ships (MARPOL), as well as the need for specialized equipment on board of ships.

Ship-generated nutrient discharges into the Baltic Sea mainly include food waste and sewage. Regarding food waste, its discharge after grinding or comminution at more than 12 nautical miles from the nearest land is still allowed and common practice on the Baltic Sea. Nevertheless, a more sustainable approach may include its valorisation through, for example, anaerobic digestion or composting, either on board of ships or following delivery at port reception facilities. This would allow recovering valuable nutrients as a fertilizer product, all while producing bioenergy in the case of anaerobic digestion. These products could be used on board of ships (for example, for ship-based food production), at the port, or marketed elsewhere. It should be emphasised, however, that priority must still be given to the reduction of food waste production at the source, mainly in the case of cruise ships.

Ship-generated sewage includes black and grey water. Black water includes sewage generated by toilets, urinals and medical facilities, while grey water comes from showers, baths, sinks, laundry and dishwashers. Typically, less water is used on board of ships as compared to land-based applications; hence, sewage on ships is typically two to three times more concentrated as compared to its land-based equivalent. The discharge of untreated black water on the Baltic Sea is prohibited, but no special limitations exist to date for grey water discharge. Since 2019, advanced treatment systems treating nitrogen and phosphorus are required on all new passenger ships in the Baltic Sea area, or the black water must be delivered to port reception facilities for treatment. Although multiple advanced treatment systems are available today that meet the required discharge regulations, further improvement regarding the sustainability of these systems is possible. Current research at the BioEngine research team on Green Process Engineering and Biorefineries (Université Laval, Canada) looks at the recovery of these nutrients instead of their removal. This would allow for their valuable reuse, for example as mineral fertilizer products. Reuse of the valuable resource, water itself, is also being looked at. Moreover, wastewater treatment also typically produces a residual sludge stream, which should be disposed of properly. The latter could be valorised through anaerobic digestion or composting, along with food waste as indicated above. All of this could help to further reduce the environmental, economic and social impact of ship-generated wastes on the Baltic Sea.

In order to facilitate decision-making regarding the selection of the most sustainable waste management option, research has been initiated at the BioEngine research team aiming at the development of a decision-support system for ship-based organic waste valorisation, including food waste and sewage. The software tool should allow determining, comparing and optimizing the economic, environmental and social benefits of various waste valorisation strategies.


Expert article 3143

> Back to Baltic Rim Economies 5/2021

To receive the Baltic Rim Economies review free of charge, you may register to the mailing list.
The review is published 4-6 times a year.