Phosphorus and nitrogen in the waste discharged from ships are low compared to the total load of nutrients that enter the Baltic sea. However, the shipping in the Baltic Sea is intense and expected to increase, one of the key goals by the European Commission is a shift of medium distance passenger and freight journeys from road to rail and waterborne transport. And with increasing growth of maritime transport and cruise shipping, effective food waste management becomes a pressing issue, Magda Wilewska-Bien writes in her thesis.
Food waste excepted from regulations
In the Baltic Sea discharges of sewage from passenger ships will soon be prohibited, but food waste and grey water (wastewater from dishwashing, shower, laundry etc.) are not included in the coming regulations. Food waste can either be stored for disposal in port or handled at sea. It is allowed to, with some exceptions and limitations, to discharge ground food waste at sea when the ship is moving at the distance of minimum 12 nautical miles from nearest land and the food waste pieces should not be larger than 25mm.
It’s a challenge, Marie Wilewska-Bien writes, to get a clear picture of how much food waste that is disposed in the Baltic Sea ports, since much information is not publicly available. But an estimation is that the food waste from cargo ships is 0,2-0,5 kg per person and day. For cruise ships 2 kg per person and day. An earlier study, made in Norwegian waters, showed that about 2% of the total generated food waste was discharged to the sea from passenger ships, 40% from bulk carriers, 52% from dry bulk carriers and 92% from general cargo vessels.
The annual contributions of nutrients from ship generated food waste is about 182 tonnes nitrogen and 34 tonnes phosphorus. In the light of an expected global phosphorus scarcity, there is a potential to recover phosphorus and therefore it is preferable to encourage ships to dispose the waste ashore where it can be recycled further to recycle the phosphorus.
In Magda Wilewska-Biens thesis, a sustainable solution for ship-generated food waste is based on three pillars: the food waste should be separated from other waste streams (1) it should be measured (2) and constantly reduced (3). It should preferably be disposed onshore, where it further is managed to recover energy and valuable constituents.