Management of ship-generated waste - illustrated from the Baltic Sea perspective
Globally around one-third of food produced for human consumption is wasted or lost. Although the food waste issues on land are being widely discussed, the food waste generated on ships seems not to receive similar attention. The Baltic Sea suffers from elevated nutrient levels and has been, as the first region in the world, designated special area under MARPOL Annex IV where discharges of sewage from passenger ships are prohibited. The food waste and grey water are not included in the coming regulations. The annual contribution of nutrients from ship generated food waste is about 182 tonnes N and 34 tonnes P, which is 2-3 times lower than nutrient contribution from ship-generated sewage. Nitrogen and phosphorous in the waste discharged from the ships are low compared to the total load of nutrients that enter the Baltic Sea. The phosphorus discharged with the waste is of interest in analysing the impact on cyanobacteria growth. It has been calculated, for areas with high cruise ship traffic that the phosphorus load in close vicinity of the ship is comparable to the load of phosphorus from the air deposition. The calculated P load is however most likely very temporary due to the ship and water movements. The waste generated on board ships operating in the Baltic Sea contain phosphorous estimated to be 100 tonnes annually and in the light of expected global phosphorus scarcity there is potential to recover this element. Therefore, it is preferable to encourage ships to dispose the waste ashore, where it can be processed further to recycle the phosphorus. In the processing of wastes, it is important to consider also the rest-products and their further fate. Combustion of solid waste generates ash streams that need to be disposed. The suggested washing process helps to reduce leaching of soluble salts from the cyclone ash from municipal solid waste. Antimony however was mobilized by the ash treatment and this should issue be monitored. In this work a sustainable solution for the ship-generated food waste in the region is based on three pillars: the food waste should be (1)separated from other waste streams, (2) it should be measured and (3) constantly reduced. The food waste preferably should be disposed onshore in a well-working cooperation between actors from ship and land, where it further is managed to recover energy and valuable constituents. However, the pathways towards this scenario vary according to the individual ships and their unique characteristics and the ship operators may use tools from technology, economy, management and regulations areas. The solutions used on land can be also applied in shipping, but with modification to fit the maritime environment.