The cruise ship industry, in recent years, has begun to worry about the environmental impact. Cruise ships generally use Heavy Fuel Oil (HFO), which is a low-cost fuel with a particularly high viscosity and density [1]. Since 1960s HFO has been by far the most used fuel, and it has been one of the reasons for the robust growth of international maritime trade. But, besides of being a low-cost fuel, HFO is also a low-quality fuel, and it has raised concerns over its environmental impact and its contribution to anthropogenic climate change caused by the greenhouse gases emitted by the burning of HFOs to power shipping. In particular, HFO contains high levels of asphalt, carbon residues, sulfur and metallic compounds. Its high sulfur content (up to 4.5%) leads to particularly high sulfur oxide (SOx) emissions thus contributing in a significant manner to the global emissions of sulfur dioxide (SO2).
In the 1970s the International Maritime Organization (IMO) issued MARPOL 73/78 in order to minimize pollution of the oceans and seas, including dumping, oil and air pollution.
