International regulations putting limits on emissionsAs a response to these issues, environmental regulations in the shipping sector are becoming increasingly stringent. In September 2017, the Ballast Water Management Convention came into force. More recently, the International Maritime Organization's (IMO) 2020 regulation put a cap on the maximum sulfur content allowed in maritime fuels. The shipping industry has been one of the greatest emitters of sulfur dioxide, which can cause respiratory issues in humans, as well as the formation of acid rain and particulate matter. In an effort to curb SOx emissions, the IMO established a cap of 0.5 percent m/m (mass by mass) on marine fuels. Alternatively, ships that still use heavy fuel oil (HFO) must install exhaust gas cleaning systems (also known as scrubbers) to comply with the emissions reduction standards.
However, the increasing use of scrubbers brings about a new problem. Scrubbers remove pollutants by spraying seawater over the ship’s exhaust gases. This mixture of seawater and pollutants – called scrubber wash water – is then discharged overboard, where it can damage marine ecosystems. The concentration of scrubber wash water is especially high in ports, driving some countries to ban wash water discharge in their ports.