The Israeli Navy has installed a bio-treatment facility, which separates contamination from wastewater coming out of the diesel engines of its ships. Engine wastewater from many ships is collected into a single, large tank. A biological treatment agent is added, which cleans the water to the extent that it may be returned to the sea.
http://www.jpost.com/Sci-Tech/Article.aspx?ID=301451&R=R1