Destruction of marine sewage using conventional engine technology

Ship operators are under mounting environmental pressure to reduce, and in certain cases totally eliminate, the discharge of waste into the sea. At the moment, beyond the twelve mile limit, untreated sewage can be legally discharged into the open oceans. For some types of waste, there is international nil-discharge legislation which prohibits any dumping in certain sea areas. In the future, sewage is likely to be identified as one of these nil-discharge waste materials. Thus, there may soon be a requirement for onboard sewage systems that are capable of meeting this requirement. In this paper, the novel concept of using marine diesel engines to thermally destroy sewage streams is considered. The main constituent of such effluents is water, about 90% and an appreciable amount of the solid content is combustible. As direct water injection is now an established technology for NO/sub x/ reduction from marine diesel engines, it appears feasible, at least technically, to use such technology in sewage stream treatment. Preliminary estimates have shown that the sewage stream quantities produced onboard large marine vessels could be treated using the ships' existing diesel engines. The outline requirements for such marine diesel engines to be operated as sewage processors are discussed in this paper.