The National Shipbuilding Research Program. Waste Water Treatment Technology Survey

The objective of this project was to investigate methods for treating the ballast water from naval vessels that have compensated fuel tanks. For a repair availability these tanks must be emptied cleaned and gas freed before they can be worked on. This process needs to be performed quickly to avoid delays and associated costs in the yard. The goal was to identify treatment technologies that could process the ballast water at 500 gpm and clean it sufficiency to discharge it back into the local navigable waters. There are about 100 vessels in the group of ships with compensated fuel tanks. With an oil and water interface there is some mixing of fuel and water so that free oil and emulsified oil are part of the ballast water. The free oil can be separated from the water more easily than the emulsified oil. Testing of the ballast water turned up different amounts of emulsified oil which at less than 10 ppm can still leave a sheen on the water. A number of treatment solutions were studied with a combination of coalescing tanks or specialized high speed centrifuges, along with dissolved or infused air flotation surfacing as the best treatment methods for a 500 gpm system. Use of a storage system to hold the water until processed by a slower system was also studied. Cost benefit and sensitivity analyses are presented. In the final analysis there are a number of options to choose from for a shipyard facing this problem. Tools are provided for a yard to perform its own analysis.

Prepared in cooperation with National Steel and Shipbuilding Company, San Diego, CA.