In the past, wastewater on board ships has been discharged directly to the ocean. Several years ago, the International Maritime Organizations Marine Pollution Convention (MARPOL) restricted that discharge, whereby graywater and blackwater had to be treated to remove harmful microbiological organisms and reduce its biological oxygen command (BOD) and chemical oxygen demand on the environment. Graywater is the water coming from showers and dishwashing facilities, while blackwater originates from the degradation of sewage and garbage material.
This project was designed to develop a process to treat graywater prior to discharge to meet the anticipated effluent quality requirements of the U.S. Environmental Protection Agency and Annex IV of the MARPOL protocol.
Membrane filtration was selected as the most viable treatment option that will meet anticipated discharge standards. It is affordable (with respect to capital, logistics, and manpower), compact (both in space and weight), reliable, and safe. A first-generation, membrane-based graywater treatment system was demonstrated successfully in the laboratory using Navy-generated land-based graywater mixtures. The first stage of the system uses large-bore, polymeric membranes to trap coarse and fine solids and to remove a significant amount of BOD and fecal coliform bacteria. A second-stage nanofilter enables the system to remove dissolved organics and further reduce the effluent concentrations of BOD and suspended solids.
Tests were conducted on graywater from the USS L.Y. SPEAR while pierside at Norfolk Naval Base, VA. A 3 gal/min prototype unit was evaluated for 850 hours. Results showed that the membrane system potentially can meet anticipated U.S. and international discharge standards for graywater. In consultation with membrane experts from academia and industry, the Navy will use data from these pierside tests to determine the final design parameters for a shipboard graywater treatment system. This project was completed in FY 1996.
The graywater treatment process will be suitable for backfit into existing Department of Defense surface ships. Benefits include extended operational time in environmentally sensitive waters, ability to dock in domestic and foreign ports that do not have pier side waste collection facilities, and cost avoidance related to those facilities that do.