Thermal destruction is the centerpiece of an Integrated Liquid Discharge System (ILDS) for future ships, whereby several of the systems currently under development by the Navy (oily ultrafiltration, non-oily wastewater ultrafiltration, and vortex incineration) will be brought together, along with ship-wide effluent collection systems. ILDS will avoid the need for large tankage volumes and, as long as incineration is allowed in port, will free ships from barge and pierside connections. Because of the need to integrate extensive piping networks to collect liquid wastes, process them through concentration systems, discharge clean effluents, and bring the concentrates to a centralized location, there is little e potential for backfitting the entire system.
Compensated fuel ballast systems (CFBSs) are intended to maintain ship stability by keeping the fuel tanks always full of fuel and/or seawater. The differing sizes, Configurations, and complex internal structure of the fuel tanks in a CFBS, combined with high refueling rates, create turbulent and dynamic fluid flow conditions that cause mixing of the fuel and ballast seawater and often results in the inadvertent discharge of ballast water containing more than 15-ppm oil. This problem also greatly reduces the amount of fuel that can be contained in the tanks because of water "hideout." The design of these fuel systems has been driven primarily by structural and ballasting considerations rather than the environmental impact of accidental fuel releases. The current Fleet strategy for minimizing the chance of oily discharge during refueling relies on manpower-intensive watchstanding and fueling rate reductions (which prolong the refueling evolution). The NAVSEA RDT&E program is using CFD simulation and physical modeling to identify the causes and locations of fuel-water mixing within the CFBS and to identify design and operational modifications to preserve fuel-water separation during refueling so that only clean ballast water leaves the system. This will not only address a growing Fleet environmental issue, but also ship fuel capacity and manning problems. It is expected that some relatively simple "fixes" can be adopted by existing CFBS ships and that new design guidance will make CFBS more attractive for new ships.
As mentioned previously, 25 shipboard liquid wastes will require MPCDs under the legislatively-mandated UNDS program. Graywater, bilgewater, and compensated fuel ballast water are three of these wastes. The remaining 22 UNDS discharges are: aqueous film-forming foam, catapult water brake tank and post-launch retraction exhaust, chain locker effluent clean ballast, controllable pitch propeller hydraulic fluid deck runoff, dirty ballast, distillation and reverse osmosis brine, elevator pit effluent firemain systems, gas turbine water wash, hull coating leachate, motor gasoline compensating discharge, non-oily machinery wastewater, photographic laboratory drains seawater cooling overboard discharge, seawater piping biofouling prevention, small boat engine wet exhaust, sonar dome discharge, submarine bilgewater, bilgewater ship husbandry, and welldeck discharges. An MPCD can be hardware or a management practice and, furthermore, it may already be employed on some or all vessels of the Fleet. Therefore, RDT&E may not be necessary to develop or engineer a suitable technology for every MPCD that must be implemented.
RDT&E is to begin in FY00 on two of these UNDS discharges: hull coating leachate and underwater hull cleaning. Both of these 6.4 Demonstration/Validation efforts will transition from ONR science and technology (S&T) successes. Reduction of leachable toxic constituents (mainly copper and zinc) from hull antifouling coatings on Navy vessels will focus, in the long tern, on new low-release formulations and, in the long term, on new non-toxic easy-release coating systems. In additios to at least matching the antifouling performance of the Navy's existing copper-based coating while reducing the release of regulated constituents to the marine environment, the new coatings will hopefully have longer service lives and therefore, reduce maintenance costs and support the Navy's desire for longer drydocking intervals. For hull husbandry, a novel underwater hull cleaning vehicle with advanced sensors and cleaning mechanisms will be developed, along with an effluent capture and pierside treatnent system.
