Liquid Wastes
Navy ships also produce tremendous volumes of blackwater (from toilets and urinals), graywater (from showers, sinks, laundnes, galleys, and sculleries), and oily waste (primarily bilgewater). Blackwater and graywater generatio, like solid wastes, are a function of crew size, whereas oily waste generation is more a function of the type and age of ship.
Most Navy ships are equipped with tankage to hold blackwater while within 3 nm of land. One class of amphibious ship is outfitted with biological treatment systems for b Blackwater, but they are targeted for removal due to serious operational problems. Two classes of destroyers have vortex incinerators that burn vacuum-collected blackwater, but these have experienced significant reliability problems that discourage their use. To determine whether this decades-old incinerator design is still an appropriate shipboard technology. NAVSEA recently defined Fleet problems and identified and tested a range of improvements. It was found that vortex incineration is a simple yet efficient process and that the current incinerators remain a valid approach for blackwater disposal if certain modifications are made in materials, controls. operating procedures, maintenance, documentation, and training. Improvements are also needed in the VCHT system that feeds the incinerator.
Navy ships do not have the capability to hold glnaywater, although they can collect it and pump it to piercide connections or barges when in port. Until recently, there has been no legal or regulatory incentive to control shipboard grayuater, but some states have been attempting to restrict discharges and there is now a Federal regulatory program (UNDS) that will require some shipboard control to be implemented. A graywater treatment system consisting of aeration polymeric membrane ultrafiltration and ultraviolet disaffection is under development at NAVSEA. This system will produce an effluent clean enough to discharge under foreseeable regulatory schemes and a concentrated stream that could be held or fed into a future thermal destruction device. This system will also be tested with blackwater to determine the prospect for a total non-oily wastewater treatment solution.
Navy ships do not hold bilgewater, but rather pass it through a gravity oil/water separator (OWS) and hold the concerntrated reduced-volume stream. The OWS contains parallel plastic plates that promote the aggregation and buoyancy of oil droplets, which can be removed as a floating layer from the top of the separator. A downstream turbidity-based oil content monitor (OCM) will divert OWS effluent back to the oily waste processing system when oil concentrations exceed: about 15 ppm rather than allow it to be discharged overboard. Unfortunately, OWS operation is adversely affected by detergents and other emulsifiers (especially AFFF) commonly found in bilgewater, resulting in higher-than-allowed oil concentrations in the effluent. An oily waste treatment system is being developed that can tolerate bilgewater contaminants while producing an effluent with oil levels lower than can be achieved with current OWSs. Prototype systems on two ships are being allowed to discharge effluent in port (Mayport and San Diego). This technology is based on ceramic ultrafiltration membranes and will be used in conjunction with gravity oil-water separation. A high-flow system is being developed for large ships and a new space-efficient system that combinence bulk oil separation with ultrafiltration is being designed for potential future applications.
As for solid wastes, the Navy envisions thermal destruction as the ultimate solution for the disposal of high-volume shipboard liquid wastes (blackwater, graywater, and bilgewater). Refurbishment of a shipboard blackwater vortex incinerator and related computational fluid dynamics (CFD) modeling indicates that vortex combustion is a very efiicient and simple process for burning liquid effluents. NAVSEA is now studying the feasibility of modifying the Navy's existing vortex incinerator to bum concentrated graywater, concentrated bilgewater, and waste oil, in addition to concentrated blackwater. An Engineering Development Model (EDM) vortex incinerator is being used to burn concertrated graywater and blackwater in the laboratory while air emissions are being closely analyzed.
