Naval Surface Warfare Center, Carderock Division (NSWCCD), WP-201708, has begun the laboratory evaluation of a High Shear Rotary Membrane System (HSRMS) for treatment of shipboard produced bilgewater. Expectations of HSRMS are to reduce both the cost of operation and shipboard footprint – in comparison to the bilgewater treatment systems aboard Armed Forces vessels.

Bilgewater is the wastewater from a variety of sources that accumulates in the lowest part of the vessel (the bilge). Bilgewater consists of water and other residue that accumulates in a compartment of the vessel’s hull or is collected in the oily waste holding tank or any other oily water holding tank. The primary sources of drainage into the bilge are the main engine room(s) and auxiliary machinery room(s), which house the vessel’s propulsion system and auxiliary systems (i.e., steam boilers and water purification systems), respectively.

Figure 1: Membrane and operational schematic

The composition of bilgewater varies from vessel-to-vessel and from day-today on the same vessel. The propulsion and auxiliary systems use fuels, lubricants, hydraulic fluid, antifreeze, solvents, and cleaning chemicals as part of routine operation and maintenance. Small quantities of these materials enter the bilge as leaks and spills in the engineering spaces. Bilgewater generation rates vary by vessel and by vessel class because of the differences in vessel age, shipboard equipment (e.g., type of propulsion system), operations, whether the vessel segregates its nonoily wastewater from the bilge, and other procedures. 

Typical bilgewater may be (1) offloaded to a shore-installation for proper handling, which includes treatment and discharge; (2) left onboard as ballast; (3) fully treated and discharged at sea in accordance with DoD environmental regulation.  The objectives of this laboratory evaluation are to determine performance, reliability, maintainability, and availability in processing the highly variable bilgewater found Armed Forces ships in support of (3); producing an effluent that meets success-measures (below) and the discharge requirement of having an oil concentration of less than 15 ppm.

System Processing Performance • Membrane Life • Membrane Regeneration Reliability • Availability • Maintainability • Operability

Figure 2: Onboard Stacked Membranes

HSRMS uses ultrafiltration membranes to separate oils including small, stable oil-in-water emulsions from bilgewater. During typical membrane separation, contaminant accumulations at the membrane surface contribute to the need for frequent cleanings and reduced membrane life. HSRMS generates shear forces by rotating the membranes in the process fluid with turbulence. This action generates baffles which clean contaminant accumulation from the membrane surface.

With a successful laboratory performance evaluation, the system will undergo a full-scale shipboard demonstration.  Military Sealift Command has identified a candidate platform to host the prototype HSRMS shipboard demonstration.  Figure 2 depicts the approximate footprint of the stacked membrane system as it would be installed onto a vessel.

Stakeholders for this project include:

  • Naval Sea Systems Command (NAVSEA) Wet Environmental Systems and Discharges Technical Warrant Holder (05P5)
  • Military Sealift Command (MSC)