The objective of this effort is to demonstrate the full scale performance and integrated operation of advanced high shear rotary membrane technology through laboratory performance verification and shipboard demonstration and validation for subsequent implementation. This effort integrates advanced high shear rotary membrane technology and performance-based operating configurations for the effective treatment of shipboard bilgewater. The technical objectives of this project are divided into two segments, (1) successful performance-based laboratory demonstration and (2) successful shipboard installation and performance demonstration and validation.
High Shear Rotary Membrane System (HSRMS) uses ultrafiltration membranes to separate small, stable solids and liquids (e.g. oils, particulates, fibers, colloidal particles) from liquid waste streams. During typical membrane separation, contaminant accumulations at the membrane surface and concentration polarization (CP) contribute to decreasing flux, causing the need for frequent cleanings or reducing membrane life. Conventional membrane systems apply high cross-flow velocities with large pumps to promote shear forces, creating turbulence and mixing at the membrane surface to minimize CP. The HSRMS generates shear forces by rotating the membrane within the process fluid. This approach allows for simpler configuration, trading pumps for mechanical drives to simulate cross-flow conditions. Methods to further enhance turbulence and shear at the membrane surface include incorporating stationary shear elements between each rotating membrane disk or to interleave or nest multiple disk stacks. Also, because the feed delivery and pressurization are decoupled from turbulence or shear promotion, the HSRMS can be operated at lower transmembrane pressures which decreases solute boundary layer compaction and pore plugging in comparison to conventional membrane systems, which extends cleaning frequencies and membrane life. Previous HSRMS research was conducted by the Naval Surface Warfare Center, Carderock Division (NSWCCD) and University of Maryland, Baltimore County (UMBC) through the Strategic Environmental Research and Development Program (SERDP), project WP-1671, and co-sponsored by the Office of Naval Research (ONR). This work investigated the correlation between membrane disk diameter, material, pore size, rotation rate, and the effects of back pulsing and continuous surface cleaning performance of Navy shipboard waste streams, specifically bilgewater. Only the ceramic disk membranes manufactured by KERAFOL proved capable of being configured and used to treat simulated bilgewater containing chemical emulsions and solids to an effluent oil concentration of 15 parts per million (ppm) or less in compliance with Federal and international discharge regulations. Based on cumulative findings from WP-1671, NSWCCD investigated currently available commercial HSRMSs though Environmental Security Technology Certification Program (ESTCP) Project WP-201520, which could accept ceramic disks recommended from SERDP studies for bilgewater treatment at a level adequate to demonstrate and validate the technology for dynamic shipboard use.
In-port disposal of bilgewater incurs high cost to Armed Forces vessels, an expense which increases if an oily water separator (OWS) is ineffective and cannot reduce the oil content to below 15 ppm necessitating holding and shore transfer. A successful demonstration will provide Armed Forces vessels with a capable, single OWS system that can effectively treat bilgewater with stable oil-in-water emulsions and free oil. Additional benefits include a reduced foot print due to higher flux rates, lower consumable cost, and a simpler system configuration in comparison to conventional OWS/Navy membrane systems. The HSRMS also has the potential to be significantly smaller and lighter than current OWSs installed aboard Armed Forces vessels. The rotation-induced continuous-cleaning ability of the HSRMS should result in sustaining high flux rates throughout membrane use, decreasing the cost and burden of maintaining the Oil Pollution Abatement (OPA) system. Demonstration of this technology as a full-scale effort could provide the Armed Forces with the current benefits of ceramic membrane technology such as environmental compliance, regeneration ability, chemical robustness, and lower cost. These benefits cannot be attained in conventional ceramic membrane and OWS systems.