The current U.S. Navy Fleet has more than 170 oil/water separators (OWS) as primary treatment systems and 30-35 of these ships now have membrane-based ultrafiltration systems for secondary treatment. The presence of solids or particulate matter in Navy shipboard oily waste processing streams is known to negatively impact the operation and performance of oil pollution abatement (OPA) equipment. Solids removal is a critical step in the treatment of ships' oily waste streams, e.g., bilgewater. Wastewater solids build up rapidly on currently available filters, resulting in frequent backflushing. Solids that are not properly managed contribute to increased maintenance requirements, system downtime, and associated costs that may otherwise have been avoided. Inspections of OWS' plate stack assemblies have shown that over time, unprocessed particulate matter accumulates in the system, reducing performance and requiring more frequent maintenance. Solids can also cling to oil droplets suspended in water, making the droplet neutrally or negatively buoyant and resulting in oil passing through the OWS and accumulating on the membrane faces. Clogging of the openings to the ceramic membrane lumens (axial channels through which the wastewater flows) has been a continuing problem. Solids blocking the lumen entrances can (1) severely reduce the membrane flow rate resulting in much lower bilgewater processing rates, (2) increase membrane regeneration frequency, and (3) require manual removal and cleaning of the membranes. These maintenance issues are directly attributable to the inability of current treatment system filters to reliably remove solids from the waste stream.
The objective of this project is to demonstrate the ability of the Bacti-Twist Filter Media (BTFM) or POM-POM technology to retain solids from shipboard generated oily waste with measurement of key effluent quality parameters.
The POM-POM filter is a black spiral-shaped plastic media made of polypropylene material, which is hydrophobic, giving it the ability to attract the complex hydrophobic mixture of oil, fine solids, and surfactants present in bilgewater. These contaminants have hydrophobic properties making them attracted to each other and the hydrophobic material or media. There is a piling-on-effect that occurs after particles begin to attach to the polypropylene media. With captured solids entrained, the 18-inch diameter POM-POM (0.5 lb dry weight) can weigh anywhere from 9 to 26 lb each. The POM-POM filter can be cleaned and reused, as trapped solids are easily removed through a quick shake-and-rinse procedure. The POM-POM filter has 95 sq ft of surface area per cu ft. It is highly resistant to cracking and has a melting point of 160°C. It is highly resistant to most alkalis and acid, organic solvents, and degreasing agents. The POM-POM material is nontoxic. The POM-POM filter has been demonstrated in three configurations: (1) as a dispersion device; (2) as a filter media, which is the application in this project; and (3) as a replacement for laminar plates and packing in a wastewater clarifier.
The project will conduct laboratory and shipboard evaluations to validate the performance of the POM-POM filter. Additionally, the evaluations will determine the system's reliability, operation, maintenance, and integration requirements.
A successful demonstration and validation of the POM-POM filter will provide Armed Forces ships with a filter media system that would allow the ships to process their oily waste without being hindered by solids. Maintenance for an OWS with the POM-POM will be lower than one without the technology. The filter will reduce the frequency of solids clogging membranes and membrane face plugging events. The filter should also help decrease the manpower requirement and costs associated with operating and maintaining the OPA treatment systems. The life of the primary and secondary treatment stages will be longer with the POM-POM filter. (Anticipated Project Completion - 2015)