Combined Centrifugal Separator/Membrane Ultrafiltration System for Shipboard Treatment of Bilge and Ballast Water

Ships generate large volumes of bilge and ballast water which, to meet new environmental regulations, will require treatment prior to overboard discharge. Such wastewaters contain high levels of emulsified and free-phase oil and suspended solids. Treatment by ultrafiltration can produce dischargeable water, but all currently available membranes are finely porous and only moderately hydrophilic. They are, therefore, subject to severe fouling by oil and particulates. In this project, a process combining a centrifugal separator as the pretreatment step and a novel class of a fouling-resistant composite ultrafiltration membrane as the polishing step will be developed. The centrifugal pretreatment will provide an efficient removal of solids and large oil droplets, a high turndown ratio for handling highly variable wastewater output, low cost and footprint, and the ability to withstand oscillations of the ship. Membrane Technology and Research, Inc.'s novel fouling-resistant membrane will comprise a thin layer of a highly water-permeable, nonporous, fouling-resistant polymer on a microporous support. The Phase I objective is to demonstrate that a centrifugal separator/membrane ultrafiltration system can treat the bilge and ballast water generated on ships efficiently and economically. The organic solute rejection, water flux, chemical stability, and fouling resistance of the membrane will be determined. An integrated system combining the centrifugal separator and the ultrafiltration unit will be tested extensively for reliability and consistency of operation. In Phase II, the process will be demonstrated on actual shipboard wastewater streams. If successfully developed, the proposed system will not only reduce operating costs by as much as 50 percent, but also will cost 25 percent less to install compared with existing membrane systems. This is expected to lead to immediate and wide adoption for shipboard use and subsequently for industrial applications that require the separation of dissolved and emulsified oil from water.