Economic viability of treating ballast water of ships by ultrafiltration as a function of the process position

Abstract

Ballast water is fresh or seawater taken onboard to stabilize a ship. By traveling with the vessels, different species can be introduced into a new area with potentially high impact on health, economy, and environment. Some conventional treatments may reach their limit because of the high variability of water quality found worldwide: for example, UV treatments efficiency can be low for highly turbid water. Currently, 30% of ballast water treatment uses UV, while 45% use a chlorine generation process. Membrane filtration could be a promising alternative, or complementary treatment. An efficient ballast water management system is required to discharge treated water into the environment. The aim of this paper is to compare, from an economic perspective, ultrafiltration with UV treatments applied to fresh and seawater. This comparison takes into account the location of the treatment, and the specific challenges associated with each location. This modeling, based on feedback from various ship-owners, includes ballast water discharge flow, as well as ballast loading and discharge times. These operations stop the ship and increase its annual down time. Several scenarios of ballast water treatment were studied following the various condition: during ballast loading or ballast water discharge; on-board processing with batch treatment; barge-based processing with semi-continuous treatment, or with continuous treatment to ballast several ships per day; with or without UV post-treatment. The on-board ultrafiltration installation does not appear economically viable, whereas the barge-based installation is very competitive and retains better suspended matter and organisms.