Full Scale Particle Removal Performance of Three Types of Mechanical Separation Devices for the Primary Treatment of Ballast Water

Abstract

The Great Lakes Ballast Technology Demonstration Project has undertaken a multi-year program to demonstrate and evaluate ballast treatment methodologies that might minimize the potential for the introduction of additional nonindigenous aquatic species into the Great Lakes and other U.S. waters. Full-scale mechanical and biological testing of primary and secondary treatment options has been performed on both operating vessels and a ballast treatment testing barge facility located in Duluth and Two Harbors, Minnesota. Mechanical testing results for three candidate primary mechanical separation devices obtained over a four-year period on the barge installation are presented and compared. Results are presented for the particle removal efficiency at a nominal 340 m3 /h (1500 U.S. gpm) for a 50 micron (µm) screen-type surface automatic backwash filter, a 100 µm rated cyclonic separation device, and a 100 µm disk-type depth automatic backwash filter. The screen-type and disk-type automatic backwash filters showed particle removal efficiencies at and above their removal rating of over 90%. Although more complicated, the disk-type depth filter exhibited a significant advantage through a longer time between backwash cycles and, thus, a greater net filtration throughput. The hydrocyclone demonstrated significantly lower effectiveness (about 30%) in removing particles that included both neutrally buoyant biota and other materials such that, while much simpler, these devices are not considered appropriate for this application requiring the effective removal of both particulate material and larger biota.