Moffitt, C. M., B. J. Watten, A. Barenberg, and J. Henquinet. 2015. Hydroxide stabilization as a new tool for ballast disinfection: efficacy of treatment on zooplankton. Management of Biological Invasions. 6:263-275.
Abstract
Effective and economical tools are needed for treating ship ballast to meet new regulatory requirements designed to reduce the introduction of invasive aquatic species related to ship traffic. We tested the efficacy of hydroxide stabilization as a ballast disinfection tool in replicated, sequential field trials on board the M/V Ranger III in waters of Lake Superior. Ballast water was introduced into each of four identical 1,320 L stainless steel tanks during a simulated ballasting operation. Two tanks were treated with NaOH to elevate the pH to 11.7 and the remaining two tanks were held as controls without pH alteration. After retention on board for 14 - 18 hours, CO2 rich gas recovered from one of two diesel propulsion engines was sparged into the tanks treated with NaOH for a period of 2 hours to force conversion of NaOH ultimately to sodium bicarbonate thereby lowering pH to our target of about 7.1. The engine exhaust was treated, prior to use, by a unique catalytic converter/ wet scrubber process train. Following carbonation, the contents of each tank were drained and filtered through 35 µm mesh plankton nets to collect zooplankton. The composition and relative survival of the contents of each tank were evaluated in the laboratory by microscopy. Zooplankton populations were dominated by rotifers, but also included copepods and cladocera. Hydroxide stabilization was 100% effective in killing all zooplankton present at the start of the tests. Our results suggest hydroxide stabilization has potential to be an effective and practical tool to disinfect ship ballast. Further, the end product of the reaction utilized provides an increase in alkalinity as well as a net reduction in ship engine CO2 emissions.