Great Ships Initiative: Final Report of Land-Based Freshwater Testing of a Ballast Water Treatment Involving Sodium Hypochlorite (NaOCl)

Abstract

The Great Ships Initiative (GSI) provides independent, no-cost performance/verification testing services to developers of ballast water treatment systems (BWTSs) at the bench, land-based and shipboard scales. GSI has the expertise and resources to perform tests consistent with the requirements of the International Maritime Organization’s (IMO’s) International Convention for the Control and Management of Ships’ Ballast Water and Sediments (IMO, 2004) and the United States Environmental Protection Agency’s (USEPA’s) Environmental Technology Verification Program’s Generic Protocol (ETV; USEPA, 2010). GSI performs formal verification tests appropriate to market-ready prototype BWTSs, and informal status testing for BWTSs that are still in the research and development stages. GSI procedures, methods, materials and findings are publicly accessible on the GSI website (www.greatshipsinitiative.org). In early 2011, researchers from the National Parks of Lake Superior Foundation (NPLSF) in Marquette, Michigan, and the Michigan Technological University (MTU) in Houghton, Michigan, applied to GSI for land-based tests of a BWTS involving sodium hypochlorite (NaOCl), in the same formulation used for household bleach. The BWTS was proposed for emergency treatment of ballast water in tanks of Great Lakes vessels passing through the Welland Canal system of the St. Lawrence Seaway into the upstream lakes. The method involves multiple steps: • Determination of the natural chlorine demand of the ballast water one day ahead of treatment application, i.e., prior to the vessel’s entry into the Canal, for example, in Montreal, Quebec, Canada; • Determination of the necessary volume of 6.15 % NaOCl solution to be added to the ballast water to overcome the natural chlorine demand and deliver a predetermined chlorine concentration; • Mixing using a method designed by the researchers; • Retention of the treated ballast water in tank for a predetermined length of time (i.e., exposure period); • Determination of residual chlorine concentration, and determination and application of the amount of a neutralizer necessary to fully neutralize the treated water for safe discharge; and • Verification of complete neutralization prior to the vessel’s departure from the Canal system. Tests took place at GSI’s Land-Based Research, Development, Testing and Evaluation (RDTE) Facility in Superior, Wisconsin, in October 2011, with the goal of status testing for research and development purposes. As such, the testing was based on, though not strictly consistent with, the IMO’s G8 Guidelines for Approval of Ballast Water Management Systems (IMO, 2008a), the IMO’s G9 Guidelines for Approval of Ballast Water Management Systems that make use of Active Substances (IMO, 2008b) and the USEPA ETV Program’s Generic Protocol for the Verification of Ballast Water Treatment Technology, v.5.1 (USEPA, 2010). During the test, GSI implemented the entire proposed NaOCl BWTS method with the exception of the automated mixing system; trialing the mixing apparatus at a land-based facility would offer little insight into its capability on board a ship in any case. GSI evaluated the BWTS for its ability to: • Deliver the target concentration of chlorine (above natural chlorine demand) using a 6.15% NaOCl solution, and deliver the target concentration of neutralizer; • Reduce densities of live organisms in intake water from prescribed threshold densities to below densities allowed by the Ballast Water Performance Standard of the IMO Convention (IMO, 2004); and • Result in treatment water safe to discharge in terms of residual chlorine concentration and whole effluent toxicity (WET). Disinfection by products (DBPs) were also measured and reported. The GSI test of the NaOCl BWTS yielded mixed results. In terms of operational performance, GSI was able to accurately dose a sampled volume of water with 6.15 % NaOCl solution to a predetermined chlorine concentration by factoring in the natural chlorine demand. The neutralization process recommended by the BWTS developer did require additional neutralizer additions, which could be problematic in an actual shipboard situation. More research is needed on the effect of temperature and water quality on the ability of sodium bisulfite (NaHSO3) or a neutralization substitute to successfully neutralize NaOCl-treated water for BWTS application in the real-world. Second, the BWTS reduced live densities of organisms ≥ 50 μm which were adequately plentiful in the intake to meet IMO testing guidelines, relative to control discharge. But BWTS live discharge densities were well above the IMO benchmark (IMO, 2004). The BWTS did reduce live densities of organisms > 10 and <50 μm minimum dimension to below benchmark levels within the IMO Convention, but intake densities of these organisms also were below IMO testing guidelines due to the late season timing of the tests (IMO, 2004). Finally, the treated and neutralized discharge water was found to be safe to discharge (though, in some cases only after multiple neutralization steps) and free from toxicity in Whole Effluent Toxicity (WET) tests conducted by GSI. Measurable concentrations of DBP were found in the treatment discharge, specifically trihalomethanes (THM) and haloacetic acids (HAA). Overall, the GSI results show that the NaOCl BWTS both warrants and would benefit from further research and development on its potential as an emergency BWTS with relevancy in the Great Lakes.