John Wiley & Sons, Ltd.

An evaluation of the residual toxicity and chemistry of a sodium hydroxide‐based ballast water treatment system for freshwater ships

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Non‐native organisms in the ballast water (BW) of freshwater ships must be killed to prevent the spread of invasive species. The ideal BW treatment system (BWTS) would kill 100% of BW organisms with minimal residual toxicity to organisms in receiving waters. The residual toxicity and chemistry of a BWTS was evaluated: sodium hydroxide was added to elevate pH to > 11.5 to kill BW organisms, then reduced to pH<9 by sparging with wet‐scrubbed diesel exhaust (the source of CO2). Cladocerans (Ceriodaphnia dubia), amphipods (Hyalella azteca), and fathead minnows (Pimephales promelas) were exposed for 2 days to BWTS water under an air atmosphere (pH drifted to ≥ 9), or a 2.5% CO2 atmosphere (pH 7.5 to 8.2) then transferred to control water for 5 days to assess potential delayed toxicity. Chemical concentrations in the BWTS water met vessel discharge guidelines with the exception of concentrations of copper. There was little to no residual toxicity to cladocerans or fish, but the BWTS water was toxic to amphipods. Maintaining a neutral pH and diluting BWTS water by 50% eliminated toxicity to the amphipods. Toxicity of BWTS water would likely be minimal due to rapid dilution in the receiving water with sub‐surface release likely preventing pH rise. This BWTS has the potential to become a viable method for treating BW released into freshwater systems. This article is protected by copyright. All rights reserved

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