In-water Treatment of Biofouling in Internal Systems: Field Validation of Quaternary Ammonium Compound (QAC) Chemical Treatment Protocols

Mussel growth in the internal sea water systems of Navy vessels can result in significant performance issues and biosecurity concerns for affected vessels. The primary in-water treatment method for mussel fouling of the internals of Navy vessels is to flush with a 1% detergent solution containing quaternary ammonium compounds (QAC). Parameters for the application of this treatment are based on previous research; however, much of the research has been conducted at small-scales under laboratory conditions. This study examined the efficacy of two commercial QAC solutions for treating mussel biofouling under realistic field conditions using experimental sea water piping systems. The efficacy of the QAC solutions was found to be highly dependent on the size of the mussels present. All treatment solutions were effective at killing large sized mussels in the pipework and sea chest of the system following a 24 h dosing period. In contrast, small mussels appeared resilient to the majority of treatment regimes tested. Changes in water temperature and increased exposure time to treatment chemicals did not enhance efficacy of treatment.