Characteristics and treatment of wastewater generated during underwater hull cleaning operations of U.S. Navy ships

Abstract

For the last 15 years the U.S Navy has been using an underwater diver-operated brush mechanism to clean marine fouling on ship hulls. During this operation, it has been shown that 1 to 2 mils of antifouling paint (which is 40-50 percent cuprous oxide by weight) are removed, resulting in the discharge of up to 1300 pounds of copper into the surrounding surface waters. This paper reviewed and summarized the recent studies which have been conducted relating to hull cleaning. Among other things, the studies measured dissolved copper in the wastewater ranging from 0.13 mg/L to 4.3 mg/L. These values exceeded the Environmental Protection Agency water quality criterion of 2.9 micro g/L for dissolved copper. Nevertheless, one study even concluded that hull cleaning wastewater may not be toxic to microalgae in the surface waters because the measured dissolved copper concentrations during hull cleanings were lower than the observed IC50 values for the microalgae. Calculations determined the approximate amount of waste that would be generated and the concentration of copper in the waste. From these estimates, four treatment technologies were discussed as possible alternatives for treatment of the wastewater containing antifouling paint: ion exchange, dissolved air flotation, crossflow microfiltration, and living and non-living biological treatment systems. In addition, an economic analysis was undertaken to compare three levels of treatment: off-site treatment by a commercial facility, on-site treatment to meet minimum sanitary sewer discharge limits using a dissolved air flotation system, and on-site treatment to meet minimum surface water limits using crossflow microfiltration and ion exchange.