Survey of Contamination in Fuel Tanks of DD-963 Class Ships

A survey has been made of sludges collected from tanks on DD-963 class ships to assess sources of particulate matter, especially that generated by microorganisms. More than eighty tanks on eight different ships were sampled and examined microscopically for the presence of microorganisms and other debris. Assays for viable fungi, yeast and bacteria, including sulfate reducers, were made. Centrifugal fractionation separated the fuel and aqueous phases of the sludges and allowed the volumes of low-density particulates (lighter than water) and sediment to be estimated. The pH and salinity of the aqueous phase were measured and analyses made for organic matter, sulfide and metallic elements in the particulate matter. There were considerable variations in amount, quality and microbial content of the sludges in different tanks even on the same ship. Viable microorganisms were always found but the dominant genera differed considerably. A high aqueous pH and the presence of sulfide were usually correlated with active sulfate-reducing bacteria and a low aqueous pH was always associated with high yeast and fungal content. In some tanks, including service tanks, fungal material made up a substantial portion of the sludge. Nevertheless, it appeared that well maintained centrifugal purifiers could keep the total volumes of sludge accumulated in service tanks at acceptably low levels.