Characterization of tributyltin in shipyard waters and removal through laboratory and full-scale treatment

Abstract

Characterization and treatment studies were conducted in an effort to evaluate treatment options capable of removing tributyltin (TBT) in shipyard waters from above 1,000,000 ng/L to effluent concentrations below 50 ng/L. Laboratory studies and operation of a full-scale treatment plant were used to examine treatment options for TBT removal and included physicochemical treatment processes of coagulation-clarification, filtration, and granular activated carbon (GAC) adsorption. Significant variability was observed in TBT-containing shipyard waters (generated from different ships) in terms of their particulate solids, conductivity, and TBT and dissolved organic carbon concentrations. Laboratory tests with aluminum sulfate and ferric sulfate showed that on average 90% of TBT in shipyard waters could be removed by coagulation-flocculation-clarification under optimum conditions. No statistically significant difference was found in TBT removal capabilities between the two metal salts when compared at equivalent metal doses and coagulation pH. Much lower removals were observed for the coagulation-flocculation-clarification portion of the full-scale plant while the complete full-scale treatment plant averaged 99.8% TBT removal over a period of 3 years. While relatively high % removals were achieved, the total treatment process did not consistently remove TBT to levels that would meet the regulatory requirements proposed (50 ng/L) at the time the study was conducted. Based on the results from limited efforts to characterize the dissolved and particulate TBT fractions in the full-scale treatment plant effluent, particulate TBT was observed to be the dominant component of the effluent TBT from the full-scale plant and may be associated with polymer carry through.