This regulatory action lead to an intensive research effort to develop a treatment method for ship s wash water waste stream that could consistently remove TBT to levels below this discharge standard.
Coagulation studies have concentrated on evaluating the performance of two metal-salt coagulants and their ability to remove copper and zinc with the large amount of the particulate material that is typically present in shipyard wash waters.
The primary variables that control particulate material removal, and also the adsorption of adsorption-amenable organic compounds, are coagulation, pH and coagulant dose.
As an example, Figure 1 and 2 below show the typical effect of increasing coagulant dose and increasing pH, respectively, on the percent reduction of copper from Sample CV6.
The maximum percent removals observed were generally a function of the coagulation pH related to copper and zinc solubility.
In this series of tests the sample wash water (influent) was first treated by batch coagulation, the resultant flocculent removed, and the clarified supernatant (coagulated influent) fed into the process train.
Sample 1 was removed after the sample had passed through the sand filter, and Samples 2 and 3 were taken after the sample had passed through the respective activated carbon columns.
The purpose of the sand filter was to determine if additional removal of fine particulates from the sample could significantly reduce the copper and zinc levels.
A review of Table 4 indicates that on average, coagulation treatment was most effective, reducing copper and zinc levels to 86% and 72% their initial concentration, respectively.
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