Biocides typically have an adverse impact on overboard water. THPS (tetrakishydroxymethyl
phosphonium sulfate), one of the most commonly used biocides offshore has a similar effect on
produced water. The effect of THPS on seawater used for hydrotesting and bulk storage is seldom
studied and rarely documented. The effect of temperature, pH, water depth, dissolved oxygen
concentration and various ions in the system is important to note. Once a certain volume of water is
treated with any chemical, it is now deemed to be chemically treated seawater which cannot be
discharged unless verified using the NOEC (No Observable Effect Concentration) testing method.
This experience will provide a detailed understanding of the discharge of chemically treated seawater
as well as the interaction of THPS with potential ions in the matrix. Additionally, regular sampling and
associated analyses will be presented that demonstrate the degradation and half-life of the THPS
molecule in varying temperatures.
Periodic sampling of the THPS chemical in the seawater has provided a detailed understanding of the
half-life degradation of the chemical. The interaction of the chemical with the cations present in the
system and subsequent aversion to the neutralization reaction with hydrogen peroxide has also been
studied and presented.
Key Words: Biocide, THPS, NOEC, NPDES, Hydrotest, MIC, Microbially Induced Corrosion