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Abstract Biocide dose response studies are commonly conducted on water solutions containing bacteria to determine the effect of chemical treatments before application. Biocide product labels provide broad guidelines for dosing. However, site water chemistry and bacteria biology make the minimum effective dose differ for each location difficult to determine. A large volume culture of sulfate reducing bacteria (SRB) was prepared and allowed to grow until 4 log bacteria were present. The sample as then split into four identical 500 ml samples. The four samples were dosed at 0, 5, 50 and 400 ppm of tetrakis (hydroxymethyl)-phosphonium sulfate (THPS) based biocide. The effect on bacteria levels were tested using an enzyme-based bacteria metabolism test after 0.2, 1, 8, 24 and 96 hr. This study showed that a single application of 50 ppm of biocide could be as effective as a 400 ppm on high numbers of planktonic SRB.
James Fajt (Sun,) studied this question.