the initial TRO in ballast tanks; the direct seawater electrolysis
during seawater intake, or the dilution of high concentration of
electrolyzed seawater. Regardless of the choice, the typical initial
TRO concentration range in ballast tanks is 5–10 mg/L as Cl2 (Techcross
(www.techcross.com), communication with PANASIA). To
simulate the practical conditions of inactivation occurring in the
ballast tank by seawater electrolysis, the seawater was first electrolyzed
until the TRO reached to 300 mg/L as Cl2, and was then diluted
to 6 mg/L as Cl2 into the same seawater containing pre-added
B. subtilis spores, and was allowed to stand for varying contact
times. Inactivation results are shown in Fig. 7. The inactivation pro-
file was similar to the case observed in Fig. 5 achieving up to a
maximum of one log reduction with tailing, which conforms to
typical bromine inactivation. The inactivation results from the continuous
seawater electrolysis (Fig. 6A) cannot be obtained by this
dilution method. This is because, even though concentrated electrolyzed
solution (TRO = 300 mg/L as Cl2) contains largely OCl
(=250 mg/L as Cl2) and HOBr (=50 mg/L as Cl2), as projected by
Fig. 3B, once it diluted to the TRO (=6 mg/L as Cl2), the diluted seawater
will initially contain 5 mg/L (as Cl2) of OCl and 1 mg/L (as
Cl2) of HOBr. The initially present OCl in diluted solution will rapidly
transform to OBr, and then to HOBr at pH = 8 seawater conditions
according to reaction (7). Another set of experiments was
performed in the same water matrix condition. In this set, instead
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