Biocide replacement in an aluminum cold rolling mill. A case history

An aluminum cold rolling mill changed microbicides when effectiveness of 2-(hydroxymethyl)-2-nitro-1,3-propanediol (TN) diminished after 10 years use. Preliminary studies indicated relative resistance to the microbicide. The mill was monitored during the changeover period with coolant samples collected every 2-3 hours for enumeration of bacteria. Twenty-four hours into the experiment, the new microbicide, hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine (HTT), was added to the coolant. The effect was immediate and dramatic, decreasing the total population by 4-5 orders of magnitude in less than two hours. The bacterial population was maintained at 103 organisms/mL (down from 108 organisms/mL) for the duration of the monitored period. This new microbicide proved to be chemically incompatible with the coolant formulation, necessitating a second biocide switch, to a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (IT). This biocide was also monitored during the switchover period and performed adequately in controlling the bacterial numbers in the mill coolant.