Mixed-oxidant application in cooling tower maintenance

Tests using the MIOX-generated mixed-oxidant solution instead of oxidizing biocides (chlorine or bromine) for cooling tower maintenance, and eliminating all other biocides, in first an established cooling tower and subsequently in two new cooling towers found: (1) aerobic bacteria counts consistently less than 1000/mL in the cooling water (no colonies on the standard Easicult TTC1 dip slide test), a result rarely achieved using chlorine alone or chlorine with other biocides; (2) ease in maintaining Free Available Chlorine (FAC) concentrations at 0.2 – 0.3 mg/L using a standard ORP controller; and (3) removal of biofilms from small areas of cooling surfaces where they had accumulated in the previous maintenance program, and a consequent reduction or complete elimination of microbiologically-induced corrosion. Using organic corrosion inhibitors, metal coupon tests showed higher rates of pitting-type corrosion on steel using the mixed-oxidant solution than using oxidizing biocides or chlorine. When the corrosion inhibition program was shifted toward stabilized phosphate with the pH controlled at 7.4 – 7.5, pitting-type corrosion on steel was eliminated, and levels of general corrosion were within industry norms and equal to those using oxidizing biocides or chlorine. Azoles used for corrosion control on copper heat exchange surfaces were unaffected by the mixed-oxidant solution and copper corrosion rates were normal.

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