Abstract
This paper is the conclusion of a six month study using ozone as the sole water treatment for a 600 ton cooling tower at the AT&T complex in Pleasanton, California. The use of ozone without any additional water treatment chemicals has been heralded as a means of radically reducing water consumption, occasionally to the point where bleed streams (blow-down) have been eliminated. At AT&T water meters were installed to monitor the make-up and blow-down streams. Using an overall water balance, a comparison of total water usage was made. The period during which traditional chemicals were used was contrasted with the period when ozone was the sole treatment.
As a bactericide ozone is many orders of magnitude more effective than currently available chlorinated/brominated chemicals. It is also more effective over a greater range of pH. Water samples were taken for biological analysis while the cooling tower was being treated with chemicals, and then while ozone was used as the bactericide. This was done to determine the suitability of ozone as a sanitizer in a cooling tower application.
Differing data has been reported regarding the corrosion rates due to ozone oxidation in cooling water streams. Corrosion coupons of hot dipped galvanized steel, copper, and mild steel were installed at AT&T. The results from this study were correlated and compared to corrosion rates considered acceptable by engineers at a major chemical company, which specializes in the treatment of cooling towers.
