The use of non-oxidizing biocides in water cooling towers, to prevent problems arising from the microorganisms is an important subject. During the 16 months period, sodium hypochlorite was injected to the system instead of these biocides. Production of sodium hypochlorite made its selection as a substitute for biocides, logical and too cost effective. Sodium hypochlorite was injected into the tower basins so that the extent of free residual chlorine was between 0.3 - 0.6 ppm .The microbial results indicated, TBC reduced to less than 30 cell /ml. The existence of SRB was mostly negative.

Corrosion Results

The test conducted by using corrosion coupons indicated that corrosion rate was less than 1MPY most times. Apart from coupon test , Ryznar Stability Index ,RSI, Which determines corrosive or scaling tendency of water was calculated . The optimal range of RSI was found to be between 5.5 to 6.5, in that case water has neither corrosive nor scaling tendency. Results show that seven out of the eleven water plants, the RSI monthly mean index had constantly remained at the optimal level of 5.5-6.5 during the control period . It is important to note that no month's average was within the corrosive or scaling limit. Generally , considering that every plant achieved more than 70 percent of the suitable level on Ryznar Stability index , also, with a view of coupon test results , corrosion and scaling control in water cooling towers had been successful, with changing the method of microorganisms control.