Abstract
Although a laboratory test showed that up to 100 mg/L chlorine dioxide (ClO2) at pH of about 7.5 did not degrade a polyamide (PA) reverse osmosis (RO) membrane, field testing was required before ClO2 could be recommended for use as a biocide in RO plants. ClO2 without any free chlorine byproduct was generated from sodium chlorite by electrochemical or catalytic methods. ClO2 was effective in preventing biofouling and made it possible to remove existing biofilm in RO elements. At one plant, 0.3 mg/L ClO2 was required during summer with high temperatures to prevent biofouling, but the required concentration was less at lower temperatures. The dose rate of ClO2 was high enough when ClO2 was detected in permeate and concentrate. Before being used in large scale, it must be determined at which conditions ClO2 can be used without degrading PA RO membranes.