COMPARISONS OF ON-LINE ORP AND CHLORINE RESIDUAL MONITORING/CONTROL SYSTEMS FOR WASTEWATER TREATMENT PLANT FINAL EFFLUENT CHLORINATION

Fifteen field tests of eight different chlorination process monitoring instruments, representing five manufacturers and four different technologies, were conducted. Field testing was employed to evaluate online oxidation reduction potential (ORP) and residual chlorine measurement technologies for their suitability in chlorination dose monitoring/control under conditions typical of those experienced in a field environment. The overall purpose of the field tests is to identify the differences, drawbacks, advantages, and overall strengths and weaknesses of ORP and residual chlorine measurement technologies (total residual chlorine (TRC) and monochloramine) for wastewater chlorination monitoring/control. The field tests were conducted under the Water Environment Research Foundation Project No. 99-WWF-6 “Oxidation Reduction Potential vs. Residual Control for Chlorine”. Initial examinations of the field test results indicate that elevated ORP levels may not be required to ensure effective disinfection and that ORP levels required for effective disinfection are site specific. In addition, ORP appears to provide more sensitivity in measuring fluctuating free chlorine residual levels than for fluctuating combined chlorine residual levels. At test sites with high effluent ammonia, a significant amount of total chlorine residual (up to a 80 % portion) detected by test instrumentation was not detected as monochloramine residual. This may indicate the significant presence of organic based chloramine residuals at test sites with high effluent ammonia levels.