P7.2.1.7 Preventive ClO2 residual Low ClO2 Identify cause maintenance concentration. residual (see of fault and ClO2 programme. Appendix). rectify. generator Maintenance malfunction. log. E. coli or Dose with coliforms is chlorine until detected in system can be 100 mL sample brought back of water leaving on line. the treatment Soften the used Clear scale plant. to make up the from lines and sodium chlorite Frequent valves. solution to avoid repairs needed. clogging by scale (if water is hard). P7.2.1.8 (See Guide P7.1 for preventive measures, checks and corrective actions.) Chlorine flow not reaching generator. P7.2.1.9 Carry out pilot tests ClO2 residual Low ClO2 Modify to determine concentration. residual (see chemical feed ClO2 optimum chemical Appendix). rates until generation Supplier’s feed rates for ClO2 ClO2 chemistry not certificate of E. coli or production. production optimised analysis for coliforms maximised. (wrong Check chemical chemicals detected in chlorine and flows are correctly used. 100 mL sample chlorite ratio, set; pH set point is of leaving correct. the treatment or pH); plant. Ensure chemicals Change chemicals of are of adequate Unsatisfactory chemical unsatisfactory quality. Obtain chemical supplier. quality; or manufacturer’s quality. Require wrong certification. chemical chemicals Ensure chemical supplier to used. storage containers only deliver are properly when the labelled and an operator is operator is present present. to supervise delivery. Event: CHLORINE DIOXIDE (ClO2) CONCENTRATION TOO LOW cont’d P7.2.1.10 Routine ClO2 residual Low ClO2 Identify and maintenance of concentration. residual (see rectify causes ClO2 supply pumps dosing ClO2 Appendix). of pump adequate, but solution. failure. insufficient Injector ClO2 reaching Pump capacity too blockages. Obtain a new dosing low to meet pump. Pump failure. maximum ClO2 Inadequate demand. pump specifications.
P7.2.1.7 ClO2 generator malfunction. Preventive maintenance programme. Soften the used to make up the sodium chlorite solution to avoid clogging by scale (if water is hard). ClO2 residual concentration. Maintenance log. Low ClO2 residual (see Appendix). E. coli or coliforms is detected in 100 mL sample of water leaving the treatment plant. Frequent repairs needed. Identify cause of fault and rectify. Dose with chlorine until system can be brought back on line. Clear scale from lines and valves. P7.2.1.8 Chlorine flow not reaching generator. (See Guide P7.1 for preventive measures, checks and corrective actions.) P7.2.1.9 ClO2 generation chemistry not optimised (wrong chlorine and chlorite ratio, or pH); chemicals of unsatisfactory quality; or wrong chemicals used. Carry out pilot tests to determine optimum chemical feed rates for ClO2 production. Check chemical flows are correctly set; pH set point is correct. Ensure chemicals are of adequate quality. Obtain manufacturer’s certification. Ensure chemical storage containers are properly labelled and an operator is present to supervise delivery. ClO2 residual concentration. Supplier’s certificate of analysis for chemicals used. Low ClO2 residual (see Appendix). E. coli or coliforms detected in 100 mL sample of leaving the treatment plant. Unsatisfactory chemical quality. Modify chemical feed rates until ClO2 production maximised. Change chemical supplier. Require chemical supplier to only deliver when the operator is present. Event: CHLORINE DIOXIDE (ClO2) CONCENTRATION TOO LOW cont’d P7.2.1.10 ClO2 supply adequate, but insufficient ClO2 reaching dosing Routine maintenance of pumps dosing ClO2 solution. Pump capacity too low to meet maximum ClO2 demand. ClO2 residual concentration. Low ClO2 residual (see Appendix). Injector blockages. Pump failure. Inadequate pump specifications. Identify and rectify causes of pump failure. Obtain a new pump.