Upstream TOC/colour Optimise processes levels highly upstream removing variable. processes to substances reduce contributing to the ozone ozone demand demand. from the water. Inadequate Replace ozone dose Ensure ozonator ozonator with even when has sufficient one with ozonator capacity. sufficient running at capacity. maximum. P7.3.1.6 Stand-by Electricity Poor continuity Refuel generator. supply. of power generator (if failure. supply. appropriate). P7.3.1.7 Ensure that Ozone Low ozone Obtain contactor design residual (see engineering Poor has been proven after Appendix). advice to contractor effective contact assess what design E. coli or elsewhere before period. modifications coliforms construction/ can be made Calculated detected in 100 installation. to improve contact time. mL of treated contactor Undertake water r. design. testing of contactor before construction. P7.3.1.8 Determine Ozone Low ozone Introduce a whether there is a residual (see system for Water pH too need to pH control after Appendix). pH high (favours prior to the contact adjustment. rapid E. coli or contactor, and period. coliforms install if of ozone). detected in 100 necessary. mL of treated water. P7.3.1.9 Provide staff Analysis Audits show Identify staff training in sample records. monitoring training Ozone analysis and inaccuracies. needs and monitoring record keeping. provide samples training. taken Develop incorrectly, monitoring or incorrectly schedule and recorded roster. (see Guide D4). P7.3.1.10 Provide staff Analysis Audits show Identify staff training in sample records. monitoring training Method of analysis and inaccuracies. needs and record keeping. provide training. incorrect, incorrectly calibrated, or analysis reagents have deteriorated. Event: EXCESSIVE FORMATION OF OZONATION BY-PRODUCTS Possible hazards: Bromate, bromoform (and other organic DBPs containing only bromine), formaldehyde. Level of risk: Low–moderate2
TOC/colour levels highly variable. Inadequate ozone dose even when ozonator running at maximum. Upstream processes removing substances contributing to the ozone demand from the water. Ensure ozonator has sufficient capacity. Optimise upstream processes to reduce ozone demand. Replace ozonator with one with sufficient capacity. P7.3.1.6 failure. Stand-by generator. Electricity supply. Poor continuity of power supply. Refuel generator (if appropriate). P7.3.1.7 Poor contractor design Ensure that contactor design has been proven effective elsewhere before construction/ installation. Undertake testing of contactor before construction. Ozone after contact period. Calculated contact time. Low ozone residual (see Appendix). E. coli or coliforms detected in 100 mL of treated water r. Obtain engineering advice to assess what modifications can be made to improve contactor design. P7.3.1.8 Water pH too high (favours rapid of ozone). Determine whether there is a need to pH control prior to the contactor, and install if necessary. Ozone after contact period. Low ozone residual (see Appendix). E. coli or coliforms detected in 100 mL of treated water. Introduce a system for pH adjustment. P7.3.1.9 Ozone monitoring samples taken incorrectly, or incorrectly recorded (see Guide D4). Provide staff training in sample analysis and record keeping. Develop monitoring schedule and roster. Analysis records. Audits show monitoring inaccuracies. Identify staff training needs and provide training. P7.3.1.10 Method of incorrect, incorrectly calibrated, or analysis reagents have deteriorated. Provide staff training in sample analysis and record keeping. Analysis records. Audits show monitoring inaccuracies. Identify staff training needs and provide training. Event: EXCESSIVE FORMATION OF OZONATION BY-PRODUCTS Possible hazards: Bromate, bromoform (and other organic DBPs containing only bromine), formaldehyde. Level of risk: Low–moderate2