P8.4.2.1 Ensure treatment TOC Treatment Implement, processes removing concentration. achieves little or or optimise, Fouling of GAC organic matter are no reduction in upstream by bulk in place, and TOC. processes organic functioning for removing matter, or properly, prior to natural other the GAC bed. organic contaminants, matter. in the water. P8.4.2.2 Ensure any GAC TOC Treatment Add GAC to lost from the concentration. achieves little or the bed. Too little GAC contactor/ filter bed no reduction in in the GAC bed Carry out is replaced. TOC. calculations bed to Ensure initial GAC and trials, if continue to bed depth is this has not provide sufficient for the already been adsorption planned number of done. until planned bed-volumes of GAC water to be run replacement. through it, using calculations and pilot trials. Determine the Reduce maximum backwash backwash rate that can be rate. tolerated without significant loss of GAC and limit rates to this value. Event: GERMS GROW IN THE GRANULAR ACTIVATED CARBON BED Possible hazards: Germs4 Level of risk: Moderate–high5 P8.4.3.1 Provide treatment Heterotrophic Ensure there to improve the quality of count is a Poor quality microbiological water before higher following disinfection water passing quality of the water, and after the GAC bed stage through the and its organic treatment. than before. following the GAC. matter content, GAC. prior to GAC treatment. 1 Too little PAC may result in less natural organic matter being removed from the water before the disinfectant is added. This is likely to lead to increased concentrations of disinfection by products. 2 The risk associated with this is probably low except in situations in which reliance is placed on the activated carbon to remove algal toxins. In these instances the level of risk should be regarded as high. 4 The germs may be free in the water or carried on fine carbon particles. 5 The consequences of the event, and therefore the level of risk, will be influenced by the efficacy of subsequent disinfection processes. Contingency Plans If an happens despite preventive and corrective actions you have taken, you may need to consult with the Medical Officer of Health to assess how serious a problem is.
P8.4.2.1 Fouling of GAC by bulk organic matter, or other contaminants, in the water. Ensure treatment processes removing organic matter are in place, and functioning properly, prior to the GAC bed. TOC concentration. Treatment achieves little or no reduction in TOC. Implement, or optimise, upstream processes for removing natural organic matter. P8.4.2.2 Too little GAC in the bed to continue to provide adsorption until planned GAC replacement. Ensure any GAC lost from the contactor/ filter bed is replaced. Ensure initial GAC bed depth is sufficient for the planned number of bed-volumes of water to be run through it, using calculations and pilot trials. TOC concentration. GAC bed Treatment achieves little or no reduction in TOC. Add GAC to the bed. Carry out calculations and trials, if this has not already been done. Determine the maximum backwash rate that can be tolerated without significant loss of GAC and limit rates to this value. Reduce backwash rate. Event: GERMS GROW IN THE GRANULAR ACTIVATED CARBON BED Possible hazards: Germs4 Level of risk: Moderate–high5 P8.4.3.1 Poor quality water passing through the GAC. Provide treatment to improve the microbiological quality of the water, and its organic matter content, prior to GAC treatment. quality of water before and after treatment. Heterotrophic count higher following the GAC bed than before. Ensure there is a disinfection stage following the GAC. 1 Too little PAC may result in less natural organic matter being removed from the water before the disinfectant is added. This is likely to lead to increased concentrations of disinfection by products. 2 The risk associated with this is probably low except in situations in which reliance is placed on the activated carbon to remove algal toxins. In these instances the level of risk should be regarded as high. 4 The germs may be free in the water or carried on fine carbon particles. 5 The consequences of the event, and therefore the level of risk, will be influenced by the efficacy of subsequent disinfection processes. Contingency Plans If an happens despite preventive and corrective actions you have taken, you may need to consult with the Medical Officer of Health to assess how serious a problem is.
treatment-trace-organics-removal-feb14-v2.docx