Event: PARTICLES NOT REMOVED Possible hazards: Germs not removed (particularly Giardia and Cryptosporidium). Level of risk: High1 P6.1.1.1 Ensure and type Visual Turbidity more Change type, of medium are inspection of than 0.5 NTU number and/or suitable for the quality filter. after the filter. depth of filter deficiencies. of the water being media. Post-filter: Aluminium filtered and flow rate. residual more Turbidity than 0.15 mg/L Aluminium filter. residual Frequent elevated turbidity in filtered P6.1.1.2 Determine and Post-filter: Turbidity more Restrict document acceptable than 0.5 NTU maximum flow Turbidity flow and check after the filter. rate. flow rates. Aluminium regularly. Include Aluminium Redesign filter residual summer versus winter residual more hydraulics. flows and ensure both than 0.15 mg/L can be matched to after filter. media specifications. Frequent Avoid sudden Modify elevated changes in flow rates operational turbidity in in dirty filters. practices. filtered Ensure operators are Identify staff trained in correct training needs operational and provide procedures for the training. specific filters in use. 1 The consequences of the event, and therefore the level of risk, will also be largely influenced by the quality of the source water and the effectiveness of pre filter treatment processes. Preventive measures Checking preventive measures Corrective action Causes What to check Signs that action is needed Event: PARTICLES NOT REMOVED cont’d P6.1.1.3 Determine Frequent Change Headloss parameter(s) will be elevated trigger Incorrect Time used to start the turbidity in parameter for filter Turbidity backwash cycle, and filtered water. backwash. backwash implement these Post-filter: procedure. Turbidity more controls. than 0.2 NTU Turbidity after the filter.
Event: PARTICLES NOT REMOVED Possible hazards: Germs not removed (particularly Giardia and Cryptosporidium). Level of risk: High1 P6.1.1.1 deficiencies. Ensure and type of medium are suitable for the quality of the water being filtered and flow rate. Visual inspection of filter. Post-filter: Turbidity Aluminium residual Turbidity more than 0.5 NTU after the filter. Aluminium residual more than 0.15 mg/L filter. Frequent elevated turbidity in filtered Change type, number and/or depth of filter media. P6.1.1.2 flow rates. Determine and document acceptable flow and check regularly. Include summer versus winter flows and ensure both can be matched to media specifications. Post-filter: Turbidity Aluminium residual Turbidity more than 0.5 NTU after the filter. Aluminium residual more than 0.15 mg/L after filter. Frequent elevated turbidity in filtered Restrict maximum flow rate. Redesign filter hydraulics. Avoid sudden changes in flow rates in dirty filters. Ensure operators are trained in correct operational procedures for the specific filters in use. Modify operational practices. Identify staff training needs and provide training. 1 The consequences of the event, and therefore the level of risk, will also be largely influenced by the quality of the source water and the effectiveness of pre filter treatment processes. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: PARTICLES NOT REMOVED cont’d P6.1.1.3 Incorrect filter backwash procedure. Determine parameter(s) will be used to start the backwash cycle, and implement these controls. Headloss Time Turbidity Post-filter: Turbidity Frequent elevated turbidity in filtered water. Turbidity more than 0.2 NTU after the filter. Change trigger parameter for backwash.
treatment-rapid-sand-filtration-feb14-v2.docx