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.
Determine and implement effective backwash cycle procedure. Consider: timing of air scour, settling and water wash turbidity criteria set for protocol before putting filter back in service a log to record identified problems, and what was done to rectify them optimisation of the filter ripening operation. Aluminium residual Filter log. Frequent backwashes. Mud-balls and/or cracks in filters. Boil-up and/or dead during backwash. Loss of media. Change procedure for backwash cycles. Make sure operators are trained in correct maintenance and operation procedures for the specific filters in use. Identify staff training needs and provide training. P6.1.1.4 Inadequate filter Develop and use pump maintenance schedule. Schedule should follow manufacturer’s recommendations and include: lubrication; replacement cycle for elastomeric components (eg, flexible couplings) component inspection (valves, pumps, compressors etc) inspection logbook. Maintenance log book (see also P6.1.1.3). (See also P6.3.1.3.) Increase frequency of media and filter inspection if excess residual coagulant detected in the treated water. Inspect and chemically clean media at least annually. Ensure operators are trained in correct maintenance procedures for the specific filters in use. Start chemical cleaning programme. Identify staff training needs and provide training. Event: NATURAL ORGANIC MATTER NOT REMOVED Possible hazards: Germs; disinfection by-products (trihalomethanes, haloacetic acids, chloral hydrate (chlorine), chlorite (chlorine dioxide), bromate, bromoform, formaldehyde (ozone)). Level of risk: Moderate1