P8.2.1.4 KMnO4/air dose set-point incorrect/ dose calculation incorrect. Use bench-scale and pilot-scale tests to determine the best KMnO4 dose or aeration rate. Use a dose controller (eg, controller) that will take account of changes in water chemistry, or monitor the manganese concentration often enough so that changes in water chemistry can be matched. From time to time have a second person check the dose calculations. Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). Carry out manual checks on manganese removal and adjust oxidant dose accordingly. Start calculation checks. P8.2.1.5 Dosing controller incorrectly calibrated. Regular manual checks on controller calibration. Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly oxidation (metals must be insoluble to be removed). Calibration schedule not signed off. Recalibrate controller. Increase oxidant dose rate until recalibration can be undertaken. P8.2.1.6 KMnO4/air supply exhausted. Install an alarm to warn when the KMnO4 supply is running low. Ensure a reserve supply of KMnO4 is kept on site. Keep records of oxidant use to provide a guide to the length of time the chemical supply is likely to last. Schedule a preventive maintenance programme for air pumps. Manganese. Maintenance log. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly oxidation (metals must be insoluble to be removed). Install alarm system. Urgently order replacement chemicals. Start log of oxidant use. Initiate pump maintenance programme. Event: NOT ALL THE MANGANESE REMOVED cont’d
P8.2.1.9 dosing solution concentration incorrect, or prepared with incorrect chemical. From time to time have a second person check calculations used for preparation of KMnO4 dosing solution. Check KMnO4 concentration in each new batch of dosing solution prepared. Ensure that chemicals are delivered to the correct bin, that bins are labelled, and that an operator is there to supervise chemical delivery. Check quality of KMnO4 delivered. Manganese. in dosing solution. Supplier’s certification of analysis. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). Checks show frequent incorrect calculations. Re-calculate chemical quantities required for the dosing solution, and prepare a new solution. Provide for staff additional training in calculations for solution preparation. Ensure that chemical supplier is of the need for the operator to be present when chemicals are delivered. Obtain a new batch of chemical from the supplier, if quality P8.2.1.10 Poor air circulation for droplet, or thin-film, aerator. Do calculations and during design to ensure air circulation will allow enough oxygen to dissolve in the water. Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). Calculations show air circulation too low. If aerator relies on natural draft, consider installation of blowers to provide forced draft. Modify the aerator to minimise obstructions to air flow. P8.2.1.11 Poor nozzle design in spray aerator. Design to ensure droplets are given longest possible time in the air to allow oxygen exchange (nozzle design and trajectory are important). Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). Replace nozzles. Modify spray trajectory.
Event: NOT ALL THE MANGANESE REMOVED cont’d P8.2.1.12 Poor design of aerator. During design do pilot trials to check that the type of aerator chosen, and its design, will provide adequate oxidation of the metals. Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). show design is unsatisfactory. Replace or modify the aerator. P8.2.1.13 Poor removal of precipitated metal by filtration. See P6 Guide series for a discussion of events, causes, preventive measures etc. associated with the use of standard filters, and those using greensand for combined oxidation and filtration. P8.2.1.14 Greensand performance inadequate. Ensure KMnO4 dose (in the influent, or in off-line regeneration) is adequate to maintain the oxidising capacity of the bed. Ensure that concentrations of other chemically reduced determinands in the water (eg, organic matter, nitrite, ammonia and hydrogen sulphide) are not so high that they exhaust the bed’s oxidising capacity. Provide sufficient time for the bed to “ripen” after bringing it back on-line. Schedule routine filter maintenance. This should check for channelling for example (see also Guide P6.1). Manganese. Manganese concentration is more than 50% of the MAV. No sign of insoluble manganese formation directly after oxidation (metals must be insoluble to be removed). Adjust dose rate. Undertake a more complete check on the water chemistry and reconsider this treatment option if reduced determinand are high. Modify operational procedure. Start a filter maintenance programme. P8.2.1.15 Power failure. Provide stand-by generator to ensure continuity of power. Continuity of power. Loss of power. Refuel generator, if appropriate. Event: OXIDANT DOSE TOO HIGH Possible hazards: Manganese (if KMnO4 used as an oxidant), chlorine, chlorine dioxide or KMnO4. Level of risk: Moderate
P8.2.2.5 KMnO4 dosing solution concentration too high. Check the concentration of the KMnO4 dosing solution when it is first prepared. Separate chemical storage from dosing solution preparation tanks to reduce the likelihood of chemical spillage into the tanks. KMnO4 dose. KMnO4 in the dosing solution. Manganese concentration more than 50% of its MAV. Pink concentration in the dosing solution above the level expected. Determine the cause of the high KMnO4 concentration and rectify. Provide training in the preparation of oxidant solutions (including calculations). Identify the reasons for any spillage and rectify if possible. Event: GERMS INTRODUCED DURING AERATION Possible hazards: Germs. Level of risk: Moderate1 P8.2.3.1 introduced into the water during aeration, either in the airstream or through animals entering the aerator. netting over aerator grills to stop entry of larger animals (eg, birds, rats, etc). Provide disinfection following aeration to inactivate germs that get into the water. water quality. E. coli or coliforms detected in a 100 ml sample taken after the aerator. Disinfection of the water following aeration. 1 The consequences of the event, and therefore the level of risk, will be influenced by how well following disinfection processes works. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Removal by ion exchange Event: INCOMPLETE REMOVAL OF MANGANESE Possible hazards: Manganese. Level of risk: Low organisms
P8.2.5.1 Organic matter and trapped in the resin bed. Regeneration of the resin at the frequency recommended by the manufacturer. This will also back-flush the bed and remove organic material. Regularly (de-foul) the resin beads with the recommended cleaning agent if iron or manganese are present in the water. out treatment to remove organic matter from the water before the softener. quality. Calcium. Magnesium. Iron. Manganese. High counts of total bacteria. Hardness not reduced. Iron and/or manganese not removed. Odour. Regenerate and Clean resin to remove bead fouling. Disinfect the water after the 1 The consequences of the event, and therefore the level of risk, will be influenced by how well subsequent disinfection processes work. Contingency Plans If an event 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. Event – Faecal matter gets into the water through the aerator Indicators: Faecal indicator or pathogens are continually detected in the water leaving the plant. Knowledge of an animal having entered the aerator. Widespread sickness in the community linked to the water supply. Required actions: Follow the actions given in Figure 3.2 of the DWSNZ:2000. Identify the reason for the failure and rectify. Record cause of system failure and steps taken to correct. Modify your water safety plan if necessary. Responsibility: Manager designated responsible for the water supply. Event – Very high oxidant concentration