A media filter is a type of filter that uses a bed of sand, activated carbon, peat, crushed granite or other material to filter water. For example: sand and activated carbon filters.
Table 32. Troubleshooting media filter issues
| Probable causes | Preventive measures | Checking preventive measures | Corrective action | |
|---|---|---|---|---|
| What to check | Signs that action is needed | |||
| Observation: Rapid increase in head loss and short filter runs Possible hazards: Reduced efficacy of pre-treatment |
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| Incoming water too dirty | Pre-treatment | Colour Turbidity | Turbidity and colour are high after filter | Improve pre-treatment performance. |
| Inadequate backwashing | Increase frequency of backwashing to a rate that resolves the problem | Colour Turbidity | Turbidity and colour are high after filter | Look at backwash rates and other features. |
| Air blinding in the filter | Optimise system | Flow Pressure | Pressure variations | Consider revising filter control or design. Water depth above the filter may need to be increased, for example. |
| Observation: Visible mud balls or cracking Possible hazards: Reduced efficacy of pre-treatment |
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| Backwash unable to remove mud and silt | Increase frequency of backwashing / cleaning to a rate that resolves the problem | Colour Turbidity | Turbidity and colour are high after filter | Investigate increasing backwash and air scour rates. The mud balls may have to be physically removed. |
| Observation: Encrustation of media (which changes media size and shape) Possible hazards: Reduced efficacy of pre-treatment |
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| Build-up of scale or other fouling on media | Increase frequency of cleaning to a rate that resolves the problem | Alkalinity | Scale | Fouling can usually be cleaned off using chemicals. |
| Observation: Filter media in troughs Possible hazards: Reduced efficacy of pre-treatment |
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| Loss of media with the backwash water | Replace media Monitoring | Water flow Media outside of the tank | Visual inspection | This problem has a range of possible causes that will need to be resolved as appropriate if losses are significant. Replace media. |
| Observation: Spikes in filtered water turbidity during a filter run Possible hazards: Reduced efficacy of pre-treatment |
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| Sudden changes in flow rate to a filter or filters | Monitoring | Flow Pressure | Flow variation | Identify and control situations where flow rate changes suddenly. |
| Observation: High turbidity at the end of a filter run Possible hazards: Reduced efficacy of pre-treatment |
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| Initiating backwashes too late | Schedule regular backwashing – the frequency will depend on site-by-site factors. Monitoring | Colour Turbidity | Turbidity and colour are high after filter | More regular backwashing needed |
| Observation: High turbidity at the start of a filter run Possible hazards: Reduced efficacy of pre-treatment |
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| Residual turbidity being washed out of media | Increase frequency of backwashing to a rate that resolves the problem Monitoring | Colour Turbidity | Turbidity and colour are high after filter | Only restart a dirty filter after backwashing it first. Bring filters into service by ramping up the flow very slowly. |
