The following tables details disinfection issues, their probable causes and possible corrective action that could be undertaken to control issues. Please refer to Applicability of pre-treatments and disinfection techniques to different situations (Table 47) for a summary of water disinfection treatment methods and their effectiveness against common water quality problems.
Table 34. Troubleshooting disinfection and sanitation issues
| Probable causes | Preventive measures | Checking preventive measures | Corrective action | |
|---|---|---|---|---|
| What to check | Signs that action is needed | |||
| Observation: Poor coliform kills Possible hazards: Microbes not killed by disinfection |
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| Dosing malfunction | Routine controller and dosing pump maintenance. Replace controller if suspect. Install an alarm to indicate when the disinfection residual has gone outside the intended range. | ORP less than 650mV. Frequent repair needed. Maintenance logs not signed off. Problems with disinfection effectiveness. | Identify the cause of the fault and rectify. Replace controller. |
|
| Dose rate set incorrectly | Monitoring of organic matter using an independently calibrated meter Routine maintenance and replacement of pre-treatment Monthly calculation of contact time | ORP less than 650mV. Problems with disinfection effectiveness. | Adjust dose and/or contact time. | |
| Power failure | Stand-by generator or battery bank. | Poor continuity of power supply. Problems with chlorination effectiveness. | Refuel generator (if necessary). | |
| Chemical supply exhausted | Install alarms to indicate when dosing solution, or gas cylinder, is running low. Record chemical use to provide a guide to the length of time the chemical supply is likely to last. Maintain a reserve chemical supply on-site. Consider long term arrangement with suppliers. Investigate alternative chemicals or suppliers if critical, e.g. single supplier. | Chemical use record not maintained. | Order urgent supply of chemical. | |
| Incorrect chemical used, chemical of poor quality, or dosing solutions prepared at the wrong strength | Make sure chemicals supplied are delivered to the correct bins or containers. Clearly label bins, and have an operator on-site when chemicals delivered. Check the strength of solutions or purity of chemicals, supplied. Implement a system of independent checks on dosing solution preparation. | Chemical concentrations have degraded Chemical bins not labelled Problems with disinfection effectiveness | Label chemical bins. Require supplier to ensure that the operator is present when chemicals are delivered. |
|
| Chemical supply adequate, but insufficient solution or gas reaching the dosing point | Check chemicals supplied for the presence of health-significant chemical contaminants. Conduct routine maintenance schedule for pumps. Conduct routine maintenance schedule to ensure chemical supply lines are not blocked. | Problems with disinfection effectiveness | Change supplier Identify pump fault and repair or replace Clear, or replace, blocked chemical feed lines |
|
| Poor mixing | Design system that will adequately mix. | Variable disinfectant residual after the contact time | Change the mixing rate Move feed points |
|
| Chlorine is in the form of chlororganics and chloramine | Remove more organic matter from the system Adjust pH Lower nitrogen in the system | Total chorine is significantly higher than free chlorine | Adjust pH Lower nitrogen in the system Adjust inadequate dosage Move feed points |
|
| Unit not feeding properly | Maintain and repair units on a regular schedule and inspect chemicals. | Equipment malfunction Leaks | Clean mechanical drives Replace damaged parts |
|
| Lack of spare parts for key disinfection equipment, e.g. UV bulbs, filters | Ensure spare key pre-treatment and disinfection equipment is in place. | Stocktake shows lack of equipment | Ensure there are spares of key pre-treatment and disinfection equipment on site. | |
| Particles are masking the effect of the chlorine | Use filtration system to reduce turbidity | Turbidity and colour are high after filtering Disinfectant residual is lower than expected | Improve the upstream treatment processes to reduce turbidity so that microbes are not sheltered inside particles. Turbidity should be less than 1 NTU. | |
| Observation: Low disinfection residual Possible hazards: Microbes not killed by disinfection |
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| Disinfection system is not reliable | Design and operate the system appropriately. | ORP less than 650mV Disinfection residual is highly variable | Ensure robust disinfection system is in place with appropriate monitors and alarms on key equipment. | |
| Dosing malfunction | Routine controller and dosing pump maintenance. Replacement of controller if suspect. Install an alarm to indicate when the disinfection residual has gone outside the intended range. | ORP less than 650mV Frequent repair needed Maintenance log not signed off Problems with disinfection effectiveness | Identify the cause of the fault and rectify. Replace controller. |
|
| Dose rate set incorrectly | Monitor organic matter using an independently calibrated meter. Routine maintenance and replacement of pre-treatment. Monthly calculation of contact time. pH not optimal for disinfectant. | ORP less than 650mV Problems with disinfection effectiveness | Adjust dose and/or contact time. Increase contact tank capacity or reduce the flow rate to achieve appropriate contact time. Adjust pH. Consider alternative treatment. |
|
| Power failure | Stand-by generator or battery bank. | Poor continuity of power supply. Problems with chlorination effectiveness. | Refuel generator (if necessary). | |
| Chemical supply exhausted | Install an alarm to indicate when the dosing solution, or gas cylinder, is running low. Record chemical use to provide a guide as to the length of time the chemical supply is likely to last. Maintain a reserve chemical supply on-site. | Chemical use record not maintained. | Order urgent supply of chemical. | |
| Incorrect chemical used, chemical of poor quality, or dosing solutions prepared at the wrong strength | Make sure chemicals supplied are delivered to the correct bins or containers. Clearly label bins; have an operator on-site when chemicals delivered. Check the strength of solutions supplied, or purity of chemicals supplied. Implement a system of independent checks on dosing solution preparation. | Chemical concentrations have degraded. Chemical bins not labelled. Problems with disinfection effectiveness. | Label chemical bins. Require supplier to ensure that the operator is present when chemicals are delivered. |
|
| Chemicals used after expiration date – ineffective chemicals | Use a reputable supplier. Check the strength of solutions supplied, or purity of chemicals supplied. | Lower residuals over time Degradation of chemical Old chemicals | Inspect chemicals to ensure expiry date has not been exceeded. Ensure chemical storage is appropriately sized. |
|
| Chemical supply adequate, but insufficient solution or gas reaching the dosing point | Check chemicals supplied for the presence of health-significant chemical contaminants. Routine maintenance schedule for pumps. Routine maintenance schedule to ensure chemical supply lines are not blocked. | Problems with disinfection effectiveness. | Change supplier. Identify the pump fault and repair or replace the pump. Clear, or replace, blocked chemical feed lines. |
|
| Destruction of chlorine residual by inorganic reducing compounds, i.e. Fe++, Mn++, H2S or by organic material | Conduct water analysis. | Perform water quality checks, i.e. temperature, pH, turbidity, reducing inorganic agents and TOC increases. | Low residual Red and black scale High colour water after disinfection | Clean deposits from the bottom of basins. Flush sediments from the system. Organic matter pre-treatment Scale pre-treatment |
| High disinfectant demand from the water | Conduct water analysis. Cleaning and maintenance of the system. Additional pre-treatments. Increase the effectiveness of pre-treatments. | Turbidity and colour are high after filter Red or black scale | Increase chlorine dose. | |
