Shed issues: ineffective microbial treatment

Table 36. Troubleshooting ineffective microbial treatment

Operational monitoring
Parameter	Target criteria	Critical limits	Monitoring method
Escherichia coli	0CFU/ml	Specific chlorine residual set to achieve a minimum contact time requirement based on maximum flow and minimum storage times	Online, continuous chlorine residual analyser, flow and pH. 24-hour monitored alarms on residual monitoring, pH and disinfectant dosing equipment. Regular turbidity and temperature monitoring and disinfectant demand calculations. Appropriate electronic or hard copy monitoring records.
Disinfectant residual	1–2ppm
pH	pH 6.5–7.5
Flow rate	Set to achieve minimum contact time
Chlorine dose	Set to achieve residual at end drinker
Turbidity	<1 NTU
Corrective action Any breach in critical limits or target criteria should result in any of the following operating procedures as necessary: inspect and calibrate equipment, adjust flow rate, adjust the disinfectant dose or feed point, carry out additional monitoring, increase sampling and testing, recalculate contact time values, implement unplanned maintenance procedure, secondary or booster disinfection, use alternative supply or divert water, engage backup equipment, plant automatic shutdown, implement emergency response, and record actions to be taken and report (internally or externally as required).
Verification Calibration and maintenance of equipment Drinking water quality monitoring Satisfactory production Evaluation and audit