First start-up and daily operation of a membrane system

Before start-up

• Pretreatment is commissioned and fully flushed; its output passes the SDI15 test.
• Free chlorine in the feed is below 0.1 mg/L, with no other oxidants.
• High-pressure pump, instruments, valves and dosing pumps are installed, calibrated and tested.
• Product drain valve, feed control valve and concentrate control valve are fully open.

Flushing

Push the air out of the elements and vessels with low-pressure, low-flow pretreated water at 2.5–3 bar, and check pipes and valves for leaks.

• Wet elements: flush for at least 30 minutes, then close the product drain valve.
• Dry elements: flush at low pressure for more than 6 hours, or flush 1–2 hours, soak overnight and flush again for about 1 hour.

Starting the high-pressure pump

Throttle the flow with the valves before starting, so that a sudden surge of flow and pressure cannot damage the elements. Never raise the pressure faster than 0.7 bar/s. Open the feed valve while closing the concentrate valve until the design output is reached.

Going into service

After 1 hour of continuous operation, measure product conductivity and check the water quality. When it passes, record the initial operating data, open the product delivery valve and close the product drain valve.

Daily log

• SDI15 above 5: risk of fouling; adjust pretreatment.
• Free chlorine above 0.1 mg/L: can damage the membrane; dose sodium bisulfite (SBS).
• pH out of range: risk of scaling or membrane damage; adjust dosing.
• Cartridge filter pressure drop rising fast: adjust pretreatment at once.

Also log concentrate and product flow, pressure at each stage, and feed, concentrate and product conductivity. Fix anything abnormal at once; never keep running a faulty system.

Disinfection

If microbial growth increases, disinfect promptly: replace the water in the system with 0.1% NaOH or 0.025% Na-SDS solution, soak for 1–12 hours depending on the fouling, circulate for 30 minutes, then drain and flush clean.