1.Pre-startup inspection

·Verify that feed-water (city, well or RO permeate) meets design conductivity, hardness, free-chlorine (<0.05 mg L⁻¹) and SDI (<5).

·Open all concentrate, product and vent valves; prime the high-pressure pump to avoid cavitation.

·Check 5-µm cartridge ΔP (<0.5 bar) and oil level in the pump; rotate the shaft by hand.

2. Start-up sequence (applies to single-pass or double-pass RO + EDI skids)

a. Flush at low pressure (≤3 bar) for 5–10 min to remove preservatives and trapped air.

b. Ramp to 60 % design pressure over 30 s; watch permeate flow and conductivity.

c. When permeate conductivity is <80 % of feed (typically <10 µS cm⁻¹), divert to service tank; close reject recycle after 2 min.

d. For EDI: start only after RO permeate <5 µS cm⁻¹ and CO₂ <5 ppm; apply 20 A m⁻² current, then raise to set-point over 5 min.

3. Normal operating window

·RO recovery 70–75 % for tap-water, 80–85 % for softened feed.

·ΔP across one stage <1.5 bar; concentrate flow ≥10 % of feed to minimise fouling.

·EDI product resistivity >15 MΩ·cm, silica slip <5 ppb, outlet pressure 0.5–1 bar higher than RO permeate to guarantee positive flow through UV and 0.22-µm final filter.

4. Data to record every shift

·Feed & product conductivity, temperature, flow, pressure, pH, ORP, chlorine, hardness, SDI, cumulative runtime, pump current.

·Trend charts detect membrane degradation (gradual salt passage rise) versus sudden seal failure (step change).

5. Cleaning criteria for RO

·Normalised permeate flow ↓10 %, or

·ΔP ↑15 %, or

·Salt passage ↑10 %.

·Use alkaline (pH 11–12, 30 °C) for bio/organic fouling; citric acid (pH 2.5) for CaCO₃; HCl (pH 2) for BaSO₄. Flush with permeate until pH matches feed.

6. CIP for EDI

If product resistivity drops <12 MΩ·cm and module ΔP >0.7 bar, circulate 1 % NaCl + 0.2 % NaOH at 40 °C for 30 min, followed by 1 % HCl 20 min; final rinse with RO permeate until outlet conductivity <2 µS cm⁻¹.

7. Sanitisation

·Hot-water sanitisable RO: 80 °C for 60 min every 2–4 weeks.

·EDI: limit 45 °C; therefore loop is sanitised with 85 °C water via heat exchanger bypass while EDI is isolated.

·UV sleeves wiped quarterly with alcohol; lamp replaced annually or when intensity <70 % of new value.

8. Seasonal adjustments

·Winter: feed temperature may fall to 5 °C; viscosity rises → reduce recovery 5 % or install feed heater to keep flux ≥15 L m⁻² h⁻¹.

·Summer: temperature >25 °C increases bio-growth; raise sanitisation frequency, lower pH to 7–7.5 and dose 0.5–1 ppm non-oxidising biocide in pre-tank (stop 2 h before RO).

9. Common alarms & quick fixes

·High pump current: check concentrate valve not closed, feed temperature >30 °C, or bearing seizure.

·Low permeate flow: membrane fouling, cold feed, or brine seal leakage—perform differential pressure test.

·EDI low resistivity: verify current set-point, module hydraulics (short-circuit), and CO₂ breakthrough—inject caustic upstream or add vacuum degasser.

10. Annual preventive tasks

·Replace cartridge filters, pump oil, O-rings, UV lamp, conductivity cell cal-bridge.

·Extract one lead and one tail RO element for autopsy: measure weight gain, SEM for scale, ATP for biofilm.

·Recalibrate pressure transmitters and flow meters; validate data-logger 21 CFR Part 11 records.

Following the checklist keeps permeate conductivity <1 µS cm⁻¹ and EDI product >18 MΩ·cm with minimum unplanned downtime.