Raw → Process Water

Water Treatment Plant

Water Treatment: Match Water Quality to Its Intended Use

Water acceptable for one duty may be unsuitable for another. Define the required quality before selecting treatment or interpreting results. Depending on the application, relevant parameters can include hardness, conductivity, silica, suspended solids, organic content, or microbiological quality.

Reverse osmosis separates a feed stream into permeate and concentrate. Its performance changes with temperature, pressure, feed composition, and recovery. Normalization helps distinguish operating-condition changes from deterioration.

Reference: DuPont — Reverse Osmosis.

Recovery and Rejection Are Different

Recovery (%) = permeate flow ÷ feed flow × 100.

For a feed of 20 m³/h and permeate of 15 m³/h, recovery is 75%. A simple steady-state balance gives 5 m³/h of concentrate, assuming no other flows or accumulation.

Salt rejection (%) = (1 − permeate salt concentration ÷ feed salt concentration) × 100.

For illustrative concentrations of 1,000 mg/L in the feed and 20 mg/L in the permeate, apparent system rejection is 98%.

These results answer different questions. Recovery describes water yield; rejection describes the relative reduction in the measured dissolved-salt concentration. Neither number alone proves suitability for drinking, pharmaceutical use, or boiler feed.

Investigate Trends, Not Just Today's Value

Record feed temperature, pressures, stage pressure drops, stream flows, feed and permeate quality, pretreatment condition, and maintenance events. Use the membrane supplier's normalization method and criteria for performance assessment.

Conductivity can help trend ionic content, but its relationship to total dissolved solids depends on composition and temperature. Do not mix unlike analytical bases in a rejection calculation.

Reference: DuPont — FilmTec RO/NF Technical Manual.

Next step: Verify the water-quality specification and compare normalized performance before proposing membrane cleaning or replacement.

Record observations only where it is safe. Inspection inside equipment, electrical testing, chemical work and changes to protective controls require qualified personnel, approved isolation and the installed equipment manual. Never bypass a trip or repeatedly restart unsafe equipment. Engineering disclaimer

Measurements To Record

Raw-water and product-water quality
Filter and membrane differential pressures
Feed, permeate and reject flows where applicable
Conductivity, hardness and disinfectant measurements as relevant

Maintenance Checklist

Log flows, pressures and product quality.
Calibrate meters and verify sampling methods.
Trend membrane performance using appropriate normalisation.
Service filters and regeneration equipment using supplier instructions.

Evidence-Based Diagnosis

Low RO permeate flow

Possible Causes: Temperature change; fouling; inadequate feed pressure; pretreatment issue.
Evidence To Collect: Compare normalised performance with the clean baseline and review feed quality and pressure.
Qualified Follow-Up: Have the membrane specialist identify the cause and select an approved cleaning or corrective procedure.

High product conductivity

Possible Causes: Feed-quality change; membrane integrity issue; leakage; measurement error.
Evidence To Collect: Verify instruments and compare feed/product conductivity and rejection trend under similar conditions.
Qualified Follow-Up: Investigate integrity and operating conditions; segregate off-spec water according to the site procedure.

Hardness breakthrough

Possible Causes: Exhausted resin; poor regeneration; bypass leakage; high loading.
Evidence To Collect: Confirm hardness testing and review regeneration and flow records.
Qualified Follow-Up: Inspect regeneration and valves against the system design; verify quality before returning to normal service.

Record The Confirmed Result

Keep the asset model, time, load, ambient conditions, alarm code and relevant readings together. Compare with the last healthy baseline. Record the confirmed cause, approved corrective action and readings after restoration; check that the improvement persists before closing the investigation.

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RO Membrane CIP — Alkali And Acid Cleaning

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How It Works

1
Raw water clarified with coagulant, then filtered on sand/multi-media.
Raw water is dosed with coagulant (alum/PAC) and settled in a clariflocculator or tube settler, then filtered through a multi-grade/pressure sand filter at 10–15 m/h. Target outlet turbidity is <1 NTU and SDI₁₅ <5 — anything worse will foul RO membranes within weeks.
2
Activated carbon removes chlorine and organics.
The activated carbon filter adsorbs free chlorine, chloramine, organics, colour and odour. Removing chlorine is mandatory ahead of polyamide RO membranes and ion-exchange resin, both of which are destroyed by oxidants; where carbon cannot be trusted, SMBS is dosed and ORP is monitored instead.
3
Softener exchanges Ca²⁺/Mg²⁺ for Na⁺.
The softener's strong acid cation resin in sodium form swaps Ca²⁺ and Mg²⁺ for Na⁺, dropping hardness below 5 ppm as CaCO₃. When exhausted it is regenerated with 8–10 % brine (100–150 g NaCl per litre of resin) through backwash → brine draw → slow rinse → fast rinse, either on a timer or, better, on a throughput meter.
4
Reverse osmosis rejects dissolved salts (95–99%).
RO pushes water through semi-permeable spiral-wound membranes at 10–15 bar. Salts, silica and organics stay behind in the reject; permeate carries 1–3 % of the feed TDS. Antiscalant plus pH control prevent CaCO₃, CaSO₄ and silica scaling; recovery is held at 70–80 % with part of the reject recirculated. Normalise permeate flow, ΔP and salt passage daily — a 10–15 % change is the CIP trigger.
5
Mixed-bed / EDI polishes to boiler / ultrapure quality.
Final polishing removes the last traces of ions: a mixed bed of cation and anion resin (regenerated with HCl and NaOH) or an EDI stack that uses an electric field and membranes to regenerate continuously with no chemicals. Output reaches <0.1 µS/cm and >16 MΩ·cm for high-pressure boiler feed, power-plant or pharma use.

Key Components

MMF/PSF

Removes suspended solids

Multi-grade/pressure sand filter with graded silex, gravel and sand beds in an FRP or MS-rubber-lined vessel. Backwash on 0.5–0.7 bar ΔP or daily; measures success in turbidity and SDI, not appearance.

ACF

Dechlorination, organics

Activated carbon filter (coconut-shell granular carbon) for dechlorination, organics, colour and odour. Empty-bed contact time of 8–10 min is needed for full chlorine removal; hot-water or steam sanitisation keeps it from becoming a bacterial bed.

Softener

Hardness removal

Strong acid cation resin in Na form, with brine tank, injector and multiport/diaphragm valve set. Sized on hardness × flow between regenerations. Hardness slip to the boiler shows up fast as scale — check outlet hardness every shift.

RO Skid

Desalination via membranes

High-pressure pump, cartridge filter (5 µm), spiral-wound TFC membranes in FRP pressure vessels, arranged in a 2:1 or 3:2 array with reject recirculation. Instruments: feed/permeate/reject flow, conductivity, ΔP, ORP and pH. CIP with citric/HCl for scale and NaOH/SDBS for organics and biofilm.

MB / EDI

Final polishing

Mixed bed: cation and anion resin intimately mixed for a final ion polish, regenerated separately after air-separation. EDI: continuous electro-deionisation using ion-exchange membranes and DC current — no acid or caustic, but it demands RO permeate quality feed with low hardness and CO₂.

Typical Operating Parameters

These reference ranges are illustrative context, not approved operating limits. Verify the installed model, duty, fuel or water conditions and applicable site requirements before use.

RO Recovery

70 – 80 %

RO Rejection

> 98 %

Soft Water Hardness

< 5 ppm as CaCO₃

DM Conductivity

< 0.1 µS/cm

Safety Notes

•Acid/alkali handling for regeneration — full PPE.
•Eye wash & safety shower near regen area.
•Neutralize spent regenerant before discharge.

Maintenance Schedule

•Daily: pressure drop across filters, conductivity trends.
•Regen cycles as per throughput.
•Annual: RO CIP (clean-in-place), resin sampling.

Problem Solving Matrix

Listed causes are hypotheses, not confirmed findings. Any corrective work requires qualified assessment, approved procedures and follow-up measurements.

Issue	Likely cause	Fix
High RO ΔP	Membrane fouling	CIP with acid/alkali
Poor rejection	Damaged membrane / seal	Probe & replace element

Equipment Running-Cost Estimate

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