Seawater Desalination Systems — SWRO with Energy Recovery for Islands, Coasts & Industry
UF pretreatment → single-pass SWRO with energy-recovery → remineralisation, producing potable or process water from seawater (TDS ≈ 35,000 ppm) at 2.5–4 kWh/m³. Engineered for island communities, coastal industries, resorts and emergency supply, from 10 m³/day container units to 10,000+ m³/day plants.
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Why SWRO Is an Energy-and-Reliability Problem Before It Is a Water Problem
Seawater is the hardest feed a water plant faces: ~35,000 ppm TDS, algae, organic fouling and temperature swings. The economics hinge on energy consumption (kWh per m³), and the reliability hinges on pretreatment that protects the membranes. A plant without proper energy recovery wastes 30–60% of its energy; a plant without UF/safe pretreatment fouls membranes in weeks instead of years. We design to hold the industry's 2.5–4 kWh/m³ band with energy-recovery devices (pressure exchangers/ERDs), and to WHO potable or your process spec for the product water.
| Parameter | Seawater feed | Product target |
|---|---|---|
| TDS | ≈ 35,000 ppm | < 500 ppm (potable), < 200 ppm typical |
| Chloride | ≈ 19,000 ppm | < 250 ppm (WHO aesthetic) |
| Boron | 4–6 ppm | < 0.5–2.4 ppm (WHO / crop-dependent) |
| SDI / fouling | Algae, silt, oil risk | SDI < 3 after UF pretreatment |
| Energy | — | 2.5–4 kWh/m³ with ERD |
Our Standard SWRO Process Train
| Stage | Equipment | Function | Key spec |
|---|---|---|---|
| ① Intake & screening | Open/beach-well intake, drum screen | Remove debris, protect downstream | Well intake preferred where geology allows |
| ② Pretreatment | UF (hollow-fibre) or DMF + antiscalant | Remove algae/silt to protect RO | SDI < 3, turbidity < 0.5 NTU |
| ③ Cartridge + dosing | 5 µm + antiscalant/SHMP dosing | Final protection vs scaling | Antiscalant per LSI/Stiff-Davis |
| ④ SWRO train | High-pressure SWRO membranes | Desalination to < 500 ppm | Recovery 40–50%, 55–70 bar |
| ⑤ Energy recovery | PX / ERD pressure exchanger | Recover concentrate pressure | Up to 60% energy saving |
| ⑥ Remineralisation | Limestone/CO₂ or blending | Corrosion control + taste | LSI > 0, hardness per WHO |
| ⑦ Product storage | Potable-grade tank | Stable supply to distribution | Chlorination as needed |
Boron removal (for irrigation/crop water or strict potable limits) is an additional second-pass RO or selective resin step — specified when your target requires it.
Materials We Use (Seawater Is Corrosive)
| Component | Material | Why |
|---|---|---|
| RO vessels & high-pressure piping | Duplex SS 2205 / FRP with epoxy liner | Chloride stress-corrosion resistance |
| Low-pressure piping | uPVC / HDPE / GRP | Seawater-tolerant, low cost |
| Energy-recovery device | PX / ERD (ceramic/SS internals) | High-efficiency concentrate recovery |
| Membranes | High-rejection SWRO TFC | Salt rejection ≥ 99.5% |
| Product piping | HDPE / SS (post-treatment) | Corrosion-safe potable delivery |
Standard Capacities (SWRO)
| Model | Output | Energy | Typical application |
|---|---|---|---|
| SW-10 | 10 m³/day | ~1.5 kW | Container unit, small island/village |
| SW-100 | 100 m³/day | ~14 kW | Resort, coastal industry |
| SW-500 | 500 m³/day | ~65 kW | Island community, hotel group |
| SW-2000 | 2,000 m³/day | ~250 kW | Municipal, large resort |
| SW-5000+ | 5,000+ m³/day | Custom | Municipal / industrial plant |
Containerised units are self-contained (intake → product tank) for fast deployment; larger plants are skid-based with on-site civil works.
Engineering Reference — 500 m³/day SWRO for an Island Community
| Parameter | Design value |
|---|---|
| Feed | Open seawater, TDS ≈ 35,000 ppm, temperature 25–31 °C |
| Product | 500 m³/day, TDS < 300 ppm, chlorine residual maintained |
| Energy | ≈ 3.2 kWh/m³ with PX energy recovery |
| Train | UF pretreat (SDI < 3) → SWRO (45% recovery, 60 bar) → remineralisation |
| Boron | < 1.5 ppm (single-pass, suitable for potable) |
| Packaging | Containerised / skid, diesel or solar-hybrid power ready |
| Delivery | 14–20 weeks from PO; deployment 2–4 weeks on site |
5 Pitfalls We Design Around
- Biofouling from open intake — beach-well intake where geology allows; UF + chlorination/dechlorination ahead of RO where not.
- Energy wasted without recovery — PX/ERD recovers up to 60% of concentrate pressure; we always model energy per m³.
- Boron exceedance for crops/irrigation — second-pass RO or selective resin where your target is < 1 ppm.
- Scale from high recovery in warm water — antiscalant dosed per LSI/Stiff-Davis; recovery capped conservatively.
- Corrosive product water — remineralisation to balance LSI protects your distribution pipes from aggressive RO water.
Standards We Design To
- WHO Guidelines for Drinking-water Quality
- ASTM D4195 — Standard guide for seawater RO
- IDA (International Desalination Association) practices
- ISO 9001 / ISO 14001 / ISO 45001
Frequently Asked Questions
Q1. What does SWRO cost to run per m³?
With energy recovery, expect roughly 2.5–4 kWh/m³ (about 3.2 in our 500 m³/day reference). Total cost depends on power price, intake type and staffing — we give a full opex estimate with every sizing.
Q2. How reliable is it in a remote island setting?
Containerised units are self-contained with minimal civil works, designed for limited local technical support. We supply remote monitoring and a spares kit sized for 12 months of autonomous operation.
Q3. Can it run on solar / diesel-hybrid power?
Yes — SWRO pairs well with solar-hybrid because ERD cuts the power peak. We size the power system (solar, battery or diesel hybrid) to your load profile.
Q4. How do you handle boron for drinking or irrigation water?
Single-pass SWRO typically delivers ~1–1.5 ppm boron at warm temperatures. If you need < 1 ppm (irrigation, some crops, strict potable), we add a second-pass RO or selective resin step.
Q5. What is the delivery lead time?
Containerised units 14–20 weeks from PO, then 2–4 weeks on-site deployment. Larger skid plants have a longer engineering phase — we give a schedule at quotation.
Q6. Do you provide full installation and training?
Yes — transport, on-site installation, commissioning, operator training and a documented handover are included. Remote video support after handover is standard.
Q7. What is the warranty?
12 months on the complete system plus 36 months on critical parts (SWRO membranes, ERD, UF modules). On-site labour and travel included in the first 12 months.
Q8. Can you integrate a bagged-water or bottling line?
Yes — we supply complete island packages: SWRO product water plus remineralisation and a bagged-water filling line, engineered as one train.
Related Equipment & Industries
RO-4000 — Reverse Osmosis · UF-2000 — Ultrafiltration · DW-2000 — Drinking Water
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Request an SWRO Sizing Sheet Talk to a desalination engineerTechnical content reviewed by Ella Liu, Industrial Water Treatment Specialist at Rong Water — 10+ years sizing SWRO, energy-recovery and UF systems for island, coastal and industrial desalination clients.