Seawater Reverse Osmosis (SWRO) Desalination Lab

Model high-pressure membrane transport, isobaric pressure exchangers (ERD), osmotic pressure gradients, Specific Energy Consumption (SEC), and Levelized Cost of Water (LCOW).

Presets:
Net LCOW ($/m³)
$0.84
Levelized water cost per m³
Total SEC
3.12 kWh/m³
Specific energy consumption
Connected Power
13.0 MW
RO trains + intake & boost
Total CapEx
$165.0M
Installed facility CapEx

Hydraulic & Membrane Parameters

Permeate Production (m³/day): 100,000 m³/d
Feedwater Salinity (ppm TDS): 36,000 ppm
Ocean baseline is ~35,000 ppm; Mediterranean ~38,000 ppm; Arabian Gulf 42,000–48,000 ppm.
Feedwater Temperature (°C): 22 °C
Recovery Ratio (% Permeate / Feed): 42 %
Higher recovery reduces intake pumping but concentrates brine, increasing osmotic pressure & risk of mineral scaling.

Energy Tariffs & Capital Finance

Electricity Tariff ($/MWh): $55
Installed CapEx ($/m³·day capacity): $1,650
Water Purchase Agreement Tariff ($/m³): $1.15

Cost Stack Breakdown ($/m³ Freshwater)

  • Electricity (RO HPP & Aux): $0.172
  • Membrane Replacement (15%/yr): $0.055
  • Pre-treatment Chemicals & Antiscalant: $0.048
  • Operations, Labor & Overhead: $0.080
  • Cartridge Filters & Plant Spares: $0.042
  • Total Operating Cost (OpEx): $0.397
  • Annualized Capital Amortization: $0.443
  • Net Levelized Cost of Water: $0.84
SWRO Train & Isobaric Energy Recovery Architecture 96% ERD Efficiency
FEEDWATER SALINITY 36,000 ppm HPP OPERATING PRESSURE 64.5 bar REJECT BRINE SALINITY 62,069 ppm SPECIFIC ENERGY CONSUMPTION 3.12 kWh/m³ POTABLE WATER PRODUCTION 100,000 m³/d OCEAN INTAKE Wedge-Wire Screen UF FILTRATION HPP PUMP 65 bar VFD PX ERD 96% Energy Recov RO PRESSURE VESSELS (8-inch) 60 bar BRINE RECYCLE TO ERD ◀ Brine Outfall Diffuser CALCITE REMINERAL TDS < 300 ppm ► POTABLE WATER
Net Present Value
$74.5M
20-year @ 7.5% WACC
Internal Rate of Return
15.2%
Project equity/debt IRR
Simple Payback
5.8 yrs
Capital amortization

5x5 Sensitivity Matrix: Levelized Cost of Water ($/m³)

Feed Salinity vs Electricity Tariff
Salinity \ Power $30/MWh $50/MWh $70/MWh $90/MWh $110/MWh

20-Year Project Pro-Forma Snapshot

Period Gross Revenue Total OpEx EBITDA Net Cash Flow Cumulative Cash

Mastery Assessment: Desalination Engineering & Economics

1. What physical phenomenon enables reverse osmosis to separate freshwater from saline seawater?
2. How does an isobaric rotary pressure exchanger (PX) reduce the Specific Energy Consumption (SEC) of an SWRO plant?
3. What is the single largest operating cost (OpEx) line item in modern seawater reverse osmosis facilities?
4. Why does operating an SWRO facility in a high-salinity environment (e.g. 45,000 ppm TDS in the Arabian Gulf) increase LCOW?

Frequently Asked Questions

Seawater reverse osmosis uses semi-permeable polyamide thin-film composite membranes to extract potable freshwater from saline ocean water. By applying hydraulic pressure higher than the natural osmotic pressure of seawater (typically 27 to 35 bar, requiring operating pressures of 55 to 80 bar), water molecules are forced through the dense polymer matrix while >99.7% of dissolved salts and minerals are rejected into a concentrated brine stream.

In an SWRO plant operating at 40% to 50% recovery, more than half of the high-pressure feed stream exits as reject brine at nearly full hydraulic pressure (50 to 75 bar). Isobaric pressure exchangers (PX) transfer this hydraulic energy directly to incoming pre-treated seawater with over 96% efficiency without an intermediary motor-generator step, slashing plant specific energy consumption from ~8.0 kWh/m³ down to 2.8–3.5 kWh/m³.

Modern world-scale SWRO facilities achieve a Levelized Cost of Water between $0.70 and $1.40 per cubic meter ($2.65 to $5.30 per 1,000 gallons). Electrical power is the largest operating expense (accounting for 35% to 50% of total OpEx), followed by annualized capital recovery (CapEx amortized over 20 to 30 years), membrane replacement (12% to 18% annual turnover), and pre-treatment coagulant/antiscalant chemicals.

Higher feedwater salinity (such as 45,000 ppm TDS in the Persian Gulf vs 35,000 ppm in the Pacific) increases osmotic pressure, requiring higher feed pressure and consuming more power per cubic meter. Colder water temperatures increase water viscosity, reducing membrane flux and requiring higher driving pressure, whereas warmer water increases membrane permeability but slightly reduces salt rejection.

Modern SWRO plants utilize subsurface beach wells or low-velocity open intakes equipped with 1-2 mm cylindrical wedge-wire screens to prevent marine organism impingement and entrainment. Concentrate brine is discharged through offshore multiport diffusers engineered to rapidly blend high-salinity discharge with ambient seawater currents, ensuring salinity returns to baseline within a few dozen meters of the outfall.

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