Desalination turns seawater or highly brackish water into fresh water. Large municipal plants may use thermal processes, but for most industrial, hospitality and community projects the technology is seawater reverse osmosis (SWRO).
Seawater typically contains around 35,000 mg/L of dissolved solids, and considerably more in enclosed seas such as the Arabian Gulf and Red Sea. That high salinity drives everything else: pressure, energy use, materials and pretreatment.
What a seawater RO system includes
- Intake
- Open-sea intakes with screening, or beach wells, which provide naturally pre-filtered water where geology allows.
- Pretreatment
- Media filtration or ultrafiltration, cartridge filters and chemical dosing such as coagulant, antiscalant and dechlorination.
- High-pressure pumps
- SWRO commonly operates at around 55–70 bar, depending on salinity, temperature and recovery.
- Energy recovery devices
- Isobaric pressure exchangers or turbochargers transfer pressure from the concentrate back to the feed. They are the main reason modern SWRO is far more efficient than older plants.
- Post-treatment
- Remineralisation (for example calcite contactors, or lime with carbon dioxide) and disinfection. Raw permeate is low in minerals and corrosive to distribution pipework.
- Brine discharge
- Outfall and diffuser arrangements that meet local environmental permits.
Specifications to compare before you request quotes
- Capacity across the temperature range
- Output and feed pressure at both minimum and maximum seawater temperature.
- Recovery
- SWRO commonly runs at roughly 35–50% recovery. Higher recovery reduces intake and pretreatment size but raises pressure and scaling risk.
- Specific energy consumption
- kWh per m³ with the energy recovery device included. A well-designed SWRO stage with isobaric energy recovery is commonly in the region of 3–4 kWh/m³. Ask what is included in the figure (RO only, or intake and pretreatment too).
- Permeate quality
- Guaranteed TDS, chloride and boron. Drinking water and irrigation of sensitive crops may need a second RO pass to meet boron limits.
- High-pressure materials
- Duplex or super duplex stainless steel is normally specified for high-pressure seawater service. Standard 316L stainless is prone to pitting and crevice corrosion in seawater.
- Pretreatment robustness
- How the design copes with algal blooms, storms and oil contamination, which are common causes of SWRO downtime on open intakes.
- Configuration
- Containerised, skid-mounted or built on site, and what civil and electrical works the buyer must provide.
Information to send suppliers with your enquiry
- Seawater analysis including TDS, temperature range, boron, turbidity or SDI, and any history of algal blooms or oil.
- Proposed intake location and constraints.
- Required product water volume and use (drinking, process, irrigation).
- Brine discharge rules and permits.
- Power supply and local electricity cost, since energy is the largest operating cost.
Common sourcing mistakes
- Accepting 316L stainless steel on the high-pressure seawater side.
- Skipping energy recovery on anything beyond very small units.
- Under-designing pretreatment for an open intake.
- Forgetting remineralisation, then seeing corrosion in downstream pipework.
- Not checking boron when the water is for drinking or agriculture.