Reverse Osmosis Thin Film Composite membranes are subject to fouling by suspended materials that are present in seawater. Typical seawater RO foulings are:

Seawater Desalination typical pretreatment processes:

A very cost-effective way to avoid biological fouling is seawater chlorination . Unfortunately, chlorine oxidizes the membrane material, therefore only 0.02 mg/L can be tolerated.

A common dechlorination process is the injection of sodium bisulfite or metabisulfite, classified as a chlorine scavenger. Another solution is the use of a granulated activated carbon.

NOM, particles and colloids can be removed by so-called "conventional treatment" consisting of coagulation followed by media filtration for low turbidity water . Additional steps such as flocculation and sedimentation are added in case of very turbid shallow seawater. 

The non-conventional pretreatment for NOM , particles and colloids is Ultrafiltration.

An antiscalant solution should be dosed before the reverse osmosis membranes to disperse calcium carbonate and sulfates precipitates in order to avoid scaling.

Fine filtration (5-micron) is required as a last step before the RO membranes to prevent any debris, sand particles or piping material to damage the membranes.

--> See also ULTRAFILTRATION as a reverse osmosis pretreatment <--

Desalination Key Issues

Seawater Intake

Desalination Pretreatments

• Chlorination
• Coagulation / Multi-media Filtration
• Dechlorination
• Antiscalant
• Fine filtration
• Ultrafiltration
• Flocculation / Sedimentation

Desalination Post-treatments

Reverse Osmosis Desalination Process

Desalination and Energy Costs

Brine Disposal

Membranes cleaning

Storage and Distribution

Containerization / Tropicalization

Instrumentation and Control (SCADA)