Waterworks Brackish Reverse Osmosis Systems

Brackish water has a wide range of compositions and can have total dissolve solids (TDS) concentrations anywhere between 50 – 12, 000 mg/l. For brackish water RO systems the common recovery limiting factors are:

• Chemical precipitation
• Bio fouling

As a result, the first and most important step in brackish water RO system design is an accurate analysis of the feed water characteristics including the temperature. Depending on the feed water characteristic, sodium (Na +) and chlorine (Cl -) may be added to balance the composition. The temperature is important because variations can cause scaling.

Scaling occurs when soluble salts are concentrated to their solubility limit in the concentrate stream and precipitate on the RO membrane surface. Therefore, scaling control is required to guarantee membrane performance and is adjusted according to the feed water characteristics of each RO system. The most common precipitating salts are calcium sulphate (CaSO4), calcium carbonate (CaCO3), and silica. Common scaling control methods include: Acid addition - is specifically for calcium carbonate scaling prevention and is paired with caustic dosing to neutralize the product water. Antiscalant addition - is for carbonate, sulphate, and calcium fluoride scale prevention. Antiscalant chemistry is complex and specific to each application Chlorination - is used to prevent bio fouling. Sodium metabisulfite addition – is used to reduce the chlorine concentration to protect the RO membrane which can be compromised by chlorine contact.

In addition to the scaling control methods listed above, brackish water RO systems normally involve general pre-treatment as well. Common pre-treatment methods to remove dissolved solids, bacterial and organic matter include:

• Clarification
• Coagulant dosing
• Cartridge filtration
• Multimedia filtration
• Ultrafiltration

The goal of brackish water RO treatment system design is to minimize the feed pressure and membrane costs while maximizing recovery and product water quality. Generally, brackish water RO treatment systems have lower feed pressure requirements and higher permeate transported per membrane unit area than seawater RO treatment systems.

Waterworks Technologies can design systems that meets with all water treatment needs and applications. Waterworks has over 25 years experience designing, building, installing and commissioning water treatment systems for clients around the world.