Seawater Treatment

Desalination using MF and RO may be the answer to your source water shortage.

Where fresh water is scarce, alternative sources are sought for drinking water.  Seawater is a vast and readily available resource, and its desalination is already common in arid areas of the world. The use of microfiltration followed by reverse osmosis is becoming the accepted standard for desalination. Seawater can be converted into high-quality fresh water efficiently and cost-effectively using the Pall Aria™ microfiltration system in combination with RO membranes.

Seawater desalination
Ocean water has an average salinity of 35 parts per thousand. The approximate distribution of dissolved minerals is: chloride, 55%; sodium, 31%; sulfate, 8%; magnesium, 4%; calcium, 1%; and potassium, 1%. Pretreating with the Pall Aria system followed by reverse osmosis can reduce salt content to less than 500 mg/L. Typically, for every 1,000 gallons of seawater, the desalination process produces 300 to 500 gallons of pure water.

Pretreatment processes
Seawater must be pretreated to remove organics, algae, and fine particles that, in most cases, cause RO systems to foul prematurely. Premature fouling can increase operating costs substantially. The Pall Aria system has a demonstrated ability to prevent premature fouling and clogging of RO membranes. It provides a cost-effective alternative to traditional desalination pretreatment methods such as air flotation, clarification, sand filtration, and cartridge filtration. Microfiltration membranes differ from RO membranes in that they are made of more chemically resistant materials that allow them to be cleaned more aggressively. As a result, fouling of pretreatment membranes is typically not a problem.

During storms, particulate content of seawater from an open intake is variable. The Pall Aria system uses 0.1 μm rated polyvinylidine fluoride membranes to remove even the finest particles from the water. The system has been designed to handle particulate of all types, since even fine particles can foul RO membranes.

Pretreatment with a Pall Aria system can provide the following benefits.

  • A low concentration of suspended particles, which enables the RO membranes to operate at high flux.
  • Stable pretreated water that extends the life of the RO membranes.
  • Lower costs for power, cleaning chemicals, prefilter cartridge changeouts, and labor.
  • Additional cost savings because fewer pressure vessels and RO membranes are needed.

Pall Aria system performance for desalination applications
The following statistics represent typical Pall Aria system performance for salt water pretreatment. To maintain optimal performance, a monthly clean-in-place, using caustic and chlorine followed by acid, is recommended.

Silt Density Index (SDI) Recovery Rate Membrane Flux
Approx.1.5 to feed the RO system Up to 50% combined
(Pall Aria system improves RO efficiency)
59-82 GFD