IMPLEMENTATION AND EVALUATION OF A SEAWATER DESALINATION PILOT SYSTEM USING TWO-STAGE NANOFILTRATION

A seawater desalination pilot system using a two-stage nanofiltration membrane (NF90) was designed, implemented, and evaluated. In the first stage (at a laboratory scale), the permeate flux of the NF90 membrane was 39.7 L/(m2 h), while total dissolved solids rejection reached 93.6% at a transmembrane pressure of 37 bar. In the second stage, the membrane achieved a salt rejection of 99.9% and permeate flux of 72.5 L/(m2 h) at 16 bar. The pilot system showed a similar behavior operating at 40 and 15 bar in both stages; permeate recovery was 21.0 L/(m2 h) and 51.3 L/(m2 h) in the first and second stage, respectively. As the quality of water obtained in the first stage was satisfactory, it was mixed with water from the second stage, resulting in safe drinking water that conforms to local and international standards. The system can be used to treat different types of brackish water and be coupled with renewable energies. It can provide potable water at a cost of US $ 0.75 / m3, which is a competitive price considering the small size of the system. At present, this pilot system supplies drinking water to a coastal village of Chile.