ENHANCED NITRATE ULTRAFILTRATION BY CATIONIC SURFACTANT

The removal of nitrate ions from water using ultrafiltration enhanced by tetradecyltrimethylammonium bromide has been investigated in order to purify water. It is found that the efficiency of the process is an increasing function of the surfactant concentration and a decreasing function of the ultrafiltration membrane molecular cut-off, and seems independent of the initial nitrate concentration in the feed. The observed phenomena are well explained by assuming that, above the critical micellar concentration (cmc), nitrate ions are trapped by surfactant micelles unable to cross the membrane. However, since a good nitrate rejection is also achieved with surfactant concentrations well below the cmc, surfactant monomer adsorption onto the membrane must also play an important part in the separation process.