Nanofiltration usage for fluoride removal in the sodium chloride presence

Fluorine and sodium chloride are common elements present in the water environment. According to WHO guidelines fluoride content in water cannot be not higher than 1.5 mF-/dm3. Elevated fluoride content was observed all over the world and it leads to many health issues. It can be removed with the usage of various methods (ion exchange, membrane processes, adsorption, precipitation). In this paper fluoride removal with nanofiltration usage was described. Tests were performed with the application of Amicon 86400 filtration cells. Two types of commercial nanofiltration membranes NP010P and NP030P (Microdyn Nadir) were used. Transmembrane pressure was established as 0.3 MPa. For lower fluoride concentrations (5 mgF-/dm3) NF process allowed to decrease fluoride content under level 1.5 mgF-/dm3. Removal efficiency decreased with increasing fluoride content. Membrane NP030P showed better separation properties. Sodium chloride influenced removal efficiency as well as fluoride adsorption on/in membranes during the process. According to obtained data, better hydraulic properties exhibited membrane NP010P. For both membranes decrease in permeate flux in comparison to pure water was noticed what was observed. Relative permeability was lowered even to 0.32.