Secondary pollution of permeate during micellar enhanced ultrafiltration of phosphate and nitrate solutions

The pollution of permeate with surfactant in the course of nutrients removal from aqueous solutions by micellar enhanced ultrafiltration (MEUF) was evaluated. The process was performed with the use of polyethersulfone (PES) and regenerated cellulose (RC) polymer membranes, as well as ceramic membranes that varied in terms of molecular weight cut-off (MWCO) values (1-50 kDa). Three cationic surfactant (cetyltrimethylammonium bromide, CTAB; cetylpyridimium chloride, CPC; octadecyl amine acetate, ODA) were chosen in order to bind nitrate or phosphate anions to surfactant micelles. The results of the study showed that the composition of the solution, membrane material, and membrane MWCO influenced the intensity of the secondary pollution of the permeate. The percentage of surfactant leakage from the feed to the permeate varied from 0.3 to 90.9% (CTAB), from 11.1 to 26.6% (ODA), and from 10.5 to 58.4% (CPC). The lowest intensity of the secondary pollution of MEUF permeates was observed when nitrate solutions were treated by CTAB surfactant and PES membranes were used. It was also proved that acidification of the permeate followed by ultrafiltration (UF) enabled reduction of the surfactant content in the post-treated permeate by 32-60% (in relation to the surfactant content in the initial MEUF permeate).