Application of micellar-enhanced ultrafiltration in the simultaneous removal of nitrate and phosphate

Abstract

The removal characteristics of nitrate and phosphate in the micellar-enhanced ultrafiltration (MEUF) were investigated according to the condition of feed solution such as type of surfactant, pH of the solution, and the presence of humic substances. Three different surfactants were tested: two of them were alkyldimethyl amineoxide (PENTANOX 4X and PENTANOX 24X) and the other was alkyldimethyl amine derivative (L-PAN50). PENTANOX 4X showed the highest removal efficiency of nitrate and phosphate, and L-PAN50 showed the lowest removal efficiency of them due to the lowest rejection of surfactant. It seemed that the formation and characteristics of micelle were influenced by the type of surfactant monomer and composition of surfactant solution. The removal of phosphate was affected by the pH of solution. The ionic form of phosphate changed in order of $H_2PO_4^{-}$, $HPO_4^{2-}$, and $PO_4^{3-}$ as the pH increased, and the electrostatic interaction of phosphate is the strongest with valance of (-3). Because the electrostatic interaction was the dominant mechanism of MEUF to remove nutrients from wastewater, the highest removal of phosphate was achieved at the highest solution pH. The removal of nitrate and phosphate decreased by the presence of humic acid (HA) in feed solution. At the low concentration of surfactant, the functional groups of HA compete with nutrient for the binding on micelle. Practically, greater than 3 molar ratio of surfactant to pollutant was not seriously influenced by the 100 ppm of HA in view of removal efficiency or flux. To evaluate the feasibility of MEUF in field application, a semi-pilot scale of cross-flow MEUF was developed. Over 86 % of nitrate and 93 % of phosphate was removed by 3 molar ratio of cetylpyridinium chloride (CPC), and the removal was independent of the pore size of membrane. During the filtration, a small decline of flux was observed initially, and then the flux level was maintained throughout the experiment. As a ...