Phosphorus removal using nanofiltration membranes

A high concentration of phosphorus in wastewater may lead to excessive algae growth and de-oxygenation of the water. In this work, nanofiltration (NF) of phosphorus-rich solutions is studied in order to investigate its potential in removing and recycling phosphorus. Wastewater samples from a pulp and paper plant were first analyzed. Commercial membranes (DK5, MPF34, NF90, NF270, NF200) were characterized and tested in permeability and phosphorus removal experiments. NF90 membranes offer the highest rejection of phosphorus; a rejection of more than 70% phosphorus was achieved for a feed containing 2.5 g/L of phosphorus at a pH <2. Additionally, NF90, NF200 and NF270 membranes show higher permeability than DK5 and MPF34 membranes. The separation performance of NF90 is slightly affected by phosphorus concentration and pressure, which may be due to concentration polarization and fouling. By adjusting the pH to 2 or adding sulfuric acid, the separation performance of NF90 was improved in removing phosphorus. However, the presence of acetic acid significantly impairs the rejection of phosphorus.