Phosphorus removal by NF90 membrane: Optimisation using central composite design

Increasing phosphorus emission in water bodies has accelerated eutrophication process and it becomes an alarming issue in most of the countries. This present study was to investigate the removal of phosphorus using nanofiltration technology. Statistical analysis was done with central composite design to understand the interaction effect of the investigated process parameters on the rejection and permeate flux, followed by optimising the process condition. The optimum condition was found to be at 9.3 bar, 34 °C and pH 7.2 which gave the highest rejection and permeate flux of 99.77% and 88.74 L/m2 h, respectively. The performance of NF90 was further investigated with extremely high phosphorus containing solutions in the optimum condition as determined. The comparison with literature showed that NF90 membrane used in the optimum condition gave its superiority in rejection over the other membranes. The transport mechanism of the phosphorus ions through the nanofiltration membrane was studied using extended Nernst Planck equation. The results showed that the convective transport dominated at increased pressure and pH, while diffusive transport dominated at increased temperature and this finding is in agreement with the experimental observation.