Influences of temperature on the retention of PPCPs by nanofiltration membranes: Experiments and modeling assessment

Abstract

Nanofiltration (NF) is an effective technology for micropollutants retention for production of high quality reclaimed water. However, limited information is available about the effects of temperature on the performance of NF on micropollutants rejections. In this paper, the behaviors and mechanisms of micropollutants rejections by two commercial NF membranes (VNF1 and VNF2) were studied under different temperatures. Based on the Donnan Steric Pore Model with Dielectric Exclusion (DSPM-DE) model, the mathematical functions were firstly established to describe the relationship between pore size (rp) and temperature (T) as well as the relationship of water permeability (A) with temperature (T). The DSPM-DE model incorporated with temperature functions were used to predict micropollutants rejections by NF membranes at given temperature values. The results showed that the increase of temperature could lead to the increase of NF membranes' pore sizes, water fluxes as well as the micropollutants’ diffusivities. The rejection rates of positively and neutrally charged micropollutants decreased with temperature increased, which was mainly due to the attenuation of steric hindrance effect. For the negatively charged micropollutants, temperature had negligible effect on them, which was possibly facilitated by the co-function of electrostatic repulsion and steric hindrance effect. Our study also showed that the predicted rejection values of neutrally and positively charged micropollutants decreased with temperature increased, in agreement with those of the experimental data. Compared with the real experimental rejections, the average relative errors of predicted values were 6.20% and 9.03% for VNF1 and VNF2, respectively. But for benzotriazole, the average relative error was as higher as 20.44%, possibly due to its adsorption onto VNF membranes. This work provides valuable insights for NF engineering applications and designs at different temperatures.