Permeate flux enhancement with dilute nanofluidic colloidal suspension in membrane distillation system

Membrane distillation (MD) is a commonly used method for water treatment, but the issue of temperature polarization often leads to low vapor flux, which severely restrict the development and application. In order to improve MD performance, a novel method to create a porous layer on hydrophobic polytetrafluoroethylene (PTFE) membrane surface by Al2O3 dilute nanofluidic colloidal suspension is proposed in this study. Successful deposition was confirmed using different characterization techniques (SEM, EDS, CA). The effects of nanoparticle size and nanofluid concentration on DCMD performance at different feeding temperatures have been studied experimentally. Results demonstrate that the vapor flux enhancement varied non-linear with the increased nanofluid concentration, and the maximum enhancement of 32.46 % in vapor flux was achieved at feed temperature of 60 ℃. A robust deposition layer created by Al2O3 nanoparticles was confirmed with distillation experiment of 9 h. A fouling layer on the membrane surface was formed by flowing the nanofluid at higher concentration, which resulted in a deterioration of MD performance. Furthermore, the deposited membrane is able to maintain the high permeability when handling a 3.5 wt% NaCl solution. The work provides a simple method to enhance membrane distillation flux and a new perspective for nanofluidic suspensions in MD process.