Novel Janus composite hollow fiber membrane-based direct contact membrane distillation (DCMD) process for produced water desalination

In this study, an innovative Janus composite hollow fiber membrane-based direct contact membrane distillation (DCMD) process was boosted for desalination of actual produced water with elevated total dissolved solids (TDS) of 154,220 mg/L. The Janus composite hollow fiber membrane (Janus-HFM) was characterized with a thin and hydrophobic polyvinylidene difluoride (PVDF) and superhydrophobic silica nanoparticles (Si-R) outer layer, and a thick porous and hydrophilic PVDF and polyethylene glycol (PEG) inner layer. Compared to the neat PVDF hollow fiber membrane, the Janus-HFM showed both increased permeate water flux and improved energy efficiency with more than 99.99% salt rejection. The long-term desalination performance of the Janus-HFM was investigated via 200 h of continuous DCMD experiment. The results showed that the permeate water flux declined from 25.41 kg/m2h to 15.21 kg/m2h, and the salt rejection was 98.4% at the end of the operation. It was found that both scales and dissolved organic matters induced foulants accumulated at the feed side of the membrane due to the complex composition of the produced water. Nonetheless, the desalination performance decline can be effectively inhibited from 40% to 9.7% with a simple physical cleaning process by using the permeate water that recovered in the DCMD process.