In this study by researchers in Singapore and Saudi Arabia, a novel forward osmosis (FO) process for the removal of heavy metal ions from wastewater has been demonstrated for the first time.
The proposed FO process consists of a thin-film composite (TFC) FO membrane made from interfacial polymerisation on a macrovoid-free polyimide support, and a novel bulky hydroacid complex Na4[Co(C6H4O7)2]·2H2O (referred to as Na–Co–CA) as the draw solute to minimise reverse solute flux.
The researchers successfully demonstrated the removal of six heavy metal solutions: Na2Cr2O7, Na2HAsO4, Pb(NO3)2, CdCl2, CuSO4, Hg(NO3)2.
Water fluxes around 11 L/m2/h were harvested with heavy metals rejections of more than 99.5% when employing 1M Na–Co–CA as the draw solution to process 2000 ppm (1 ppm = 1 mg/L) heavy metal solutions at room temperature.
This FO performance outperforms most nanofiltration (NF) processes. In addition, the high rejections were maintained at 99.5% when a more concentrated draw solution (1.5M) or feed solution (5000 ppm) was utilised.
Furthermore, rejections greater than 99.7% were still achieved with an enhanced water flux of 16.5 L/m2/h by operating the FO process at 60°C.
The impressive heavy metal rejections and satisfactory water flux under various conditions suggest great potential for the newly developed FO system in the treatment of heavy metals wastewater.