A Dendrimer-Based Forward Osmosis Draw Solute for Seawater Desalination

Abstract

A dendrimer-based forward osmosis (FO) draw solute, poly(amidoamine) terminated with sodium carboxylate groups (PAMAM-COONa), was investigated for seawater desalination. Compared with existing FO draw solutes, PAMAM-COONa offers unique advantages: (1) Its aqueous solution can generate high osmotic pressure because of the large number of −COONa groups. (2) The low viscosity of PAMAM-COONa solution can reduce internal concentration polarization (ICP), which adversely affects FO water flux. (3) PAMAM-COONa has a relatively large molecular size, favoring reduced reverse solute flux. In our FO tests using 2.5-generation (2.5G) PAMAM-COONa draw solution (33.3 wt %) and seawater (Singapore coast) feed solution, a relatively high water flux of 9 L m–2 h–1 was achieved with commercial HTI FO membrane. In addition, a considerably reduced reverse solute flux of PAMAM-COONa compared to that of NaCl was attained. After FO testing, the diluted PAMAM-COONa solution was reconcentrated to its original osmotic pressure with membrane distillation to produce desalinated water and to regenerate the draw solution. In addition to seawater desalination, the dendrimer-based FO draw solute may find applications in wastewater treatment and protein enrichment.