Characteristics of flux decline in forward osmosis process for asymmetric cellulose membrane

Abstract

This study examined the effect of concentration polarization on permeate flux in forward osmosis (FO) membrane process for saline and sucrose solution. The reduction in permeate flux during the FO membrane process is largely due to the formation of concentration polarization on membrane surfaces. The flux reduction due to internal concentration polarization formed on the porous support layer was larger than that due to the external concentration polarization on the active membrane surface. Water permeate flux through the FO membrane increased nonlinearly with the increase in osmotic pressure. The water permeability coefficient was 1.8081×10-7 m/s·atm for draw solution on active layer (DS-AL) mode and 1.0957×10-7 m/s·atm for draw solution on support layer (DS-SL) mode in NaCl solution system. The corresponding membrane resistance was 5.5306×106 and 9.1266×106 s·atm/m, respectively. With respect to the sucrose solution, the permeate flux for DS-AL mode was 1.33~1.90 times higher than that for DS-SL mode. The corresponding variation in the permeation flux (J) due to osmotic pressure (π) would be expressed as J=-0.0177+0.4506π-0.0032π2 for the forward and J=0.0948+0.3292π-0.0037π2 for the latter.