Nanofiltration of sweet whey by spiral wound organic membranes: Impact of hydrodynamics

Abstract

The influence of permeation flux J and wall shear stress τw, on performances of the nanofiltration of concentrated sweet whey at volume reduction ratio 2, 18°C and using organic membranes was studied. It was concluded that sweet whey nanofiltration could be optimised through the parameter J/τw, since J and τw act together in a competing mechanism of convection/erosion at the membrane surface, that governs membrane fouling and selectivity. Hence, the overall fouling was strongly dependent on the ratio J/τw, with a critical J/τw value of approximately 6.0. When J/τw < 6.0, the total membrane fouling was relatively low and almost independent on operating conditions. For higher ratios of J/τw, there was a spectacular increase in fouling and a very strong dependence between the fouling index and J/τw. Simultaneously, selectivity was altered under these conditions, with higher retention of monovalent ions and lower retention of lactose. Finally, optimal hydrodynamic conditions were defined in the range 3-6. Under these conditions, longer operating times, lower chemical oxygen demand in permeate and higher demineralization could be expected at lower processing costs.