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

The influence of permeation flux J and wall shear stress tau(w), on perform ances of the nanofiltration of concentrated sweet whey at volume reduction ratio 2, 18 degrees C and using organic membranes was studied. It was concl uded that sweet whey nanofiltration could be optimised through the paramete r J/tau(w), since J and tau(w) act together in a competing mechanism of con vection/erosion at the membrane surface, that governs membrane fouling and selectivity. Hence, the overall fouling. was strongly dependent on the rati o J/tau(w), with a critical J/tau(w), value of approximately 6.0. When J/ta u(w) < 6.0, the total membrane fouling was relatively low and almost indepe ndent on operating conditions. For higher ratios of J/tau(w), there was a s pectacular increase in fouling and a very strong dependence between the fou ling index and J/tau(w). Simultaneously, selectivity was altered under thes e conditions, with higher retention of monovalent ions and lower retention of lactose. Finally, optimal hydrodynamic conditions were defined in the ra nge 3-6. Under these conditions, longer operating times, lower chemical oxy gen demand in permeate and higher demineralization could be expected at low er processing costs.