Microfiltration: Effect of retentate protein concentration on limiting flux and serum protein removal with...

The objective of our study was to determine if the limiting flux and serum protein (SP) removal were different at 8, 9, or 10% true protein (TP) in the microfiltration (MF) retentate recirculation loop using 0.1-µm ceramic graded permeability membranes with 4-mm-channel diameters operated at 50 °C using a diluted milk protein concentrate with 85% protein on a total solids basis (MPC85) as the MF feed. The limiting flux for the MF of diluted MPC85 was determined at 3 TP concentrations in the recirculation loop (8, 9, and 10%). The experiment was replicated 3 times for a total of 9 runs. On the morning of each run, MPC85 was diluted with reverse osmosis water to an MF feed TP concentration of 5.4%. In all runs, the starting flux was 55 kg/m(2) per hour, the flux was increased in steps until the limiting flux was reached. The minimum flux increase was 10 kg/m(2) per hour. The limiting flux decreased as TP concentration in the recirculation loop increased. The limiting flux was 154 ± 0.3, 133 ± 0.7, and 117 ± 3.3 kg/m(2) per hour at recirculation loop TP concentrations of 8.2 ± 0.07, 9.2 ± 0.04, and 10.2 ± 0.09%, respectively. No effect of recirculation loop TP concentration on the SP removal factor was detected. However, the SP removal factor decreased from 0.80 ± 0.02 to 0.75 ± 0.02 as flux was increased from the starting flux of 55 kg/m(2) per hour to the limiting flux, with a similar decrease seen at all recirculation loop TP concentrations.