Fractionation of dairy wastewater into a protein-rich and a lactose-rich produce

Fractionation of dairy wastewater into lactose-enriched and protein-enriched streams using an ultrafiltration membrane technique was examined. Three different sizes (3, 5 and 10 kDa) of regenerated cellulose membranes were used to determine the most efficient membrane for the process. Performance was determined under various operating conditions that included membrane size, temperature and transmembrane pressure (TMP) on the lactose and protein separation. The experiments were initially conducted with a made-up solution of (1) pure lactose, and (2) lactose solution with protein at different concentrations. After the behaviour of the membrane towards lactose and protein were assessed the experiments were performed with dairy wastewater supplied by a local dairy processing plant. From the results it was found that the 3, 5 and 10 kDa membranes provided 70-80, 95-100 and 100% recovery of lactose, respectively, from the made-up solution of pure lactose. The 10 kDa membrane results also showed a 100% recovery of lactose from the wastewater sample. At high temperatures, the lactose removal was higher by a minimum of 5% and a maximum of 18%. In general, increase in TMP increased the permeate flux which increased the percentage of lactose being removed. Other experiments conducted with wastewater showed that the permeate flux decreased initially for 25 min until a steady state was reached. The addition of protein to the made-up lactose solution decreased the percentage of lactose being removed. The 5 kDa membrane shows 90-95% rejection of protein, whereas the 10 kDa membrane yields low protein rejection at lower TMPs, but high rejection at higher TMPs. For the membranes considered (i.e. cellulose-based material and the cassette-type module), the most effective membrane for lactose recovery from made-up solution, as well as from dairy wastewater, is 10 kDa. Protein rejection from a made-up solution of lactose and protein was low while using a 10 kDa membrane. Fouling was found to be very significant from the experiments with wastewater.