Treatment of whey, which is a by-product of cheese manufacturing process, has been a significant problem due to its high organic load with 100,000 mg O-2/L COD. In this study, treatment of two different types of whey by using different membrane processes namely Ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) was investigated to produce cleaner discharge and to recover the proteins In whey for re-use. Membrane modules were tested as one stage operations and cascade operations by employing a combination of membrane modules in series. Nanofiltration, when operated in one stage, produced the best results from the point of treatment capacity, COD removal, and protein recovery. 30.8 L/m(2)h of permeate flux value at transmembrane pressure (TMP) of 8 bar was reached with nanofiltration which produced permeate with COD load of 2,797 mg O-2/L, and the protein rejection was 88%. Additionally, the influent whey was concentrated 6.8 times its original Volume. Among the applied cascade operations, the NF + RO combination produced the best results. Another achievement of this combination is its capability of recovering both protein and lactose separately, protein recovery in the first stage and lactose recovery in the second stage.