Application of membrane processes for whey treatment

Abstract

Whey is a by-product of cheese manufacturing process containing significant amounts ofprotein and lactose. Treatment of whey has been a big problem due to its high organic loadwith an approximate chemical oxygen demand of 100,000 mg O2/L. In this study, treatment of two different types of whey by using different membrane processes such as ultrafiltration,nanofiltration, and reverse osmosis was investigated. Recovery of proteins in whey for re-usewas also investigated.6 different types of membrane modules (one ultrafiltration module, three nanofiltration modules, and two reverse osmosis modules) were tested as one stage operations and cascadeoperations by employing a combination of membrane modules in series. Nanofiltration, whenoperated in one stage, produced the best results from the point of treatment capacity andprotein recovery. 30.8 L/m2/h of permeate flux value at transmembrane pressure of 8 bar was reached with nanofiltration and the protein rejection was 88 %. Additionally, the influentwhey was concentrated 6.8 times its original volume. However, the COD removal efficiencyof the same process was very low, 77 %, producing effluent with COD value of 23,502 mgO2/L due to high lactose content in it. Cascade operations were investigated in order to designate a process stream efficient intreatment capacity namely high permeate flux, protein recovery and also COD removalefficiency. An initial stage of nanofiltration for the purpose of protein recovery and afollowing stage of reverse osmosis for polishing turned out to be the best combination among the available modules. This combination produced an effluent stream with COD value of2,450 mg O2/L that can easily be treated by means of conventional treatment. Anotherachievement of this combination was its capability of recovering both protein and lactoseseparately, protein recovery in the first stage and lactose recovery in the second stage.