Transport properties and fouling issues of membranes utilized for the concentration of dairy products by air-gap membrane distillation and microfiltration

Abstract

The work contains results related to the application of membrane separation processes (i.e., membrane distillation and microfiltration) in dairy products processing. The performance of titania ceramic membranes (pristine as well as hydrophobized) was studied in the microfiltration process of whey and lactose solutions. On the other hand, polymeric porous hydrophobic membranes, (polypropylene—PP and polytetrafluoroethylene—PTFE) were tested in the air-gap membrane distillation (AGMD) process in contact with whey and lactose solutions. The extended material and physiochemical characterization (including fouling issues) of membrane materials before and after the separation process was performed. Transport of lactose solution across the membranes was characterized by higher effectiveness comparing with whey solution. Lactose played an important role and reduced the interactions with membrane material. Lactose solution possessed lower adhesion ability than whey what influenced the fouling and reduction of permeate flux. Membrane distillation was found to be a process that generates high-quality water with retention > 99% while simultaneously concentrating whey or lactose solutions. Microfiltration process was characterized by a rejection of lactose in the range of 80–90% for pristine ceramic membrane and hydrophobized one, respectively. The tendency to fouling in the case of AGMD process was associated with the higher contribution of polar part (29%) of the surface free energy SFE for PTFE membrane. The lowest value of normalized flux decline was observed for PP membrane, and that was correlated with the smallest contribution of polar interaction in SFE, the lowest value of roughness (RSM), contact angle (CA), and contact angle hysteresis (HCA), determined for the membrane after its utilization in the separation process.