Fouling mechanisms of dairy streams during membrane distillation

Abstract

This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) using polytetrafluoroethylene (PTFE) membranes. Structural and elemental changes along the fouling layer from the anchor point at the membrane to the top surface of the fouling layer have been investigated using synchrotron IR micro-spectroscopy and electron microscopy with associated energy dispersive X-ray spectroscopy (EDS). Initial adhesion of single components on a membrane representing a PTFE surface was observed in-situ utilizing reflectometry. Whey components were found to penetrate into the membrane matrix while skim milk fouling remained on top of the membrane. Whey proteins had weaker attractive interaction with the membrane and adhesion depended more on the presence of phosphorus near the membrane surface and throughout to establish the fouling layer. This work has given detailed insight into the fouling mechanisms of MD membranes in major dairy streams, essential for maintaining membrane distillation operational for acceptable times, therewith allowing further development of this emerging technology. 2 IntroductionMembrane distillation (MD) is a thermally driven membrane process and relies on a highly hydrophobic porous membrane to maintain a liquid-vapour interface. Common membrane materials for MD are polypropylene (PP), polyvinylidene fluoride (PVDF) and PTFE [1,2]. The highest performing membrane material for MD is PTFE due to its high hydrophobicity, chemical inertness and open porous structure [3]. Fouling in the MD process is different to that observed in pressure driven processes such as RO. The low operating pressure used in MD may potentially lead to a less compact, more easily removed, fouling layer. Also, since only volatile compounds pass through the membrane pores, the potential for in-pore fouling is minimized in MD applications. Studies of MD processes have, however, revealed that penetration of foulants into the membrane can occur in some instances [4]. There is a need for a better understanding how dairy components interact with MD membranes and accumulate at the membrane surface. This understanding may allow better control of performance of membrane distillation via better mitigation of fouling.The high hydrophobicity of MD membranes can result in the establishment of hydrophobic interactions between the membrane and any solutes that have hydrophobic components, such as proteins and fats. While hydrophilic coatings may be a possible avenue to reduce the fouling that results from these hydrophobic interactions [5][6][7], simple uncoated membranes have advantages in terms of lower cost and can be easier to manage over time as there is no requirement to maintain a specialised surface coating.There are numerous studies on fouling phenomena occurring with dairy components [8][9][10][11][12][13], however little can be found on the actual mechanisms behind the fouling. Most studies focus on membrane performance, not investigating kinetics behind fouling phenomena observed. In cases wh...

Characteristic properties of crude pineapple waste extract for bromelain purification by membrane processing

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Performance of a Two-Stage Membrane System for Bromelain Separation from Pineapple Waste Mixture as Impacted by Enzymatic Pre-Treatment and Diafiltration

“…The Total Organic Carbon (TOC) analyzer with Total Nitrogen (TN) detector (TOC-V, Shimadzu, Kyoto, KYT, Japan) has been employed for the protein determination (23). It involved Please note that this is an unedited version of the manuscript that has been accepted for publication.…”

Fouling in Membrane Distillation, Osmotic Distillation and Osmotic Membrane Distillation

“…Analysis of fouling process and identification of foulants by means of characterization techniques are important to determine suitable treatment methods for fouling control. It is worth noting that very few studies have been published so far on fouling mechanisms in MD, OD and OMD and investigations on the kinetics behind fouling phenomena and fouling mitigation remain very scarce [12,13]. Two review papers have been published on fouling and scaling in MD but not on OD and OMD [14,15].…”

“…Two review papers have been published on fouling and scaling in MD but not on OD and OMD [14,15]. Moreover, when fouling is studied, the considered characterization techniques focused only on the average physico-chemical properties of the surface deposits but not on the underlying deposit layers [12].…”