The processing of acid whey, a by-product of cream cheese making, casein production and strained yogurt manufacture, has been a challenge in the dairy industry. The high lactic acid concentration causes operational problems in downstream spray drying operations due to increased powder stickiness. In this work, electrodialysis, a well proven demineralisation technology is used to remove the lactate ions from acid whey. If the ratio of lactic acid to lactose is to be reduced to the same level found in sweet whey, 80% of the lactate ions must be removed. For both laboratory prepared solutions and acid whey samples, the lactate ions were removed at a slower rate compared to other anions present in the system. Increasing the pH (from pH 4.6 to pH 6) of the feed solution led to a small enhancement in the rate of lactate ions removal at 5°C. No impact was observed, however, at 30 and 45°C where membrane resistance and solution viscosity is lower. To achieve the same level of lactate ion removal, the processing time in a batch process was three times shorter at 45°C, compared to that at 5°C. This means that significantly less membrane area is required in a continuous industrial electrodialysis operation. The energy consumption (~0.014 kWh/kg whey processed) for achieving 90% demineralization of the acid whey was comparable to the energy requirement reported for sweet whey demineralization in a typical commercial electrodialysis unit, illustrating the feasibility of this approach.

Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.

Fouling of dairy components on hydrophobic polytetrafluoroethylene (PTFE) membranes for membrane distillation, Journal of Membrane Science, http://dx.doi.org/10.1016/j. memsci. 2013.03.057 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThis study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds -skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hours at 54 °C feed inlet temperature and 5 °C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency.Skim milk flux was found to be lower but stable over time compared to whey. The study using single components as well as combinations thereof revealed that fouling was primarily driven by proteins and calcium, but only in combination. Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration, but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchor point to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins; however salts were needed to form a thick and dense cake layer. Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer. Whey proteins, on the other hand, deposited to a lesser extent. In general, membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk.

No 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...