Performance assessment of membrane distillation for skim milk and whey processing

Abstract

Membrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10 kPa). At higher cross-flow velocities (around 0.141 m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12 kg/h·m(2) for skim milk of 20% dry matter concentration and approximately 20 kg/h·m(2) after 18 h of operation with whey at 20% dry matter concentration.

Effect of module design and flow patterns on performance of membrane distillation process

“…The solute present in the feed can affect the MD flux in several possible ways: by building up the fouling layer at the membrane surface that offers an additional resistance to mass and heat transfer, by lowering the vapor pressure of feed solution, by adsorbing on the membrane surface and by introducing concentration polarization if the convective flux is high. Initial high reduction in flux is consistent with the previous MD studies [50] carried out on whey solution where a rapid flux decline was observed mainly due to adhesion of certain whey components with membrane surface. Time interval ($3 h) over which the major flux decline takes place is different in current study as compared to one mentioned in [50] perhaps due to different type of whey and membrane used.…”

Scaling and fouling in membrane distillation for desalination applications: A review

“…This leads to an increase in the concentration of dissolved ions close to the membrane interface, reducing the local vapor pressure and thereby reducing flux, in addition to increasing tendency to precipitate [124].…”

Membrane distillation and membrane electrolysis of coal seam gas reverse osmosis brine for clean water extraction and NaOH production

“…At concentration factor of above 10, inorganic salts in the feed exceeded their saturation limits, precipitated on the membrane surface, and induced membrane scaling. A scaling layer was formed on the membrane, reduced the active surface for water vapour transport through the membrane [40,41] and partial water vapour pressure on the membrane surface [42,43], thus decreasing water flux. The scaling layer could also promote membrane wetting [44,45].…”