▶ Membrane is a thin subject that affects the transfer rate of substances without phase boundaries.
It even enables the dissolution of solids or gases in the liquid.
▶ This is a more advanced level of filtration when compared to the former methods.
(Spiral Wound Membrane & hollow Fiber Membrane)
Classified by the particle sizes in membrane segregation objects
▶ MF membrane; Microfiltration Membrane
• MF membranes have pole that we can only see through microscopes.
• Mainly over 0.01㎛ of particles are the subjects of segregation. Segregation capacity is shown as various pole sizes.
Since big poles allow the smaller sized substance to pass, density polarization does not appear during the process.
• Colloid, bacteria, seaweeds are the major subjects.
▶ Membrane UF ; Ultrafiltration Membrane)
• UF mainly segregates high/low density particles and cannot be seen even with the help of microscopes.
• Generally it is designed in asymmetric structure with selective function of activated surface and porous supporting classes.
• The filter filtrates substances with the size that is bigger than the pole; smaller particled substances are removed by spread
• Bacteria, colloid, protein, pr, and high density organic matters with 5,000~30 of molecules are removed.
(the unit of segregation capacity is indicated as MWCO, not ㎛).
(Classified By The Particle Sizes in Membrane Segregation Objects)
▶ Membrane NF ; Nanofiltration Membrane
• NF is a complex membrane that has intermediate features of RO and UF membranes with interface
• NF blocks some of the salts and has 200~500 molecules about organic matters.
• The theory of segregation mainly depends on spread of liquids on ROs. Divalents or simple molecular substances are often the objects.
• Economically inefficient due to the high manipulation pressure, but expected to be used in electrical treatments to removing ions in vaporing methods.
▶ Membrane RO ; Reverse Osmosis Membrane
• RO has the capacity of segregating substances that are in the status of ions; it mainly uses asymmetric membranes which adopts the fundamentals of dissemination of fluids.
• Pole sizes in membrane RO is known as Å; according to another theory it is said that there's no poles at all, however.
• Water particle sizes are about 2 Å, Salt ion sizes are about 4 Å
• RO can even segregate ionized substances; thus used for distillation of sea water, cleaning waste fulid, dealing with wastewater from plating, etc.
Classified by forms membrane modules
▶ Spiral-Wound Module
• Spiral-Wound Module has a space which allows produced water to flow; its Mesh spaces(betweenmembranes) allow the flow
of original water.
• Mesh spaces are made from Polypropylene; it promoted the transmisiion of substances and decreases density polarization.
• Spiral-wound module is the most widely used system because it's the most compact and cheapest.
• It can adapt to various environments and proceses as it does not have certain type of settled forms.
• In actual processes, 2~6 of Spiral-wound modules are connected to pressure vessels in series.
▶ Hollow -Fiber Module
• Hollow -Fiber Module is made up of thousands of fiber strings with spaces in them in pressure vessels.
• It is composed of micro directed polyamide that is thinner than human hair. The fiber has dense level of asymmetric groups
about 0.1∼1 μm. Near to the surface, however, exists a relatively thick (about 20∼30μm) porosity level.
• High density with widest surface area by unit volume.
• Fibers are attached with epoxy on both ends; it is difficult to use them in high pressure environment because they are not
supported by membranes
• Inner pressure method enables high movement of flux; but it has high rate of pressure loss and tend to block the path.
(Hollow -Fiber Modul)
※ Inside feed vs Outside feed
♦ Inside feed
• Active layer on the inside, which provides protection from damage
• Controlled hydrodynamics
• High velocity in b/w; stable efficient operation, without the need for air
• Suits PES flbre
♦ outside feed
• Twice the membrane surface area for a 0.8mm id, 1.3mm od fibre
• Can use air for cleaning, which reduces b/w usage
• Can work well with SUB or PD configurations
• Suits PVDF fibre
▶ Tubular Type Module
• It is composed of various membrane elements that look like pipes withing the internal pressure instrument.
• Mostly it is driven with inner pressure and cleansed with sponge balls.
• The density of membranes is low; however, sections in the membranes are big enough to apply to liquids with big sized molecules.
(Tubular Type Module_Ceramic Membrane & PES and PVDF)
▶ Plate & Frame Type Module
• Plate & Frame Type Modules are attached to the supporting plates and modulized by grouping small spaces.
(Monolith Type Module)
※ Major functions of membranes are segregation, concentration and demarcation. Isolation, fixation, and adsorption are
other techniques also used in the segregation processes.
• Basic feature of membrane filtrations is capable segregation of solid/liquid, liquid/liquid matters or gas without changing the phases or adding chemicals.
• membrane MF, UF : Uses screening filtration technique
• membrane NF, RO : Uses the difference in movement rate within membranes
• Oftentimes these segregations require complex treatments rather than a single operation.
• It is about dividing solutes or corpuscles according to their molecular sizes.
• membrane MF : Mf checks the demarcation function with a bacterium filtration by comparing the indication germs or particle filtration.
• membrane UF : performance measure by Molecular Weight of Cut-off method
• segregation means to divide two other liquids or substances getting mixed between membranes.
• on one side of the membrane keeps liquids, on the other side it keeps gas or other kind of liquids
▶ Fixation, absorption
• Membrane UF and MF have big surface area that are leachy; they simultaneously perform the segregation and absorption of membranes because they have relatively big poriferous inner surface.