Microfiltration

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Microfiltration (commonly abbreviated as MF) is a type of physical filtration process in which contaminated liquids are passed through a special pore-sized membrane to separate microorganisms and suspended particles from process liquids. These are usually used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a stream of products that are free of undesirable contaminants.

Video Microfiltration

General principles

Microfiltration usually serves as a pre-treatment for other separation processes such as ultrafiltration, and post-treatment for granular media filtration. Particle sizes commonly used for microfiltration range from 0.1 to 10 Âμm. In case the approximate molecular weight of this membrane can separate the molecular weight macromolecules is generally less than 100,000 g/mol. Filters used in microfiltration processes are specially designed to prevent particles such as sediment, algae, protozoa or large bacteria bypassing specially designed filters. More microscopic, atomic or ionic materials such as water (H ₂ O), monovalent species such as Sodium (Na ) or Chloride (Cl ^- ) ion , dissolved or natural organic matter, and small colloids and viruses will still pass through the filter.

The suspended fluid is passed at relatively high speeds of about 1-3 m/s and at low to moderate pressures (about 100-400 kPa) parallel or tangential with semi-permeable membranes in sheets or tubular shapes. Pumps are usually installed on the processing equipment to allow the liquid to pass through the membrane filter. There are also two pump configurations, either pressure-driven or vacuum-driven. Differential or differential pressure gauges are usually installed to measure the pressure drop between the outlet and the inlet flow. See Figure 1 for general settings.

The most abundant use of microfiltration membranes in water, beverage and bio processing industries (see below). The outgoing process flow after treatment using a micro filter has a recovery rate that generally ranges around 90-98%.

Maps Microfiltration

Application range

Water treatment

Perhaps the most prominent use of microfiltration membranes is related to the treatment of drinking water supplies. Membranes are a key step in the major disinfection of absorption water flow. Such a stream may contain pathogens such as Cryptosporidium and Giardia lamblia protozoa which are responsible for various outbreaks of disease. Both species exhibit gradual resistance to traditional disinfectants (ie chlorine). The use of MF membranes presents the physical means of separation (barrier) as opposed to chemical alternatives. In this case, both screening and disinfection take place in one step, eliminating the additional cost of chemical dosage and appropriate equipment (required for handling and storage).

Similarly, MF membranes are used in secondary waste water to remove turbidity but also to provide treatment for disinfection. At this stage, coagulants (iron or aluminum) are potentially added to precipitate species such as phosphorus and arsenic that should have dissolved.

Sterilization

Another important application of the MF membrane lies in the sterilization of cold drinks and pharmaceuticals. Historically, heat has been used to sterilize beverages such as juice, wine, and beer in particular, but the loss of delicious flavors is evident during warming. Similarly, drugs have been shown to lose their effectiveness in the addition of heat. MF membranes are used in this industry as a method to remove bacteria and other unwanted suspensions from liquids, a procedure referred to as 'cold sterilization', which negates the use of heat.

Petroleum refining

Furthermore, the microfiltration membrane finds increased use in areas such as petroleum refining, where removal of particulates from flue gases is of particular concern. The main challenge/requirement for this technology is the ability of the membrane module to withstand high temperatures (ie maintaining stability), but also the design must be such as to provide very thin tarp (thickness & lt; 2000 angstrom) to facilitate increased flow. In addition, the module should have a low fouling profile and, most importantly, be available at a low cost in order for the system to be financially feasible.

Milk processing

Apart from the above applications, MF membranes have found a dynamic use in key areas in the dairy industry, especially for the processing of milk and whey. MF membranes help remove bacteria and related spores from milk, by rejecting dangerous species through. It is also a precursor for pasteurization, allowing to extend product shelf life. However, the most promising technique for MF membrane in this field is related to the separation of casein from whey protein (ie serum milk protein). It produces two streams of products that are highly relied upon by consumers; a casein-rich concentrate stream used for cheese making, and a further processed whey/serum protein stream (using ultrafiltration) to make whey protein concentrate. The whey protein stream undergoes further filtration to remove fat to achieve higher protein content in the final WPC (Whey Protein Concentrate) and WPI powder (Whey Protein Isolate).

Other apps

Other common applications utilize microfiltration as the main separation process including

• Clarification and purification of the cell broth in which macromolecules must be separated from other large molecules, proteins, or cell debris.
• Other biochemical and bio-processing applications such as dextrose clarification.
• Cat Production and Adhesives.

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Main process characteristics

Membrane filtration process can be distinguished by three main characteristics: driving force, retentate flow and permeate flow. The microfiltration process is a pressure driven with suspended particles and water as solvent and dissolved solvent plus water as a seep. The use of hydraulic pressure accelerates the separation process by increasing the flow rate (flux) of the liquid stream but not affecting the chemical composition of the species in the retentate and the product stream.

The main characteristic that limits the performance of microfiltration or membrane technology is a process known as fouling. Fouling describes the precipitation and accumulation of feed components such as suspended particles, dissolved dissolved water-soluble or even permeable solutes, on membrane surfaces and or within membrane pores. Fouling of the membrane during the filtration process lowers the flux and thus the overall operating efficiency. This is shown when the pressure drop increases to a certain point. This happens even when constant operating parameters (pressure, flow rate, temperature and concentration) Fouling is largely irreversible although some of the fouling layers can be reversed by cleaning for short periods of time.

Microfiltration membranes can generally operate in one of two configurations.

Crosslinking: where liquid passes tangentially with respect to the membrane. The portion of the feed stream containing the treated liquid is collected under the filter while the parts of the water pass through the untreated membrane. Crossflow filtering is understood as a unit operation rather than a process. See Figure 2 for a general schematic for the process.

Ultimate-die filtering; all process fluid streams and all particles larger than the pore size of the membrane are stopped on the surface. All bait water is treated at once subject to cake formation. This process is mostly used for semi-continuous or semi-continuous filtration of a low concentration solution, See Figure 3 for a general schematic for this process.

 NOTE: Figures 2 and 3 are missing from the article  

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Design processes and tools

The main problems affecting the selection of membranes include

Site-specific issues

• Facility capacity and request.
• Percentage recovery and rejection.
• Fluid characteristics (viscosity, turbidity, density)
• Quality of fluid to be treated
• Pre-treatment process

Membrane specific issues

• Procurement and material manufacturing costs
• Operating temperature
• Trans membrane pressure
• Flux membrane
• Handles fluid characteristics (viscosity, turbidity, density)
• System monitoring and maintenance
• Cleaning and maintenance
• Disposal of process residue

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Process design variables

• Operate and control all processes in the system
• Construction materials
• Equipment and instrumentation (controllers, sensors) and costs.

Basic design heuristics

Some of the important design heuristics and assessments are discussed below:

• When treating raw contaminated liquids, hard sharp materials can wear and tear porous cavities in micro-filters, making them ineffective. Fluids should be pre-treated before passing through the microfilter. This can be achieved by variations in macro separation processes such as filtering, or granular media filtering.
• When performing a cleanup, the strain of the membrane will not dry out after it has been contacted by the process flow. Thorough water rinse from the membrane module, pipeline, pump and other unit connections should be done until the final water appears clean.
• Microfiltration modules are usually set to operate at pressures of 100 to 400 kPa. Such pressure allows removal of materials such as sand, crevices and clay, as well as bacteria and protozoa.
• When the membrane module is used for the first time, that is when starting the plant, the conditions need to be well designed. In general, slow-start is required when feeds are inserted into the module, because even a slight disturbance over the critical flux will result in an irreversible fouling.

Like other membranes, microfiltration membranes are susceptible to fouling. (See Figure 4 below) It is therefore necessary to have regular maintenance to extend the life of the membrane module.

• A 'backwash' routine, used to accomplish this. Depending on the specific application of the membrane, backwashing is done in a short period of time (usually 3 to 180 seconds) and in fairly frequent intervals (5 minutes to several hours). The turbulent flow conditions with Reynolds number greater than 2100, ideally between 3000 - 5000 should be used. But this should not be confused with 'backflushing', a more thorough and thorough cleaning technique, commonly done in particulate and colloid fouling cases.
• When primary cleaning is required to remove trapped particles, CIP (Clean In Place) techniques are used. Cleansing agents/detergents, such as sodium hypochlorite, citric acid, caustic soda or even special enzymes are usually used for this purpose. The concentration of these chemicals depends on the type of membrane (its sensitivity to strong chemicals), but also the type of material (eg scaling due to the presence of calcium ions) to be removed.
• Another method of increasing the life of the membrane may be feasible to design two microfiltration membranes in series. The first filter will be used to pre-treat fluid passing through the membrane, where larger particles and deposits are captured on the cartridge. The second filter will act as an additional "check" for particles capable of passing through the first membrane as well as providing filtering for particles in the lower spectrum of the range.

Design economics

The cost of designing and producing membranes per unit area was about 20% less than in the early 1990s and generally continued to decline. Microfiltration membranes are more advantageous than conventional systems. Microfiltration systems do not require expensive foreign equipment such as flocculants, chemical additions, flash mixers, precipitation and basin filters. However the cost of replacing the cost of capital equipment (membrane cartridge filters etc.) may still be relatively high because the equipment can be made specifically for the application. Using the heuristic design and general plant design principles (mentioned above), the membrane life span may be increased to reduce this cost.

Through the design of a smarter process control system and efficient plant design, some general tips for reducing operating costs are listed below

• Running plants on flux or reduced pressure during low load period (winter)
• Take the off-line plant system for a short time when extreme feed conditions.
• Short shutdown period (approximately 1 hour) during the first flush of the river after rain (in a water treatment application) to reduce cleaning costs in the initial period.
• Use of more cost-effective cleaning chemicals when appropriate (sulfuric acid rather than citric acid/phosphate.)
• Use of flexible control design system. Operators can manipulate variables and setpoints to achieve maximum cost savings.

Table 1 (below) discloses indicative guidelines for membrane filtration modal and operating costs per unit of flow.

Table 1 Estimated Cost of Filtration Membrane per unit of flow

note:

• Capital Cost is based on dollars per gallon of processing plant capacity
• The design flow is measured in millions of gallons per day.
• Membrane Fee only (No Pre-Care Maintenance or Post-Care equipment is considered in this table)
• Operating and Yearly Expenses, based on the per thousand gallon dollars per treated.
• All prices are in current US dollars in 2009, and are not adjusted for inflation.

Process tools

Membrane material

The materials that make up the membranes used in microfiltration systems can be organic or inorganic depending on the contaminants that are desired to be removed, or the type of application.

• The organic membranes are made using various polymers including cellulose acetate (CA), polysulfone, polyvinylidene fluoride, polyether sulphon and polyamide. It is most often used because of its flexibility, and its chemical properties.
• The inorganic membrane is usually composed of sintered metal or porous alumina. They are capable of being designed in various forms, with varying pore size and permeability.

Membrane equipment

The general membrane structure for microfiltration includes

• Screen filters (Particles and materials that are the same size or larger than the screen openings are maintained by the process and collected on the surface of the screen)
• Depth Filters (Materials and particles embedded in constriction in filter media, filter surfaces contain larger particles, smaller particles captured in narrower and deeper parts of filter media.)

Microfiltration membrane module

Dishes and frames (flat sheets)

The membrane module for microfiltration of dead ends is primarily a platen and frame configuration. They have flat and thin composite sheets where the plates are asymmetric. Thin, thin skin is supported on a thicker layer that has larger pores. The system is compact and has a robust design, Compared with cross-flow filtering, plate and frame configurations have reduced capital expenditure; but operating costs will be higher. The use of plate and frame modules is best suited for smaller and simpler scale (laboratory) applications that filter out aqueous solutions.

Spiral-luka

This particular design is used for cross-flow filtering. The design involves a pleated membrane folded around a perforated perforated core, similar to a spiral, usually placed inside a pressure vessel. This particular design is preferred when the solution is handled highly concentrated and under high temperature conditions and extreme pH. This particular configuration is commonly used in large scale industrial scale microfiltration applications.

The fundamental design equations

When separation is achieved by sieving, the main mechanism of transfer for microfiltration through a porous micro membrane is mass flow.

Generally, because the small diameter of the pore flow in the process is laminar (Reynolds Number & lt; 2100) The velocity of fluid moving through the pores can be determined (by the Hagen-Poiseuille equation), the simplest of them. assuming parabola speed profiles.

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Transmembrane Pressure (TMP)

The transmembrane pressure (TMP) is defined as the mean pressure applied from the feed to the concentric side of the membrane minus the pressure of the permeate. This applies to dead-end filtering primarily and is an indication of whether a system is sufficiently littered to guarantee replacement.

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Dimana

• ${\ displaystyle P_ {f}}  ÂÂ$ adalah tekanan pada Sisi Umpan
• ${\ displaystyle P_ {c}}  ÂÂ$ adalah tekanan dari Konsentrasi
• ${\ displaystyle P_ {p}}  ÂÂ$ adalah tekanan dari Permeate

Permeat Flux

Fluks permeat dalam mikrofiltrasi diberikan oleh hubungan berikut, berdasarkan Hukum Darcy

${\ displaystyle J_ {v} = {\ frac {1} {A_ {M}}} * {\ frac {dV} {dt}} = {\ frac {\ Delta P} {\ mu * (R_ {u} R_ {c})}}}  ÂÂ$

Dimana

• ${\ displaystyle R_ {u}}  ÂÂ$ = Pasang hambatan aliran membran ( ${\ displaystyle m-1}  ÂÂ$ )
• ${\ displaystyle R_ {c}}  ÂÂ$ = Meniru ketahanan kue ( ${\ displaystyle m-1}  ÂÂ$ )
• ? = Rekatkan viskositas (kg m-1 s-1)
• ? P = Penurunan Tekanan antara kue dan membran

Resistensi kue diberikan oleh:

${\ displaystyle R_ {c} = r * {\ frac {V_ {S}} {A_ {m}}}}  ÂÂ$

Where

• r = Special cake resistance (m-2)
• Vs = Cake volume (m3)
• AM = Area of ​​membrane (m2)

Untuk partikel berukuran mikron, Resistensi Kue Spesifik adalah kasar.

${\ displaystyle r = {\ frac {180 * (1- \ epsilon)} {\ epsilon ^ {3} * d_ {s} ^ {2}}}}  ÂÂ$

Where

• ? = Porosity of cake (no units)
• d_s = Average particle diameter (m)

Strong design equations

To provide a better indication of the precise determination of the extent of cake formation, the one-dimensional quantitative model has been formulated to determine factors such as

• Complete Blocking (Pores with an initial radius of less than pore radius)
• Standard Blocking
• Sublayer Formats
• Cake Formation

See External Links for more details

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Environmental, safety and regulatory issues

Although the environmental impact of membrane filtration processes differs according to application, the common evaluation method is life-cycle assessment (LCA), a tool for environmental load analysis of membrane filtration processes at all stages and contributes to all types of impacts to the environment including land, water and air emissions.

In the case of microfiltration processes, there are a number of potential environmental impacts to consider. They include the potential for global warming, potential photo-oxidant formation, potential eutrophication, potential human toxicity, potential freshwater ecotoxicity, potential ocean ecotoxicity and potential terrestrial ecotoxicity. In general, the potential environmental impacts of this process depend heavily on maximum transmembrane flux and pressure, but other operating parameters remain a factor to consider. A special comment on the proper combination of operational conditions will result in the lowest load on the environment not being able to do because each application will require different optimizations.

In a general sense, membrane filtration process is a relatively "low risk" operation, that is, a small dangerous danger potential. But there are some aspects that must be considered. All pressure-driven filtration processes including microfiltration require pressure levels to be applied to the feed liquor stream as well as imposed electrical problems. Other factors that contribute to safety depend on process parameters. For example, processing of dairy products will lead to the formation of bacteria that must be controlled to comply with safety and regulatory standards.

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Comparison with similar process

Microfiltration membranes are essentially the same as other filtration techniques utilizing the pore size distribution for physically separate particles. This is analogous to other technologies such as ultra/nanofiltration and reverse osmosis, however, the only difference exists in the sustained particle size, as well as the osmotic pressure. The main ones are described in general below:

Ultrafiltration

The ultrafiltration membrane has a pore size ranging from 0.1 Âμm to 0.01 Âμm and is capable of maintaining protein, endotoxin, virus and silica. UF has a wide range of applications ranging from waste water treatment to pharmaceutical applications.

Nanofiltration

The nanofiltration membrane has pores measuring from 0.001 Ã,Âμm to 0.01Ã,Âμm and filtering of multivalent ions, synthetic dyes, sugars and certain salts. When the pore size falls from MF to NF, the osmotic pressure requirement increases.

Reverse osmosis

Reverse Osmosis is the best available membrane separation process, pore size ranges from 0.0001 Âμm to 0.001 μm. RO is able to retain most of all molecules except water and because of the size of the pore, the required osmotic pressure is significantly greater than for MF. Both reverse osmosis and nanofiltration are essentially different because the flow is opposite to the concentration gradient, because the system uses pressure as a means to force water to flow from low pressure to high pressure.

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Recent developments

Recent advances in MF have focused on manufacturing processes for membrane and additive development to promote coagulation and therefore reduce the fouling of the membrane. Because MF, UF, NF and RO are closely linked, this progress applies to many processes and not MF only.

Recent studies have demonstrated a dilute prehydration KMnO4 combined FeCl3 capable of promoting coagulation, leading to decreased fouling, specifically KMnO4 preoxidation exhibiting effects that decrease irreversible membrane fouling.

Similar research has been carried out into the high polyfoam polyester (trimethylene terephthalate) (PTT) construction of nanofiber, which focuses on increasing throughput. Specific heat treatment processes and membrane internal structural processes show results showing 99.6% rejection rates of TiO2 particles under high flux. The results show that this technology can be applied to existing applications to improve their efficiency through high flux membranes.

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See also

• Membrane Technology
• Ultrafiltration
• Nanofiltration
• Reverse osmosis
• Membrane bioreactor

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References

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External links

• Polyakov, Yu, Maksimov, D & amp; Polyakov, V, 1998 'On Theoretical Design of Microfilters' Foundation of Chemical Engineering, Vol. 33, No. 1, 1999. & lt; http://web.njit.edu/~polyakov/docs/Microfiltration_TFCE_English.pdf>
• Layson A, 2003, Microfiltration - Current Know-how and Future Directions, IMSTEC, accessed October 1, 2013 https://web.archive.org/web/20131015111520/http://www.ceic.unsw.edu. au/centers/membran/imstec03/content/papers/MFUF/imstec152.pdf & gt; University of New South Wales Chemical Engineering Web site.

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