Microfiltration compare with Conventional Pretreatment Systems

Water filtration is important to get pure water for people. The traditional pretreatment for RO has been conventional treatment with deep bed granular media filters.  These are made up of layers of graded sands, gravel and anthracite.  Suspended solids are removed from the feedwater as it flows downwards through the media    Filter media have erratic performance because of the way they remove particles, which includes straining, sedimentation, interception, adhesion and adsorption, generally created by a filter aid or flocculant dosed into the feedwater to the filter.   Filter media can achieve removal down to particle sizes of 10 – 20 micron or, with the addition of upstream coagulant dosing, removal down to 1 micron.

A microfilter removes particles as the feedwater flows through the microfilter membrane.   Microfilters remove particles down to 0.1 micron in size – 10 to100 times finer than media filters. Microfiltration is a purely physical process in which particles are captured on the surface on the membrane.   Any particle larger than the pore size of the membrane cannot squeeze through.

Conventional pretreatment has limitations in its effectiveness as pretreatment to RO, related to the variable quality of the treated water produced.   Microfiltration is ideal as RO pretreatment because it produces filtrate of a consistent quality irrespective of variations in the feedwater.   The Silt Density Index (SDI), an empirical parameter, is used by RO membrane manufacturers as an indicator of the propensity of a feedwater to foul membranes.  For most manufacturers, an SDI of 5 is the maximum recommended.   The conventional pretreatment system often achieves an SDI of approximately 5, while MF pretreatment typically achieves an SDI less than 3.

In the past, cellulose acetate (CA) RO membranes were used in water reuse applications, because  of the ability of CA membrane to withstand high chlorine dosages (as biocide) that reduced its fouling tendency compared to polyamide composite membranes.  The disadvantage to using CA membranes is that they require significantly higher pressures to achieve the same production rate as polyamide composite membranes.  Polyamide membranes, although able to operate at lower pressures and produce higher quality product water, were subject to rapid fouling and possible irreversible bio-fouling due to their incompatibility with oxidants.  The adoption of MF as the pretreatment for RO systems reduced this fouling potential, enabled the reliable use of polyamide composite membranes on wastewater and allowed for a 20% increase in flux, resulting in a significant reduction in capital and operating costs. So microfiltration has wide applicaiton in filtration field.

Membrane Technology versus Non-Membrane Media

Longer Bag Life, Lower Emissions Rates, Lower Pressure Drops, Better Gas Throughput

Non-Membrane Depth Filtration

Filtering Mode

  1. Dust is filtered inside of filter media
  2. Internal dust cake buildup required
  3. Particles enter into filter media and can pass through
  4. Might not filter finest particles
  5. Efficiency requires careful balance between filter, particulate, and system conditions

Cleaning Mode

  1. Difficult to remove particles, only surface dust cake is removed
  2. Dust deep inside media can cause higher Dp and blinding with time
  3. Dust buildup inside media can lead to emissions after cleaning

Membrane Filtration

Filtering Mode

  1. Dust filtered at membrane surface
  2. No dust cake buildup required
  3. No particles enter backer
  4. Capable of submicron filtration
  5. Maintains capture efficiency over wide range of system conditions

Cleaning Mode

  1. Almost all dust falls off membrane surface
  2. Particles do not build up inside backer
  3. Surface is hydrophobic, even wet dust cakes can still be handled

Introduction of Lab Filter Membrane Properties

Membrane Types
Cellulose Nitrate
(CN) membrane is the most popular membrane used in analytical and laboratory filtration. CN membrane has excellent wetting properties and gives fastest flow rates with aqueous solutions.
Mixed Cellulose Ester
Membrane provides a more uniform and smoother surface compared to pure nitrocellulose membrane. This membrane is typically used to count or analyze particles contained in liquids or captured from aerosols.
Cellulose Acetate
Membrane is a mixture of cellulose triacetate and diacetate that creates a strong membrane in both lateral and longitudinal directions. In addition, the membrane has a low static charge, a very low aqueous extractability, and good solvent resistance to low molecular weight alcohols.
Regenerated Cellulose (RC)
Regenerated Cellulose is an hydrophilic, solvent resistant, low protein binding membrane. RC membrane is ideal for removing particulates from HPLC samples, prior to injection. This membrane is compatible with all HPLC solvents, and can be utilized for particle removal and de-gassing of these solvents. RC membranes are also compatible with aqueous solutions in the pH range of 3 to 12. Extractables with water are less than 1%. Regenerated Cellulose membranes exhibit low non-specific adsorption, thus they are well suited for filtration of biological samples, where maximum recovery of protein is important. When used with a glass pre-filter in the same housing, this membrane is ideal for filtration of tissue culture media, as well as general biological sample filtration. RC membranes can be sterilized by gamma radiation, autoclaving, ethylene oxide, or dry heat.
Cellulose Esters (MEC)
Cellulose Esters is a very low protein binding membrane that is ideal for aqueous based samples. MEC membranes are an excellent choice when maximum protein recovery in the filtrate is critical. Laboratory studies show that MEC membranes bind less protein than PVDF or Polysulfone membranes. When used with a glass pre-filter in the same housing, these membranes are ideal for filtration of tissue culture media and sensitive biological samples. The pre-filter increases yield.
Polyethersulfone (PES)
Membrane is hydrophilic and low protein binding. No external wetting agents are required, resulting in low extractables. PES membrane generally offers fast flow rate and better chemical resistance than cellulose acetate membranes.
Membrane is strong, highly porous, and inert to most chemically aggressive solvents, strong acids, and bases. Chemical and thermal limitations are imposed by the backing material.
Membrane is strong, inherently hydrophilic, and compatible with a broad range of aqueous solutions including alcohols and solvents used in HPLC work.
New low extractable Nylon membranes combine the solvent resistance of Nylon with a membrane that exhibits very low extractables. Nylon is commonly used for general laboratory filtration, and filtration of HPLC samples prior to injection. Nylon binds protein, and should not be used when maximum protein recovery is important. Nylon can be sterilized by autoclaving at 120C, gamma radiation, or ethylene oxide.
Polypropylene (PP)
Polypropylene membrane is a hydrophilic membrane that exhibits a wide range of chemical compatibility to organic solvents. PP membranes are a good choice for filtration of HPLC samples when performing protein analysis by chromatography. In addition to being highly solvent resistant, these membranes are low non-specific adsorbing membranes, which results in maximum protein recovery for critical analysis. PP membranes are also well suited for biological sample filtration.
Glass Media
Glass Media membranes are commonly used as pre filters in many filtration devices. Specialized glass membranes are used for DNA recovery and clean-up
PVDF (polyvinylidene difluoride) is a hydrophilic, solvent resistant membrane that exhibits low levels of UV absorbing extractables. PVDF is useful for HPLC sample filtration, as well as general biological filtration. PVDF is considered to be one of the low protein binding membranes.
Teflon� (PTFE)
Teflon� (Polytetrafluoroethylene) is hydrophobic, and chemically resistant to all solvents, acids and bases. PTFE, membrane does not impart any extractables to the filtrate. PTFE is an ideal membrane for transducer protectors, since it blocks water vapor. PTFE is ideal for filtering and de-gassing chromatography solvents.

Knowledge for Liquids Membrane Filtration

     Membrane filters are used for the terminal sterilization of heat labile liquid products, and for the sterilization of gases.  Where possible, the FDA prefers sterilization by heat. The large-volume parenterals (LVP) solutions employed in intravenous administrations are rendered sterile by being steam autoclaved rather than by being sterile filtered, although either technique will be effective. Even when a product is heat or gamma sterilized, filtration finds its need, as a bioburden reducing filtration to avoid elevated endotoxin levels after the sterilization step. The LVP industry utilizes routinely 0.45 or 0.2 micron rated filters to reduce the bioburden before heat sterilization.

     However, while thermal sterilizations are preferred, not all products can withstand damage by heat.  Proteins may be denatured by heat, and oxidative degradations are promoted by it.  Hence, the utility of sterilization by filtration.   However, the achievement of a sterile filtration requires validation, a confirmation derived from documented experimental evidence (see Filter Validation).  
The microporous membranes are usually designated by pore size ratings of 1.2 micron to 0.04 micron.  The pores of these filters are artificial enlargements of the interstitial spaces that separate the polymeric chain sections as present in the bulk solid phase.  Used as final filters for the sterilization of solutions, they are usually of the 0.45, 0.2/0.22 or 0.1  micron ratings. In their higher ratings they may serve as prefilters to prolong the service lives of final filters.
As depth filters retain contaminants within the fiber matrix, membrane filters are surface retentive filters and therefore have the distinct disadvantage of blocking faster. The filter industry therefore pleats such membranes to install a higher effective filtration area into a filter device. Still such effort has its limitation, due to a maximum allowable pleat density. Having reach the limit, the only option is the use of prefilters or membranes of different pore sizes or structure to gain a fractionate retention and therefore a prolong lifetime of the filter. Some membrane filter configurations have such membrane or depth filter prefilter build into the filter cartridge. This is convenient for the filter user in respect to lowered hardware costs and hold-up volume. In comparison to depth filters, membrane filters have a narrow pore size distribution, which results in a by far sharper retention. Pore size ratings are facilitated to differentiate membrane filters and the performance of such. Commonly a sterilizing grade filter is labeled 0.2 micron and retains 107 B. diminuta per square centimeter at a differential pressure of 2 bar (30 psig). Another advantage and necessity of membrane filters, is the fact that these are integrity testable, impossible with depth filters. Possible flaws or defects can be detected, which is critical due to the function of membrane filters, mainly to separate microorganisms from biopharmaceutical solutions.
Membrane filters are made in a wide variety of pore sizes.  The effective pore size for membranes vary and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF).  RO membranes are widely used in water treatment to remove ionic contaminations from the water. These membranes have an extreme small pore size and therefore require excellent pretreatment steps to reduce any fouling (organic) or scaling (anorganic) of the membrane, which would reduce the service lifetime. RO membranes are used by extensive pressures on the upstream side of the filter membrane to force the liquids through the pores.
Ultrafilter (UF) retention ratings are also not measured in pore size, but rather in MWCO (Molecular Weight Cut-Off), i.e. the molecular weight of the substance to be retained. UF filter systems are most often used in Cross-Flow (tangential flow) mode. The feed stream is directed over the actual membrane to diminish blockage of the membrane. Depending on the pressure conditions, the fluid (penetrate) penetrates through the membrane, whereby the remaining fluid is recirculated (retentate). UF filter systems find applications in concentration, diafiltration and removal steps within pharmaceutical downstream processing. Microfiltration (MF) can be used as dead end filtration (the feed is directed to the membrane resulting into a filtrate, separated from the contaminant) or tangential flow mode. The tangential flow characteristic for MF is commonly used for cell or cell debris removal in downstream processing. MF membranes typically differ from UF membranes in the morphology of the membrane’s cross-sectional cut.  The symmetry of sterilizing-grade microfilters usually ranges from being uniform to being slightly asymmetric.  Ultrafilters on the other hand are highly asymmetric with the rejecting layer consisting of a tight skin (0.5-10 µm thick) supported by a thick spongy structure of a much larger pore size.
MF is used in a large variety of filtration applications, from fine cut prefiltration to sterilizing grade filtration in aseptic processing. Often sterilizing grade filters are the terminal step before filling or final processing of the drug product. MF is available for air and gas applications and liquid clarification or sterilization. For the different applications specific membrane configurations and materials have been developed.

Asymmetric membrane filtration for the removal of leukocytes from blood

Scientists from Membrane Solutions invented asymmetric membrane filters for the removal of leukocytes from blood. As part of a study on the mechanisms of leukocyte filtration, the influence of pore size distribution on filter efficiency was investigated. Conventional leukocyte filters are not suitable for model studies, as these filters are composed of tightly packed synthetic fibers, with a poorly defined porous structure. Therefore, open cellular polyurethane membranes with pore size distributions varying from approximately 15 to 65 m were prepared. Filtration experiments with stacked packages of these membranes showed that leukocytes are best removed (>99%) by filters with a pore size distribution of 11-19 m. These pore sizes approach the size of leukocytes (6-12 m). However, due to fast clogging, blood flow through these filters is rapidly reduced, which results in a low filter capacity. With an asymmetric membrane filter, in which the pore size decreases from about 65 to 15 m in the direction of blood flow, both moderate removal of leukocytes (>80%) and maintenance of flow (0.2 mL/s) are obtained. This results in efficient leukocyte removal. From cell analysis of both filtrate and filter, it is concluded that adhesion rather than sieving is the major filtration mechanism. Thus, further optimization of the filter may be achieved by surface modification.

Application of Membrane for Blood Filtraiton in Removal HMGB1

Membranes have application in blood filtration. When the invasion of sepsis or trauma is applied to the organism, systemic inflammation occurs. In the cascade from invasion to inflammation, as one of the chemical mediators of systemic inflammation, the relationship of HMGB1 to the onset of AKI and ARDS has been pointed out. In this study we investigated the ability to remove HMGB1 by the hemofiltration membrane in vitro.

We dissolved HMGB1 in bovine serum, using a blood filtration membrane filter made of two types of membrane: heparin graft AN69ST (oXiris) and a membrane filter made of polyarylether sulfone (HF set). Filtration experiments were performed in vitro. The HMGB1 concentrations of the serum of inlet and outlet of the filter and of the filtrate were measured over time up to 120 minutes. Using an electron microscope, HMGB1 adsorption on the membrane was taken.

oXiris removed HMGB1 in a short time; its mechanism has been shown to be adsorption. HMGB1 can be removed from the blood, and there is a possibility to control the excessive inflammatory response during severe invasion to an organism in vivo.

Membrane Filtration for Treatment of Waste Water

Waste water need treatment. Membrane filtration is an important technology for the treatment. Although still a young technology, membrane filtration for treating waste water has already established itself worldwide. Ultrafiltration with membranes enables large volumes of heavily contaminated waste water and surface water to be treated without structural extensions to existing plants. One problem, however, is the surplus activated sludge – a fine sludge with a special composition which has to be dewatered and disposed of.

Dewatering the surplus sludge

The solution is the new MBR decanter designed by GEA Westfalia Separator  Group especially for the dewatering of surplus sludge.

In the membrane bioreactor (MBR), hollow fiber membranes purify the water from the biological waste water treatment plant, either in the activation tank or secondary sedimentation basin. The membrane-filtered purified water is discharged and a fine surplus activated sludge remains which cannot be compared with the coarse sludge obtained with alternative technologies.

MBR decanter: Maximum dewatering at high throughput capacities

GEA Westfalia Separator Group has designed the MBR decanter specifically  for maximum dewatering of the very homogenous fine sludge at high  throughput capacities. A special rotor geometry, with a specific inlet  and discharge diameter, has been developed for the scroll and bowl of  the decanter for this purpose. As a result of this modification, the  dewatering efficiency of the MBR decanter is up to five percent higher  than standard decanters available on the market or up to ten percent  higher than can be achieved with alternative technologies such as  strainer belt presses. This means approximately 20 to 30 percent less  residual volume and thus considerably lower disposal costs for the  operator of the MBR machines. Membrane Solutions will give you help in waste water treatment.

What is ultrafiltration in terms of membrane filter technology?

Membrane Solutions is specialized in water treatment in US. Ultrafiltration (UF) is a type of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane.  A semipermeable membrane is a thin layer of material capable of separating substances when a driving force is applied across the membrane. Once considered a viable technology only for desalination, membrane processes are increasingly employed for removal of bacteria and other microorganisms, particulate material, and natural organic material, which can impart color, tastes, and odors to the water and react with disinfectants to form disinfection byproducts (DBP). As advancements are made in membrane production and module design, capital and operating costs continue to decline.

Ultrafiltration  uses hollow fibers of membrane material and the feed water flows either inside the shell, or in the lumen of the fibers. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane. This separation process is used in industry and research for purifying and concentrating macromolecular (103 – 106 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from reverse osmosis, microfiltration or nanofiltration, except in terms of the size of the molecules it retains. When strategically combined with other purification technologies in a complete water system, UF is ideal for the removal of colloids, proteins, bacteria, pyrogens, proteins, and macromolecules larger than the membrane pore size from  water. The primary removal mechanism is size exclusion, though surface chemistry of the particles or the membrane may affect the purification efficiency. UF can be used as pretreatment for reverse osmosis systems or as a final filtration stage for deionized water.

The primary advantages of low-pressure UF membrane processes compared with conventional clarification and disinfection (post chlorination) processes are:

  • No need for chemicals (coagulants, flocculates, disinfectants, pH adjustment);
  • Size-exclusion filtration as opposed to media depth filtration;
  • Good and constant quality of the treated water in terms of particle and microbial removal;
  • Process and plant compactness; and  
  • Simple automation.

How To Use a Bio Water Filter

Everyone who talks about survival eventually talks about water filtration. You see all kinds of reviews on this water filter and that—whichever is the favorite of the person doing the writing. Yet, almost all of them have one failing in common; the filter element eventually has to be replaced. While there are a few filters on the market that are backflushable to clean them out, there are only a few.

Of course, if there’s a general breakdown in society, for whatever reason, availability to filters or filter cartridges will be essentially cut off. That means that whenever your filter supply runs out, you’re going to be left with a huge problem. Since the water probably won’t be safe to drink, you’ll have to boil or distill enough for your needs, a slow process.

The biggest risk in drinking most water is that of waterborne pathogens. Bacteria, protozoa, and other microscopic parasites can be found in almost any water supply, some of which can kill you, and many of which can make you wish you were dead.

The other problem that you might end up facing is chemicals in the water. Basically, filtering systems ignore this problem, concentrating on dealing with the much more common problem of those pathogens. About the only effective ways of dealing with chemicals is by neutralizing them or by distillation. Even with distillation, it is possible to end up with some chemicals in the water, if the chemicals’ vapor point is lower than that of water.

Bio-filters, a Great Alternative

Another option, instead of buying expensive commercial filters and stockpiling them, is to build a bio-filter. This simple filtering system is used worldwide to purify water for drinking. While it may not get out every pathogen in the water, it will get out enough that you can safely drink the water, allowing your body to destroy the few that manage to get through the filter.

Actually, a bio-filter works almost the same way that a sewage treatment plant does. The standard for water treatment plants is that the water that leaves it must be clean enough to drink. To accomplish that, they use a multi-stage approach to removing anything harmful from the water. Likewise, a bio-filter uses a multi-stage approach to removing impurities and pathogens from the water, so that the water that remains is drinkable. The only difference is that you can make it yourself.

Membrane Solutions challenge leads to new water filtration system

Membran Solutions is a world lead filtration company. With today’s technology, we can launch Angry Birds into space and integrate beer bottle openers into iPhone cases. But how about something to address a bigger issue, like the fact that nearly one-fifth of the world doesn’t have water to drink?

That was the daunting challenge tackled by an enterprising team of young designers from Vancouver’s Simon Fraser University. The result of their work is not an app at all – it’s a working prototype of a rainwater filtration system, dubbed Mitto.
According to the World Health Organization, more than 1 billion people around the world don’t have access to potable drinking water. Many resort to drastic and unsafe measures to sate their thirst, leading to disease and worse. Five students set out to change all that, using the design and prototyping approach embraced by digital designers. This is no smart-phone add-on. It’s something more, even if it comes from the same design sensibility as the latest iTunes phenomenon.   “Given the situation where you don’t have access to power and other forms of technology, we used the same set of [design] principles to create something that can save your life,” Fung said.
The simple, portable filter they produced has already been lauded at a pair of interactive design and technology gatherings. One – February’s Touch Point 2012 – put student proposals in front of design leaders from some of the heavyweights of the interactive world. Seen alongside some of the digitally-driven ideas presented at Touch Point – apps, gadgets and even a design for a new smart-grid energy plan for Vancouver – the Mitto proposal looks spare and surprisingly low-tech. And it is.
The Mitto design consists of a 30 cm-long tube containing a microbiological filter that will work in most conditions short of toxic waste and a large nylon cloth designed to catch rainwater and funnel it into the filter. Simple. But, according to the judges at Touch Point – simply elegant as well. In a symposium heavy on digital thinking, they awarded the design third prize, giving the Mitto team their first media exposure thanks to a story broadcast by Canada’s Global TV. Soon enough, design bloggers caught wind, hailing the gadget as both ingenious and innovative.