Sterlitech Blog

Your source for new information on filtration equipment applications and processes.

  1. Get a handle on your liquid storage with our Special Carboy Promo!

    Get a handle on your liquid storage with our Special Carboy Promo!

    Purchase of each package listed on the sheet below includes one carboy, the standard closed-cap and open-cap adapter as well as two additional Quick-Connect VersaCaps, one with 2 hose-barb ports and one with 3 hose-barb ports for easy filling, siphoning, and/or venting.
    PDF Carboy Special Promo Details 

  2. Hydrodynamic conditions in bench-scale membrane flow-cells used to mimic conditions present in full-scale spiral-wound elements

    Hydrodynamic conditions in bench-scale membrane flow-cells used to mimic conditions present in full-scale spiral-wound elements

    Researchers frequently ask, “what is the purpose of the shims and spacers for use with the membrane test cells, and do I need them?” Curious to know more? In response to this common question Sterlitech’s own Sepideh Jankhah explores this topic in her recently published Paper, which investigates the hydrodynamic conditions in a bench-scale membrane flow-cell (CF042 Cell). It looks at the ways in which parameters such as the feed crossflow velocity, geometry of the cell, and feed spacers, affect system hydrodynamics.

  3. On PM 2.5 Filters, Let’s just clear the air between us; ok?

    On PM 2.5 Filters, Let’s just clear the air between us; ok?

    In the area of a former military building complex in the Chaoyang District of Beijing is a unique and thriving artistic community.  In the middle of this art district, is a strange 7-meter tall tower shaped like an avant-garde metallic pineapple.  Designed by Dutch artist Daan Roosegaarde, it is both an artistic creation and a functional tool meant to test a possible solution for Beijing’s worsening air pollution.  The tower is a giant silver-colored ionizer and  particulate trap designed to pull in and hold tiny pollutants, known collectively as PM 2.5’s.  The tower works by releasing charged ions into the air nearby, causing the PM 2.5 particles to become trapped on the metallic fins as they are pulled from the air.

    While it appears the sculpture is capturing quite a bit of particulate, the full data on its effectiveness is not yet confirmed; it seems there may be too much pollution for it to reduce air pollution except in the immediate vicinity. However, it does also remind people to think about the effects of air pollution and exactly what makes up these PM 2.5 particles.

    PM 2.5 particles are so named as they are smaller than 2.5 microns in size, and represent a significant health risk to people. To compare sizes: human hair is about 100 microns across, and red blood cells are 8 microns across. PM 2.5s can travel deep into and lodge in the furthest parts of the human lung, putting people at elevated risk for respiratory and cardiac illnesses. Air pollution alone is estimated to cause about 7 million deaths annually across the globe, according to the WHO. Areas undergoing significant economic growth and rapid industrialization are seeing the worst of these effects; heavily industrialized areas like Beijing, Delhi, Karachi, and Dhaka are breathing some of the dirtiest air around.

    In addition to the potential respiratory and cardiac effects, new research from the University of Washington suggests that poor sleep is also a consequence of PM 2.5 air pollution. The highest levels of PM 2.5s increased the odds of poor sleep by nearly 50 percent in one study group. Researchers also found the more participants were exposed to air pollution, the more hours in a day they spent awake.

    To help combat this sooty foe, a small filter is used to analyze air quality and has an easy name to remember – the PM 2.5 filter. PM 2.5 filters are a special type of high-purity polytetrafluoroethylene (PTFE) membrane filter designed to capture these particulates in standard EPA test methods for monitoring air quality, and Sterlitech is now offering these filters to users in the industrial hygiene and workplace safety fields.

    PTFE is normally a very flexible material when made into a thin membrane, so these filters have a strong and rigid polypropylene support ring, enabling ease of handling and use. The PM 2.5 filters have a pore size rating of 2.0 microns, and are tested to conform to the EPA requirement of DOP particle capture efficiency of 99.7% or better. Each membrane filter is sequentially numbered to aid with traceability of test results. The low tare mass allows for accurate gravimetric measurements. No glues or adhesives are used in making the membrane filters; the resulting stable design eliminates curling and keeps the filters flat and uniform, allowing for automation. To order the PM 2.5 filters, or get technical information, please contact Sterlitech Corporation at or 877-544-4420.


  4. Focus on Microfiltration Part 3: Extending Service Life Using Prefiltration

    Focus on Microfiltration Part 3:  Extending Service Life Using Prefiltration

    Last month we examined filter selection strategies for maximizing service life in continuous use applications.  In this 3rd installment, we will examine the use of prefilters to extend service life.

    Clarifying liquids with high levels of suspended solids is challenging, especially for applications requiring submicron filtration.  In these applications, filter users who experience frustratingly short service life should consider using prefilters.  A suitable prefilter will reduce the particle fouling of the final filter and, consequently, the combination will have better total throughput than the final filter alone.

    In general, the amount of particulate a filter can accommodate before becoming clogged is related to its pore size rating.  As filter pore sizes decrease, the smaller pores have reduced void volumes and reduced capacity for holding particulate.  Conversely, as filter pore sizes increase, the larger pores have increased void volumes and increased capacity for holding particulate.  It follows that the finer pore structures of membrane filters have less dirt holding capacity when compared to the larger pore structures of nonwoven media filters.  Therefore, nonwoven media filters can be an excellent prefilter choice to extend the service life of membrane filters.

    Prefilters are selected with a pore size rating larger than that of the final filter.  This takes advantage of the inherent greater dirt holding capacity of larger pore sizes.  Typically, binderless glass fiber media filters are chosen as prefilters for membrane disk filter applications.  These nonwoven media filters have very good dirt holding capacity, are typically less expensive than membrane filters, and have broad chemical resistance.  For membrane filters rated at <1 micron, Sterlitech Grade B glass fiber filters can be good prefilter candidates.  For membrane filters rated at >1 micron, Sterlitech Grade D glass fiber filters may be a better prefilter option.  For applications where glass fiber media cannot be used, polypropylene nonwoven filters (listed as “polypropylene nominal prefilters”) can be considered.

    When nonwoven media disk filters are used as prefilters in pressure and vacuum disk filter holders, they are selected with diameters that are slightly smaller than the o-ring seals in the holders.  This ensures they do not interfere with o-ring seals and cause leaks or bypass.  To determine the correct prefilter size, please refer to the “application/specification” tab on the product page for the holder.  For example, the correct prefilter diameter for the KG47 47mm vacuum filter holder can be read from the “Application/Specification” tab to be 35mm.

    For users preferring the convenience of syringe filters, several of the non-sterile membrane options are available with incorporated glass fiber prefilters:  cellulose acetate (CA),  nylon , polypropylene , and PTFE .  Alternatively, standalone glass fiber syringe filters may be used as prefilters for any syringe filters or disk filter pressure holders.  Sterlitech also offers custom syringe filters that may be specified with a variety of incorporated prefilters.

    Some applications may have particle size distributions that contain too many small particles for nonwoven media prefilters to be effective.  In these applications, a membrane prefilter may be considered.  For membrane filters with symmetric pore structures, such as nylon or CA membranes, the pore size of the prefilter is typically selected that is two or three pore size rating steps larger than the pore size of the final filter. For example, a 0.65 or 0.8 micron rated nylon membrane prefilter would be selected for a 0.2 micron rated nylon membrane final filter.  For membrane filters with asymmetric pore structures, such as PES membranes, the pore size of the prefilter is typically selected that is three or four steps larger than the pore size of the final filter.  For example, a 1.2 or 5.0 micron rated PES membrane prefilter would be selected for a 0.45 micron rated PES final filter.  Some experimentation is often required to select a prefilter pore size rating that is optimal for total throughput.

    When membrane prefilters are used in pressure and vacuum disk filter holders, they are selected with the same diameters as the final filters.  It is presumed that the prefilter membrane filters will achieve good seals with the o-rings.  If polycarbonate track-etch (PCTE) or polyester track-etch (PETE) membrane disk filters are stacked on top of each other, polyester drain disks should be used between the filters to ensure good flow and prevent pore blinding.  For proper closure and to avoid excessive pressure drop, we recommend that you do not use more than two disk filters simultaneously in the pressure and vacuum disk filter holders.

    For continuous use applications with high levels of suspended solids, incorporating a larger pore size prefilter ahead of the target pore size final filter can often result in a combination that has lower overall filtration costs than operating the final filter by itself.  An optimal prefilter reduces the particle loading experienced by the final filter and, consequently, extends the service life of the final filter. 

    When considering cost, performance, and longevity, it can be complicated to select the optimal filters for an application.  Experimentation and analyses are beneficial, if not required, to assist with filter selection.  We hope you’ve found this series helpful for selecting filters for your projects.  Please feel free to contact us if you need any guidance or technical assistance. 

  5. Acrylic Sepa Test Cell with 34 mil Channel Depth

    Acrylic Sepa Test Cell with 34 mil Channel Depth

    Sterlitech now offers an Acrylic Sepa Test Cell in an additional channel depth: 34 mil. The original Acrylic Sepa Test Cell utilizes a 75 mil channel depth and has been widely used by researchers over the years. In many experiments involving the Sepa cells, combinations of stainless steel shims and polymeric spacers (with differing thicknesses) are installed in the cell to reduce the channel depth or mimic the hydrodynamic conditions of commercially available spiral-wound elements.

    However, when it comes to the Acrylic Sepa Test Cell, the ability to visually investigate the hydrodynamic conditions inside the cell or to visually observe local fouling at the membrane surface is critical and the basis for the development of the cell. In some cases, use of the stainless-steel shims and spacers in the Acrylic Sepa Test Cell can obstruct viewing of the cell’s interior and the membrane surface. Reducing the channel depth to 34 mil eliminates the need for stainless-steel shims when using thin spacers. The 34 mil depth was selected as common spacer thicknesses in commercially available spiral-wound elements range from 31-34 mil.

    Sterlitech offers a selection of Polypropylene and PTFE spacers for use in the Acrylic Sepa test cells when needed. For more information about this new cell, spacers, or other membrane test materials and equipment, contact a membrane process specialist at Sterlitech at or 253.437.0844.

  6. A History of Chemically Resistant Membranes

    A History of Chemically Resistant Membranes

    The use of polymeric membranes for filtration of non-aqueous solutions started around 1960 and has been developed significantly since then [1]. Today, non-aqueous membrane filtration applications in chemical and pharmaceutical processing account for more than 25% of the global total polymeric membrane market [2].

    To put into perspective the potential significance of membrane filtration for non-aqueous solutions, one must realize that conventional separation processes still accounts for up to 70% of capital (CAPEX) and operational (OPEX) expenditures in the chemical and pharmaceutical industries [2,3]. Therefore, to reduce CAPEX and OPEX, developing membrane separation processes that can be more efficient and cost effective than conventional separation processes has been of great interest for these industries and a growing field of research.

    Sterlitech has observed this growing demand from the research community for solvent resistant membranes that can be used in non-aqueous separation processes. These membranes are generally required to withstand use in harsh environments containing organic solvents that are often at elevated temperatures. To meet this demand, Novamem and Evonik membranes were strategically added to Sterlitech’s product offerings. Novamem membranes primarily in the range of microfiltration, are made of chemically resistant polyether ether ketone (PEEK) or polyvinylidene difluoride (PVDF), and can be operated up to 120-180°C. Evonik membranes, primarily in the range of nanofiltration, are made of modified polyimide, and are commonly used for organic solvent nanofiltration (OSN) applications.

    History of Chemically Resistant Membrane Filters

    Membrane ProductEvonik: PuraMem and DuraMemNovamem: PEEKNovamem: PVDF
    Applications and Specifications

    • Removal of polymeric impurities

    • Product purification

    • Monomer/dimer separation

    • Molecular fractionation

    • Room temperature solvent exchange

    • Catalyst recovery and recycle

    • Color removal

    • Solvent recycling

    • Low protein binding

    • Filtration of particles & molecules from solvents, acids and bases

    • Purify and concentrate active pharmaceutical ingredients (API)

    • Dialyze monomers & polymers in solvents

    • Degassing of harsh chemicals

    • Membrane pervaporation & distillation

    • Hydrophobic

    • Blotting: protein sequencing and immunoblotting

    • Membrane distillation: desalting, removal of ammonium

    • Membrane pervaporation

    • Filtration of corrosive solutions and aggressive acids

    • Degassing of aqueous solutions under high pressure

    To learn more about the availability, technical specifications, and applications of these membranes, please visit or contact a membrane process specialist at Sterlitech: E: or T: 253.437.0844.



    [2] Membranes Market by Type (Polymeric membranes, Ceramic membranes, and others), by Technology (MF, RO, UF, Pervaporation, Gas Separation, Dialysis, NF, and Others), by Region (North America, Europe, Asia-Pacific, the Middle East & Africa, and Latin America), and by Application - Global Forecast to 2020 (October 2015), Market and Market, Report Code: CH 2635

    [3] Global Water Market 2017 (April 2016) Global Water Intelligence

  7. What’s Hiding in the Water?

    What’s Hiding in the Water?

    As we grow in understanding the significance different organisms have in the ecology of an environment, it helps tremendously if we know which organisms inhabit that environment – whether they’re supposed to be there or not.  One method that is gaining widespread use, and relies on a simple filtration method, is the analysis of environmental DNA (eDNA) from local waterways.

    As animals inhabit a river, lake, or pond, they shed off skin cells and other body waste that often contains that animal’s own unique DNA.  These shed cells and their DNA can be easily isolated, by filtering a sample of collected water and then sequencing the captured DNA in a lab.  The data is then compared against known organisms for that area.  The data allows researchers to identify the presence or absence of organisms based on small gene sequences that turn up from the analyzed unique eDNA, just like a fingerprint on a crime scene. Sterlitech offers the 47mm, 934-AH glass fiber filters, MCE membrane filters, magnetic filter funnels, and manifolds  often used in these analysis methods.

    By now, many of us are aware of the serious threat to aquatic environments from invasive species.  Asian carp were imported into southern states in this country in the 1970s to help keep catfish farm ponds clean; the Asian carp are filter feeders and eat plankton.  But a series of floods allowed some of the carp to escape to nearby rivers where they soon flourished as a result of no natural predators.

    The carp are voracious feeders and can consume up to half their body weight in plankton every day, and females can lay a half million eggs during breeding season.  With nothing to control their spread in these waterways, they can quickly strip the base out of a local food chain in the rivers where they’re found. Now they’re slowly making their way north up the Mississippi and have only recently reached the outlets of the Great Lakes, where they pose a grave threat to the lakes’ ecology.  eDNA sampling and filtration laid the groundwork for much of the monitoring as an inexpensive means to track their advance north.

    Zebra mussels are another example of a species that set up house where they don’t belong.  In the 1980s, cargo ships entering the Great Lakes that originated in Russia and Eastern Europe (where the zebra mussels normally live) would dump ballast water and inadvertently release free-floating mussel larvae.  These larvae then attached to solid surfaces like irrigation water intake pipes, clogging them, and onto the hulls of boats and ships, reducing their efficiency. They are also known to grow on, and smother, the larger native lake mussels.  Here too, eDNA is being used to track their spread across the country.

    eDNA monitoring is not only used to monitor invasive species, but also to track endangered or threatened species in remote areas where populations are not known, or to monitor animals attempting a return to their native habitat.  In the US Northwest, the Bull trout (pictured upper left) is a threatened species and are losing their habitat through decreasing water quality and warming temperatures; cold water is critical to their spawning success.  If we know where the fish live, we can better direct resources and funding to maintain, protect, or restore the habitat.  eDNA sampling represents the bulk of this survey method, and the use of the small 47mm filters saves tremendous time and effort!

    In prior studies, researchers would attempt to capture any/all fish in a given area of a stream to see what was there.  This process is incredibly laborious and costly, and only samples a tiny fraction of the entire waterway.  eDNA testing allows for a single researcher to walk the length of a stream, and collect periodic samples by passing water through a filter.  In one studya from the University of Montana, a single crew of 1-2 people sampled 98km of three different high mountain streams in about 8 days.  Protocols already exist for grayling, shrimp, lamprey, river otters, and dozens of trout and salmonids.  More tests are being developed for toads, sculpins, bass, turtles, and chubs, and all are based on eDNA surveys.

    Sterlitech’s 934-AH filters, MCE filters, and vacuum equipment are perfectly suited for this type of work and are readily stocked on hand.  The filters ultimately chosen should reflect the requirements of the standard procedure for your eDNA sampling process. Contact Sterlitech at to order or learn more about these products.


  8. Focus on Microfiltration Part 2: Filter Longevity and Filter Selection

    Focus on Microfiltration Part 2:  Filter Longevity and Filter Selection

    Last month, we described the considerations associated with predicting filter service life and how total throughput can be estimated through experimentation.  In this second installment, we will examine four filter selection strategies for maximizing service life in continuous-use applications. These aspects consider chemical compatibility, temperature, binding characteristics, and pore size.

    At the most basic level, selecting filters that are compatible with the application’s chemistry is the key to success.  Filters with poor compatibility to the liquid being filtered typically fail well before normal clogging due to limitations associated with filter deterioration.  The filter chosen must exhibit both good chemical compatibility with the fluid and good physical compatibility with the operating conditions.  PTFE and polyether ether ketone (PEEK) filters exhibit some of the best resistance in applications using very harsh solvents.  Nylon, polypropylene, and polyvinylidene difluoride (PVDF) filters have good chemical resistance and are more economical for less severe applications.  Polyethersulfone (PES) membrane filters have very good resistance to pH extremes and some oxidizers.  In addition to the primary fluid, the consumer must also consider compatibility with filter sanitization or cleaning regimens if they are used.  The fluids used for sanitization or cleaning must be filtered to at least the same pore size as the filter being treated; otherwise particles in the cleaning fluid will reduce service life.

    For applications with elevated operating temperatures, it is important to realize that chemical compatibility and resistance to differential pressure may be diminished.  The filter’s recommended maximum service temperature must be carefully considered.  Pure PTFE, silver, glass fiber, alumina oxide, and quartz filters all have good resistance to very high temperatures. 

    In some life science filter applications, the fluids may contain high levels of suspended proteins.  These fluids include tissue culture media, serums, lysates, and fermentation extracts.  For maximum service life, the consumer should select membrane filters with inherent low protein binding characteristics, such as polyethersulfone (PES) or cellulose acetate (CA).  Filters with surfaces that readily adsorb proteins, such as mixed cellulose esters (MCE) or nylon,  may be rapidly clogged in these applications.

    Finally,  for maximum service life, the consumer should select the largest pore size rating that can reliably achieve the filtration goal.  In general, as the pore size rating gets smaller, the particle loading capacity of a filter is reduced.  It is a common temptation to select pore sizes smaller than necessary based on misconceptions that smaller pore sizes result in better quality filtrate, or that smaller pore sizes are indicative of better quality filters.  Avoid this temptation and you can reduce filtration costs by using longer lasting filters.  For applications requiring pore size ratings >1µm, consider using nonwoven fiber media filters, such as glass fiber filters or polypropylene fiber filters, as these will typically have better dirt holding capacity than conventional membrane filters.

    In addition to selecting optimal filters based on the four criteria described above, there are other strategies that filter consumers can employ to maximize total throughput in continuous-use applications.  Next month, in the third installment of this series, we will describe the use of pre-filters.

    There are often other factors besides service life that must be considered when selecting filters.  Sterlitech offers a guide for helping with filter selection at  For personalized technical guidance on selecting the best filters and parameters for your application, please contact Sterlitech’s membrane experts at or call us at 253.437.0844 (local) or 877-544-4420 (toll free).

  9. DURAMEM® and PURAMEM® for Organic Solvent Nanofiltration

    DURAMEM® and PURAMEM® for Organic Solvent Nanofiltration

    DuraMem® and PuraMem® membranes are now available as a valuable addition to our Chemically Resistant Membranes product line. Duramem® and Puramem® polymeric membranes, made by Evonik, are market leaders for Organic Solvent Nanofiltration (OSN).

    Organic Solvent Nanofiltration, i.e. separation of molecules dissolved in organic solvents through a semipermeable membrane, has gained great traction over the last decade. Advantages of OSN over conventional separation processes include lower energy requirements, conservation of expensive materials, and system robustness.

    DuraMem® offers long term stability in most polar and polar aprotic solvents (acetone, tetrahydrofuran, dimethylformamide, isopropanol, acetonitrile, methylethylketone, ethyl acetate, and more), while PuraMem® series is stable in apolar hydrocarbon-type solvents (toluene, heptane, hexane, methylethylketone, methyl-isobutylketone, ethyl acetate, and more).

    Technical Specs

    • Material: P84® polyimide

    • Molecular weight cutoff range:

      • Duramem®: 150 to 900 Da

      • PuraMem®: 280 to 600 Da

    • Recommended maximum temperature: 50°C (122°F)

    • Recommended maximum operating pressure: from 20 to 60 bar (290 to 870 psi)

    Main Application Areas for DuraMem® and PuraMem® Membranes1

    • Removal of impurities or product purification

    • Monomer/dimer separation

    • Molecular fractionation

    • Room temperature solvent exchange

    • Catalyst recovery and recycle

    • Color removal

    • Solvent recycling

    Both DuraMem® and PuraMem® series are available in a flat sheet format as well as spiral wound elements. For more information about these membranes and their applications, contact a Membrane Process Specialist at Sterlitech: E: or T: 253.437.0844.

    1 Source: Evonik Corporation:

  10. Tipping Back An “Interesting” Pint

    Tipping Back An “Interesting” Pint

    How about a nice tall glass of ice-cold beer… made from recycled sewage water?

    Did you hesitate? Well, now let’s think about it: most breweries use some combination of hops, malted barley, yeast, and…. well… clean water! But beer from recycled wastewater? That’s exactly what took place March 19-10 at the 2017 WateReuse California Annual Conference in San Diego. The City of San Diego’s Pure Water San Diego program hosted a fun competition event at the conference, where they asked homebrewers to concoct their favorite pale ales or IPAs using water exclusively sourced from the reuse program, and then offer samples of the created goods to attendees.

    In addition to the competition, local San Diego breweries such as Stone Brewing and Ballast Point also showed off a few specialty brews made from water sourced from the program and offered samples to attendees. So how did this process work?

    The program in San Diego uses what is known as “Title 22” water, which is secondary effluent collected from specified wastewater treatment plants. The water is treated in much the same way as any other treatment plant, but then is sent through a more in-depth process of ozonation, activated carbon filters, microfiltration (gotta get those bugs out!), reverse osmosis, and UV oxidation. At the end, the water is so pure that minerals must be added back in so it does not corrode the pipes used to transport it. (remember, water is the universal solvent!) So, was the beer any good?

    If attendance was any indicator, the conference event drew a packed exhibitor hall with fans lining up for the homebrewer competition to sample their favorite beer. Three local homebrewers were awarded cash prizes as the winners, based on their frothy works. Bear in mind though, the reclaimed water program is still under development as the full infrastructure is slowly phased in. The city does not yet supply this water as standard product to regular breweries in San Diego. So don’t go sidling up to the bar at one of these breweries in San Diego and yell out to the barkeep for the “Sewage Ale!” or “Commode Stout!” or “Shower Water Pilsner!” If you do, you’ll probably be asked to leave. But fear not, with over 750 craft breweries in California alone, and on the heels of the State’s chronic drought issue, it won’t be long before this program is in full swing and satisfying thirsts up and down the Golden State every Friday & Saturday night.

    Until then, the hard-working folks at Sterlitech Corporation will continue to develop and offer cutting edge filtration technology to help ensure researchers at utilities, university labs, private R&D, and yes microbreweries, have the tools they need to keep water a top priority in our communities.