Sterlitech Blog

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

  1. Silver Membranes in Monitoring Respirable Crystalline Silica

    Silver Membranes in Monitoring Respirable Crystalline Silica

    Crystalline silica, most commonly found in the form of quartz, is a basic component of the earth; it’s found in soil, sand granite, and other minerals. During many industrial processes, crystalline silica is released as particles that are 100 times smaller than beach sand.1 Due to their size, these mineral particles cannot easily be cleared by human lungs. Instead, they persist in the respiratory system and form scar tissue, contributing to serious health problems for those experiencing prolonged exposure. The associated silicosis and other forms of cancer are a threat to workers in mining, construction, and other industrial trades.2

    There is a global awareness of this seriousness of this issue, and the World Health Organization has published assessment documents detailing the negative health effects of exposure. Here in the US, the Occupational Safety and Health Administration (OSHA)  released a Final Rule on Occupational Exposure to Respirable Crystalline Silica, to provide guidance for the safety of industrial workers.3 The ruling published in March 2016 puts the responsibility on companies to create a low-risk environment, with enforcement in the form of fines (potentially over $12,000 per day) going into effect for some industries starting in September 2017.3 Beyond recommending proper personal protective equipment, ventilation systems, and replacement of silica when safer materials can be used, this ruling establishes a permissible exposure limit (PEL) at 50 μg/m3. This means that only 1/5th of the previously allowed PEL is now considered safe in the workplace.2

    To monitor levels of crystalline silica, employers can take routine samples and have them analyzed in a lab. A portable sampler is used to collect air from the worker’s respirable area during a full shift. The dust captured on the filter is then analyzed using a standard method, such as NIOSH 7500.4 In this method, the filter is then dissolved and redeposited on a 0.45 micron silver membrane for measurement using x-ray diffraction. Silver membranes have become the standard for x-ray diffraction analysis due to their high sample-load capacity and characteristically low background noise during analysis.

    The results of these analyses help employers understand whether they need to be taking more action to protect their workers. OSHA estimates that the steps advised in their ruling will save 600 lives and prevent 900 cases of silicosis every year.5 For now, companies in regulated industries are developing control plans and training workers to ensure compliance with the new rules. It remains to be seen what the full impact of enforcement will mean for their employees and their business.

    [1] Dangers of Crystalline Silica | Taylor Made Diagnostics. Taylormadediagnosticscom. 2018.
    [2] Spafford A. OSHA Silica Dust Permissible Exposure Limit 2016 Update. Pro Tool Reviews. 2018.
    [3] Occupational Exposure to Respirable Crystalline Silica. Federal Register. 2018.
    [4] Safety and Health Topics. Respirable Crystalline Silica - Sampling and Analysis. Occupational Safety and Health Administration. Oshagov. 2018.
    [5] Everything You Need to Know About OSHA's Respirable Crystalline Silica Final Rule. Occupational Health & Safety. Occupational Health & Safety. 2018.

  2. Wetlands act as valuable urban water treatment

    Wetlands act as valuable urban water treatment

    As cities and urban landscapes expand across the globe, water resource management continues to pose a huge challenge. Natural wetlands are often built over as cities grow, but a recent strategy of green infrastructure applies the opposite principle – wetlands are protected and constructed as part of city planning.

    Wetlands, whether natural or man-made, act as large-scale storage and filtration centers for water streams. Beyond providing a habitat for wildlife and greenery in otherwise urban landscapes, they can remove many harmful contaminants from water, including heavy metals, excess nutrients, pesticides, and bacteria.1

    Wetlands can improve an area’s resilience to extreme weather by storing excess flood water. For example, the Staten Island Bluebelt Project created 400 acres of freshwater wetlands that resolved seasonal flooding issues and saved New York City the $300 million it would have required to accomplish this by constructing storm sewers.2 In the Wade Park Wetland off the coast of North Carolina, a study indicated that up to 75% of storm runoff was being retained in this system and that an average 2-log reduction in fecal coliform load was achieved.3

    Growing cities have the opportunity to integrate wetlands into sustainable water management systems. Protecting and expanding the presence of these habitats will help ensure future generations benefit from their ecological, economic, and aesthetic value.

    [1] “The Case for Green Infrastructure: Joint-Industry White Paper” The Nature Conservancy with Dow, Swiss Re, Shell, and Unilever Companies.
    [2] “The Staten Island Bluebelt: A Study in Sustainable Water Management”. The Cooper Union.
    [3] Buranen M. “Green Infrastructure Helps Coastal Wetlands” Forester Network.

  3. Technology trends in Membrane filtration use: Is industry leading R&D or vice versa?

    Technology trends in Membrane filtration use: Is industry leading R&D or vice versa?

    A significant amount of resources have been allocated each year to the research and development (R&D) of membrane filtration technology. However, it remains unclear how closely research goals align with solving industry needs. Our Product Manager, Sepideh Jankhah, examines the history and evolution of membrane filtration technology applications and investigates R&D trends in this area based on peer-reviewed literature1.


    Membrane filtration technology: who sets the tone for the future? 

    Our research indicates that research goals (as represented by the number of published peer reviewed literature) have closely followed industry demands for the last decade. Industry has benefited from the developments achieved by research initiatives, and the observed positive correlation between industry and R&D goals is expected to continue as we face new challenges. This symbiosis should result in more efficient processes and new products or applications that will address the shortcoming of current industry solutions1.

    You can read the full article in Filtration+Separation

    [1] Jankhah, S. (Feb, 2018) Technology Trends in Membrane Filtration Use, Filtration+Separation. 30-33.
    [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

  4. Transparent Polyester Membrane Filters Enable High Resolution Microscopy

    Transparent Polyester Membrane Filters Enable High Resolution Microscopy

    Sterlitech now offers transparent polyester track-etch (PETE) membrane filters with sufficient clarity to perform high resolution optical imaging through the membrane.  The key attribute of this material is a special, low density pore structure that mitigates light diffusion and renders the filters highly translucent. Furthermore, the membrane has very uniform thickness and flat surfaces so tissue cultures lie in one focal plane. Our transparent PETE filters are available in the 0.4 µm pore size rating commonly used for cell cultures.

    Track-etch membranes have a long history of use in tissue culture experimentation, including use in multiwell plates and cell culture inserts. These membranes can act as scaffolding to create physiological microenvironments promoting growth of attachment-dependent cell cultures. The pore structures in this material allow for nutrient and environmental access to both the free surface (apical) and attached surface (basolateral) of cells. The successful growth of these tissue cultures enables a multitude of investigations into cell attachment, cell growth, cell differentiation, cell migration, and cell to cell signaling. These tissue cultures can also be utilized to model transport, secretion, and diffusion through tissue barriers. They are useful in the study of metastatic behavior of tumor cells, chemotaxis, cytotoxicity, and stem cell induction.

    In many tissue culture applications, researchers utilize high resolution optical imaging techniques.  Although they are made with transparent base films, the pore structures of conventional polycarbonate and polyester track-etch membrane filters have light scattering properties that result in varying degrees of opacity. As a result, it is not typically possible to perform high resolution imaging through these membrane filters. Investigators are instead forced to perform live imaging from only the free surface of the cell culture or are forced to dissect, fix, and mount their culture samples to facilitate microscopic imaging studies.

    With this new and optimized transparent polyester, it is now possible for researchers to image live tissue cultures in high resolution and obtain real-time assessment of cell viability, cell structure, cell interaction, and cell maturity.

  5. Come Visit Sterlitech at Pittcon 2018, Booth #3034

    Come Visit Sterlitech at Pittcon 2018, Booth #3034

    Sterlitech will be in Orlando exhibiting our filtration products at Pittcon 2018. This year, the annual global expo for analytical lab sciences is being held at the Orange County Convention Center. Pittcon brings together a wide variety of laboratory science companies and professionals to showcase the latest technology in our industry.

    Last year there were over 14,000 attendees from 88 different countries. Pittcon offers a unique opportunity to participate in product demonstrations, attend seminars and short courses, and connect with technical experts. This is Sterlitech’s 16th year participating in Pittcon and we are excited to continue sharing our products with the lab science community.

    If you are attending the conference, we encourage you to stop by booth #3034 and chat with our representatives.  Please send us an email if you would like to arrange a specific appointment time.  In attendance will be Tauni Wright, Kensen Hirohata, Steve Dulin, Molly Harris, and Mark Spatz.

  6. Sterlitech Now Offering Hollow Fiber Membranes

    Sterlitech Now Offering Hollow Fiber Membranes

     Are you looking for Hollow Fiber (HF) membranes to build your own pressurized or submerged membrane filtration system?

     Hollow fiber membranes are now available. These membranes are composed of uncoated, permanently hydrophilic PVDF with 4-5 times the mechanical strength of standard NIPS (non-solven induced phase separation) HF’s.

    These membranes can be used in both pressurized and submerged modules, and have several advantages compared to the flat sheet and /spiral wound membrane modules. They have high membrane specific area and packing density, low fouling intensity (suitable for filtering solutions with high solid content), high mechanical strength, and resistance suitable for filtering hard- to- treat solutions.

    HF membranes can be utilized in applications such as:

    • Industrial membrane bioreactors (MBR)

      • High strength waste water

    • Municipal MBR

      • Direct potable reuse (DPR), with direct integrity testing via application of air @ 25 psi

    • Process separations

      • High MWCO separations (>250 kDa)

      • Beer cold filtration (microfiltration membrane)

    • Grey water filtration for reuse

    • Oily waste water (<5 ppm Free Oil)

    Memstar USA1 HF Membrane Specifications



    About Memstar USA:
    [1] Memstar USA is a sister company/business unit of the Singaporean PVDF membrane manufacturing company, Memstar Private Limited (part of the large diversified Chinese company, Citic group). Memstar products account for > 1,500 MGD of installed membrane plants in global pressurized and submerged MF/UF applications.

  7. An open area to discuss porosity

    An open area to discuss porosity

    When discussing physical characteristics of filtration media and membranes, researchers often interested in pore size and porosity. The pore size of a filter, normally stated in micrometers (µm) or Dalton (Da), is determined by the diameter of a particle that is retained by the filter or by a bubble point. In contrast, porosity is defined as the ratio of the void pore volume to the total volume of a membrane, usually indicated as a percentage (1). Where there is a standard method to measure pore size via bubble point, porosity is a bit more mysterious (2).

    Due to the wide variation in void space based on polymer composition, there is no one method that can be applied for all porosity measurements (3). For some membrane types with consistent pore structures, porosity can be estimated using geometric analyses facilitated by imaging methods. These include scanning electron microscopy (SEM), transmission electron microscopy (TEM), or atomic force microscopy (AFM) (4). For microfiltration (MF) membranes, porosity is often quantified using empirical methods. Specialized devices called porometers use capillary flow porometry to characterize porosity and pore size distribution. Porometers are necessarily complex and quite expensive; and as an alternative in cases where approximations are sufficient, it is possible to simply estimate porosity by carefully measuring the mass of water, or liquid, a membrane can hold. Beyond these methods, there are other creative and precise options, from mercury intrusion to nitrogen adsorption with Brunauer–Emmett–Teller (BET) analysis (3).

    We understand that researchers and engineers need to have access to pore size or porosity data to characterize or select membranes. Sterlitech lists membrane pore size and/or porosity data (when characterized) under the Applications/Specifications tab on each product page.

    How do you use pore size or porosity currently? Have you found the data to be readily available or is it necessary to measure these in the lab? Feel free to share your experience and comments below.

    [1] Tarleton, E., & Wakeman, R. (2008). The dictionary of filtration and separation. Exeter: Filtration Solutions.
    [2] ASTM International. (2011). Standard Test Methods for Pore Size Characteristics of Membrane Filters by Bubble Point and Mean Flow Pore Test. ASTM F316 – 03.
    [3] Amziane, S., & Collet, F. (2017). Bio-aggregates Based Building Materials (pp. 39-69). Dordrecht: Springer.
    [4] Dietz, P., Hansma, P., Inacker, O., Lehmann, H., & Herrmann, K. (1992). Surface pore structures of micro- and ultrafiltration membranes imaged with the atomic force microscope. Journal Of Membrane Science, 65(1-2), 101-111.

  8. Stocking up filtration equipment for marine expeditions

    Stocking up filtration equipment for marine expeditions

    February is here, and for many research teams across the world, that means it’s time to set sail. Shoulder seasons are an important time to conduct marine research because many algal and microbial species are in bloom. Whether your research has you voyaging the open sea or cruising in coastal waters, Sterlitech is here to stock the ship with all your laboratory filtration needs.

    We are proud to have our membrane filters take part in the adventure. Our customers utilize silver, glass fiber, and polycarbonate track etch (PCTE) membrane filters in aquatic research.1, 2, 3 These filters travel the seven seas, treating collected sea water samples for retention and analyses of algae, microorganisms, and microscopic particles.1, 4

    Track etch polycarbonate membrane filters are particularly well-suited for these applications because they are translucent and have a smooth, flat surface. These features allow for easy microscopic observation, as well as recovery of aquatic microorganisms and particulates retained by the membrane. Sea ice diatoms have been captured for imaging using 5 µm PCTE, and bacterial abundance has been studied using black-dyed 0.1 µm PCTE.5,6 Our unique 20 µm pore size PCTE also enables filtration of large-volume sea water samples; customers process up to 6L through a single disk filter. In past expeditions, researchers have used these filters to study iron cycling off the coast of New Zealand.7

    There is a vast array of applications for membranes in aquatic studies: chlorophyll estimation, mass spectrometry analyses, size fractionation of organisms and microplastics, and quantifying metal and organic pollutant concentrations, to name a few. Our membrane filters are also used for a wide variety of marine eDNA research.

    We’d love to hear about studies happening on the ocean this spring! Please feel free to share your research applications in the comment section below.

    [1] Van der Merwe, P., Lannuzel, D., Bowie, A., & Meiners, K. (2011). High temporal resolution observations of spring fast ice melt and seawater iron enrichment in East Antarctica. Journal Of Geophysical Research, 116(G3).
    [2] Sipler, R., Baer, S., Connelly, T., Frischer, M., Roberts, Q., Yager, P., & Bronk, D. (2017). Chemical and photophysiological impact of terrestrially-derived dissolved organic matter on nitrate uptake in the coastal western Arctic. Limnology And Oceanography, 62(5), 1881-1894.
    [3] Malpezzi, M., Sanford, L., & Crump, B. (2013). Abundance and distribution of transparent exopolymer particles in the estuarine turbidity maximum of Chesapeake Bay. Marine Ecology Progress Series, 486, 23-35.
    [4] Rahav, E., Shun-Yan, C., Cui, G., Liu, H., Tsagaraki, T., & Giannakourou, A. et al. (2016). Evaluating the Impact of Atmospheric Depositions on Springtime Dinitrogen Fixation in the Cretan Sea (Eastern Mediterranean)—A Mesocosm Approach. Frontiers In Marine Science.
    [5] Pogorzelec, N., Mundy, C., Findlay, C., Campbell, K., Diaz, A., & Ehn, J. et al. (2017). FTIR imaging analysis of cell content in sea-ice diatom taxa during a spring bloom in the lower Northwest Passage of the Canadian Arctic. Marine Ecology Progress Series, 569, 77-88.
    [6] Allan, E., & Froneman, P. (2008). Spatial and temporal patterns in bacterial abundance, production and viral infection in a temporarily open/closed southern African estuary. Estuarine, Coastal And Shelf Science, 77(4), 731-742.
    [7] Ellwood, M., Nodder, S., King, A., Hutchins, D., Wilhelm, S., & Boyd, P. (2014). Pelagic iron cycling during the subtropical spring bloom, east of New Zealand. Marine Chemistry, 160, 18-33.

  9. Gasket Placement Dos and Don’ts

    Gasket Placement Dos and Don’ts

    If the goal of your vacuum filtration is purification using a membrane with an absolute pore size, Sterlitech recommends utilizing glass filter holder assemblies. Compared to Buchner funnels, these systems create a tight seal to prevent liquid bypass around the membrane. Without this seal, the benefit of a highly retentive membrane disappears.

    It is typical to experience some leaking in many vacuum filtration applications, but minimizing this will significantly improve yield. There are a few ways to ensure optimal sealing, including proper set-up of the apparatus and running under the manufacturer’s recommended conditions.

    To illustrate this, we ran trial liquid filtration on our 150 mm assembly with improper gasket placement (below support) and compared it to filtration with proper gasket placement (on top of support). Membrane filters should be placed on top of the gasket to achieve vacuum seal. Please view the video below to see the difference gasket placement can make in vacuum assembly performance. 

    Please feel free to reach out with any questions or concerns on best practices for vacuum filtration. 

  10. eDNA Studies Enabled by Disposable Funnels

    eDNA Studies Enabled by Disposable Funnels

    In a recent article, we described how environmental DNA (eDNA) has been used to detect the presence of aquatic species in lakes and rivers.  eDNA studies have demonstrated great potential for surveillance of rare, endangered, and invasive species by simply collecting and analyzing water samples from target habitats.  Dr. Caren Goldberg, of Washington State University, is one researcher using a unique combination of Sterlitech filters in her investigations of Yangtze giant softshell turtles in southeast Asia, tiger salamanders in California and Arizona, and fairy shrimp in southern California.

    Many of our eDNA end-user researchers utilize disposable filter funnels for this application. These are convenient, presterilized single-use vacuum holders that contain 0.45µm rated mixed cellulose esters (MCE) membrane filters. This membrane material is great for retaining very small particles potentially holding eDNA; however, the small pore size posed a problem for Dr. Goldberg, as her lake and wetland samples often had sediment that would cause the filters to clog prematurely.  Fortunately, these disposable funnels are designed with a removable filter.  Normally the filters are removed after use for subsequent analysis, but this design feature also allows users to replace the filter before use to optimize the funnels for their applications.  For example, Dr. Goldberg and her colleagues determined that 5.0µm rated Polyethersulfone (PES) membrane filters worked well for their water samples, allowing them to process larger volumes while still retaining target particles.

    A fascinating aspect of eDNA studies is the wide diversity of the filters being used, as shown by Dr. Goldberg and others.  Instead of the filters converging into one or two standard types, the filters being used are almost as diverse as the studies themselves; researchers have the freedom to select filters that are optimal for their studies.