Sterile filtration is essential for industries like pharmaceuticals, and food & beverage, where hygiene and product integrity are crucial. This guide explains how sterile filtration works, types of membrane filters, and key factors to consider such as pore size, validation, and integrity testing.
What is sterile filtration
When it comes to the disinfection or sterilization of liquids there are two common ways. These are heat treatment or pasteurization and sterile filtration.
Sterile filtration is a method of removing unwanted microorganisms from liquids without heat. It offers a cost-effective alternative to pasteurization, preserving sensitive ingredients like flavours or dyes.
Sterile filters use membrane pores to trap contaminants. The smaller the pore size, the more effective the filter is at completely blocking contaminants - like unwanted organisms.
Membranes for sterile filtration
To better illustrate what's pointed out above, consider that bacteria in liquids usually range from 0.2 μm to 0.5μm. To remove them, a 0.22µm sterile-grade membrane filter is used. This means, the membrane of this filter element consists of millions of pores with diameters between 0,2µm and 0.4µm and a typical maximum of around 0.28µm.
When using such a sponge-like membrane, nearly 100% of all bacteria are blocked. It’s worth to mention, that the name “sterile grade 0.22µm” is not referring to the pore size but to the microorganism retained. And according to the “FDA Guideline on Sterile Drug products produced by Aseptic Processing” from 2004 a sterile grade filter element is supposed to retain 10Exp7 microorganisms of the type of Brev. Diminuta (ATCC 19146) per cm² of the filtration surface. And Brev. Diminuta is 0.22µm or larger in diameter.
Common membrane materials:
- PES (Polyethersulfone)
- PVDF (Polyvinylidene fluoride)
- Nylon
These membranes are supported by polypropylene or polyester layers.
Important criteria for sterile filtration
- Chemical Resistance: Ensure filter materials are compatible with the fluid you want to filter. Additionally, make sure, the materials are also compatible with the solvents you use for cleaning purposes.
- Integrity Tests: Always test filters (e.g. Bubble Point Test) before use to verify performance. By doing this you make sure, your filter elements are integer and reveal no damages or leakages.
- Validation: Confirm the filter's effectiveness against relevant microorganisms, not just standard ones.
- Sterilisation: Reusable filters must be sterilised, often via steam at 121°C for 30 minutes to make sure that all retained microorganisms have been killed and the filter element might be used again for the next sterile filtration.
Additional factors for sterile filtration
- Clogging: Premature clogging of filter elements during a sterile filtration is always a vexation resulting in unwanted machine downtime and a costly cleaning process. Use pre-filtration and SDI testing to extend service life and reduce downtime.
- Regeneration: Clean filters regularly using compatible agents listed in product documentation.
- Optimised Service Lifetime: Proactive replacement can reduce costs and carbon footprint. We experienced an average cost reduction of 35% and CO2 reduction around 67% for each filter installation optimized. Please contact us to learn more.
We're here to help
We hope the information contained in this article provides a good overview about sterile filtration. If you'd like more information about any topic covered, our team is happy to point you in the right direction. We're also available to discuss the full range of products we offer for process filtration. Get in touch with us today.
