Microbiological testing of water is not just a regulatory requirement – it is a direct safeguard for public health. When a membrane filter produces a false negative, a contaminated water source can be cleared as safe. The consequences extend far beyond the laboratory.
ISO has recognized this risk and responded with a significant update. ISO 7704:2023 introduces more rigorous performance testing requirements for membrane filters used in direct enumeration of microorganisms by culture methods.
Key Change: ISO 7704:2023 now requires membrane filters to be tested alongside culture media, not independently, to ensure the complete system produces accurate results.
Which Testing Methods Are Affected?
If your laboratory uses any of the following ISO methods, you are subject to the updated ISO 7704:2023 requirements:
- EN ISO 9308-1:2014 – Enumeration of Escherichia coli and coliform bacteria
- EN ISO 16266:2006 – Detection and enumeration of Pseudomonas aeruginosa (membrane filtration method)
- ISO 7899-2:2000 – Detection and enumeration of intestinal enterococci
- ISO 11731:2017 – Enumeration of Legionella
- ISO 8199:2018 – General requirements and guidance for microbiological examinations by culture
- ISO 14189:2013 – Enumeration of Clostridium perfringens (membrane filtration method)
These methods all rely on membrane filtration combined with selective culture media. Under the updated standard, the membrane filter you use must be demonstrated to not interfere with or negatively affect the performance of the media. Testing the membrane alone is no longer sufficient for compliance.
What the Updated Standard Requires
ISO 7704:2023 enhances two critical performance criteria: specificity and selectivity. By evaluating the membrane filter in conjunction with the culture medium, the standard ensures:
- Neither the membrane material nor the culture medium produces adverse effects on test outcomes
- Results are traceable and supported by a validated, complete system
- Laboratories can more readily identify and investigate the root cause of any false negative results
- Laboratory proficiency is supported by a rigorous, standardized validation process
Sterlitech MCE Membranes: Tested and Compliant
Sterlitech's Mixed Cellulose Ester (MCE) Membrane Disc Filters are tested to ensure compliance with ISO 7704:2023. This means your laboratory can use these membranes with confidence, knowing that the filtration component of your workflow meets the updated standard requirements for combined system performance.
MCE membranes are widely used in water quality microbiological testing due to their consistent pore structure, low extractables, and compatibility with a broad range of culture media. Sterlitech offers both sterile gridded and sterile non-gridded formats in 0.22 µm and 0.45 µm pore sizes — the configurations most commonly required for the ISO methods listed above.
Available ISO 7704:2023 Compliant MCE Membrane Filters
| SKU | Item Description | Pore Size (µm) | Diameter (mm) | Gridded |
| MFMCE047022GWS | Nitrocellulose Mixed Ester (MCE) Membrane Filters, Sterile, Gridded, 0.22 Micron, 47mm, 100/Pk | 0.22 | 47 | Yes |
| MFMCE047045GWS | Nitrocellulose Mixed Ester (MCE) Membrane Filters, Sterile, Gridded, 0.45 Micron, 47mm, 100/Pk | 0.45 | 47 | Yes |
| MFMCE047022S | Nitrocellulose Mixed Ester (MCE) Membrane Filters, Sterile, 0.22 Micron, 47mm, 100/Pk | 0.22 | 47 | No |
| MFMCE047045S | Nitrocellulose Mixed Ester (MCE) Membrane Filters, Sterile, 0.45 Micron, 47mm, 100/Pk | 0.45 | 47 | No |
Next Steps for Your Laboratory
Transitioning to an ISO 7704:2023 compliant membrane filter does not require a complete overhaul of your workflow. In most cases, it means verifying that your current membrane is certified under the updated standard or switching to one that is.
Need help choosing the right MCE membrane for your workflow? Ask an expert to help you identify the correct product and provide supporting compliance documentation.
Reference:
ISO 7704:2023 - Water quality — Requirements for the performance testing of membrane filters used for direct enumeration of microorganisms by culture methods
Hold up volume in Skid Mount Membrane Systems can lead to inefficiencies, contamination, and inaccurate measurements. Removing it is essential for optimal performance in filtration and process applications. Alongside our Vacuum Recovery Kit, another effective method is using pressurized air to purge unwanted fluid from lines, valves, and fittings.
What You'll Need
- A source of clean, dry pressurized air
- Access to the system's compression fittings (e.g., feed and concentrate bulkheads)
Steps to Remove Hold Up Volume
- Isolate the target section. Our systems have two lines: the main feed line and the bypass line. Identify which line you want to purge.
- Close the bypass valve. If purging the main feed line, ensure the bypass valve is fully closed before proceeding.
- Connect the air line. Remove an accessible compression fitting in the target line — such as the feed or concentrate bulkhead on top of the skid — and connect your pressurized air source there.
- Gradually apply air pressure. Slowly increase air pressure and direct airflow through the section, forcing any residual liquid out. Keep the tank cover closed to prevent splashing.
- Repeat for additional lines. Connect the air line to the appropriate port for each remaining line, closing the relevant valves as needed, and repeat the purge process.
Pro Tip: If you plan to do this regularly, consider installing a T-fitting with a ball valve on the feed line. This makes it quick and easy to connect the pressurized air line without removing fittings each time.
Ask an expert today if you have any questions about maintaining your system.
