At a Glance
Costs vary significantly with scale, membrane type, and application. Use untangle.bio for project-specific estimates.
How Microfiltration Works
Microfiltration uses membranes with pore sizes of 0.1–10 µm to physically separate particles, cells, and debris from dissolved molecules. It is the coarsest membrane separation technique, operating at low transmembrane pressures. MF is typically the first membrane step in downstream processing.
Two Outputs
Retentate (heavy): Cells, cell debris, precipitates, and large particles that cannot pass through the membrane pores.
Permeate (light): All dissolved molecules — proteins, sugars, salts, amino acids, organic acids, and water — pass freely through MF membranes.
Operating Modes
| Mode | Purpose | Description |
|---|---|---|
| Harvest Clarification | Cell removal | Remove cells and debris from fermentation broth to recover dissolved product in permeate |
| Cell Recovery | Cell concentration | Concentrate cells in retentate for whole-cell products or biomass recovery |
| Bioburden Reduction | Sterile filtration | 0.2 µm dead-end filtration removes bacteria; 0.1 µm for mycoplasma removal |
Pore Size Selection Guide
Rule of thumb: Choose pore size 5–10× larger than your target molecule (if it should pass) or 5–10× smaller than particles to retain.
| Pore Size | Retains | Passes | Common Use |
|---|---|---|---|
| 0.1 µm | All cells, mycoplasma, large debris | All dissolved molecules, small colloids | Sterile filtration, mycoplasma removal |
| 0.2 µm | Bacteria, yeast, mammalian cells | All dissolved molecules | Bioburden reduction, sterile filtration |
| 0.45 µm | Most bacteria, all larger cells | Dissolved molecules, some small bacteria | General clarification, pre-filtration |
| 1.0–10 µm | Large particles, cell clumps, flocs | Individual cells, all dissolved molecules | Coarse pre-filtration, debris removal |
Best Molecules for MF Separation
| Molecule | Size | MF Behavior | Use Case |
|---|---|---|---|
| E. coli | 1–2 µm | Fully retained | Cell harvest, inclusion body recovery |
| Yeast | 5–10 µm | Fully retained | Beer clarification, yeast recovery |
| CHO Cells | 12–15 µm | Fully retained | mAb harvest clarification |
| IgG (mAb) | 150 kDa | Passes freely | Recovered in permeate after cell removal |
| BSA | 66.5 kDa | Passes freely | Recovered in permeate |
| Glucose | 180 Da | Passes freely | Removed with permeate |
Cost Considerations
Capital Cost (CAPEX)
MF systems range from simple dead-end filter housings (low CAPEX) to fully automated TFF skids. Dead-end systems are cheaper upfront but consume more membranes. TFF systems have higher CAPEX but lower membrane replacement costs due to reduced fouling.
Key CAPEX Drivers
| Factor | Impact |
|---|---|
| TFF vs. dead-end (NFF) | TFF skids 2–5× more expensive than NFF housings, but lower OPEX |
| Membrane material | Ceramic membranes 3–5× cost of polymeric but last 5–10 years |
| Scale (membrane area) | Primary cost driver — determined by flux and throughput requirements |
| Single-use vs. reusable | Single-use capsules lower validation burden but higher per-batch cost |
Operating Cost (OPEX)
MF operates at low pressures, so energy costs are modest. Membrane replacement dominates OPEX for dead-end systems (replaced each batch). TFF membranes last longer but require CIP chemicals. High-solids feeds (e.g., fungal broths) cause rapid fouling and increase membrane consumption significantly.
Frequently Asked Questions
What is the difference between MF and UF?
Microfiltration (0.1–10 µm pore size) removes particles and cells but passes all dissolved molecules. Ultrafiltration (1–100 kDa MWCO) separates dissolved molecules by size — retaining proteins while passing salts and sugars. MF typically precedes UF in a purification train.
Should I use TFF or dead-end filtration?
Dead-end (NFF) is simpler and cheaper for low-solids feeds (<1% solids) or sterile filtration. TFF is preferred for high-solids feeds (fermentation broths with cells) because tangential flow reduces cake buildup and membrane fouling.
Can MF replace centrifugation for cell removal?
Yes, in many cases. MF provides more complete cell removal and can be easier to scale. However, centrifugation handles very high cell densities better and doesn’t suffer from membrane fouling. Many processes use centrifugation followed by MF for polishing.
How do I prevent membrane fouling in MF?
Use TFF mode with adequate cross-flow velocity. For dead-end, consider depth pre-filters upstream. Optimize flux below the critical flux value. Regular backwashing (for TFF) and CIP with NaOH or NaOCl help restore permeability.
Related Separation Techniques
Design an MF Step Into Your Process
Drag-and-drop microfiltration into your flowsheet, connect streams, and simulate with real mass balance.
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