At a Glance
Costs vary significantly with scale, membrane area, and application. Use untangle.bio for project-specific estimates.
How Ultrafiltration Works
Ultrafiltration uses semi-permeable membranes with defined molecular weight cutoffs (MWCO) to separate molecules by size. In tangential flow filtration (TFF), the feed flows parallel to the membrane surface, reducing fouling and enabling continuous operation.
Two Outputs
Retentate (heavy): Molecules larger than the MWCO are retained — typically the target protein product.
Permeate (light): Smaller molecules (salts, sugars, small metabolites, water) pass through the membrane.
Operating Modes
| Mode | Purpose | Description |
|---|---|---|
| Concentration | Volume reduction | Remove water and small solutes to increase protein concentration |
| Diafiltration | Buffer exchange | Add wash water while filtering to exchange buffer or remove small impurities |
| Clarification | Particle removal | Remove cell debris or aggregates (larger MWCO, e.g., 100 kDa) |
MWCO Selection Guide
Rule of thumb: Choose MWCO 3–5× smaller than your target protein to ensure >95% rejection.
| MWCO | Retains | Passes | Common Use |
|---|---|---|---|
| 10 kDa | Most proteins (>10 kDa) | Salts, sugars, amino acids, small organic acids | Protein concentration, desalting |
| 30 kDa | Antibodies, large enzymes (>30 kDa) | Peptides, small proteins, all small molecules | mAb concentration, BSA removal from IgG |
| 50 kDa | IgG (150 kDa), large proteins | BSA (66.5 kDa, partial), smaller proteins | Antibody polishing |
| 100 kDa | Very large proteins, aggregates, viruses | Most individual proteins | Virus filtration, aggregate removal |
MW > 3× MWCO: 99% rejection | MW > 2× MWCO: 95% | MW > 1.5×: 80% | MW > 1.2×: 30% | MW near MWCO: 10% | MW < 0.5×: 0–2%
Best Molecules for UF Separation
| Molecule | MW (Da) | 10 kDa UF Rejection | Use Case |
|---|---|---|---|
| IgG (mAb) | 150,000 | 99% | Concentration & buffer exchange |
| BSA | 66,500 | 99% | Concentration, model protein |
| Whey Protein | 18,000 | 95% | Dairy protein concentration |
| Lysozyme | 14,300 | 80% | Near MWCO—partial retention |
| Lactic Acid | 90 | <2% | Passes freely (impurity removal) |
| Glucose | 180 | <2% | Passes freely (desugaring) |
Cost Considerations
Capital Cost (CAPEX)
UF systems include membrane modules, recirculation and feed pumps, TMP/flow controls, diafiltration water inlet, and CIP/SIP systems. Costs scale sub-linearly with throughput — larger systems are more cost-efficient per liter. Above ~5,000 L/hr, parallel trains are typically required.
Key CAPEX Drivers
| Factor | Impact |
|---|---|
| Membrane area (m²) | Primary cost driver — determined by flux and throughput |
| Single-use vs. reusable | Single-use cassettes lower upfront cost but higher per-batch |
| GMP vs. non-GMP | Pharma-grade systems 2–3× higher than industrial/food |
| Automation level | Fully automated skids add 30–50% vs. manual systems |
Operating Cost (OPEX)
Energy consumption is dominated by recirculation pumps (high cross-flow velocity) and feed pumps (TMP). Membrane replacement is typically every 1–3 years depending on fouling severity and CIP effectiveness. CIP chemicals (NaOH, citric acid) and water for diafiltration are additional recurring costs.
Frequently Asked Questions
What is the difference between UF and NF?
Ultrafiltration (1–100 kDa MWCO) separates proteins from small molecules. Nanofiltration (200–1000 Da MWCO) separates small molecules from each other (e.g., sugars from salts). NF operates at higher pressures and has charge-based selectivity.
When should I use diafiltration vs. just concentration?
Use diafiltration when you need to remove small impurities (salts, sugars) or exchange buffers. Each diavolume removes ~63% of permeable solutes. 5 diavolumes removes ~99.3%. Use concentration alone when you only need to reduce volume.
Can UF handle cell-containing feeds?
UF membranes can foul rapidly with cells and cell debris. Best practice is to clarify first (centrifugation or microfiltration) before UF. untangle.bio's expert rules flag this automatically and suggest prior clarification.
How do I prevent membrane fouling?
Use TFF (tangential flow) configuration with high cross-flow velocity. Pre-clarify feeds. Operate below critical flux. Regular CIP with NaOH (0.1–0.5 M). Consider pre-filtration with depth filters for lipid-heavy feeds.
Related Separation Techniques
Design a UF Step Into Your Process
Drag-and-drop UF into your flowsheet, connect streams, and simulate with real mass balance.
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