MBR membrane sizing should use a sustainable net design flux for the actual wastewater and operating cycle—not a peak clean-water value. Record the temperature, MLSS, TMP, filtration and relaxation times, aeration, cleaning basis and availability assumptions with every flux used in a design.
Distinguish the flux terms before comparing values
| Term | Practical meaning | Selection warning |
|---|---|---|
| Clean-water flux or permeability | Performance measured with clean water under stated test conditions | Useful for quality or recovery checks, not a wastewater design flux by itself. |
| Instantaneous filtration flux | Permeate rate during the active suction period | Does not include relaxation, backwash, cleaning or downtime. |
| Gross operating flux | Flux on a stated operating basis before some downtime or losses | The exact time basis must be defined. |
| Net flux | Net permeate production divided by membrane area over a stated time basis | Confirm whether backwash consumption and non-filtration periods are included. |
| Design flux | Selected flux used to size the project | Must be tied to wastewater, temperature, operation and evidence. |
| Peak flux | Temporary higher loading for a defined peak period | Requires a duration, recovery strategy and TMP/fouling assessment. |
Flux, TMP and permeability describe different signals
Flux is permeate flow per unit membrane area. Transmembrane pressure (TMP) is the pressure difference driving filtration. Permeability is commonly assessed as flux divided by TMP under a defined convention.
A rising TMP at similar flux, or declining flux at similar TMP, may indicate increasing resistance. Interpretation should also consider temperature, instrument zero, sludge condition, valve position, pump control and membrane integrity. Trend data is more useful when operating conditions and temperature correction are consistent.
Conditions that can lower sustainable flux
- Lower water temperature and higher viscosity
- High or unstable MLSS and poor sludge filterability
- Fats, oils, grease, polymers or extracellular material
- Inadequate screening or fibrous debris
- Insufficient or uneven membrane air scour
- Long filtration cycles without suitable relaxation
- Cleaning that does not recover permeability
- Hydraulic imbalance between modules or trains
- Industrial chemicals outside the approved operating envelope
Build a defensible sizing flux
- Define the wastewater and worst credible operating conditions.
- Record the membrane configuration and current supplier limits.
- Choose the exact flux definition and time basis.
- Use representative full-scale history, approved supplier evidence or pilot data.
- Adjust for temperature and operating-cycle assumptions without double counting.
- Check TMP trend, aeration and cleaning recovery at the proposed duty.
- Test average, peak and unavailable-train cases.
- Convert the selected flux into area using the MBR membrane area calculation.
Do not use one universal MBR design flux
Sustainable flux depends on wastewater, biological health, pretreatment, membrane type, module geometry, temperature, operating cycle, aeration, cleaning and the required reliability. A value from another site or a different membrane cannot be transferred without checking these conditions.
Where YiFu reference product data states a flux range, the current datasheet and its test basis must be reviewed. Any final project value should be confirmed for the selected product and application.
When pilot testing or staged verification is valuable
Pilot work may be appropriate for high-strength industrial wastewater, oil-bearing streams, unusual chemicals, severe seasonal variation, uncertain biological treatability or applications without relevant operating history. The pilot should reproduce screening, sludge, temperature, flux, aeration, filtration cycle and cleaning conditions closely enough to support a decision.
A short clean-water or start-up test cannot establish long-term sustainable flux. Record flux, TMP, permeability, temperature, MLSS, aeration, cleaning and water-quality trends together.
Connect flux back to module procurement
After selecting a defensible flux and preliminary area, use the MBR module selection guide to check configuration, tank fit, aeration, cleaning, access and approved documentation. For existing systems, use the replacement checklist to compare current operating history with the proposed module.
Information to send YiFu
- Wastewater source and representative analysis
- Temperature range and seasonal minimum
- MLSS and sludge filterability information
- Average, maximum-day and peak flow
- Existing or proposed membrane configuration
- Current flux, TMP and permeability trends
- Filtration, relaxation, backwash and cleaning cycles
- Aeration rate and distribution basis
- Cleaning chemicals, recovery and frequency
- Required availability and train arrangement