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Membrane Bioreactor (MBR)
Activated sludge combined with membrane filtration for solid-liquid separation
Overview
MBR combines biological treatment with membrane filtration (0.03-0.4 μm pores), eliminating secondary clarifiers. Produces high-quality effluent (TSS <1 mg/L, turbidity <0.2 NTU) suitable for reuse. Operates at high MLSS (8,000-15,000 mg/L), reducing tankage by 50%. Higher capital and O&M costs than conventional AS.
Theory - Basic Mode
Same as activated sludge plus membrane filtration:
$$\text{TSS}{effluent} = 1-5 \text{ mg/L}$$ $$\text{Turbidity} < 1 \text{ NTU}$$ $$\text{BOD} = 95-99%$$
Theory - Advanced Mode
Membrane Flux:
$$J = \frac{TMP}{\mu \times (R_m + R_c + R_f)}$$
Where:
- J = permeate flux (L/m²·h, LMH)
- TMP = transmembrane pressure (kPa)
- μ = viscosity
- R_m = membrane resistance
- R_c = cake resistance
- R_f = fouling resistance
Critical Flux:
$$J_{crit} = f(\text{MLSS}, \text{aeration}, \text{SRT})$$
Typically 15-35 LMH for municipal wastewater
Parameters
| Parameter | Typical Range | Units |
|---|---|---|
| MLSS | 8,000-15,000 | mg/L |
| SRT | 10-40 | days |
| F/M | 0.05-0.15 | kg BOD/kg MLSS·d |
| HRT | 3-8 | hours |
| Flux (design) | 15-25 | LMH |
| Flux (peak) | 25-35 | LMH |
| TMP (operating) | 10-40 | kPa |
| Aeration (membrane) | 0.5-1.5 | Nm³/m²·h |
Worked Example
Given: MBR for 10,000 m³/d Calculate: Membrane area
- Design flux: 20 LMH
- Peak flux: 30 LMH (peak flow 1.5× avg)
- Peak flow: 15,000 m³/d = 625 m³/h
- Required area: 625,000 L/h / 30 LMH = 20,833 m²
- With 15% contingency: 24,000 m²
What the simulator actually computes
The advanced flux equation above is implemented in the .NET simulation tier as a resistance-in-series fouling model with filtration/relaxation cycling, air scour, CEB and CIP cleaning, constant-flux and constant-TMP duties, and a membrane energy balance. Every parameter (membraneResistance, specificCakeResistance, airScourRate, cebIntervalHours, …) sits on the MBR node's parameter form, and each run reports the TMP time series, the resistance breakdown, the next-clean ETA and the specific energy in kWh/m³.
Set operatingHours — hours since the last recovery clean — to choose the point of the cleaning cycle the results are reported at. A steady-state run has no clock, so leaving it at 0 reports a clean membrane.
Equations, defaults, outputs and limitations: MBR membrane fouling and TMP dynamics.
References
- Metcalf & Eddy (2014)
- Judd, S. (2011). The MBR Book, 2nd Ed
- Field, R.W. et al. (1995). Critical flux concept for microfiltration fouling. J. Membr. Sci. 100