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Biological process calculator

Membrane Bioreactor Quick Sizing Calculator

Use this interactive tool to translate wastewater flow, organic loading, solids-retention time, and MLSS assumptions into preliminary MBR volume, HRT, membrane area, and biological-process checks.

Part of the Biological Process Calculators collection. For a dedicated operational solids inventory, WAS-flow, and SRT mass-balance check, use the Solids Balance & SRT Calculator.

Input Parameters

m³/day (cubic meters per day)
Ratio of peak to average flow (typically 1.5–2.0)
L/(m²·h) – typical range 15–30 for UF membranes
days – longer SRT improves nitrification
mg/L – mixed liquor suspended solids concentration
mg/L – biochemical oxygen demand

Calculated Results

Enter parameters and click "Calculate" to see results.

Design Basis and Use

Calculation basis and limits: Q is average daily flow; peak factor is applied only to membrane-area screening; flux is treated as net operating flux; BOD is influent BOD applied; and Y and MLVSS/MLSS are assumptions. This simplified estimate does not model decay, inert solids, nitrification, oxygen demand, recycle, redundancy, cleaning downtime or temperature correction. Confirm with representative site data, the selected membrane OEM and a qualified process engineer before design or procurement.

This calculator provides preliminary sizing estimates based on standard MBR design relationships. The results are useful for feasibility studies and initial design phases; detailed engineering requires representative wastewater data, membrane supplier requirements, and site-specific process verification. The calculator uses the selected SRT and MLSS to calculate a solids-balanced bioreactor volume and hydraulic retention time (HRT). Biomass production uses a default sludge yield coefficient (Y) of 0.40 kg biomass per kg BOD applied, and the calculated solids inventory uses a default MLVSS/MLSS fraction of 0.80.