Membrane-process calculator

Membrane Air-Scour Demand Calculator

Calculate the air flow required for membrane cleaning from the active membrane-train area, supplier or pilot specific aeration demand, and selected scour duty cycle. The result distinguishes full-duty demand from time-weighted normal-air demand for blower and energy screens.

Use the active scour area, not the total installed area. Standby trains may be installed for resilience but normally do not receive scour air. Supplier/pilot SAD_m values and the actual operating sequence supersede preliminary assumptions.

Membrane train and scour inputs Enter the same train basis used by the membrane flux and train-sizing calculation.

Flow and membrane train arrangement

Average Permeate Flow

m³/day; calculation case

Reference Flow for Installed Trains

m³/day; duty-train sizing basis

Operating Days per Year

days/year

Effective Area per Module/Cassette

m²/module

Modules per Train

equal modules per train

Duty Trains Normally Online

normal filtration trains

Standby / Maintenance Trains

installed but not normally online

Active Trains for Scour

cannot exceed installed train count

Membrane air-scour basis and site conditions

Specific Aeration Demand, SAD_m

Nm³/(m²·h) at full scour duty

Scour-Air Duty Factor

percent of time scour air is active

Site Elevation

m above sea level

Inlet-Air Temperature

°C

Air-scour demand results Normal-air results are time weighted and can be carried into blower and energy screening.

Governing equations

The calculation first derives the active membrane area from the selected train configuration. It then applies the full-duty specific aeration demand and duty factor to obtain the time-weighted normal air-flow demand.

A_scour,fixed = N_{active scour trains} × modules/train × area/module

A_scour,linked = A_scour,fixed × (Q_calculation ÷ Q_reference)

Q_N,full = SAD_m × A_scour,linked

Q_N,avg = Q_N,full × f_{scour duty}

SAD_p = Q_N,avg ÷ (Q_permeate,avg ÷ 24)

Q_actual = Q_normal × (T_actual/T_standard) × (P_standard/P_ambient)

Normal-air flow uses 20°C and 101.325 kPa absolute as its standard reference. The actual-inlet-flow conversion is included for a site-condition cross-check; it is not a final blower selection.

Engineering interpretation

The fixed train arrangement provides the installed scour-air capacity at its reference flow. The flow-linked screen scales the active scour area and air demand with the calculation flow; it is suitable for early comparison only. Use the Membrane Flux, Area & Train Sizing Calculator to select final discrete trains and then confirm the supplier-required scour sequence. Time-weighted normal flow includes the duty factor and is the appropriate hand-off for annual air volume and preliminary energy calculation. Do not multiply this averaged hand-off by the duty factor again.

Membrane air-scour calculation basis

Documentation revision: 2026-10-02. This page documents the calculation basis so an engineer can trace the inputs, units, assumptions, and review needs. Results are preliminary screening estimates; they are not a permit determination, OEM guarantee, or construction/procurement approval.

Method and source basis

Full-duty air is calculated as SADm multiplied by the selected active scour area. Average air applies the entered duty fraction, and specific air divides average normal air by average permeate flow. A separate temperature/elevation conversion estimates actual inlet volume under the page's stated reference convention.

The sources below provide technical context or analytical/design methodology. They do not endorse this calculator's defaults, and any jurisdiction-specific requirement applies only where that authority has jurisdiction.

U.S. EPA, Membrane Bioreactors Wastewater Management Fact Sheet (2007)
Oklahoma DEQ, Guidance WQD-002: Membrane Bioreactor (2017)
WEF Manual of Practice No. 36, Membrane Bioreactors
NIST, Pressure and Gas Flow Unit Conversions

Assumptions, limitations, and review actions

SADm is membrane-, module-, sequence-, and wastewater-specific. The 0.40 default is an editable illustrative starting value, not a universal design value.
Use full-duty simultaneous demand for blower, header, valve, electrical, and redundancy checks; use time-weighted air only for energy screening. Do not apply the duty factor twice.
The page does not model diffuser submergence, backpressure, pipe/manifold losses, air distribution, fouling, blower efficiency/turndown, sequence timing, or process-aeration interaction.

Professional review checkpoint

Before using the result for specification or operation, reconcile it with representative site data, the applicable permit and design standard, the selected equipment or membrane supplier's current data, and a qualified wastewater/process engineer. Record the input basis, date, units, and any pilot, bench-test, or comparable full-scale evidence used to select the assumptions.