UF Net Production & Backwash Calculator

Translate gross UF filtration capacity into net water production after backwashing, flushing and chemically enhanced backwash.

Why net UF production matters

Gross filtration capacity describes the water produced while the membranes are filtering. Part of that filtrate is used for backwashing and chemically enhanced backwash, while cleaning and flushing reduce the time available for production. Net product flow is the average quantity remaining for downstream use after these allowances.

This distinction matters when UF supplies a reverse osmosis plant or another process with a specified water demand. Matching the demand to gross filtration capacity alone can overstate the useful output of the installation.

How to interpret your results

Use Size for a required net flow to estimate a whole number of operating modules from your selected membrane area, filtration flux and cleaning cycle. Use Check an existing module count to explore how changes in operating settings affect the calculated average output.

The reported recovery is net product volume divided by total feed volume within the calculator's boundary. Filtrate used for backwashing and CEB reduces net production; feed-side flushing increases feed demand and wastewater. Include all relevant cleaning volumes and downtime, and avoid counting the same event twice.

Selecting flux and cleaning settings

Enter values appropriate to the selected membrane and feedwater. A higher flux or longer filtration interval can increase calculated output, but the arithmetic alone does not show whether that operating condition is sustainable. Review the settings against the membrane manufacturer's guidance and operating experience for the application.

The interval comparison is a sensitivity check: it holds other inputs constant. It does not predict fouling, cleaning effectiveness or membrane life.

From average capacity to a complete installation

The calculated module count covers average operating capacity. A complete design also considers train arrangement, standby capacity, filtrate storage, instantaneous backwash demand and longer cleaning shutdowns. Where uninterrupted downstream supply is required, assess how storage and the operating sequence bridge periods when modules are not filtering.

Calculation basis

This calculator represents a repeating dead-end UF cycle. Backwash and CEB consume stored filtrate; feed-side flushing consumes additional feedwater. It assumes negligible filtration-stage reject and accounts for entered water volumes only.

• Gross filtrate per cycle = membrane area × filtration flux × filtration time.
• Backwash water per cycle = membrane area × backwash flux × backwash duration.
• Cycle time = filtration + backwash + other entered downtime.
• Average net flow per module = normal-cycle net rate × (1 - CEB downtime fraction) - additional CEB filtrate use per hour.
• Feed flow = average gross filtrate production + feed-side flush demand.
• Wastewater = feed flow - net product; recovery = net product / feed.

Calculations convert minutes, seconds and litres to consistent units. A CEB interval refers to scheduled operating time, including CEB downtime. Results are long-run averages; an actual day can have a different number of cleaning events.

Module counts are rounded up to whole operating modules. No standby module, train allocation, peak backwash pump duty, temperature correction, fouling model, CIP shutdown, chemical dose or membrane compatibility limit is included. Additional chemical solution volumes and external utility water are excluded unless entered as equivalent cleaning water. Select flux and cycle settings using the chosen membrane manufacturer's guidance and feedwater assessment.

Reference background: DuPont IntegraTec Process & Design Manual.