Ultrafiltration Membrane Design Calculator

Water flux equals pressure minus osmotic pressure over sum of resistances

Solution

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How It Works

Ultrafiltration (UF) pushes water through membranes with pore sizes of 0.01–0.1 μm, removing bacteria, colloids, and large organic molecules while passing dissolved salts. Water flux depends on the net driving pressure (applied pressure minus osmotic back-pressure) divided by the total resistance from the membrane itself and any gel or fouling layer that builds up during operation.

UF is commonly used as pretreatment before reverse osmosis, or as a stand-alone step for surface water treatment and wastewater reclamation.

Example Problem

A UF membrane operates at ΔP = 3 bar, osmotic pressure Δπ = 0.5 bar, membrane resistance Rm = 1×1012, and gel resistance Rs = 0.5×1012. What is the water flux?

  1. Jw = (3 − 0.5) / (1×1012 + 0.5×1012)
  2. Jw = 2.5 / 1.5×1012 = 1.67×10−12

Flux units depend on your input units -- typically expressed as L/(m²·h) or m³/(m²·s) in practice.

Frequently Asked Questions

What is the difference between ultrafiltration and reverse osmosis?

UF membranes have larger pores (0.01–0.1 μm) and remove particles, bacteria, and large molecules at low pressure (1–5 bar). RO membranes reject dissolved salts and ions at much higher pressures (10–70 bar). UF is often used as pretreatment for RO.

What causes membrane fouling in ultrafiltration?

Fouling occurs when particles, organic matter, or biofilm accumulate on or within the membrane, increasing resistance and reducing flux. Regular backwashing and chemical cleaning (CIP) are needed to maintain performance. The gel layer resistance Rs captures this effect in the flux equation.

What is a typical water flux for UF membranes?

Clean UF membranes typically produce 50–200 L/(m²·h) at 1–3 bar. As fouling develops, flux can drop by 30–50% between cleaning cycles. Membrane manufacturers specify sustainable flux rates for design purposes.

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