A membrane biocide is a chemical agent used to prevent or control biological fouling in membrane systems such as reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), and microfiltration (MF) units. Biofouling—caused by bacteria, fungi, algae, and other microorganisms—can severely reduce membrane efficiency, shorten membrane life, and increase operational costs.

Common Membrane Biocides

Key Features of a Good Membrane Biocide

• Compatible with membrane materials (e.g., polyamide)

• Broad-spectrum microbial control

• Fast action with short contact time

• Low environmental toxicity or easy neutralization

• Stable under wide pH and temperature ranges

Biocides Are Used in Membrane Systems

• Dosed intermittently or continuously depending on system design and fouling risk

• Circulated during CIP (Cleaning in Place) processes to remove biological deposits

• Used in pretreatment or feedwater to limit biofilm formation

Precautions

• Do not use oxidizing biocides (e.g., chlorine) on polyamide RO membranes, unless followed by a dechlorination step (e.g., sodium bisulfite).

• Always follow manufacturer dosing instructions and flush the system before restarting service.

• Ensure biocide is approved for potable or food-grade use if used in those applications.

When to Use Biocides

• Persistent biofouling seen in SDI (Silt Density Index) or pressure drop trends

• High microbial counts in feedwater

• Seasonal increases in biological activity (e.g., warmer months)

• During long shutdowns to prevent biofilm formation