Brief Introduction

SDI is a key indicator of membrane fouling potential caused by fine suspended particles in water (e.g. mix of organic colloids, corrosion by products (like iron oxides), precipitated metal hydroxides, algae, and other microscopic debris.

Interpretation of SDI Result

• SDI < 3 : Low Fouling Potential. Low Fouling Potential. Suitable for RO/NF systems
• SDI 3-5 : Moderate Fouling Potential. Moderate Fouling Potential. Pre-treatment recommended Pre-treatment recommended (media filtration, UF)
• SDI > 5 : High Fouling Potential. Advanced pre-treatment needed Advanced pre-treatment needed (coagulation, sedimentation)

What Affects SDI?

• Suspended Solids : raise SDI levels & clog filters
• Colloidal Matter : remain dispersed in water & block membrane pores
• Organic Content : contribute to biofouling Water Source (Seawater / Brackish Water)

Where Is SDI Testing Used?

• Desalination Facilities, to ensure seawater feed is suitable for RO membranes.
• Industrial Operations, to maintain clean process water for cooling towers and boiler systems.
• Municipal Water Treatment, to assess water quality before membrane-based purification steps.