Particle counting as a tool to predict filterability in membrane bioreactors activated sludge?

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Wastewater Management

Background:

• Activated sludge quality significantly impacts membrane bioreactor (MBR) flux decline.
• Sludge filterability, a measure of physical properties, is crucial for MBR performance.
• Decreased filterability is often associated with an increased presence of submicron particles.

Purpose of the Study:

• To investigate if particle counting techniques can detect sludge deflocculation into submicron particles.
• To assess the relationship between particle size distribution and sludge filterability in MBRs.
• To identify factors influencing sludge filterability and explore improvement strategies.

Main Methods:

• Collected 105 activated sludge samples from four full-scale municipal MBRs.
• Assessed sludge filterability using deltaR20 measurements.
• Employed particle counting techniques for particles in the 2-100 micrometer range.

Main Results:

• 88% of membrane tank samples exhibited filterability ranging from good to poor (0 < deltaR20 < 1).
• Filterability was influenced by season, MBR operational stability, and recirculation ratio.
• Particle counting (10-100 micrometers) yielded reproducible results but did not fully explain filterability differences.
• Low recirculation ratios improved membrane tank filterability.

Conclusions:

• Particle counting in the 10-100 micrometer range did not directly correlate with MBR sludge filterability changes.
• Submicron particles, possibly from deflocculation, remain a potential cause of filterability deterioration.
• Sludge filterability is a dynamic parameter affected by operational and environmental factors.