Biomass density and filament length synergistically affect activated sludge settling: systematic quantification and...

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Biomass settling in biological wastewater treatment is crucial but often problematic.
• Filamentous bacteria content is a known factor influencing settleability.
• Biomass density is an emerging factor impacting settling performance.

Purpose of the Study:

• To systematically investigate the combined effects of filament content and biomass density on microbial biomass settling.
• To analyze density variations within the range observed in full-scale wastewater treatment systems.
• To develop a model for understanding the interplay between these two parameters.

Main Methods:

• Operated a laboratory-scale bioreactor to generate biomass with varying filamentous bacterium content.
• Systematically adjusted biomass density using synthetic microspheres to isolate effects.
• Utilized fluorescent in-situ hybridization to identify dominant bacterial species (Sphaerotilus natans).

Main Results:

• Established a linear correlation between an image-based filament metric and traditional measurements.
• Developed a non-linear, semi-empirical model demonstrating synergistic effects of filament content and density on settleability.
• Found that filament content's impact on settling is density-dependent, with low-density biomass being more susceptible.

Conclusions:

• Biomass density significantly influences the effect of filament content on sludge volume index (SVI).
• A synergistic relationship exists between filament content and biomass density affecting settleability.
• Considering both parameters is essential for improved operation and troubleshooting of biological solids settling.