The duplicity of floc strength

Area of Science:

• Environmental Science
• Water Treatment Engineering
• Colloid and Surface Chemistry

Background:

• Floc breakage is governed by the cohesive strength of inter-particle bonds.
• Understanding floc behavior under stress is crucial for water purification processes.

Purpose of the Study:

• To characterize the breakage and regrowth behavior of different floc types under shear.
• To analyze the impact of shear forces on floc aggregate integrity and particle size distribution (PSD).

Main Methods:

• Three floc types (coagulant precipitate, turbidity, organic matter) were subjected to increasing shear levels using a jar tester.
• Floc size dynamics were monitored using laser diffraction, providing detailed particle size distribution (PSD) data.
• Analysis of PSD data allowed identification of large and small-scale floc degradation events.

Main Results:

• Organic matter flocs demonstrated the highest resistance to breakage across all tested shear rates.
• All floc types showed minimal potential for regrowth after experiencing breakage.
• Precipitate and organic flocs exhibited slightly improved re-aggregation of smaller particles post-breakage.

Conclusions:

• Floc resistance to shear varies significantly depending on floc composition.
• Dynamic PSD analysis is effective for identifying floc degradation events.
• Limited regrowth potential suggests that once broken, flocs are difficult to reform in treatment systems.