Effect of floc size and structure on biosolids capillary suction time

Area of Science:

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

Background:

• Wastewater solids (biosolids) dewaterability is crucial for efficient treatment and disposal.
• Hypotheses suggest both size and structure of biosolids flocs impact dewaterability, but empirical data is scarce.
• Understanding these relationships is key to optimizing wastewater treatment processes.

Purpose of the Study:

• To investigate the impact of activated sludge floc size and structure on dewaterability.
• To elucidate the relative importance of floc size versus structure in determining dewatering performance.
• To provide data validating or refuting existing hypotheses on biosolids dewaterability.

Main Methods:

• Controlled alteration of activated sludge floc size and structure.
• Assessment of dewaterability using the capillary suction time (CST) test.
• Determination of floc size and structure via small-angle light scattering (SALS).

Main Results:

• Floc structure was identified as a major determinant of capillary suction time (CST).
• Changes in floc size did not always correlate with significant changes in CST.
• Similar CST values were observed for flocs with significantly different median sizes but comparable fractal dimensions.

Conclusions:

• Biosolids floc structure plays a more critical role in dewaterability than floc size.
• Controlled manipulation of floc structure could be a viable strategy to improve wastewater treatment efficiency.
• Further research into structure-property relationships in biosolids is warranted.