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Effect of solids retention time on floc structure.
S N Liss1, B Q Liao, I G Droppo
1Department of Chemistry, Biology and Chemical Engineering, Ryerson University, Toronto, Ontario Canada. sliss@acs.ryerson.ca
Summary
Increasing solids retention time (SRT) in activated sludge systems promotes more spherical and stable flocs. Higher SRTs lead to denser extracellular polymeric substances (EPS) layers, enhancing floc protection and stability.
Area of Science:
- Environmental Science
- Microbiology
- Biotechnology
Background:
- Activated sludge flocs are crucial for wastewater treatment efficiency.
- Floc structure is influenced by operational parameters like solids retention time (SRT).
- Understanding floc morphology is key to optimizing treatment processes.
Purpose of the Study:
- To investigate the impact of varying solids retention times (SRTs) on activated sludge floc structure.
- To correlate floc characteristics with operational conditions for improved wastewater treatment.
Main Methods:
- Correlative microscopy techniques, including optical microscopy, environmental scanning electron microscopy (ESEM), and transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS).
- Analysis of floc shape, hydration, extracellular polymeric substances (EPS) arrangement, and presence of granules.
Main Results:
- Lower SRTs (4-9 days) resulted in irregular floc shapes.
- Higher SRTs (16-20 days) yielded more spherical and compact flocs.
- Higher SRT flocs exhibited a dense, less hydrated EPS layer and extracellular osmiophilic granules, indicating increased lipid production.
Conclusions:
- Elevated SRTs enhance activated sludge floc stability and structural integrity.
- The dense EPS layer at higher SRTs protects interior cells and reduces surface roughness.
- Findings suggest SRT is a critical factor in controlling floc properties for efficient wastewater treatment.