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Diffusivity of oxygen in aerobic granules
1Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan.
Biotechnology and Bioengineering
|April 7, 2006
Summary
This study measured oxygen diffusivity in aerobic granules, finding it depends on carbon source and granule size. Acetate-fed granules showed higher diffusivity than phenol-fed granules, linked to pore structure and extracellular polymer content.
Area of Science:
- Environmental microbiology
- Biochemical engineering
- Mass transfer phenomena
Background:
- Aerobic granules are key in wastewater treatment, but their internal oxygen diffusion is poorly understood.
- Oxygen availability is critical for aerobic microbial activity within granules.
- Carbon source impacts granule properties and microbial community structure.
Purpose of the Study:
- To quantify apparent oxygen diffusivity (D(app)) in acetate-fed and phenol-fed aerobic granules.
- To investigate the influence of carbon source and granule size on oxygen diffusivity.
- To correlate oxygen diffusivity with granule morphology and composition.
Main Methods:
- Measurement of dissolved oxygen (DO) at the granule center following a sudden change in bulk DO.
- Application of a one-dimensional diffusion model with minimized external mass transfer resistance.
- Fluorescence In Situ Hybridization-Confocal Laser Scanning Microscopy (FISH-CLSM) for imaging granule structure.
- Quantification of extracellular polymer (ECP) content.
Main Results:
- Oxygen diffusivity varied significantly between acetate-fed (1.24-2.28 x 10(-9) m2/s) and phenol-fed (2.50-7.65 x 10(-10) m2/s) granules.
- Diffusivity decreased with decreasing granule diameter for both types.
- Acetate-fed granules showed diffusivity proportional to size, while phenol-fed granules showed it proportional to the square of size.
- Phenol-fed granules had higher ECP content and larger pores, correlating with lower oxygen diffusivity.
Conclusions:
- Carbon source significantly affects aerobic granule diameter and apparent oxygen diffusivity.
- Granule size and internal structure (pores, ECP) are critical determinants of oxygen diffusion rates.
- Understanding these factors is crucial for optimizing aerobic granular sludge processes in wastewater treatment.
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