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Effect of dissolved oxygen concentration on sludge settleability
A M P Martins1, J J Heijnen, M C M van Loosdrecht
1Kluyver Laboratory for Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
Applied Microbiology and Biotechnology
|July 8, 2003
Summary
Low dissolved oxygen levels (< 1.1 mg O2 L−1) in activated sludge systems negatively impact sludge settleability, promoting filamentous bacteria growth, especially at high chemical oxygen demand loads. Substrate gradients, not polymer storage, are key to floc structure.
Area of Science:
- Environmental microbiology
- Water treatment engineering
- Biotechnology
Background:
- Sludge settleability is crucial for efficient operation of activated sludge systems.
- Filamentous bacteria proliferation can impair sludge settling, leading to operational issues.
- Understanding factors influencing sludge settleability is vital for optimizing wastewater treatment.
Purpose of the Study:
- To evaluate the impact of dissolved oxygen concentration and storage polymer accumulation on sludge settleability.
- To investigate the role of substrate and oxygen gradients in the development of filamentous structures.
- To compare settling characteristics under different reactor configurations and operating conditions.
Main Methods:
- Laboratory-scale sequencing batch reactor (SBR) systems were used to simulate specific oxygen and substrate availability regimes.
- Dissolved oxygen concentration, chemical oxygen demand (COD) loading rate, and sludge settleability were monitored.
- Microbial community analysis was implicitly considered through the observed proliferation of specific filamentous bacteria types.
Main Results:
- Low dissolved oxygen concentration (≤ 1.1 mg O2 L−1) significantly worsened sludge settleability.
- High chemical oxygen demand loading rates exacerbated the negative effect of low dissolved oxygen.
- Contrary to hypothesis, polyhydroxyalkanoate (PHA) production and acetate uptake rates were similar in both poor- and well-settling sludge.
Conclusions:
- Substrate and dissolved oxygen gradients within sludge flocs are critical for the development of filamentous structures.
- Compartmentalized aerobic contact tanks with low dissolved oxygen may be detrimental to sludge settleability compared to completely mixed systems.
- The study highlights the importance of managing oxygen profiles to control filamentous bacteria and improve sludge settling in wastewater treatment.