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Roles of high/low nucleic acid bacteria in flocs and probing their dynamic migrations with respirogram
Zheng-Hong Wen1, Shuang-Shuang Zhang1, Pian Zhao1
1Key Laboratory of Northwest Water Resource, Environment, and Ecology, MOE, School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
The Science of the Total Environment
|June 25, 2023
Summary
Bacterial migration influences activated sludge stability. High nucleic acid (HNA) bacteria form the floc backbone, while low nucleic acid (LNA) bacteria fill, impacting stability under various conditions.
Area of Science:
- Environmental Microbiology
- Wastewater Treatment Engineering
Background:
- Bacterial migration is critical for activated sludge stability but poorly understood.
- Extracellular polymeric substances (EPS) play a role in bacterial distribution within sludge flocs.
Purpose of the Study:
- To investigate bacterial migration patterns within activated sludge under normal and extreme conditions.
- To elucidate the roles of low nucleic acid (LNA) and high nucleic acid (HNA) bacteria in floc stability.
Main Methods:
- Analysis of bacterial concentration and distribution after EPS extraction.
- Monitoring bacterial migration during denitrification and aeration cycles.
- Observing bacterial responses to copper ion (Cu2+) shock.
- Utilizing respirograms to correlate microscale migrations with system-scale measurements.
Main Results:
- HNA bacteria primarily reside within sludge flocs, acting as the structural backbone, while LNA bacteria are found in the supernatant or outside flocs.
- Denitrification promotes LNA migration out of flocs; aeration causes LNA to attach to flocs during feast phases and disperse during famine phases.
- Severe famine or Cu2+ shock induces HNA bacteria dispersion, leading to floc breakdown.
- Respirograms effectively correlate bacterial migration with system performance and can serve as an early warning system.
Conclusions:
- The HNA-backbone theory proposes that HNA bacteria maintain floc stability, with LNA bacteria playing a secondary role.
- Understanding bacterial migration dynamics, particularly the HNA-backbone structure, offers a novel approach for regulating activated sludge stability.
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