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Antimicrobial Effectiveness01:28

Antimicrobial Effectiveness

The effectiveness of antimicrobial agents depends on various factors influencing their ability to eliminate microbial populations. Larger microbial populations require more time for complete eradication, emphasizing the importance of population size analysis when evaluating antimicrobial efficacy.Microbial resistance to antimicrobial agents varies significantly. Highly resilient microorganisms include endospores, gram-negative bacteria, and non-enveloped viruses, while prions are exceptionally...

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Evaluation of the Efficacy of Organic Peroxyacids for Eradicating Dairy Biofilms Using an Approach Combining Static and Dynamic Methods
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Experimental evaluation of decrease in bacterial activity due to cell death and activity decay in activated sludge.

Xiaodi Hao1, Qilin Wang, Xiangping Zhang

  • 1The R & D Centre for Sustainable Environmental Biotechnology, Beijing University of Civil Engineering and Architecture, Beijing 100044, PR China. xdhao@hotmail.com

Water Research
|June 19, 2009
PubMed
Summary

Bacterial activity decrease in activated sludge stems from both cell death and activity decay. This study differentiated these factors, finding activity decay significantly impacts ammonium and nitrite oxidizing bacteria, and ordinary heterotrophic organisms.

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Area of Science:

  • Environmental microbiology
  • Wastewater treatment

Background:

  • Activated sludge microbial activity decline is caused by cell death and activity decay.
  • Differentiating these factors is crucial for understanding microbial dynamics in wastewater treatment.

Purpose of the Study:

  • To experimentally distinguish between cell death and activity decay as sources of reduced microbial activity.
  • To quantify the contributions of cell death and activity decay for key bacterial groups in different reactor types.

Main Methods:

  • Maximal oxygen uptake rates were measured.
  • Live/dead staining assessed membrane integrity.
  • Fluorescence in-situ hybridization (FISH) with 16S rRNA probes identified specific bacterial groups.
  • Decay and death rates were determined for ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and ordinary heterotrophic organisms (OHOs) in nitrifying and heterotrophic sequencing batch reactors (SBRs).

Main Results:

  • In nitrifying SBRs, activity decay contributed 47% and 82% to decreased AOB and NOB activity, respectively, while cell death accounted for 53% and 18%.
  • In the heterotrophic SBR, activity decay accounted for 78% of OHO decreased activity, with cell death responsible for 22%.
  • Differences in cell death contributions may relate to substrate storage, cryptic growth/death-regeneration in OHOs, and nutrient sources for AOB/NOB.

Conclusions:

  • Activity decay is a major contributor to reduced microbial activity in both nitrifying and heterotrophic activated sludge systems.
  • Cell death plays a more significant role in the decline of ammonium oxidizing bacteria compared to ordinary heterotrophic organisms.
  • Understanding the balance between cell death and activity decay is essential for optimizing activated sludge processes.