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Related Experiment Video

Updated: Jul 4, 2026

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1
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INT-dehydrogenase test for activated sludge process control.

J M Lopez1, B Koopman, G Bitton

  • 1Laboratory of Environmental Microbiology, Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida 32611, USA.

Biotechnology and Bioengineering
|July 1, 1986
PubMed
Summary
This summary is machine-generated.

The redox dye INT measures dehydrogenase activity in activated sludge, showing sensitivity to sludge age and chlorine stress. This method offers a reliable alternative to oxygen uptake rate for assessing microbial activity.

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Area of Science:

  • Environmental microbiology
  • Wastewater treatment
  • Biochemical assays

Background:

  • Activated sludge is crucial for wastewater treatment.
  • Assessing microbial activity is key to optimizing treatment processes.
  • Dehydrogenase activity is an indicator of microbial metabolic function.

Purpose of the Study:

  • To investigate the use of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) as a redox dye for measuring dehydrogenase activity in activated sludge.
  • To compare INT-dehydrogenase activity (INT-DHA) with oxygen uptake rate (OUR) as indicators of microbial activity.
  • To evaluate the influence of INT dosage, biomass concentration, pH, and sludge age on INT-DHA.

Main Methods:

  • Activated sludge samples were subjected to dehydrogenase activity assays using varying concentrations of INT.
  • INT-DHA and OUR were measured under different pH conditions and sludge ages.
  • The impact of INT dosage on microbial viability was assessed.
  • Correlations between INT-DHA and OUR were analyzed, particularly under chlorine stress.

Main Results:

  • INT-DHA was directly proportional to INT dosage and inversely proportional to biomass concentration within specific ranges.
  • INT concentrations above 2.5 mM exhibited toxicity to activated sludge.
  • Optimal pH for INT-DHA was 9, while peak OUR occurred at pH 8.
  • Both INT-DHA and OUR decreased with increasing sludge age, with INT-DHA showing greater sensitivity.
  • Significant correlations were observed between INT-DHA and OUR in chlorine-stressed sludge.

Conclusions:

  • INT is a viable and sensitive indicator for measuring dehydrogenase activity in activated sludge.
  • INT-DHA provides a valuable metric for assessing microbial activity and stress in wastewater treatment systems.
  • INT-DHA is more sensitive than OUR to variations in sludge age and can be effectively used alongside OUR for monitoring treatment efficiency.