The dehydrogenase assay with resazurin: practical performance as a monitoring system and Ph-dependent toxicity of phenolic compounds.

The dehydrogenase assay with resazurin as an oxidoreduction dye was used for monitoring the performance of six laboratory-scale sewage treatment plants. The dehydrogenase activity measured proved to be a reliable monitoring parameter, although it did not always positively correlate with the simultaneously estimated respiration activity. With the help of the dehydrogenase assay, the toxicity of different phenolic compounds was determined. It was found that the toxicity of 2.4-dichlorophenol, 3.5-dichlorophenol, and 2.4-dinitrophenol was clearly dependent on the pH. These data were supported by shock loading experiments in laboratory-scale sewage treatment plants.