Biological test systems for monitoring the operation of wastewater treatment plants

Four different biological test systems were used for monitoring the biological activity of a laboratory-scale wastewater treatment plant which was operated with municipal wastewater. The heterotrophic respiration activity test (HRA), dehydrogenase activity test (DHA) and nitrification activity test were used for monitoring the biological activity of the activated sludge, and the luminescent bacteria test was used for screening the effluent of the treatment plant. In shock loading experiments with 2.3-dichlorophenol and 3.5-dichlorophenol it was shown that both the nitrification and heterotrophic respiration activities and the TOC degradation in the treatment plant were significantly reduced, whereas no clear effect on dehydrogenase activity was found. Screening of the effluent revealed a clear increase in luminescent bacteria inhibition during the shock loading experiments.