Bioindicators in a Nitrification Denitrification System

ABSTRACT

The nitrification denirtification wastewater treatment processes have been studied in laboratory conditions, using a system of two completely mixed reactors and a secondary clarifier. Wastewater and activated sludge were taken from the Sofia Wastewater Treatment Plant (Sofia WWTP). Four steady states, differing in sludge age were investigated. For each steady state microbiological and biochemical analyses were carried out. The aim of the study was to establish the reliable bioindicators for assessment and management of the nitrogen removal processes. The amount of the more important physiological groups of microorganisms varies insignificantly in the four steady states, whereas the dehydrogenase activity corresponds closely to the organic substrate utilization rate in anoxic conditions. These results confirm the expected conservatism of the microbiological structural indicators, on the one hand, and the possibility of using the dehydrogenase activity as a reliable biological indicator, on the other hand.