Inhibition of nitrification by the metabolic uncoupler, 2,6-dichlorophenol (2,6-DCP) in a sequencing batch reactor

The nitrification inhibition induced by a metabolic uncoupler, 2,6-DCP was investigated in a sequence batch culture during the 60-day operation. Batch tests indicated that pH and temperature were the two key parameters affecting the nitrification performance. Significant inhibition of nitrification was observed on the initial addition of 2,6-DCP, then nitrification recovered to a higher level again. The extracellular polymeric substance (EPS) matrix functioned as a protective barrier for the bacteria inside sludge flocs to 2,6-DCP, resulting in the gradual recovery of nitrification efficiency. DGGE analysis showed the bacteria communities continued to evolve in the sludge over 60 days. Moreover, the addition of 2,6-DCP increased the activated sludge activity and enhanced the dewatering ability of excess sludge. SOUR tests suggested that 2,6-DCP was much more toxic to autotrophic microorganisms than heterotrophic microorganisms. Thus, the application of metabolic uncoupler for excess sludge reduction should be very prudent.