The Dynamic Response of Nitrogen Transformation to the Dissolved Oxygen Variations in the Simulated Biofilm Reactor

Lab-scale simulated biofilm reactors, including aerated reactors disturbed by short-term aeration interruption (AE-D) and non-aerated reactors disturbed by short-term aeration (AN-D), were established to study the stable-state (SS) formation and recovery after disturbance for nitrogen transformation in terms of dissolved oxygen (DO), removal efficiency (RE) of NH 4 + -N and NO 3 − -N and activity of key nitrogen-cycle functional genes amo A and nir S (RNA level abundance, per ball). SS formation and recovery of DO were completed in 0.56–7.75 h after transition between aeration (Ae) and aeration stop (As). In terms of pollutant REs, new temporary SS formation required 30.7–52.3 h after Ae and As interruptions, and seven-day Ae/As interruptions required 5.0% to 115.5% longer recovery times compared to one-day interruptions in AE-D and AN-D systems. According to amo A activity, 60.8 h were required in AE-D systems to establish new temporary SS after As interruptions, and RNA amo A copies (copy number/microliter) decreased 88.5%, while 287.2 h were required in AN-D systems, and RNA amo A copies (copy number/microliter) increased 36.4 times. For nir S activity, 75.2–85.8 h were required to establish new SSs after Ae and As interruptions. The results suggested that new temporary SS formation and recovery in terms of DO, pollutant REs and amo A and nir S gene activities could be modelled by logistic functions. It is concluded that temporary SS formation and recovery after Ae and As interruptions occurred at asynchronous rates in terms of DO, pollutant REs and amo A and nir S gene activities. Because of DO fluctuations, the quantitative relationship between gene activity and pollutant RE remains a challenge.