Achieving nitritation at low temperatures using free ammonia inhibition on Nitrobacter and real-time control in an...

Free ammonia (FA) inhibition on nitrite-oxidized bacteria (NOB) and real-time control are used to achieve nitrogen removal from landfill leachate via nitrite pathway at low temperatures in sequencing batch reactor. The inhibition of FA on NOB activity during the aerobic period was prolonged using real-time control. The degree of nitrite accumulation was monitored along with variations of the ammonia-oxidizing bacteria and NOB population using fluorescence in situ hybridization techniques. It is demonstrated that the end-point of ammonia oxidization is detected from the on-line measured dissolved oxygen, oxidization-reduction potential, and pH signals, which could avoid the loss the FA inhibition on NOB caused by excess aeration. At low temperature (13.0-17.6°C), the level of nitrite pathway rapidly increased from 19.8% to 90%, suggesting that nitritation was successfully started up at low temperature by applying syntrophic association of the FA inhibition and real-time control, and then this high level of nitrite pathway was stably maintained for as long as 233 days. Mechanism analysis shows that the establishment of nitritation was primarily the result of predominant ammonia-oxidizing bacteria developed in the nitrifying bacteria population compared to NOB. This was mainly due to a gradual reduction of nitrite amount that is available to provide energy for the growth of NOB, eventually leading to the elimination of NOB from the bacterial clusters in sequencing batch reactor sludge system.