Achieving the nitrite pathway using FA inhibition and process control in UASB-SBR system removing nitrogen from landfill leachate

An up-flow sludge blanket (UASB) and sequencing batch reactor (SBR) system was introduced to remove organics and nitrogen from landfill leachate. The synergetic effect of free ammonia (FA) inhibition and process control was used to achieve the nitrite pathway in the SBR. In previous research, inhibition of FA on nitrite oxidizing bacteria (NOB) activity has been revealed and the process control parameters (DO, ORP and pH) exactly indicate the end-point of nitritation. The method was implemented in the SBR achieving stable nitrogen removal via the nitrite pathway from landfill leachate. The degree of nitrite accumulation during the nitritation was monitored along with the simultaneous and advanced removal of organics and nitrogen in the UASB-SBR system. The nitrifying bacteria community was quantitatively analyzed by fluorescence in situ hybridization (FISH) techniques. Batch tests were carried out to investigate the denitritation kinetics of microbial bacteria in the SBR. Experimental results showed that the nitrite pathway could be repeatedly and reliably achieved by synergetic effect of FA inhibition and process control. FISH analysis showed the dominant nitrifying bacteria were ammonia-oxidizing β-Proteobacteria. Relationship between nitrite concentration and nitrite reduction rate followed the Monod-type equation. The maximum specific nitrite utilization rate (k) and half-velocity constant (Ks) were calculated as 0.44 gN gVSS−1 d−1 and 15.8 mg L−1, respectively.