Nitrite oxidizing bacteria suppression based on in-situ free nitrous acid production at mainstream conditions

Abstract

The application of autotrophic nitrogen removal processes in the main line of wastewater treatment plants will contribute to achieve its self-energy-sufficiency. However, the effective suppression of nitrite oxidizing bacteria (NOB) activity at the conditions of low temperature and low ammonium concentration (mainstream conditions) was identified as one of the main bottlenecks. In this study, stable partial nitritation at 16 ºC and 50 mg NH4 + -N/L was achieved maintaining inside the reactor free nitrous acid (FNA) concentrations inhibitory for NOB (> 0.02 mg HNO2-N/L), without dissolved oxygen concentration control. The FNA inhibitory concentration was generated by the partial nitritation process, and its stimulation was studied with two different inhibitors: sodium azide and nitrite. The microbiological analysis revealed that, throughout the operational period with inhibitory FNA levels, the NOB populations (dominated by Nitrospira) were effectively washed out from the reactor. This is an advantage that allowed maintaining a good stability of the process, even when the FNA concentration was not enough to inhibit the NOB, taking about 40 days to develop significant activity. The observed delay on the NOB development is expected to enable the establishment of corrective actions to avoid the partial nitritation destabilization. The use of the FNA to achieve a stable partial nitritation process is recommended to profit from the natural pH decrease associated to the nitritation process and from its favoured accumulation at low temperatures as those from the mainstream. In this research study an analysis about the influence of ammonium and alkalinity concentrations was also performed to know in which scenarios the FNA inhibitory concentration can be achieved.

Pilot-scale ELAN ® process applied to treat primary settled urban wastewater at low temperature via partial nitritation-anammox processes

“…Indeed, it was proposed that, instead of the low pH value, the actual inhibitor of both bacterial groups, and NOB, is the free nitrous acid (FNA). However, in the present study, due to the observed negligible nitrite accumulation, the maximum FNA concentration reached was of 0.007 mg HNO2-N/L, lower than the reported inhibitory values for AOB and NOB [29]. The sole pH decrease can be responsible for the inhibition of the nitrification process by provoking the deactivation of nitrifying enzymes and changes in the equilibrium carbonate-bicarbonate [28].…”

Opportunities for rotating belt filters in novel wastewater treatment plant configurations

“…Note that a side effect exists of the addition of the coagulant on the alkalinity, with a consumption of 22 mg IC for each 100 mg of FeCl3. 32 Taking into account that the further PN-anammox step requires a minimum alkalinity-to-ammonium ratio of 1-1.25 g IC per g NH4 + -N, 33 the need for an external bicarbonate addition to avoid acidification in the PN-anammox unit, which considers an ammonium concentration of 67 mg NH4 + -N/L (Table 1), would be much higher if the RBF system is not present.…”

Free ammonia resistance of nitrite‐oxidizing bacteria developed in aerobic granular sludge cultivated in continuous upflow airlift reactors performing partial nitritation

“…Bioaugmentation requires the preexistence of sidestream anammox processes capable of sparing sufficient AOB‐rich sludge to maintain the mainstream dominance of AOB (Cao, van Loosdrecht, & Daigger, 2017; Ma et al, 2016). FNA is more suitable for nitrite‐rich wastewaters such as those in sidestream but not in mainstream applications (Law et al, 2015; Pedrouso et al, 2017). The DO/ammonia ratio control does not suppress K‐strategy NOB for their high affinity to DO (Liu & Yang, 2017); consequently, FA inhibition had to be resorted to (Kowalski, Devlin, di Biase, & Oleszkiewicz, 2019a,2019b).…”