Biomass aggregation influences NaN3 short-term effects on anammox bacteria activity

Abstract

Abstract:The main bottleneck to maintain the long term stability of the partial nitritation-anammox processes, especially those operated at low temperatures and nitrogen concentrations is the undesirable development of nitrite oxidizing bacteria (NOB). When this occurs, the punctual addition of compounds with the capacity to specifically inhibit NOB without affecting the process efficiency might be of interest. Sodium azide (NaN3) is an already known NOB inhibitor which at low concentrations does not significantly affect the ammonia oxidizing bacteria (AOB) activity. However, studies about its influence on anammox bacteria are unavailable. For this reason the objective of the present study was to evaluate the effect of NaN3 on the anammox activity. Three different types of anammox biomass were used: granular biomass comprising AOB and anammox bacteria (G1), anammox enriched granules (G2) and previous anammox granules disaggregated (F1). No inhibitory effect of NaN3 was measured on G1 sludge however the anammox activity decreased in the case of G2 and F1. Granular biomass activity was less affected (IC50 90 mg/L, G2) than flocculent one (IC50 5 mg/L, F1). Summing up not only the granular structure protects the anammox bacteria from the NaN3 inhibitory effect but also the AOB act as a barrier decreasing the inhibition.

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

“…In the present study, performed at laboratory scale, a NOB inhibitor (sodium azide) acted as "activator" allowing the establishment of the inhibitory FNA concentrations for NOB activity suppression. The sodium azide effects on the anammox activity have been previously assessed in batch experiments providing different results depending on the state of aggregation of the biomass [29]. The batch tests indicated that a concentration of 5 mg NaN3/L (used in the present study) caused a 50% inhibition on the flocculent anammox biomass activity and only a 15% on the granular one.…”

“…The batch tests indicated that a concentration of 5 mg NaN3/L (used in the present study) caused a 50% inhibition on the flocculent anammox biomass activity and only a 15% on the granular one. Moreover, this inhibition was reversible in both cases [29]. Although, the application of sodium azide at laboratory scale allowed enhancing the FNA inhibition mechanism, another strategy must be applied to promote the nitritation process at full scale, to avoid the use of sodium azide (due to its toxicity).…”

Nitrite Accumulation at Low Ammonia Concentrations in Wastewater Treatment Plants

“…The free nitrous acid (FNA) concentration threshold value to suppress NOB is ~0.02 mg HNO 2 -N/L [4,9]. NOB suppression can also be achieved using an intermittent supply of DO combined with an anaerobic ammonium oxidation process [10], although selective chemicals such as hydroxylamine (NH 2 OH) [11], sodium azide (NaN 3 ) [8,12], sulfides, salts, heavy metals, chlorate, cyanate, halide, hydrazine, and organic chemicals [13,14] have also been used. Tests with toxic compounds found that NOB were more affected than AOB at an azide concentration of 0.3µm/L, and nickel and copper were equal or more toxic to Nitrosomonas sp.…”