The selective salinity and hydrazine parameters for the start-up of non-anammox-specific biomass SBR

The presence of ammonium (NH₄⁺) in wastewater above the permissible limits leads to undesirable ecological impact and public health concerns. In this study, the anaerobic ammonium oxidizing (anammox) bacteria-mediated nitrogen removal was investigated using a sequential batch reactor (SBR). Effects of different salinity levels were evaluated on the bacterial activity at: mild (below 0.2 g NaCl/L), elevated (18.2 g NaCl/L) and suitable salinity (2–0.5 g NaCl/L) levels mimicking the environmental conditions that are present in real wastewater. Within a suitable salinity period of 0.5–2 g NaCl/L, the highest average total nitrogen removal efficiencies (TNREs) and total nitrogen removal rates (TNRRs) of 67 (± 11)% and 37 (± 29) g N/m³/d, respectively, were achieved. In addition to the salinity tests, the effect of relatively high nitrite levels (> 40 mg N/L) was observed in the reactor resulting in the decrease in anammox activity, but increasing biomass potential for the treatment of high nitrite containing wastewater. Interestingly, the supplementation of hydrazine at 7.5 mg N₂H₄/L indicated enhanced anammox activity with a nitrogen removal rate of 0.7 ± 0.01 mg N/g MLSS/h, while test without hydrazine showed a rate of 0.68 ± 0.06 mg N/g MLSS/h. Therefore, denitrifying activity decreased with the addition of hydrazine, which on the other hand benefits the anammox start-up. Illumina sequencing analysis revealed that the microbial community has changed with the rise of the salinity levels and was dominated with Anaerolineae, Gammaproteobacteria, Clostridia and various key anammox organisms, such as Candidatus Brocadia and Candidatus Kuenenia strains (at 3%). Graphical Abstract: [Figure not available: see fulltext.].