Granular anammox biomass in warm climate regions: Exploring its feasibility for transitioning from sidestream to mainstream anaerobic effluent treatment

Three bench-scale up-flow reactors (R1, R2 and R3) were employed to enrich, transfer, and adapt granular anammox biomass (GAB). To perform the anammox process, an enriched portion of the GAB was transferred from sidestream (R1) to mainstream (R2) conditions. In R2, the nitrogen concentration, comprising ammonium (NH4+-N) and nitrite (NO2−-N), was gradually decreased from 232 to 50mgN/L, accompanied by a temperature reduction from 37 to 25 °C. A high nitrogen removal efficiency (NRE) of 87.3 ± 4.7 % was obtained in R2 with a nitrogen loading rate of 1.00–1.40kgN/(m3∙d). Then, R3 was inoculated with GAB from R2 to test the potential of the partial nitritation-anammox (PNA) process. Therefore, the addition of NO2−-N was discontinued to allow its production via automated intermittent aeration (AIA). Conversely, the PNA process was not stablished. The biomolecular analysis revealed a high relative abundance of the anammox Candidatus Brocadia bacteria (29.4 %), but no ammonium-oxidizing bacteria (AOB) were identified in R3. When NO2−-N supplementation was reestablished within AIA in R3, the NRE reached 55.1 ± 7.9 %. However, the absence of AOB, in conjunction with the AIA mode, limited the start-up of the mainstream PNA process. The enriched GAB, cultivated under sidestream conditions, showed resilience to reductions in both temperature and nitrogen concentration encountered in mainstream conditions. This underscores the potential effectiveness of this approach in warm climate regions.