Achieving completely anaerobic ammonium removal over nitrite (CAARON) in one single UASB reactor: Synchronous and asynchronous feeding regimes of organic carbon make a difference.

Abstract At least 11% of total nitrogen (TN) remains in the anammox effluent, making it difficult to meet increasingly stringent discharge standards. To overcome this bottleneck, an innovative process to achieve completely anaerobic ammonium removal over nitrite (CAARON) in one single up-flow anaerobic sludge blanket reactor was proposed in this study. The synchronous feeding of acetate at a C/N (nitrite) ratio of 0.6 significantly reduced the nitrogen removal capacity of anammox reactor by limiting the abundance and metabolism of anammox bacteria. In contrast, the asynchronous feeding of acetate optimized the partition of the reactor column into two specific compartments: the lower half favoring anammox and the upper half dominated by DEAMOX (DEnitrifying AMmonium Oxidation). A high TN removal efficiency of 96.2 ± 0.4% and a low effluent TN concentration of 9.3 ± 0.9 mg L−1 were obtained under a high TN loading rate of 9.0 kgN m−3 d−1. The dominant functional microbes in the CAARON process were identified as Candidatus Kuenenia and Thauera , which were responsible for the anammox and denitratation reactions, respectively. Overall, the results in this study provide valuable insight into the coupling of anammox with denitratation, which is a cost-efficient approach for treating ammonium-rich wastewaters. Graphical abstract Unlabelled Image Highlights • A novel CAARON process was achieved for complete ammonium removal over nitrite. • High total nitrogen removal efficiency of >95% was achieved in CAARON process. • High total nitrogen removal rate of 8.6 kgN m−3 d−1 was achieved in CAARON process. • The functional microbes responsible for the CAARON process were identified. [ABSTRACT FROM AUTHOR]