Alternating anoxic/oxic condition combined with step-feeding mode for nitrogen removal in granular sequencing batch reactors (GSBRs)

Alternating anoxic/oxic condition combined with step-feeding mode (AASF) has been reported to be an efficient method for nitrogen removal in granular sequencing batch reactor by our previous work. As carbon/nitrogen (C/N) ratio is one of the key factors impacting nitrogen removal efficiency, batch experiments using granules with a mean size of 1.3 mm under AASF were carried out for nitrogen removal from synthetic wastewater with C/N ratio of 5:1 and 3:1, respectively. It was found that over 90% nitrogen efficiency could be achieved for both C/N of 5 and 3. Furthermore, over 2 months operation was maintained for treating the wastewater with C/N ratio of 5:1 to investigate the long-term stability of granules under the new operational strategy. The results showed that AASF mode in GSBR could achieve over 85% nitrogen removal efficiency with great stability for long-term stability. This indicated that alternating anoxic/oxic condition combined with step-feeding mode is an effective strategy for nitrogen removal even from wastewater with low C/N ratio in granular sequencing batch reactor.

► Alternating anoxic/oxic phase combined with step-feeding was applied in granular SBR.
► Over 90% nitrogen removal was achieved for C/N ratio of 5 and 3 in batch experiments.
► Over 85% nitrogen removal was achieved for C/N ratio of 5 over 2-month operation.
► Granular sludge can maintain long-term stability under the novel operational strategy.