Dual inner circulation and multi-partition driving single-stage autotrophic nitrogen removal in a bioreactor

The single-stage autotrophic nitrogen removal (ANR) process is impeded by a long start-up cycle and unstable operation performance. In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage ANR system. AIPBR start-up period took around 38 days, the total nitrogen removal efficiency was > 85% on day 35. With the decrease of hydraulic retention time and the increase of aeration rate, the nitrogen removal rate increased to 0.85 +/- 0.02 kg-N/m(3)/day. The sludge morphology gradually changed into dark-red floc-coupled granular sludge. Nitrosomonas (9.95%) and Candidatus Brocadia (6.41%) were dominant in the sludge. During long-term operation, AIPBR achieved the dual inner circulation of sewage and sludge and then formed effective dissolved oxygen and sludge partitions to provide a suitable growth environment for various functional bacteria, promote synergy between them, and strengthen the ANR performance.

Automated summary

In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage autotrophic nitrogen removal (ANR) system. The nitrogen removal rate increased with the decrease of hydraulic retention time and the increase of aeration rate, and the sludge morphology gradually changed, providing a suitable growth environment for various functional bacteria and promoting the ANR performance.