Regular articleAchieving high performance completely autotrophic nitrogen removal in a continuous granular sludge reactor

- CANON was successfully developed in a continuous reactor with nitritation granules as inoculum.
- Superior TN removal rate of 2.83 kg N m−3 d−1 was achieved at hydraulic retention time of 0.9 h.
- Improvement of specific TN removal rate was positive related to the EPS accumulation.
- High-throughput pyrosequencing showed a co-culture of Nitrosomonas and Candidatus Kuenenia.

The start-up of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated by seeding nitritation granular sludge in a continuous stirred tank reactor with typical geometry. Nitrogen loading rate (NLR) was increased from 1.5 to 3.3 kg N m−3 d−1, by shortening hydraulic retention time from 2.0 to 0.9 h under oxygen-limiting conditions. An extremely high nitrogen removal rate (NRR) of 2.83 kg N m−3 d−1 was achieved, due to the high specific NRR of huge biomass in the reactor. With the improvement of granular structure compactness, it was believed that the EPS accumulation could be beneficial to enhance nitrogen removal performance of granules. In addition, high-throughput pyrosequencing analysis revealed that a co-culture of aerobic and anaerobic ammonium oxidizing bacteria, affiliated to genera Nitrosomonas and Candidatus Kuenenia respectively, had been established in mature CANON granules, while the growth of nitrite oxidizing bacteria (Nitrospira spp.) was effectively suppressed through substrate competitions between three groups of bacteria. Therefore, a single continuous reactor with granules is applicable to achieve high performance CANON process for treating ammonium-rich wastewater.