Comparing the nitrogen removal performance and microbial communities of flocs-granules hybrid and granule-based CANON systems

Flocs and granules tend to coexist in a single reactor. Granules can improve microbial retention capacity, however, the role of flocs in the CANON reactor remains unclear. The changes in the nitrogen removal performance and microbial communities between flocs-granules hybrid and granule-based systems were studied in this experiment. With a reduction in the flocs ratio (35% -> 10%), the nitrogen removal performance deteriorated. The average nitrogen removal efficiency and rate dropped from 81.4% to 67.2% and from 0.225 to 0.174 kg/(m(3).d), respectively. The contribution of heterotrophic denitrifying bacteria decreased from 13.5% to 1%, leading to changes in the nitrogen removal pathways between the systems. Furthermore, the activities of anaerobic and aerobic ammonium oxidizing bacteria declined dramatically, which weakened the nitrogen removal performance. Thus, the hybrid system with a flocs ratio near 35% is recommended for use in a CANON reactor. (C) 2019 Elsevier B.V. All rights reserved.