Long-term performance, microbial evolution and spatial microstructural characteristics of anammox granules in an upflow blanket filter (UBF) treating high-strength nitrogen wastewater

Granule formation, microstructure and microbial spatial distribution are crucial to granule stability and nitrogen removal. Here, an upflow blanket filter (UBF) reactor with porous fixed cylinder carriers was fabricated and operated for 234 days to investigate overall performance and the formation mechanism of anammox granules. Results showed that the UBF performed the highest nitrogen removal efficiency of 93.19 ± 3.39% under nitrogen loading rate of 3.6 kg-N/m³/d and HRT of 2 h. The tryptophan-like proteins as the key component in EPS were vital for granules formation. Further 16 s rRNA analysis indicated that SBR1031 with a relative abundance of 40.5% played an important role in cell aggregation. Thus, anammox granules were developed successfully with a two-layered spatial structure where outer-layer was ammonia oxidizing bacteria and inner-core was anaerobic ammonia oxidizing bacteria. Together, introduction of porous fixed cylinder carriers is a valid method to avoid biomass loss and floatation.