Diversity and dynamic response of anaerobic ammonia oxidation granular sludge

Red anaerobic ammonia oxidation (Anammox) granular sludge (AnGS) has been reported in successfully operating Anammox systems, and its color is associated with sludge activity. However, in long-term operating systems, AnGS exhibits different sensory colors, physical structures, community structures, and denitrification performance, but the relationship between them has not yet been elucidated. The AnGS of the Anammox system, which has been in operation for more than a decade, can be divided into two main categories: red and white. The specific Anammox activity (SAA) in conventional red AnGS increased continuously as the particle size increased from <0.51 mm to 6.02 ± 0.84 mm. The SAA of white AnGS were slightly lower than those of red AnGS with similarly-size granules but significantly higher than AnGS with smaller red granules. Compared with red AnGS, the extracellular polymeric substances of white AnGS were significantly reduced, mainly due to the higher intracellular iron content, resulting in lower heme c concentration. Thus, heme c may prove not to be an evaluative tool for measuring Anammox activity. Red and white AnGS, whether through self-aggregation or adsorption by hydroxyl apatite and other carriers, will face the fate of internal voids during particle size growth. White AnGS exhibited a more complex microbial community than red AnGS. Candidatus Brocadia was abundant in red AnGS and the abundance increased with increasing granule size. Candidatus Kuenenia and Candidatus Jettenia made significant contributions to denitrification in white AnGS. This study provides a new perspective on particle selection for anammox engineering applications.