Medium-sized anammox granules achieve the optimal synergism between AnAOB and HDB via nitrite cycle

Abstract

Anaerobic ammonium oxidation (Anammox) is acknowledged as one of the most cost-efficient nitrogen removal biotechnologies from wastewater. Anammox bacteria (AnAOB) tend to self-aggregate to form the granules, which can harbor symbiotic heterotrophic denitrifying bacteria (HDB). However, the dynamics of microbial synergism between AnAOB and HDB in size-fractioned anammox granules are still unclear. This study systematically investigated the bioactivity and bioabundance of highly enriched anammox granules with different sizes by combining specific activity tests, DNA sequencing and bioprocess modeling. The medium granules of 1.0–2.0 mm were the most distributed size in the whole reactor with the volumetric percentage of 55.7 ± 7.5%. The medium-large granules held the highest total nitrogen removal rate of 1.10 ± 0.05 mmol N2/(g VSS·h), where AnAOB and HDB co-existed with anammox contributing 93.1 ± 0.5% to N2 production. Candidatus Kuenenia, Denitratisoma and Anaerolineaceae were the only three genera that could be highly detected, dominating 52.5–65.6% of microbial communities. Kuenenia (AnAOB) only held the positive correlation with Denitratisoma (HDB) by co-occurrence network analysis. Furthermore, AnAOB were proved to have a synergistic growth with HDB, form the nitrite cycle, and maximize at the medium size by joint analysis of denitrifying functional gene and steady-state simulation. Collectively, we proposed that the medium-sized anammox granules of 1.0–2.0 mm could reach the optimal synergism between AnAOB and HDB via nitrite cycle. This work could provide insights into the microbial synergism in anammox granules and benefit the development of size-control strategy for anammox operation.