Rapid enrichment of anammox bacteria linked to floc aggregates in a single-stage partial nitritation-anammox process: Providing the initial carrier and anaerobic microenvironment

Abstract Rapid enrichment of anaerobic ammonia oxidation bacteria (AnAOB) is highly associated with the granulation process; however, the interactive mechanism remains unclear, especially for the initial granulation process. A single-stage partial nitritation-anammox (PN/A) bioreactor combined with granular/floc sludge was operated for 400 days. During the experimental period, the nitrogen removal rate increased from 0.60 to 1.21 kg N m−3 d−1, and the nitrogen removal capability improved primarily during a transition period (days 200–250), which was accompanied by a particle size increase and AnAOB proliferation (4.9 ± 1.7 days). Moreover, as observed by the biomass physio-morphology, the size distribution, and the microbial community shift, small flocs (