The influence of aeration control and temperature reduction on nitrogen removal and microbial community in two anammox-based hybrid sequencing batch biofilm reactors

Abstract

BACKGROUND: Two hybrid biofilm reactors, an integrated fixed-film activated sludge–sequencing batch reactor (IFAS-SBR) and a hybrid SBR with a mixture of activated sludge and granules, were used to reach enhanced nitrogen removal based on the anaerobic ammonium oxidation (anammox) process under intermittent aeration. RESULTS: IFAS-SBR reached a more stable performance after a rapid start-up period of 25 days, and it showed a more reliable performance than the other reactor. The highest nitrogen removal efficiency (NRE) was up to 99% based on NH4+-N concentration and 91% based on total nitrogen concentration (TIN). A nitrogen removal rate of 0.01 to 0.15 kgN m−3 d−1 was achieved throughout the operation based on the TIN. The set-point of maximum dissolved oxygen (DO) at the peak of each aeration cycle was maintained at 1.2 ± 0.1 mg L−1. The optimum working range for daily average DO concentration was 0.2–0.7 mg L−1. Cold temperatures caused a decline of NRE, but NRE > 50% for temperatures above 13 °C was achieved. CONCLUSIONS: Results implied a higher abundance of Candidatus brocadia species of anammox bacteria in the biofilm samples and Denitratisoma genus in the flocs. The most substantial contribution of shared taxa among all samples at class level was Betaproteobacteria and Gammaproteobacteria, and the least abundant class was Nitrospira. Overall, results implied that IFAS-SBR is a robust configuration for anammox-based nitrogen removal in sidestream, and controlled intermittent aeration could suppress nitrite oxidation and help to regain system efficiency.