Rapid enrichment of anaerobic ammonia oxidation bacteria by combining low nitrogen strength with microbial viability

Abstract

The rapid enrichment of anaerobic ammonia oxidation (anammox) bacteria (AnAOB) is challenging owing to their slow growth rate. Substrate supply strategies influence the AnAOB yield and anammox performance. In this study, a feeding strategy for low nitrogen strength with constant substrate concentrations and a hydraulic retention time decreasing over a gradient was investigated in an up-flow sludge blanket reactor. With increasing nitrogen load, the nitrogen removal rate increased from 0.2 to 6.3 kg-N m⁻³ day⁻¹, and the ratios among ammonium utilization, nitrite depletion, and nitrate production changed from 1:2.62:2.03 to 1:0.99:0.17. Excessive extracellular adenosine triphosphate (ATP) release occurred under famine conditions, whereas intracellular ATP accumulated under feast conditions. Rapid AnAOB growth, with a doubling time of 2 d, was associated with high microbial viability. A combined strategy of low nitrogen strength and microbial viability was proposed for the rapid growth of AnAOB. These results demonstrate accelerated process start-up and help us to understand anammox metabolism in depth.