Efficient partial denitrification-anammox process enabled by a novel denitrifier with truncated nitrite reduction pathway

Partial denitrification coupled with anaerobic ammonium oxidation (PD-anammox) is a promising technology for cost-effective nitrogen removal from wastewater. Nitrite availability is crucial to anammox performance but often limited by the slow partial denitrification process. Here we report an efficient PD-anammox system driven by the novel denitrifier Bacillus velezensis C1–3 with truncated nitrite reduction pathway. Whole-genome sequencing analysis revealed that the lack of nitrite reductase genes nirS/nirK and norBC in strain C1–3 enabled nitrite accumulation without the need for precise control of carbon dosage. By coupling it with anammox sludge, over 79 % total nitrogen (TN) removal was stably achieved, under a TN loading rate of 660 mg/L/d and a carbon/nitrogen ratio below 1.0. Mechanism explorations indicate that the niche differentiation of C1–3 and anammox bacteria facilitated their mutualism while avoiding nitrite competition. This study demonstrates a novel strategy for establishing efficient PD-anammox process by harnessing the unique metabolic deficiency of denitrifiers, shedding light on the development of stable and sustainable biological nitrogen removal technologies with minimal carbon footprint.