The mechanism and prospect of exogenous promoters enhancement Anammox at low temperatures: a review.

The anaerobic ammonium oxidation (Anammox) process has revolutionized nitrogen removal in wastewater treatment with its exceptional cost-effectiveness and carbon-neutral characteristics. Nevertheless, the intrinsic psychrophilic sensitivity of anaerobic ammonium-oxidizing bacteria (AnAOB), particularly their rapid metabolic suppression below 15 °C, poses a critical bottleneck for sustainable implementation in cold-climate regions. Recent advancements in exogenous stimulation strategies offer promising solutions to this challenge, with particular emphasis on iron supplementation and cryogenic activity regulators (CARs) due to their non-invasive operational compatibility and mechanistic versatility. This review provides a comprehensive analysis of the operational performance, functional enzyme activity, and microbial abundance associated with the use of iron and CARs as exogenous promoters in low-temperature Anammox system. Building upon current limitations in single-factor approaches, the dual-modulation strategy integrating iron-chelated CARs complexes are proposed, which leverages the complementary benefits of iron-mediated metabolic activation and CARs-induced cryoprotection, potentially enabling year-round Anammox operation under low temperatures. This mechanistic-to-applied review provides critical insights for advancing Anammox implementation in circular economy-driven wastewater infrastructures under climate change scenarios.