Anammox at low temperature: effectiveness, mechanisms and prospect of embedding immobilization to enhance AnAOB activity

Low temperature critically restricts the widespread application of anaerobic ammonium oxidation (anammox) in wastewater treatment by impairing microbial metabolic activity and nitrogen removal efficiency. To address this limitation, embedding immobilization technology (EIT) has emerged as a strategic approach to in-situ enhance the cryotolerance of anaerobic ammonium-oxidizing bacteria (AnAOB). Here, the efficacy of EIT in revitalizing AnAOB activity under low-temperature, with a focused analysis of its mechanisms, material innovations, and future research priorities are reviewed systematically evaluated. Mechanistic studies reveal that EIT establishes a protective microenvironment, mitigating temperature-induced physiological stress and significantly upregulating key enzymatic activities. Notably, at 10°C, EIT elevates hydrazine dehydrogenase (HDH) and hydrazine synthase (HZS) activities by 67% (0.16 μmol cytochrome-c/(min·mg protein)) and 85% (0.53 nmol/(min·mg protein)), respectively, thereby optimizing nitrogen metabolic flux, achieving stable ammonium removal efficiency (ARE) and nitrogen removal efficiency (NRE) of ~ 80% and ~ 90%, respectively, at 10–13°C. The effectiveness of EIT is intricately tied to the physicochemical and biological properties of encapsulation materials. Future advancements require targeted optimization of material stability, biocompatibility, and substrate permeability, alongside the integration of functional additives (e.g., conductive polymers, inorganic hybrids) to enhance electron transfer and long-term operational resilience. This review provides a theoretical and practical framework for the application of EIT technology in the low-temperature resistance of anammox.