A systematic review of anammox-based nitrogen removal in wastewater: Effects of salinity, pH, and temperature, and the potential of haloalkaliphiles

Anaerobic ammonium oxidation (anammox) has emerged as a sustainable and cost-effective biological alternative to conventional nitrification–denitrification for nitrogen removal from ammonium-rich wastewaters. This review critically examines the influence of three key operational parameters, namely salinity, pH, and temperature, on the performance and stability of anammox systems. These factors are crucial for regulating microbial activity, substrate conversion, and the nitrogen removal efficiency. We synthesized recent findings on the effects of these stressors, highlighting both synergistic and antagonistic interactions and their implications for system resilience. Special emphasis is placed on the adaptability of haloalkaliphilic and marine anammox bacteria, which hold promise for nitrogen removal under extreme conditions, such as those found in alkaline and saline industrial wastewaters, including textile and tannery effluents. The benefits of microbial acclimatization, innovative reactor configurations, and nutrient optimization strategies have also been investigated. Our analysis underscores the potential of integrating haloalkaliphilic microbes into the anammox process to overcome the limitations of conventional systems, thereby advancing robust applications for both mainstream and sidestream wastewater treatment. Although the anammox process demonstrates strong potential, optimizing microbial communities and environmental parameters remains essential for broader practical implementation. To bridge the knowledge gaps and support real-world scale-up, continued interdisciplinary research integrating microbiology, environmental engineering, chemistry, systems biology, and process modelling is vital. • This systematic review synthesizes the effects of salinity, pH, and temperature on anammox-based nitrogen removal efficiency. • Salt concentrations greater than 10 g/L cause osmotic stress and performance inhibition, but acclimatized or marine anammox bacteria show resilience. • pH critically narrows with temperature reduction, and maintaining near-neutral to slightly alkaline conditions maximizes efficiency. • Temperature fluctuations strongly influence microbial community dynamics, affecting process stability. • Haloalkaliphilic anammox bacteria are promising candidates for robust nitrogen removal under saline–alkaline wastewater conditions.