Synergism and physiological characteristics of glycogen accumulating organisms (GAOs) in anaerobic ammonia oxidation based (anammox-based) systems: Mechanisms and prospects

The recently proposed glycogen accumulating organisms (GAOs)-driven anammox process, which terminates nitrate (NO3–) reduction to nitrite (NO2–) without external carbon source addition, has emerged as a promising alternative for supplying NO2– to anammox bacteria. The endogenous partial denitrification anammox (EPDA) process demonstrates superior nitrogen elimination efficiency, cost-effectiveness, and operational stability in low C/N wastewater treatment, concurrently mitigating greenhouse gas releases. This comprehensive review presents and discusses an in-depth analysis of the notable progress in EPDA, covering the physiology and biochemistry of diverse GAO-lineages under specified conditions, intricate microbial interactions and metabolic pathways shared between GAOs and anammox bacteria, and appropriate process modifications. Strategies for sludge morphology, carbon content, and spatial distribution of functional bacteria are discussed in detail to regulate the metabolic activity of EPDA. Future research needs to focus on balancing the competitiveness between functional consortia such as GAOs, phosphorus accumulating organisms (PAOs) and anammox bacteria in the synergetic system, and countermeasures to deal with the effects of adverse conditions on nutrient removal performance of the EPDA-based processes.