Ammonia-Induced Inhibition and Its Alleviation Strategies in Anaerobic Digestion Ecosystems

Ammonia, while an essential component in anaerobic digestion, can become toxic at high concentrations, adversely affecting microbial communities and biogas production. Ammonia exists in various forms in anaerobic digestion systems, and different forms of ammonia induce different toxic mechanisms and toxicity levels. Free ammonia is more toxic to anaerobic microorganisms, especially methanogens. The mechanisms of ammonia inhibition on anaerobes encompass both direct chemical interactions between ammonia and microbial cells, and indirect effects of ammonia on the biochemical pathways crucial for energy generation. Microbial communities may employ diverse physiological strategies to tolerate toxic ammonia, such as balancing the intracellular pH, producing osmotic-compounds, and adjusting energy metabolic pathways. Various approaches can be adopted to alleviate ammonia inhibition, such as the control of suitable environmental conditions and the development of advanced biological methods (such as acclimation and bioaugmentation). All these knowledge and approaches can benefit the management of ammonia inhibition in anaerobic digestion and the improvement of system performance.