Innovative biogas process for treating ammonia-rich wastes

One of the main causes for imbalance and low substrate utilization in Danish biogas plants is the high ammonia load. Ammonia is mainly inhibiting acetate-utilizing (aceticlastic) methanogens. There is however, another metabolic pathway, the acetate oxidation pathway, where acetate is oxidized by syntrophic acetate oxidizing bacteria (SAO) to hydrogen and carbon dioxide, followed by hydrogenotrophic methanogenesis, which is much less liable to ammonia inhibition. Up to now, six SAO bacteria have been identified and five of them were classified as acetogenic bacteria. Acetogenic bacteria are following the reductive Wood-Ljungdahl pathway to produce acetate as basic end-product. Acetogenic SAO bacteria, under high ammonia conditions, use reversed Wood-Ljungdahl pathway to syntrophically convert acetate to methane in association with hydrogenotrophic methanogens. These findings are a strong indication that reversed Wood-Ljungdahl pathway of SAO bacteria has significant role in methanogenesis of high ammonia containing waste.
In the current project we’ll develop a new approach to avoid or counteract ammonia inhibition and optimize the anaerobic digestion of ammonia-rich wastes. The main objective of the project is to establish a process promoting acetate oxidation, for optimal digestion of ammonia rich waste. A pilot scale bioreactor digesting ammonia-rich wastes will implement, for further process development.