Mitigation of ammonia inhibition in anaerobic digestion of nitrogen-rich substrates for biogas production by ammonia stripping: A review

High ammonia concentration caused by mono-digestion of nitrogen-rich substrates inhibiting methanogens is a challenge in biogas production. Mitigating ammonia inhibition via ammonia stripping has gained considerable attention due to its potential for simple operation, high-performance efficiency, and the production of valuable by-products for industrial and agricultural use. This review article presents a comprehensive overview of current progress in ammonia stripping technologies applicable to anaerobic digestion systems. In addition, recent studies are reviewed, with a focus on operating conditions, ammonia recovery and its utilization, and the effect of ammonia stripping on biogas production. Findings from literature indicate that the performance of an ammonia stripping process largely depends on the pH and temperature of substrate and gas flow rate; hence it requires optimization to attain high efficiency. The advantages and disadvantages of the various ammonia stripping options and their effect on anaerobic digestion conditions, as well as microbial communities, were discussed. Side-stream and post-treatment ammonia stripping from anaerobic digesters have the potential to significantly reduce ammonia concentration to avert ammonia inhibition during biogas production and can be implemented at full-scale. Finally, challenges confronting this technology and future research direction are considered. This review article provides valuable information on the technical application of ammonia stripping in anaerobic digestion to advance the development and implementation of this technology in the digestion of nitrogen-rich substrates.