Ammonia inhibition can be a major problem during anaerobic digestion of manure and municipal and industrial sludges. Anaerobic digestion is sensitive to higher NH3-N concentrations, which are inhibiting and at certain levels even toxic for methanogen bacteria. The Nijhuis Ammonium Recovery (AECO-NAR) system can solve this problem and removes ammonium from digestate or other substrate for digestion. The AECO-NAR is a physical-chemical process based on stripping of ammonia. The ammonium is recovered as ammonium sulphate, which can be used as a fertilizer for agricultural purposes. The AECO-NAR was proven to be a robust process with a stable ammonium removal efficiency of 85–90% for anaerobic digested manure, municipal and other organic waste waters. The cost effectiveness mainly depends on the concentration of NH4-N in the influent, scale of the installation, the availability of residual heat and the local value and market for ammonium sulphate. Above 2 g/l NH4-N the AECO-NAR system is competitive and at higher NH4-N concentrations more cost efficient compared to other state of the art nitrogen removal technologies and ranges between 1 and 3 €/kg N.