Deammonification at wastewater treatment plants—process development from Austria to the world | Deammonifikation auf Kläranlagen – Verfahrensentwicklung aus Österreich in alle Welt

The DEMON process was developed in Austria in cooperation of research and practice and has been successfully implemented on international level. Nowadays, the system represents the market leader in the field of biological treatment of supernatants from anaerobic sludge treatment. The process is based on deammonification, where about 50% of the ammonia is converted to nitrite. Together with the remaining ammonia, the nitrite is then transferred anaerobically to nitrogen gas by Anammox bacteria. About 90% of the ammonia is eliminated and 10% remains as nitrate. The field of application includes digester supernatants from domestic plants as well as process waters with high ammonia loads from industrial sites. Besides large scale, more and more medium and smaller WWTPs have been equipped with DEMON stages in the recent years. Originally designed as single stage system in SBR – mode, the system is nowadays operated in continuous flow. This change was – as also the replacement of the hydro cyclones by micro screens to retain the slowly growing anammox biomass – a result of process optimization, supported by national research institutions. Since the DEMON process is patented, license fees depending on the influent load are due for implementation. On return, the performance of the system is significantly higher than given in common design guidelines. Not all raw process waters are suitable for the process; therefore an inhibition test is performed in any case to detect potentially adverse impacts of the raw water quality on the ammonia oxidizers and the anammox bacteria. In case of inhibition, piloting or long term lab testing can be applied to adapt and verify pre-treatment measures. The bases for this procedure were developed during various research projects. Sidestream deammonification has still the reputation to be complex and difficult to handle. Hence, the objectives of process optimization have been to improve operation stability beside the increase of system performance. With this background a research project has been initiated together with BOKU-University Vienna. The results confirmed the positive effects of the continuous operation on process stability and also on nitrous oxide emissions. To reach continuous flow without external biomass retention as e. g. hydro cyclones, a mesh separated reactor with one aerated and one non-aerated compartment was applied in comparison to the SBR-setup with a single reactor compartment. Both reactors were operated for six months under the same load conditions using digester supernatant from the Stockerau WWTP. After a stepwise increase of ammonia load, a volume load of 0.6 kg NH₄-N/m³/d was reached. This is comparable to the performance of many full scale reactors. Whereas the SBR-reactor and the mesh separated reactor showed almost identical treatment performance, the continuous flow led to lower air demand and hence lower alkalinity loss due to stripping. The nitrous oxide emissions were decreased by more than 50% by continuous operation. Despite the good results under constant influent characteristics, external biomass retention by e. g. micro screens should be considered to provide additional performance reserve and hence operational safety.