An innovative circular economy (CE) system was implemented at the wastewater treatment plant (WWTP) in Brunswick. The performance of the CE system was evaluated for 4 years: the thermal pressure hydrolysis enhanced the methane production by 18% and increased the digestate dewaterability by 14%. Refractory COD formed in thermal hydrolysis and increased the COD concentration in the WWTP effluent by 4 mg L−1 while still complying with the legal threshold. Struvite production reached high phosphorus recovery rates of >80% with a Mg:P molar ratio ≥0.8. Nitrogen was successfully recovered as ammonium sulfate with high recovery rates of 85–97%. The chemical analyses of secondary fertilizers showed a low pollutant content, posing low risks to soil and groundwater ecosystems. The total carbon footprint of the WWTP decreased due to enhanced biogas production, the recovery of renewable fertilizers and a further reduction of nitrous oxide emissions. Using green energy will be crucial to reach carbon neutrality for the entire WWTP.

This report summarises the theoretical design of a degasification plant to recover ammonia and carbon dioxide from organic residues, such as agricultural digestates, manure and municipal/industrial wastewater. Heat and water management had been identified as one crucial factor to optimise during this research. The chemical and physical parameters reveal the high tendency of ammonia towards water phase and underline the difficulty in ammonia stripping. Besides temperature, the volumetric gas-liquid ratio had been identified as most important factors. Regarding pH-value it had been observed, that a further increase is not sufficient once pH 9 is reached. Applied absolute pressure also has been identified of lower importance, compared to temperature and volumetric gas-liquid ratio. The latter three parameters are influencing evaporation and heat management in the desorption stage. A design model from literature according to Onda showed good correlation with the practical experiments including packings. Other column fillings as cones lead to operational problems. The understanding of the exact relations in column design are further used to design a cost-efficient process with low carbon footprint. The practical tests, as such, were reproducible, however the batch operation and limitations in the column design resulted in a limited transferability towards large scale plants. In terms of the absorption stage, the pilot needs to be further optimised to reach sufficient recovery rates. An absorption of ammonia and carbon dioxide under use of gypsum is favoured to also recover carbon dioxide and to avoid sulfuric acid dosing. In that term further tests and optimisation is needed, to have a fully quantifiable pilot system. The integration of a measure-control system is a further development step. In conclusion, the degasification process with low pressure (vacuum) reveals benefits compared to conventional air stripping in terms of heat management and the necessary gas-liquid-ratio, which has effects on column diameter and eventually column height. The necessity of aggressive chemicals dosage (as caustic in desorption) or acid (in absorption) is in view of the authors not given, hence cheap and safe alternatives (e.g. CO2 stripping) and gypsum dosage as alternative sulphur source work sufficient.