The IntenKS project, funded under the European Horizon 2020 programme (call‑number 02WCL1470A‑G), was carried out from 2019 to 2021 by a consortium of German companies and research partners. The consortium comprised Aqseptence Group GmbH (AS) in Aarbergen, Oswald Schulze Umwelttechnik GmbH (OS) in Gladbeck, and HST Systemtechnik GmbH & Co. KG (HST) in Meschede. AS coordinated the overall project management and stakeholder engagement, OS operated the pilot‑scale treatment plant and performed the laboratory and pilot experiments, while HST supplied the thermodynamic hydrolysis (TDH) and hydrothermal carbonisation (HTC) equipment and provided technical expertise on process optimisation. The project team included scientists and engineers such as Qi Liu, Sophia Keller, Florian Bleffert, and senior researchers Dr. Jiansan Zhang and Dr. Jürgen Oles, who led the experimental design and data analysis.
The main scientific objective was to adapt thermal sludge‑treatment technologies to the specific characteristics of Chinese sewage sludge, which typically contains a high inorganic fraction, a large proportion of excess sludge, and low specific methane yields. The research focused on two thermal processes: thermodynamic hydrolysis (TDH) and hydrothermal carbonisation (HTC). In the TDH experiments, the temperature, residence time, and pre‑hydrolysis pH were identified as the key variables. Within the temperature range of 120 °C to 175 °C, the release of soluble chemical oxygen demand (COD) – measured as the CSB‑free fraction – increased linearly from 27 % to 58 %. Correspondingly, the dewatering performance improved by up to 14 percentage points, and the anaerobic digestibility of the pre‑treated sludge rose between 30 % and 50 %. The residence time required for effective hydrolysis decreased with temperature: at 160 °C a 30‑minute hydrolysis was sufficient, whereas at 120 °C 50 minutes were needed. Raising the pre‑hydrolysis pH to 11 boosted the specific biogas production by 20 % compared with neutral conditions. Continuous pilot‑scale runs confirmed the laboratory findings and quantified the mass reduction of the dewatered sludge, which ranged from 38 % to 55 % for temperatures between 120 °C and 160 °C – values lower than those obtained with hydrothermal carbonisation.
HTC experiments demonstrated that the carbonised product exhibited a higher mass‑reduction efficiency (up to 60 %) and a higher calorific value than the TDH product. However, the HTC process water contained higher concentrations of refractory COD and required additional treatment. Both TDH and HTC process waters were characterised for soluble nitrogen species, and laboratory studies showed that aerobic treatment could remove 15 % to 20 % of the organic load (COD/DOC). Nitrification and denitrification steps were able to recover nitrogen and reduce the need for fossil‑fuel‑based energy inputs. The pilot plant also evaluated the impact of process water on subsequent anaerobic digestion, revealing that the presence of hydrolysis filtrate could inhibit methanogenesis unless pre‑treated by aerobic or electrochemical methods.
In addition to the technical investigations, the project performed a comprehensive policy analysis of China’s regulatory framework for sludge management, identifying gaps in the current legislation and proposing measures to facilitate the adoption of advanced thermal technologies. The findings were disseminated through peer‑reviewed publications and stakeholder workshops, providing a roadmap for German companies to enter the Chinese market and for Chinese regulators to support sustainable sludge utilisation. The IntenKS project therefore delivered both validated process data and actionable policy recommendations, bridging the gap between German technology expertise and the specific needs of China’s wastewater sector.