1 August 2023

Six scientific and practical partners have been working for two years on the question of whether a mixture of pyrolysed sewage sludge and biomass can represent a sustainable alternative to the mono-incineration of regional sewage sludge. In addition to engineering research, the practical problems and cross-cutting municipal issues are being analysed from an administrative science perspective.

The two-week construction of the pyrolysis plant on the site of the Bode-Wipper wastewater association in Bleicherode was successfully completed at the end of July. On 1 August, the handover was celebrated with representatives from politics, municipal organisations and association partners. The pyrolysis plant from Nordhausen University of Applied Sciences, which is worth around €1 million, is fully integrated into the workflow of the Bleicherode wastewater treatment plant (AWZV Bode-Wipper).

Within the project, it is planned to apply the innovative mixture #CarboMass to the potash dump in Sollstedt in order to green it. The sewage sludge will be treated using the pyrolysis process. In contrast to the classic co-incineration or mono-incineration of sewage sludge, the pyrolysis process retains the valuable nutrient phosphorus in the sewage sludge. The extent to which this is available to plants without further processing steps and how the physical, chemical and biological properties of the substance behave over time under the weather conditions will be investigated as part of the upcoming field trials.

Initial positive findings on the plant availability of the bound phosphorus were provided by the planting trials on a laboratory scale. The scientific team at Nordhausen University of Applied Sciences (ThIWert - Thuringian Innovation Centre for Recyclable Materials) will continue to support the commissioning of the pyrolysis plant. The partner IMM (Industrieabbrüche und Metallrecycling Menteroda GmbH) will provide space on the stockpile for the potential soil substitute #CarboMass. Sewage sludge is supplied by the partners AWZV Bode-Wipper and, for comparison, also by Wasserverband Südharz. The district of Nordhausen provides the biomass and, together with the town of Bleicherode, supports the IPMG (Institute for Public Management and Governance at Nordhausen University of Applied Sciences) in analysing potential inter-municipal collaborations.

From an engineering perspective, this is a great success, says Professor Uta Breuer: "The #CarboMass project was designed to show that sewage sludge can be treated sustainably and used for sustainable purposes. With the construction and commissioning of the pilot pyrolysis plant, we have taken an important step towards realising this promise, which we are proud of. Further investigations will show whether it is ultimately possible to close the cycles with the waste product sewage sludge as well."

"From a legal perspective, we cannot solve the recycling of sewage sludge regionally," says Professor Elmar Hinz. "However, we can draw attention to problematic legal framework conditions when scaling up this idea and thus bring about a rethink and, in the long term, perhaps also a change in the law."

So can a regional and recyclable solution for recycling sewage sludge be found? So far, it has been shown that the technology can show ways to utilise sewage sludge and make it viable. However, solutions need to be developed at federal level with regard to legal anchoring.