The aim of the project partners Veolia Klärschlammverwertung Deutschland GmbH (VKD), Carbotechnik GmbH, LTC Lufttechnik Crimmitschau GmbH, Pontes Pabuli GmbH and the research institutes Fraunhofer Institute for Ceramic Technologies and Systems IKTS and the Materials Research and Testing Institute MFPA at the Bauhaus-University Weimar is the practical prototype testing and demonstration of an innovative, economically and technically viable process chain for thermal sewage sludge utilization with phosphorus recycling and fertilizer production for the model region “Central German border triangle” of Saxony-Anhalt, Thuringia and Saxony.
The partners are developing and testing an innovative concept that relies on the decentralized incineration of sewage sludge using dust firing on the one hand and processes the sewage sludge ash and the contained phosphorus into marketable fertilizer products by means of the newly developed acid digestion granulation using the Pontes-Pabuli process on the other. The main focus of the developments is on the process-integrated heavy metal separation in the dust firing and acid digestion granulation.
To ensure a rapid transition of the developed technology into application, the DreiSATS project entails the scale-up of corresponding test plants for dust firing with hot gas filtration in Magdeburg (see Figures 1 and 2) and for acid-digestion-granulation using the Pontes-Pabuli process in Markranstädt (see pictures 5 to 8).
Background information on the project
At the pilot plant for dust firing at the Magdeburg site of the project partner Carbotechnik, investigations are being carried out regarding the combustion of sewage sludge and the separation of heavy metals through the addition of additives and hot gas filtration. For this purpose, the existing pulverized fuel firing plant with a thermal firing capacity of 1 megawatt (corresponds to 8,000 t/a of sewage sludge with 25 %-TS) was converted for optimized sewage sludge incineration and extended for heavy metal separation by the additive dosing and hot gas filter modules of the project partners LTC and Fraunhofer IKTS (see Fig. 3).
The Pontes Pabuli plant is located at the Veolia Klärschlammverwertung (Sewage sludge utilization) Deutschland GmbH site in Markranstädt. The planning, implementation and plant operation will be ensured by Veolia and Pontes Pabuli GmbH. The preliminary tests for scaling up the process were carried out at the MFPA in Weimar. The plant has a throughput of 35 kg/h of ash in the input. The output depends on the recipe and is around 100 kg/h of fertilizer granulate.
To evaluate the phosphorus availability and phytotoxicity of the intermediate and fertilizer products, test stands for season-independent and reproducible plant trials were developed and set up at Fraunhofer IKTS (see Fig. 9).
In addition, greenhouse tests for quality monitoring are carried out at Veolia Klärschlammverwertung Deutschland GmbH (Fig. 10).
The conversion work on the pulverized fuel firing pilot plant and the construction of the hot gas filtration and additive dosing modules were completed in 2023. Since then, combustion tests have been running with different sewage sludges on an industry-relevant scale. The aim of these tests is to determine input-dependent process parameters for incineration as well as the addition of additives and hot gas filtration for heavy metal separation.
On March 28, 2022, the P-recycling plant with the Pontes Pabuli process was commissioned on a TRL 6 scale at Veolia in Markranstädt. Following the successful completion of the test phase, the plant has been in the operating phase since October 2022. The aim is to gain extensive knowledge for practical testing and optimization of the process parameters in order to map the scalability of the plant configuration.
As a result, proof of economical and stable sewage sludge incineration with simultaneous recovery of heavy metal-depleted ash for fertilizer applications (see Fig. 4) is provided. The focus is on local and regional customer-specific solutions for thermal sewage sludge utilization. To this end, process parameters for pulverized fuel firing are being optimized and their influence on combustion behaviour and the resulting ash properties evaluated. Furthermore, the laboratory results can be transferred on heavy metal reduction and phosphorus solubilities with the help of additives added during incineration and integrated hot gas filtration to separate the gaseous heavy metals.
Interested customers can have their individual sewage sludge thermally utilized at the pilot plant and determine the ash quality. The results are directly transferable and thus a valuable decision-making aid in the ash utilization strategy or in the implementation of the phosphorus recovery obligation.
During the project, the Pontes Pabuli standard process was further developed into the Pontes Pabuli Flex process. Thanks to the EcoPlus and PerfectClean optimizations, consistently high-quality products with high phosphorus contents can now be produced, regardless of the quality of the input ashes used. This provides site-specific solutions for thermal sewage sludge utilization and phosphorus recycling, taking into account complex ecological and economic conditions.
Standardized evaluation methods for the effect of recyclates and fertilizer products on plant growth are already available at Fraunhofer IKTS for the evaluation of ashes and fertilizer products. These can be used for regular quality control and are essential for the rapid market launch and customer acceptance of recyclates.
The fertilizer granules are tested under operating conditions in outdoor test areas at Veolia in Markranstädt (Figures 11 and 12)