The switch to phosphorus recovery places high demands on municipalities and wastewater treatment plants. Creating the necessary infrastructure for dewatering, drying and incineration presents sewage treatment plants with far-reaching investment decisions. However, these decisions must be made not only at the individual plant, but also in the overall context of future developments and requirements. Accompanying the construction of the sewage sludge mono-incineration plant of Kommunale Nährstoffrückgewinnung Niedersachsen GmbH (KNRN) in Hildesheim, the SATELLITE project deals with the conversion of the individual sewage treatment plants in southern Lower Saxony and optimized management in the overall network. The upstream and downstream processes of incineration and phosphorus recovery are therefore being examined, taking into account the integration of regional nutrient and energy sources. To support this, a model-based approach is being developed that makes it possible to compare various processes and find an optimum for individual plants or entire plant networks and to establish optimized sludge management in the overall network.
The management objectives here are optimum sludge quality (calorific value, P content) at the optimum time (uniform utilization of incineration) with the lowest environmental impact (CO2e, transport) and a positive balance for the wastewater treatment plants supplying the wastewater.
Background on the project
The SATELLITE project looks at the transition to phosphorus recovery on three levels, each of which has different requirements. At the top level, the overall network of wastewater treatment plants with joint disposal is considered. At the next level, sub-networks of individual wastewater treatment plants and their specific requirements are considered. The lowest level is the individual wastewater treatment plant or an individual process.
As an example, the individual issues are examined on a large and semi-technical scale at various wastewater treatment plants, whereby a distinction is made between regional centers (WWTPs > 50,000 PE) and smaller satellite plants. Using the example of the Hildesheim wastewater treatment plant as a regional center, thermophilic high-load digestion with the inclusion of co-substrates is being investigated on a large scale. Pre-acidification of the primary sludge is also being tested here. In close proximity to the KNRN, the Hildesheim wastewater treatment plant is also investigating the fate of vapor condensates when converting old stand thickeners to partial flow treatment using deammonification.
At several wastewater treatment plants in the district of Nienburg, phosphorus removal via the sludge at the wastewater treatment plant itself is being investigated as a representative of smaller satellite plants. At the Pattensen wastewater treatment plant, the conversion from aerobic sludge stabilization to partial stabilization is being tested on an industrial scale. This makes it possible to utilize the energy potential contained in the sludge when different sludges are digested together. In addition, the separation of primary sludge via a drum screen is also being tested in Pattensen, which makes additional energy potential usable. Sewage sludge drying with sequential vapour extraction for nitrogen recovery in Hildesheim and on-demand fertilizer production in Hünxe are being tested semi-technically as individual processes.
The model region of Nienburg and the wastewater treatment plants located in the district serve as an exemplary sub-network in the SATTELITE project. Here, the flexible dewatering of sludge using a mobile centrifuge and the construction of a joint central digestion system are being investigated. The concept for regional nutrient recycling is also being developed with the construction of a prototype for nutrient forecasting and management in the model region. Logistics studies and sludge management are in the foreground for the entire network. A management tool (OptiNETZ-Tool #live) is being developed for optimized sludge management.
The model-based decision support tool for strategic investment planning (OptiNETZ tool #plan) is a core product of the SATELLITE project across all levels. The tool is based on process models (model modules) that make it possible to easily compare different process chains and incorporate various evaluation variables. They are collected in a module library within the project. Another cross-level product is the energy model, with which an energy optimum can be found by calculating the energy flows on the individual system or in the network.
The decision support tool OptiNETZ-Tool #plan has been completed and has already been successfully used for consulting in two different cases outside the SATELLITE project. For the module library (process models), the processes developed in the RePhoR measure are currently being included in addition to the classic wastewater treatment processes. In various workshops, the first of which has already taken place, the module library and its application are being presented to the outside world. For the development of the prototype of the nutrient management tool, the structure of the balancing and the methodology for forecasting the seasonal nutrient accumulation has been completed. The next step is to implement the software.
The development of the transport container and a logistics concept for the logistics of the entire network has been completed. The management tool for optimized sludge treatment is currently still being developed. The energy model has already been used in the project for decentralized drying in Göttingen and is also being used in Steyerberg.
The acceptance of the co-substrates has now been legally secured (compatibility with water and waste legislation) and the construction has been approved accordingly. The legal opinion prepared may also be useful for other sewage treatment plants with similar problems. The thermophilic high-load digestion system will go into large-scale operation in 2025 following the renovation of an old digester. The conversion of the stand thickeners to partial flow treatment is currently in the implementation planning stage. At the same time, vapour condensates from various plants with sewage sludge drying were examined and in some cases very strong inhibitions on the biology were observed. The handling of this inhibition and a control and regulation concept adapted to the input flow are currently being developed and the operating concept will be tested on an industrial scale once the deammonification has been commissioned. The trials for targeted vapor extraction during sewage sludge drying have been completed and show a high potential for nitrogen recovery, which at the same time reduces the return load for the sewage treatment plant. Whether the ammonia solution created in this way can be used directly as a raw material for fertilizer production is being investigated at the test plant for on-demand fertilizer production.
At the Pattensen sewage treatment plant, the drum screen was successfully used to produce energy-rich primary sludge. The conversion from aerobic sludge stabilization to partial stabilization was also successfully tested. This changeover was accompanied by a saving of around half the basin volume of the aeration system, which continues to be operated in this stable manner.
Some of the tools developed in SATELLITE are already operational and can be used (e.g. OptiNETZ tool #plan). The OptiNETZ-Tool #live management tool will be ready for use at the end of the project. There will be further workshops on the model library for the module library in the course of the project. It can already be used for simple process comparisons and will be fully accessible to the public at the end of the project. The energy model will also be available for consulting purposes after the end of the project. The energy model will also be available for consulting purposes after the project has been completed. The prototype for the nutrient management tool shows the methodology and approach for regional nutrient management and can thus support both nutrient distributors and local authorities in their planning.
The operational optimizations investigated on a large scale in SATELLITE will be introduced and adopted by the wastewater treatment plants (sites of the project partners). They thus form a transferable roadmap that can also be adopted by other wastewater treatment plants. The piloted individual processes will be further developed with the aim of achieving market maturity. The findings on sludge quality, logistics, nitrogen recovery and decentralized drying generated in the project with the participating wastewater treatment plants will be incorporated into the plans for the recycling center.
