RoKKa

The project "Sewage sludge as a source of raw materials and climate protection at sewage treatment plants" (RoKKa), funded by the state of Baden-Württemberg, pursues the vision of driving forward the trend reversal towards a sewage treatment plant as a biorefinery by linking innovative processes in a value-centered, climate-friendly and participatory manner. By integrating the infrastructures at wastewater treatment plants that already work efficiently for water protection, it will be possible to transfer the approach of wastewater treatment plants as biorefineries across the board and make it permanent.

RoKKa uses a total of six pilot plants at the Erbach (Danube) wastewater treatment plant to demonstrate the production of recyclable materials from the partial flow of sewage sludge treated in a high-load digestion process. Nitrogen and phosphorus recovery is coupled with the production of microalgae. Carbon capture and utilization to a basic chemical is piloted using the example of CO₂ in biogas. As a result of RoKKa, environmental protection goals of wastewater treatment plants can be considered in a multidimensional way in the future (water protection, bioeconomy, climate protection).

Funding period:

08.11.2021 – 31.10.2024

Reference number:

The project aims to demonstrate that it is possible to convert a wastewater treatment plant into a biorefinery. In addition to the goal of wastewater treatment, raw materials are extracted from the wastewater. By avoiding nutrient re-pollution, climate-relevant emissions are reduced, thus contributing to climate neutrality. The aim is to implement the project results on a large scale at wastewater treatment plants. Large-scale implementation supports the state strategy for a sustainable bioeconomy. The recycling of phosphorus and nitrogen reduces the use of fossil raw materials. The recovery of raw materials also leads to a reduction in greenhouse gas emissions by avoiding load surges. The planned combination of innovative processes can contribute to a more intensive circular economy and more climate protection. In addition to the resource efficiency strategy, the project also supports the sustainability and innovation strategy as well as Baden-Württemberg's climate protection goals.

In addition to nitrogen and phosphorus, the filtrate from the high-load digestion contains a large number of micronutrients that can be optimally used directly in the water. In contrast to plants, the microalgae used in the third piloting area of RoKKa have the ability to utilize ammonium directly as a source of nitrogen. The main objective of the piloting is to show whether the filtrate from the high load digestion can directly serve as a source of nitrogen, phosphorus and micronutrients for the microalgae production of beta-1,3-glucans. These special polysaccharides have plant-stimulating properties and can help plants defend themselves against fungal infections such as powdery mildew, which in turn can reduce the use of fungicides.

By integrating this technology into plant protection concepts, the need for copper-based fungicides could be reduced, particularly in the organic cultivation of wine, strawberries, potatoes, vegetables and herbs in Baden-Württemberg. The production of beta-1,3-glucans using microalgae takes place in a two-stage process, which is carried out in closed photobioreactors of the flat-plate airlift reactor type. A module with a working volume of 5 x 25 liters and LED lighting is used. The reactors are connected to each other using a patented process. The cultivation conditions, such as temperature, nutrient concentration and available light per cell or gram of biomass, influence the ingredient profile of the microalgae and enable targeted production. By limiting certain nutrients, primarily nitrogen, beta-1,3-glucans are enriched with a sufficient supply of light and CO₂.