Ever scarcer raw materials, the challenges of climate change, and a steadily growing world population: in the long term, there is no way around using existing resources more sustainably and efficiently. This can succeed, among other things, if nutrient and valuable material cycles in agricultural production are closed again and all raw materials and products remain in use for as long as possible. This also includes seeing residual materials as a valuable source of raw materials. The RUN cooperation project is concerned with the task of developing innovative recycling processes for biowaste and domestic wastewater and thus re-closing the material cycles between urban and rural areas.
In loose succession, the series "Heavyweights of Research" presents outstanding projects with a financial volume of at least 350,000 euros for apparatus-based research or 150,000 euros for non-apparatus-based research. In 2020, scientists at the University of Hohenheim acquired a total of 33.8 million euros in third-party funding for research and teaching. For RUN, the research teams at the University of Hohenheim receive around 680,000 euros in funding as part of the BMBF's "Agricultural Systems of the Future" program. This makes RUN a research heavyweight.
Around three-quarters of Germans live in cities and consume food there that was produced in the countryside. This has created production chains in which nutrients and valuable substances are transported from one place to another and ultimately lost for the most part with waste and wastewater.
This is where the RUN cooperation project comes in. RUN stands for Rural Urban Nutrient Partnership. In this interdisciplinary research project, partners from science and practice are pursuing the long-term goal of making agricultural systems more sustainable and climate-friendly while saving resources and energy.
This requires new technical, urban planning, and logistical structures in which the separation, processing, conversion, and return of nutrients to the cycle go hand in hand at various levels. But it also means that society needs to change its consumption behavior.
Explanatory video on the RUN project (in German)
Closing loops, conserving resources, connecting urban and rural areas
The core idea of RUN is to extract the nutrients contained in biowaste and domestic wastewater in order to produce fertilizers or recyclable bioplastic film and plant charcoal. In other words, products that can be used in agriculture to grow fruit and vegetables, for example.
These are sold at the weekly market in the city, then processed and eaten by the residents. In the process, reusable waste and wastewater are produced. In this way, a closed-loop system is created between farmers and city dwellers, with valuable nutrients and recyclable materials being used multiple times.
Designer fertilizer and plant charcoal being tested
Before this can happen, however, the necessary technologies must first be developed. To this end, researchers from the University of Stuttgart are first testing various methods of recovering and processing biowaste and domestic wastewater in laboratory experiments.
The results are so-called designer fertilizers and plant charcoal, which are then studied by Dr. Sabine Zikeli from the Center for Organic Farming at the University of Hohenheim (ZÖLUH) and her team. "The fertilizers produced are mostly struvites, which primarily contain phosphate, magnesium, and ammonium that have been extracted from the sewage sludge."
"The residues of the sewage sludge become plant charcoal through carbonization. This is very porous and can store water and nutrients in its cavities, which it then releases to plants as needed," Zikeli added.
Designer fertilizers must be efficient and safe
To always have consistent and controlled conditions, she works with plants in pots in the greenhouse: "We use ryegrass for our experiments. This has an advantage over lettuce, for example, in that we can harvest it several times, because some fertilizers dissolve slowly in the soil and release their nutrients only gradually."
To do this, the researchers just cut off the leaves of the plants. The grass then simply grows back. In this way, they can record at different harvest times how much nutrient the plants have taken up and how their biomass has changed. From this, the availability of the nutrients can be calculated and the efficiency of the designer fertilizers determined. The team also determines whether any undesirable substances, such as pollutants, are also taken up by the plants.
This is important because the designer fertilizers must, of course, be able to be used in agriculture without any concerns. "Struvites have the advantage that they are very clean and contain virtually no contamination with heavy metals, for example," Zikeli stated. "And of course, these fertilizers are also subject to fertilizer regulations."
Majority of farmers view closed-loop idea positively
The fact that the issue of safety also plays a major role among farmers can also be confirmed by Prof. Dr. Christian Lippert from the Institute of Agricultural Management: "For farmers, it is important that the fertilizer is free of pollutants, heavy metals, and bacterial contamination - and, of course, fulfills its task of supplying plants with the necessary nutrients."
"In principle, the majority of the farmers surveyed are positive about the idea of extracting nutrients from domestic wastewater and kitchen waste," was the summary of a workshop held at the start of the project. However, a number of questions still needed to be clarified, ranging from quality and price to social acceptance of the fertilizers. After all, without them, the fruit and vegetables produced could not be sold.
Promoting dialog between all stakeholders in the real lab
For this reason, research at RUN will not be conducted exclusively in research laboratories, but the project will be implemented as a real laboratory: "The plan is to try out a recycling plant as a pilot plant and demonstration in a real urban neighborhood," said Carolin Callenius from the Research Center for Global Food Security and Ecosystems. "On the one hand, this allows the laboratory experiments to be tested on a larger scale at the level of an urban neighborhood, and on the other hand, it allows the recycling idea to be tested for its practicality under real-time conditions."
The starting point is the "basic materials" of domestic biowaste and domestic wastewater. Research is still being conducted into suitable innovative logistics systems for transporting the material flows. At present, however, it seems promising to install a shredder for kitchen waste directly in households and to use vacuum lines to transport the waste away. These would then also discharge the wastewater. There is another idea for the material flow of green waste, which is also to be collected and processed: an on-demand service by local parcel delivery services is being considered for this.
An additional information and experience room has been set up to make RUN's research tangible and understandable for citizens. Here, all aspects of nutrient recycling are presented and communicated, from nutrient production in households to reuse in agriculture. Questions, concerns, and needs of the population will be answered in dialog events and will be incorporated into the project planning.
A pilot plant with a complementary experience area is very important for the success of the project: The cooperation partners can identify possible needs, requirements, or barriers that might exist towards products made from recycled waste and wastewater in a constant exchange with all stakeholders, such as farmers, engineers, urban planners, administrators, decision-makers in ministries, and citizens.
These are then included in the research at an early stage so that socially viable solutions can be developed. After all, in the end, everyone should derive a benefit from the cycle and share it in the long term.
RUN is one of eight projects of the research project "Agricultural Systems of the Future" as part of the "National Research Strategy BioEconomy 2030." It is funded by the German Federal Ministry of Education and Research (BMBF) with a total of 4.2 million euros, of which more than 680,000 euros is going to the University of Hohenheim. The project started on 1 April 2019, and is initially scheduled to run for three years.
The project is coordinated by Prof. Dr.-Ing. Martin Kranert from the Institute for Sanitary Engineering, Water Quality and Waste Management at the University of Stuttgart (ISWA). Other project partners are the Technical University of Kaiserlautern, the University of Heidelberg, the Karlsruhe Institute of Technology (KIT), the Thünen Institute in Braunschweig, as well as two consulting engineering firms as practice partners and two associated partners.
