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The prices of mineral fertilizers are rising. The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB is working on alternative production methods: Researchers have developed various processes and demonstrated them on a pilot scale to recover nutrients from locally available waste streams. Fertilizers ready for immediate use can be obtained from digestion residues, manure, and wastewater, as the institute will show at IFAT in Munich in early May. This circular approach strengthens supply security and protects water bodies and the climate.
The war in Iran is not only leading to higher costs for gasoline and kerosene. Fertilizer prices have also already risen by up to 30 percent, which will affect food prices in the foreseeable future. This is because not only gas and oil, but also nearly 30 percent of all nitrogen- and phosphorus-containing mineral fertilizers traded worldwide are shipped through the Strait of Hormuz. Nitrogen-containing synthetic fertilizers such as ammonia and urea, which is produced from it, are manufactured in the Gulf States using natural gas. In this process, molecular atmospheric nitrogen (N₂) is converted into ammonia (NH₃) under high pressure and at high temperatures.
The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB will show at IFAT in Munich from May 4 to 7 that fertilizers can also be produced without fossil fuels. Researchers are investigating how nitrogen and phosphorus can be recovered from nutrient-rich waste streams. Various methods have been developed in a wide range of projects to recycle essential mineral salts from liquid manure, digestate, or wastewater into fertilizers that can be used directly.
Locally available waste and residual materials as reliable sources of nutrients
Particularly high concentrations of nutrients are found in agricultural waste – liquid manure from livestock farming and digestate from biogas plants, but also in municipal wastewater. “In livestock farming alone, nitrogen and phosphorus are excreted across the EU each year in quantities sufficient to meet Europe’s demand for mineral fertilizers,” explains Dr. Brigitte Kempter-Regel, responsible for Business Development in the Greentech Solutions division at Fraunhofer IGB.
However, in many places, manure and digestate – which are actually valuable farm fertilizers – can no longer be applied to fields. Especially in areas with intensive livestock farming or a high density of biogas plants, there is a risk of overfertilizing the soil and thereby further polluting groundwater and surface water. Due to their high water content of 80–90 percent, transporting these materials is far from practical. One solution is to recover nutrients such as nitrogen and phosphorus.
In wastewater treatment plants, these nutrients are already removed to comply with regulatory limits and prevent the eutrophication of water bodies. However, this is usually not a recovery process. Rather, valuable phosphates are precipitated as non-bioavailable aluminum or iron salts, while ammonium nitrogen is converted via nitrate into molecular nitrogen using biological processes, which escapes into the air. To achieve this, the tanks must be well-aerated – requiring enormous amounts of energy. In addition, these processes often release nitrous oxide, whose greenhouse gas effect is 265 times stronger than that of CO₂.
Processing of manure and digestate into fertilizer, peat substitute, and irrigation water
One approach that benefits agricultural producers and wastewater treatment plants as well as the environment and the climate is the recovery of nutrients in a form that can be used directly as fertilizer. To this end, Fraunhofer IGB, together with its partners in the EU-funded BioEcoSIM project, has implemented a multi-stage process in a pilot plant that can be used to process manure and digestate into ammonium fertilizer, phosphorus fertilizer, and organic soil conditioners.
The processing procedure itself begins with acidification of the manure or digestate to completely dissolve phosphorus in the aqueous phase. Through a multi-stage filtration process, the substrate is then separated into a liquid and a solid fraction. From the liquid phase, which contains the dissolved inorganic nutrients, phosphorus is first precipitated in the form of phosphate salts. In a second step, the dissolved nitrogen is recovered and separated as an ammonium sulfate solution via membrane absorption.
The dewatered solid fraction can either be composted or dried. “When processed into compact organic soil conditioners, the product can compensate for the loss of organic soil matter and be used as a substitute for peat,” emphasizes Kempter-Regel. The resulting water can also be reused, for example for irrigation or as rinse water.
To additionally generate energy and thereby improve economic efficiency, a biogas plant can be integrated upstream of the process. This allows even odor-intensive substances in the raw manure to be metabolized and thus removed. “In a current project, we have established a mathematical model for the BioEcoSIM process with an upstream biogas plant and calibrated it using measurement data for the various process steps,” explains Michael Bohn, who is further developing the nutrient recovery process at Fraunhofer IGB. This allows the economic efficiency of the process to be predicted under various conditions. Higher prices for synthetic fertilizers, for example, have an immediate effect.
Recycling nitrogen and phosphorus from wastewater
The membrane absorption process used in the treatment of manure and digestate to produce ammonium sulfate has also been demonstrated for nutrient recycling at wastewater treatment plants, most recently as part of the “RoKKa” project funded by the Baden-Württemberg Ministry of the Environment, Climate Protection and the Energy Sector and the European Union. The concentration of ammonium in the filtrate from sludge dewatering was reduced by 90 percent. Measurements also showed that ammonium recovery resulted in lower nitrous oxide emissions.
In RoKKa, the membrane process was used downstream of the ePhos module, also developed at Fraunhofer IGB. “In this process, phosphorus is precipitated purely electrochemically – without the addition of chemicals – as magnesium ammonium phosphate, a long-term phosphorus fertilizer also known as struvite,” explains Bohn. The magnesium required for this is added in an electrolysis cell via a sacrificial magnesium anode, which is consumed in the ongoing process.
Nutrient recycling strengthens supply security, water protection, and climate protection
The benefits of a regional nutrient recycling system are clear in times of geopolitical uncertainty. “Wastewater from treatment plants, manure from agriculture, and digestate from biogas plants are reliably available locally, reducing dependence on international supply chains and strengthening the local economy,” argues Kempter-Regel.
Recovering nutrients from these waste streams helps reduce nutrient loads in wastewater treatment plants and biogas plants and generates nutrient-poor water streams that can be reused, thereby lowering freshwater consumption. In addition, large amounts of fossil energy are saved and nitrous oxide emissions are reduced – an effective contribution to combating rapidly accelerating global warming.
New business models to harness the potential
There is great interest in the agricultural sector in a decentralized technology for the value-added use of manure and digestate. In addition to business models in which large companies operate recycling facilities, cooperatives of interested farmers are also conceivable.
“Farmers don’t just benefit from recovered nutrients. Above all, they receive products that can be stored and transported, and they can easily apply the nutrient-poor manure residues,” says Kempter-Regel. The investment costs would then be recouped over time through savings on disposal and fertilizer costs and the revenue generated. Wastewater treatment plants, for their part, as plant operators involved in fertilizer production, could enter into partnerships with industry to bring their products to market.
https://www.igb.fraunhofer.de/en/press-media/press-releases/2026/fertilizer-from... Press release and more pictures on the Fraunhofer IGB website
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