Secondary resources, raw materials and water reuse

There is a great need for action in the supply of fertilisers to agriculture. Here we are developing processes to recover important plant nutrients such as phosphorus and ammonium from waste water, liquid manure, fermentation residues and sewage sludge. This involves developing and combining processes for processing or pelletising the nutrients in such a way that they are directly available to agriculture as high-quality and application-specific fertilizers.

In addition to precipitation processes, we have developed a purely electrochemical process for recycling phosphorus from phosphate-rich waste water, which supplies magnesium ammonium phosphate as a fertilizer that can be used directly.

Organic residues such as sewage sludge, fermentation residues or liquid manure are rich in dissolved nutrients, but also contain organically bound phosphorus, which we mobilize and recover enzymatically. We then process the remaining organic fractions, which are low in nutrients, into purely organic soil conditioners using various methods. The losses of organic matter in the soil can thus be compensated and soil fertility improved.

Agriculture is one of the largest consumers of water worldwide – new concepts and processes for water reuse are therefore in demand. Anaerobically treated wastewater still contains large quantities of inorganic phosphate and ammonium salts after the degradation of organic compounds – nutrients that are urgently needed in agriculture.  

In the HypoWave research project, the IGB and its partners have investigated whether and how anaerobically treated municipal wastewater can also be reused for hydroponic plant production due to its nutrient content. In this cultivation of vegetable plants in a greenhouse, the seedlings do not need soil in their planters. As a result, no water seeps into the soil and there is less evaporation. The results of a pilot trial with lettuce plants show that only a small additional nutrient supply is required for good growth – in other words, the nutrients contained in the wastewater are also meaningfully reused together with the wastewater.

The recycling of precious metals or rare earths is of great economic importance. Process and wastewater streams, e.g. from leaching baths in the electroplating industry, or landfill leachates contain significant quantities of metals overall, albeit sometimes in only low concentrations. Solids such as ashes from incineration processes also sometimes contain metals as mixtures of substances. In these cases it can be advantageous to first bring metals into solution (leaching) before they can be concentrated and separated or separated as solids. The design of these process steps determines the efficiency and sustainability of the overall process. In some Fraunhofer-internal projects we have been able to develop new technologies and optimize existing ones, so that we now have a broad portfolio and experience in the integration into process chains at our disposal.

These technologies can also be used for the processing of raw materials.

"Green" hydrogen (H₂), produced by electrolysis of water with renewable energies, is considered a key element of the energy transition. The demand for renewably produced hydrogen for a climate-friendly economy in industry, transport and heat supply is enormous. Germany and Europe are therefore relying primarily on hydrogen imports from southern countries with sufficient solar radiation all year round.

In two current projects, Fraunhofer IGB is taking a new approach to producing the climate-neutral energy carrier and industrial raw material: Using biotechnological processes, for example microorganisms (purple bacteria) or microalgae, biohydrogen is to be produced from residual material streams such as waste wood or rinse water.

Recycling raw materials as completely as possible will support the urgently needed change to a climate-neutral and environmentally friendly way of life and economy. In industrial production, recycling therefore plays an important role in increasing resource efficiency.

A reserve of potential raw materials which has been insufficiently utilized to date lies in the further use of valuable raw material components in wastewater and waste. The process approaches already presented on this page and others that have already been developed and established as unit operations are to be combined in a further step by intelligently linking biology and engineering according to the model of a refinery. In current projects, we are combining various biotechnological processes according to the principle of a biorefinery and implementing them on a larger scale in pilot and demonstration plants. In this way, we produce valuable products for industry and agriculture on the one hand and enable the reuse of the water purified in this way on the other.

For controlling and automation, digitization and artificial intelligence (AI) play a crucial role, e.g. as self-learning sensor networks in process monitoring or the use of control systems based on fuzzy logic.

Unit operations that can be combined for waste and wastewater biorefineries:

• High-load digestion for anaerobic digestion of the organic components of (municipal) wastewater streams to biogas/biomethane
• Various technologies for nutrient recovery (N, P)
• Microalgae technology for biological CO₂ fixation (bio carbon capture and utilization, CCU) and production of co-products
• Electrosynthesis processes for CO₂ conversion (carbon capture and utilization, CCU) into C₁ intermediates (formate, methanol)
• Other specific microbial conversion processes
• Energy- and CO₂-optimized drying of foodstuffs by drying with superheated steam