Secondary resources, raw materials and water reuse

With its developments in biotech and physico-chemical processes for recovering valuable materials and nutrients (P, N) from sewage and other sources of waste as well as for the reuse of treated wastewater, Fraunhofer IGB makes important contributions towards the establishment of a sustainable bioeconomy inspired by the natural cycles of materials. One example is our ePhos® system, an electrochemical process for the recovery of phosphorus from wastewaters rich in phosphates. Its efficiency has been demonstrated at the pilot plant scale.

Other approaches include new and improved technologies for the production of hydrogen from industrial residual streams, which can be coupled with algae biotechnology processes for utilizing carbon dioxide (carbon capture and utilization, CCU) from industrial and agricultural sources.


Recovery instead of disposal – generating added value from waste streams

For ferrous metals, glass, paper or many plastics, recycling processes are already established on a large scale. However, for numerous other valuable materials, especially those consisting of complex components and material matrices, no economic recycling processes have yet been established due to the lack of suitable treatment processes. Disused electronic products, for example, are true raw material stores for metals such as copper, zinc, platinum or gold and rare earths such as neodymium and dysprosium.

Our primary raw materials are finite and are often mined in politically unstable regions in a way that is neither sustainable nor socially acceptable. In order to be able to supply a growing world population with raw materials and reduce dependence on imported raw materials, we are developing processes to recover secondary raw materials from production and waste streams for reuse – in a quality equivalent to that of primary raw materials and with comparable process effort and costs.

The most selective separation possible is a fundamental and decisive step in both primary and secondary raw material processing. Up to now, the steps of stock separation have been costly and time-consuming, and therefore have a significant impact on operating costs, but also on the sustainability of the processes. In order to solve this problem, Fraunhofer IGB is developing processes which considerably increase energy and cost efficiency compared to established processes or which enable the selective separation of certain raw materials in the first place.

In the field of soil, organic residues (fermentation residues, liquid manure) and water, we design and implement processes for the recovery and treatment of dissolved or organically bound phosphorus as high-quality fertilizers. We process the remaining organic fraction, which is low in nutrients, using various processes such as drying or pyrolysis to produce humus-forming soil conditioners.

Recycling of phosphorous and nitrogen nutrients as fertilizer

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.

© Fraunhofer IGB

Soil conditioners through processing of organic residues

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.

Organic fertilizer pellets from fermented residues of olive oil production.

Wastewater treatment for water reuse

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.

HypoWave lettuce
© © ISOE Wikom
Lettuce on the HypoWave pilot plant in Wolfsburg-Hattorf.

Recovery of high-value metals for high-tech applications

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.

Biohydrogen from residues

"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.

Waste and wastewater biorefineries: Combining different technologies for complete utilization of waste streams

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
Hochlastfaulung auf der Kläranlage  Erbach.
© Franz Parockinger / Stadt Erbach
High-load digestion at the Erbach wastewater treatment plant provides the basis for upgrading the plant to a biorefinery.

Residues of food industries

Valuable ingredients can be recovered using appropriate technologies. We fractionate proteins from whey, for example, by means of electro-membrane filtration.

Using biogenic residues as raw materials

Residual materials can be converted into basic chemicals – e.g. by means of fermentative or chemical processes.

Separation technologies

Fraunhofer IGB has developed and established various separation processes for the separation of complex mixtures of substances, which can also be combined and integrated into process chains.