Wastewater as a resource: Utilization and recovery of wastewater ingredients

Wastewater – precious resource for raw materials and energy

The technological challenges in connection with water are manifold. Innovative approaches and methods are needed to use existing resources more effectively and to exploit new strategies, such as semi-centralized and adaptable infrastructure systems for collecting, treating and distributing water or – just as important – finding possibilities for reusing water.

Combining wastewater treatment with energetic and material utilization of its ingredients  

In terms of a sustainable circular economy, the decisive factor is how the wastewater is treated.

Wastewater can be purified with modern, cost-effective filter technologies; dissolved compounds that are harmful to the environment and health can be destroyed using advanced oxidation processes.

Ideally, further wastewater ingredients are recycled almost completely for energy and solids, when the wastewater is treated with adapted biological processes, which are combined with suitable recovery technologies if required. 

Material or energetic use of organic load

Most wastewater streams have high organic loads.

If the water contains high concentrations of a single compound, it may be worthwhile to separate the substance for further material use. In a project with dairy wastewater containing high amounts of lactose for example, the objective was to develop an environmentally sound process for the manufacturing of lactic acid from acid whey, in order to combine waste treatment with the production of valuable materials. We will be happy to advise you on suitable processes.

Sludge at wastewater treatment plants can be efficiently converted to biogas using a high-load digestion process. The fractions obtained with this process can be recovered in different ways (see below).

Recycling of nutrients

Besides organic solids, wastewater also contains large amounts of nutrients such as nitrogen, phosphorus, magnesium or potassium. Great efforts and in some cases huge amounts of energy are being put into eliminating nutrients from wastewater by means of nitrification, denitrification and/or biological phosphorus elimination, to prevent them from entering and eutrophying surface waters.

New concepts and processes developed at the institute aim to recover inorganic nutrients as fertilizers.

Belebungsbecken einer Klaeranlage
© Fraunhofer IGB, Marius Mohr
Wastewater contains organic ingredients and nutrients that can be used or recovered.
Hochlastfaulung Edenkoben.
© Verbandsgemeindewerke Edenkoben
High-load anaerobic digestion offers the possibility of making the ingredients in wastewater available.
© Fraunhofer IGB
Nutrients can be recovered from wastewater as fertilizer and replace conventional fertilizers.

The wastewater treatment plant as a biorefinery

The circular economy is considered a key strategy for conserving resources and achieving climate targets. The ingredients in wastewater can also be used – if it is treated in an appropriate manner. 

High-load digestion enables utilization of wastewater ingredients

The prerequisite for the utilization of the various substances involves making them available: through concentration, separation and processing.

The technical basis for this is the high-load digestion process developed at the IGB and implemented in many cases at wastewater treatment plants. High-load digestion not only converts the sludge produced at a wastewater treatment plant into biogas as a regenerative source of carbon and energy, but also supplies sludge water and sludge digestion residues (digestate) as further usable material flows.

The sludge water is rich in valuable plant nutrients, especially phosphorus and ammonium. The IGB has developed various concepts for recovering the nutrients from this water, which is produced when the sludge is dewatered, and processing it as fertilizer. Alternatively, the nutrient-rich sludge water can be used directly, for example for fertilizing irrigation or hydroponic plant production. Or as a growth medium for cultivating photosynthetic microalgae that grow with CO2 and synthesize plant-stimulating polysaccharides, for example.

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Fraunhofer IGB has investigated how wastewater can be used as a resource in a feasibility study for the Baden-Württemberg Ministry of the Environment. Dr.-Ing. Ursula Schließmann, head of the business area Environment at the IGB, explains the possibilities.

Reference projects

October 2021 – March 2024

RoKKa – The WWTP as a biorefinery?

The IGB develops a concept for the transformation of wastewater treatment plants into wastewater biorefineries with the use of residual and waste materials.


August 2020 – December 2020


In EVOBIO, process concepts were developed and demonstrated to fully utilize material flows such as wastewater, waste and exhaust gas – to produce optimized materials for innovative products.


Closed loops for process water

Removal and recovery of metals – biosorption and bioprecipitation

Metals from process wastewater can be bound to microbial surfaces by means of biosorption. In bioprecipitation dissolved metals (CuSO4, NiSO4, ZnSO4) are precipitated in the aqueous phase by microbial processes, for example with anaerobic microorganisms as catalysts and transferred to particulate components that are difficult to dissolve (CuS, NiS, ZnS). For effective process control we use immobilized or suspended biomass. In this way, heavy metals can be concentrated from solutions with metal ion concentrations in the mg/L range and precipitated as solids with metal concentrations in the g/kg range.