Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB

Treatment of process water, wastewater and sludge

Based on our many years of experience in this field, Fraunhofer IGB offers both biological and physico-chemical methods and solutions for wastewater treatment and sludge conditioning for industry and municipalities.

A particular focus is on the design of new wastewater treatment plant concepts for a "wastewater treatment plant of the future" that not only treat wastewater in compliance with the regulations, but can also generate additional value at the same time – via the production of energy sources and products such as fertilizers to biostimulants for agriculture. Another key topic is water reuse, which will become increasingly important in the future.

Our portfolio also includes customized membranes, filters and adsorbents, which will play important roles in the growing future markets for water and wastewater treatment systems.

Fraunhofer IGB – All about processing solutions for process water and wastewater

Challenges

Increasing costs for the purification and disposal of wastewater, regional and seasonal shortages of water, and also a growing environmental awareness on the part of companies are resulting in using these process waters, which are often required in large quantities, in closed cycles whenever possible, and removing impurities selectively or recovering valuable constituents.

In order to recirculate process waters and wastewater from industrial production processes, the impurities have to be removed – with as little effort and expense as possible.  

Solutions and service offers

In order to achieve a closed cycle and permanent sustainability of process water management, Fraunhofer IGB is working on process solutions that combine biology and engineering.

Current research at Fraunhofer IGB is therefore focused on processes such as adsorption, filtration, flocculation/precipitation, electrodialysis, oxidation and disinfection and a transition to biobased feedstocks. On the basis of many years of experience biological processes, both aerobic and anaerobic, are being further developed and optimized for an extremely wide range of applications, and combined with membrane and chemical-physical processes.

The integration into regional energy and material flow concepts in the spirit of the bioeconomy enables new solutions here. In addition to new requirements, the rapid development of the legal framework and local markets also offers great opportunities.

Scientific advice to our customers regarding their production process and its water flows is provided independently of technology and suppliers. In cooperation with industrial partners, new concepts and technologies for the sustainable treatment and purification of process water for a very wide range of applications are being developed and optimized at Fraunhofer IGB as well as scaled up to industrial scale.

Biological processes

Fixed-bed recirculating reactor.
© Fraunhofer IGB
Fixed-bed recirculating reactor.

Biological processes use the self-purifying power of ecosystems, in which those organisms that can degrade existing substrates most effectively prevail. A prerequisite is that the substrates are fundamentally biodegradable. Technical processes such as biomass retention ensure that these natural processes take place in a very small space and at a high intensity.

Fraunhofer IGB has developed various bioreactors for wastewater treatment, for example anaerobic and aerobic loop reactors (gaslift / airlift reactors), membrane bioreactors and a fixed-bed circulation reactor in which the particle bed is periodically recirculated.  

Mobile plants (sequencing batch reactor, SBR; expanded granular sludge bed, EGSB) are available for piloting on site. We not only advise our customers on process selection, but also support them in the selection of plant constructors, on operating models, during commissioning and during future production changes.

Anaerobic processes for wastewater with high organic load

Anaerobic wastewater purification processes are especially suitable for treating wastewater with a high biological oxygen demand (BOD5) found, for example, in the food and beverages industries, in slaughterhouses and also at airports (de-icing agents). Larger companies often run their own biological treatment plants. These are usually aerobic and have several disadvantages such as high power requirements for aeration and mixing, a common lack of nutrients (N and P) and the generation of large quantities of sewage sludge, which is expensive to dispose of. Modern anaerobic technology is much more economical and has already proven to be long-term efficient for many of our partners. The advantages are that the biogas (biomethane) formed can be used energetically and the amount of sludge is reduced by a factor of ten.

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.

Adsorption

Nanoparticles with a polymer shell and magnetizable core (magnetite) that are attracted by a magnet (on the right).
Nanoparticles with a polymer shell and magnetizable core (magnetite) that are attracted by a magnet (on the right).

In the case of pollutants with low concentrations it is sometimes of advantage to increase the concentration for efficient treatment or efficient degradation. Besides membrane technology, adsorbers offer the possibility of binding these substances safely and, on reaching the relevant load, of passing them on to the degradation processes described below by regenerating the adsorbers.

NANOCYTES® – Synthetic adsorber particles to remove pollutants

Among various approaches being pursued at Fraunhofer IGB, we remove organic trace substances (micropollutants) from water with the help of selective nanostructured polymer adsorber particles. The polymer adsorber material can be adapted individually to different trace substances. Using model solutions we have already demonstrated the specificity and efficiency of the adsorber particles with regard to e.g. bisphenol A, an endocrine-active trace substance.

Membrane filtration and membrane adsorbers

Membrane adsorber REM.
© Fraunhofer IGB
REM image of a particle-filled polyethersulfone flat membrane.

Membrane technology has proven its worth in industrial applications as a separation technology for the treatment of raw water as process water or for the purification of process wastewater. Membrane filtration is a method for separating suspended or dissolved substances on the basis of molecular weight and size. Substances smaller than the pore size of the membrane pass through as a permeate together with the solvent, whilst larger molecules and suspended solid particles are held back in the retentate.

A general advantage of membrane processes is that they function without a phase change. Further advantages are the simple equipment required, easy upscaling (modularity) and low consumption of chemicals. Here the type and size of the substances in the water that are to be separated determine the membrane process to be used.

Membrane materials, membranes and membrane processes are researched and developed at the Fraunhofer IGB for microfiltration (suspended particles, bacteria), ultrafiltration (macromolecules, viruses, colloids), nanofiltration (organic compounds, divalent ions) and reverse osmosis (monovalent ions).

Enrichment and elimination using membrane adsorbers  

A further focal point are membrane adsorbers, which combine the advantages of membranes with those of adsorber materials. For this purpose we equip membranes with special functional groups in order specifically to remove contaminants such as heavy metal ions (Pb, Cd, Cu) or organic molecules (penicillin G, bisphenol A) from process wastewater by means of adsorption. The membrane adsorbers can be operated at low pressures, they retain suspended particles and achieve water flux values in the range of MF membranes.

Membrane adsorbers are also used for concentrating solutions with a low pollutant concentration in order to treat the enriched solution energy-efficiently with AOP technologies, e.g. electrolytic, photolytic or plasma-technological oxidation processes, and to destroy the pollutant.

Physical-chemical processes

Batch-Reaktor zur UV-C/H2O2-Behandlung von Wasser.
Batch-Reaktor zur UV-C/H₂O₂-Behandlung von Wasser.

Advanced oxidation processes (AOP)

Oxidative water treatment (AOP, Advanced Oxidation Processes or AOT, Advanced Oxidation Technologies) is the term used to describe chemical treatment processes in which highly reactive hydroxyl radicals are used for the oxidation of water ingredients that are difficult to break down.

AOP processes are always used when biodegradation is not possible or not efficient, for example because the impurities contain persistent substances. Furthermore, AOP processes are the method of choice if the process wastewater has a toxic effect on the microorganisms of a biological treatment stage or if it is extremely discontinuous.

In many cases, a process combination with a reductive partial degradation is also recommended as the most energy-efficient variant. The possibility of testing various combination treatments in the laboratory and pilot plant of the IGB is one of our unique selling points.

Atmospheric water plasma on a laboratory scale.
© Fraunhofer IGB
Atmospheric water plasma on a laboratory scale.

Water purification using atmospheric plasma

Water purification with atmospheric plasma can also be included among the AOP processes. Ions, highly reactive radicals and short-wave radiation are created in an electrical discharge (plasma) from ambient air and atmospheric oxygen in order to degrade organic components in wastewater. The specific construction of the plasma reactor insures the efficient transfer of the highly reactive species formed in the plasma to the polluted water. To achieve this, the plasma has to be in direct contact with a flowing water film.

Plasma water purification is particularly suitable for poorly degradable substances such as drug residues, cyanides, pesticides, perfluorinated surfactants and PFAS (perfluorinated chemicals) in industrial wastewater or leachates.

We investigate the degradation of contaminants in your process or wastewater using various laboratory-scale plasma processes, characterize the degradation products, and scale the process according to your requirements.

Electrocoagulation with sacrificial anodes

In this process established at the IGB, the water to be treated is passed through a reactor in which an electric current flows through sacrificial electrodes. In the course of electrochemical reactions, the sacrificial electrodes dissolve, releasing their metal ions, and metal hydroxide flakes are formed. These have a high adsorption capacity and can bind to themselves finely distributed, non-sedimentable particles in the size range of a few micrometers or smaller.

During the formation of hydroxide flakes, co-precipitation and inclusion precipitation reactions also occur, in which dissolved organic and inorganic substances are precipitated. The precipitated substances can be separated mechanically by sedimentation or filtration. Thus, electrocoagulation replaces conventional chemical flocculation precipitation techniques with the advantage that the flocculants are provided electrolytically from solid electrodes directly at the place of need in dissolved form and dosed according to need. 

Desalination

Salts, if recovered in sufficiently pure form, can be directly reused as a valuable material. Since increased recycling increases the concentration of salts in process waste water, they must be increasingly removed before discharge.

Electrochemical (membrane) processes are suitable for the separation of salt ions. In these processes, only the charged particles from an aqueous solution are transported through the ion exchange membrane in an electric field. The separation processes such as electrodialysis or capacitive deionization can be economically integrated into the process chain for the recovery of valuable materials, the recycling of process auxiliaries and the treatment of wastewater.

Electrodialyis

Recovery of phosphate from wastewater

Besides organic substances, 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 and chemical phosphorus elimination, to prevent them from entering surface waters and causing eutrophication. At the same time, the worldwide demand for food and consequently the need for nutrients for the production of fertilizers is increasing continuously.

For this purpose, IGB researchers have developed and patented an electrochemical process in which nitrogen and phosphorus from municipal, industrial and agricultural wastewaters are recycled. The ePhos® process precipitates nitrogen and phosphorus with a magnesium electrode as magnesium-ammonium-phosphate (struvite), a high-quality fertilizer.

Membranes for sulfate depletion from ground and surface waters

One of the late effects of opencast lignite mining in Germany is the large-scale iron and sulfate contamination of ground and surface waters. Therefore, the aim is to develop and demonstrate a process based on forward osmosis to remove sulfate from surface and ground waters. For this purpose, hollow fibers based on celluslose acetate were developed at the IGB, which carry the separation layer on the outside and were processed from a green solvent.

Thermal processes

Thermal processes.

Thermal water treatment processes such as heating, distillation and rectification (thermal separation) are widely used in industry and commerce. The advantage of these processes is that the technologies are often relatively simple and robust in design and the thermal energy supply can usually be realized without great effort by firing, process steam or electrical heating. On the other hand, thermal treatment processes are energy-intensive, which makes new technical solutions necessary in the course of responsible handling of energy resources and increasing cost pressure.

The aim of research and development at Fraunhofer IGB is therefore to realize efficient and cost-effective thermal treatment processes by optimizing and combining different processes in order to be able to use waste heat or solar-thermally generated heat.

Processes for the concentration of industrial wastewater and the recovery of solvents are examples of processes that are being worked on at Fraunhofer IGB.

Combination of different processes and system integration

Due to the complex composition of typical industrial process waters, efficient separation of substances in one step is usually not possible. By combining and integrating different processes, we develop efficient, coordinated solutions that are optimized in terms of selectivity and energy efficiency in their overall effect as a process chain.

Automation and autonomous operation

Wherever possible, we develop process concepts so that they can be operated flexibly and, for example, are suitable for standby operation, i.e. can be switched on and off at any time. Integration into existing plants and automation up to autonomous operation or remote control are possible. Where necessary, we integrate online analytics, for example for the continuous recording of organic carbon (TOC, Total Organic Carbon), in order to ensure demand-based and consequently energy-optimized processing.

The wastewater treatment plant as a biorefinery

High-load digestion at the Erbach wastewater treatment plant.
© Fraunhofer IGB
High-load digestion at the Erbach wastewater treatment plant.

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.