Phosphorus can be removed from fodder plants with the aid of biocatalysis. This avoids nutrient-rich excretions from livestock that pollute soils and groundwater. And the scarce resource can be reused.

Phosphorus is an important building material for life. It is not only a component of bones, teeth and cells. The chemical element is involved in enabling humans and animals to produce and store energy. Feedstuffs such as cereal bran contain a lot of phosphorus in the form of phytic acid, but this is excreted undigested by animals with only one stomach, such as poultry and pigs. They lack certain digestive enzymes for this. As a result, a lot of phosphorus ends up on the fields as liquid manure, polluting the soil and groundwater. Research is now being carried out at the Technical University of Hamburg to find ways of reducing the phosphorus content of animal feed so that this environmentally harmful process is not set in motion in the first place.

Phosphorus is recycled

"We use rye bran for our research, which is a waste product from the flour industry anyway, but otherwise has excellent nutrient properties, explains Niklas Widderich, shaking a cylindrical glass vessel filled with light-colored bran powder. In a small fermenter, the process starts by adding water to the bran and creating a two-phase suspension. "Now the exciting part begins," says Widderich, who oversees the project at the Institute of Technical Biocatalysis. He uses biocatalysts in the form of enzymes. "The enzymes 'digest' the organically bound phosphorus, and the inorganic part, which we obtain from mineral sources, is retained. You can also say the phosphorus is predigested, because the resulting bran product can now be ingested by animals with single-part stomachs," the doctoral student explains. Thus, the animal is provided with a phosphorus supply that meets its needs, and excess phosphorus can be recycled and fed to other industries, such as the chemical and food industries. Next, the Hanover University of Veterinary Medicine comes into play as a project partner: "We have now produced enough feed in an extra-large fermenter so that the university can now test the digestibility of the feed in a six-week trial with animals," says process engineer Niklas Widderich.

Sustainable agriculture

In contrast to other methods in which phosphorus is only extracted at the end from already accumulated slurry (end-of-pipe approach), the TU project starts much earlier and regulates the phosphorus content in the feed already at the beginning of the value chain. Especially in the case of regionally concentrated animal husbandry, this type of feed can contribute to more sustainable agriculture because the soils are no longer oversupplied with phosphorus. Excess phosphorus leaches into groundwater and can promote algae growth in bodies of water. Legislators have therefore already increasingly reduced corresponding limits for the fertilization with phosphorus and thus the area-specific application rates to date.
Against the backdrop of steadily rising population figures - the eight billionth person was recently born - this TU project can take on even greater significance. As arable land is in short supply worldwide, fertilizer use is increasing. More phosphate rock must be mined for fertilizer production than can be regenerated over geologic time periods. Consequently, phosphorus sources are in danger of drying up. The European Union has already declared phosphate rock a non-renewable resource. Therefore, projects like Niklas Widderich's are particularly important for resource management in the context of a circular bioeconomy.

PhANG is the name of the project on phosphorus-adapted feedstuffs, which involves the Technical University of Hamburg, RWTH Aachen University and the University of Veterinary Medicine Hannover.

Scientists at the Institute of Technical Microbiology are examining the wastewater of breweries and municipalities for substances that can be used to produce electricity or hydrogen.

The project focuses its work on analyzing wastewater for organic substances that serve as substrates for microorganisms. Brewery wastewater, wastewater from the cellulose filter industry and municipal wastewater are particularly suitable for treatment. The substances multiply in so-called microbial fuel cells (MFC) or microbial electrolysis cells (MEC).

Setting the flow of electricity in motion

To understand this process, it is helpful to imagine a battery. In it, current is generated by the electrochemical flow of electrons from the anode to the cathode. Similarly, in the early 20th century, it was first observed that some species of bacteria were capable of transferring electrons to an anode, this was later called a "microbial fuel cell." Since then, many basic mechanisms of electron transfer have been studied, but a deeper understanding of the processes is needed to optimize and commercialize these processes.

Every day, large amounts of wastewater are generated from industry as well as from private households. Proper treatment and purification is mandatory before returning the water to the environment. However, this process consumes a lot of energy and/or chemicals. For this reason, great efforts are being made worldwide to develop novel methods for environmentally friendly, resource-saving wastewater treatment. "A pioneering biological process is the microbial fuel cell, as organic carbon can be removed from wastewater and electrical power can be generated at the same time" says project supervisor Ahmed Elreedy.

The concept of this process is based on the ability of some microorganisms to transfer electrons directly or indirectly to external insoluble electron acceptors such as electrodes. Electrons, protons and CO2 are produced during the biological oxidation of organic matter in the anode. This process is the basis for energy conservation and growth of microorganisms. To generate a flow of electrons (electric current), the oxygen present in the cathode is reduced by the excess electrons. What remains is water. For example, treating one cubic meter of domestic wastewater can generate electricity of up to 1000 amperes.

Wastewater becomes clean

The fundamentals of electron transfer to an anode have only been partially studied and remain the subject of current research. "Our work, in addition to studying these electron transfer processes, is mainly focused on evaluating and optimizing process efficiency when dealing with real industrial wastewater," explains Ahmed Elreedy. "With this technology, we are not only able to purify water in a resource-saving way, but at the same time use this wastewater as a substrate for the sustainable generation of electric power," he said.

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Ahmed Elreedy works as a research associate at the Institute of Technical Microbiology at Hamburg University of Technology. His research focuses on biological wastewater treatment with simultaneous energy generation using bioelectrochemical systems.