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.