Phosphorus is a vital element not only for plants but also for all living organisms. In recent times, however, farmers have been faced with a growing shortage of this essential mineral, and the price of phosphate-based fertilizers has been steadily increasing.
Struvite fertilizer recovered from wastewater is a high-quality product that slowly releases nutrients into the soil.
© Fraunhofer IGB
It is therefore high time to start looking for alternatives. This is not an easy task, because phosphorus cannot be replaced by any other substance. But researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart have found a solution that makes use of locally available resources which, as unlikely as it might seem, are to be found in plentiful supply in the wastewater from sewage treatment plants and in the fermentation residues from biogas plants: a perfect example of the old saying “from muck to riches”. The new process was developed by a team of scientists led by Jennifer Bilbao, who manages the nutrient management research group at the IGB. “Our process precipitates out the nutrients in a form that enables them to be directly applied as fertilizer,” she explains.
Mobile pilot plant for field tests
The main feature of the patented process, which is currently being tested in a mobile pilot plant, is an electrochemical process that precipitates magnesium-ammonium phosphate – also known as struvite – by means of electrolysis from a solution containing nitrogen and phosphorus. Struvite is precipitated from the process water in the form of tiny crystals that can be used directly as fertilizer, without any further processing. The innovative aspect of this method is that, unlike conventional processes, it does not require the addition of synthetic salts or bases. Bilbao: “It is an entirely chemical-free process.”
The 2-meter-high electrolytic cell that forms the centerpiece of the test installation and through which the wastewater is directed contains a sacrificial magnesium anode and a metallic cathode. The electrolytic process splits the water molecules into negatively charged hydroxyl ions at the cathode. At the anode an oxidation takes place: the magnesium ions migrate through the water and react with the phosphate and ammonium molecules in the solution to form struvite.
Energy-saving, chemical-free process
Because the magnesium ions in the process water are highly reactive, this method requires very little energy. The electrochemical process therefore consumes less electricity than conventional methods. For all types of wastewater tested so far, the necessary power never exceeded the extremely low value of 70 watt-hours per cubic meter. Moreover, long-duration tests conducted by the IGB researchers demonstrated that the concentration of phosphorus in the pilot plant’s reactor was reduced by 99.7 percent to less than 2 milligrams per liter. This is lower than the maximum concentration permitted by the German Waste Water Ordinance (AbwV) for treatment plants serving communities of up to 100,000 inhabitants. “This means that operators of such plants could generate additional revenue from the production of fertilizer as a sideline to the treatment of wastewater,” says Bilbao, citing this as a decisive advantage. Struvite is an attractive product for farmers, because it is valued as a high-quality, slow-release fertilizer. Experiments conducted by the Fraunhofer researchers have confirmed its effectiveness in this respect: crop yields and the uptake of nutrients by the growing plants were up to four times higher with struvite than with commercially available mineral fertilizers.
The scientists intend to spend the next few months testing the mobile pilot plant at a variety of wastewater treatment plants before starting to commercialize the process in collaboration with industrial partners early next year. “Our process is also suitable for wastewaters from the food-industry and from the production of biogas from agricultural wastes,” adds Bilbao. The only prerequisite is that the process water should be rich in ammonium and phosphates.
M.Sc. Jennifer Bilbao | Fraunhofer Research News
Colorectal cancer risk factors decrypted
13.07.2018 | Max-Planck-Institut für Stoffwechselforschung
Algae Have Land Genes
13.07.2018 | Julius-Maximilians-Universität Würzburg
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
13.07.2018 | Event News
13.07.2018 | Materials Sciences
13.07.2018 | Life Sciences