Urban Mining – Using Urban Wastewater to Produce Premium Fertilizer

The treatment of urban wastewater can be seen as a challenging task. Maybe it is better to see and use it as a valuable resource? It can be used as a source of energy, soil conditioner, drought-resistant source of water, and source of nutrients for agriculture. A move towards a more planned use of urban wastewater makes it possible to receive large quantities of valuable goods.

Urban wastewater can be seen as a huge renewable resource with various usage possibilities

Increasing demands for phosphate-based fertilizer and decreasing qualities of reservoirs are calling for new solutions. German scientists from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart developed a market-ready system to produce phosphate-based fertilizer eco-friendly from wastewater. The fertilizer can be used directly for agriculture. According to Fraunhofer, the patented technology is already marked by a licensee in North America.

The electrochemical process ePhos® recycles wastewater with no need of chemicals. The phosphorus recovering process does not harm the environment. The reactor is placed directly at the wastewater treatment plants. Allegedly, the obtained phosphorus is ready to be used in food production.

The extraction of nitrogen and phosphorus results in either struvite (magnesium ammonium phosphate) or potassium struvite. “Struvite is free of biomass and can be used directly in agriculture as a high-quality fertilizer that releases nutrients slowly,” explains Dr. Iosif Mariakakis, project manager at Fraunhofer IGB. It is worth drawing attention to the purely electrochemical process with no necessity to add salt or lye. “This is also good news for water treatment plant operators – the process is very straightforward and doesn’t require them to stock chemicals,” Mariakakis continues.

Meanwhile, the researchers are busy developing their reactor concept further. “We plan to expand ePhos® by adding processing modules that allow water treatment plants to recover ammonium, too,” says Mariakakis.

The recycling process for phosphorus is described by Fraunhofer researchers as follows:

Recovering ammonium (NH4+) and phosphate (PO43-) from wastewater requires an electrolysis cell. Such cells consist of one magnesium anode and a cathode. Cathodic reduction results in water splitting: hydroxide ions (OH-) form while hydrogen (H2) is released. Oxidation occurs at the anode – magnesium ions react with the phosphate and ammonium present in the water to form struvite. The process has the benefits of not requiring any additional chemicals, such as magnesium chloride (MgCl2) or sodium hydroxide (NaOH), and consuming very little energy (0.78 kWh/m³ wastewater).