Mobile demonstration plant for the precipitation of struvite

At the Fraunhofer IGB we have developed a new technology for the recovery of nitrogen (N) and phosphorus (P) from an anaerobic wastewater treatment plant. By applying an electrochemical process N and P are precipitated as magnesium ammonium phosphate (MAP, struvite) fertilizer salt. Thereby phosphorus is taken out of wastewater streams without having to add Mg-salts or bases. The procedure can also reduce the nitrogen content. Because of its composition (macro-nutrients N, P and Mg) and its good plant availability, the precipitation product MAP can be brought to market as high-quality fertilizer.

Advantages of the MAP process:

• No magnesium containing chemicals are required
• Mg is immediately available for precipitation
• No interfering substances such as chloride ions
• No additional base required for pH shift
• Low specific energy demand (70 Wh/m³ filtrate water)
• P-limit according to German wastewater regulation can be fulfilled

First long-term experiments in a pilot plant show promising results. Using the technology that was developed at Fraunhofer IGB, the P-concentrations were reduced by 99.7 percent. Therefore the limit given by the wastewater ordinance for facilities up to 100,000 population equivalents was safely come below. Based on these findings a compact and mobile demonstration plant was designed in order to duplicate the obtained results on a larger scale and to validate them.