P-Net – Regional network for resource-efficient phosphorus recycling and management

Phosphorus is an essential nutrient for plant growth. Currently, most of the phosphorus fertilizers used in agriculture are imported. However, wastewater remains unused as an important source of phosphorus, although the potential for the recovery of phosphorus from wastewater is great and the necessary technology – such as precipitation, the recovery of dissolved phosphorus from wastewater – is available. Against this background, the BMBF project “Network for resource-efficient phosphorus recycling and management in the Harz and Heath region (P-Net)” is investigating possibilities for establishing regional networks to process precipitated phosphorus involving so-called struvite plants which are wastewater treatment plants that have already established phosphorus precipitation with the aim to produce phosphorus fertilizers such as struvite. This process is a sustainable method of phosphorus recycling (P-recycling) which also makes an important contribution to the regionalization of resource cycles.

Research approach

The aim of the research association is to establish a regional network for P-recycling and management in the Harz and Heath region. Since numerous struvite plants already exist in this region, their process optimisationto reach the required recovery rates is one focus. Moreover, the practice partner Soepenberg will establish a so-called struvite hub. Here, standardized fertilizers are to be developed from the precipitated raw products of the individual plants, which will then be tested in the Harz and Heath region together with farmers and brought to market. ISOE is responsible for the real laboratory in charge of the market placement of the fertilizers and it is also in charge of interviewing the participating farmers. Furthermore, ISOE is responsible for setting up the regional network Harz and Heath” The first steps will be institutional and actor analyses.

In addition, ISOE participates in the transfer of knowledge between the research project and the operators of struvite plants. Here, the institute is responsible for national and international so-called struvite workshops”, where plant operators can obtain advice from P-Net regarding necessary plant upgrades and optimization as well as the marketing of struvite and where they can discuss and evaluate the latest P-Net results.

In the course of generalizing and disseminating results ISOE will also be responsible for the participatory scenario development and scenario comparison for the network. In cooperation with the project partners, possible future scenarios for the technology segment of precipitation and struvite production are to be developed and according recommendations should be derived.


In the course of the amendment of the Sewage Sludge Ordinance (AbfKlärV 2017), operators of wastewater treatment plant (WWTP) must recover at least 50% of the phosphorus quantity above a certain size of a WWTP. In recent years, numerous research and funding programs for phosphorus recovery were implemented both nationally and internationally, amongst them mainly processes that produce various crystalline phosphorus products through precipitation and crystallization, including magnesium ammonium phosphates (struvite). To date, however, these processes do not achieve the required recovery rates. In addition, there are currently no functioning, regional distribution channels for phosphorus products obtained from wastewater. 

Project partners

  • Technical University Carolo-Wilhelmina of Braunschweig, Institute of Sanitary and Environmental Engineering (Head of the research alliance )
  • Julius Kühn Institute, Institute for Crop and Soil Science

Practice partners

  • Wastewater Association Braunschweig (AVB)
  • Stadtentwässerung Braunschweig GmbH Abwasser- und Straßenreinigungsbetrieb Stadt Gifhorn
  • PFI-Planungsgemeinschaft GmbH & Co KG
  • Soepenberg GmbH


The project “Establishment of a network for resource-efficient phosphorus recycling and management in the Harz and Heath region (P-Net)” is funded by the German Federal Ministry of Education and Research (BMBF) within the framework of the announcement “Regional Phosphorus Recycling” (RePhoR) as part of the funding program “Research for Sustainable Development (FONA3).


Dockhorn, Thomas/Andreas Kolb/Hooman Mohammadi/Paul Keßeler/Sylvia Kratz/Elke Bloem/Joachim Clemens/Martina Winker/Jonathan Pillen/Markus Rauchecker/Michaela Rohrbach/Engelbert Schramm/Stefanie Meyer/Christoph Siemers/Franziska Gromadecki/Janina Heinze/Hans-Oskar Baron/Johannes Müller-Schaper/Oliver Hermanussen (2024): Aufbau eines Netzwerks zum ressourceneffizienten Phosphor-Recycling und -Management in der Region Harz und Heide - Erfahrungen aus dem Verbundprojekt P-Net. Gewässerschutz - Wasser - Abwasser, 257. Aachen: Gesellschaft zur Förderung des Instituts für Siedlungswasserwirtschaft an der RWTH Aachen, 57/1-57/15

Douhaire, Caroline (2023): Herstellung und Inverkehrbringung von Struvitdünger rechtssicher gestalten. Gutachten zu aktuellen rechtlichen Fragen. Mit einem Vorwort von Markus Rauchecker, Engelbert Schramm und Martina Winker. ISOE-Materialien Soziale Ökologie, 70. Frankfurt am Main: ISOE - Institut für sozial-ökologische Forschung

Pillen, Jonathan/Konrad Götz/Martina Winker (2023): Struvitdünger und seine Möglichkeiten für den Markteintritt. Zielgruppen- und Marktanalyse für die Region "zwischen Harz und Heide". ISOE-Materialien Soziale Ökologie, 71. Frankfurt am Main: ISOE - Institut für sozial-ökologische Forschung


2020/07 – 2025/06