PPS project Closing the cycle of nutrients from wastewater and process water (KNAP)

The nutrient cycle is still far from being closed in the Netherlands, with the largest leakages in the system occurring in the municipal and industrial wastewater chains. Despite various ambitions and targets (over the last 10 years), in practice nutrients are still hardly recovered and reused from wastewater.

The development and implementation of systems that return nutrients to the (food) cycle face several barriers at the intersection of technology, knowledge, regulation, cooperation and economics. For this reason, this research focuses on the integrated closure of nutrient cycles from municipal and industrial wastewater systems, closing nutrient cycles both in concept development and in practice. The aim is to take nutrient recovery and reuse from wastewater to agriculture (or beyond) to a higher level through four related work packages:

  1. Development of a quality system for recycled fertilisers from municipal and industrial wastewater, including system and scenario analysis for (macro)nutrients;
  2. Realisation of cases regarding municipal wastewater, where the recovery of nutrient-rich products (centralised and decentralised recovery) is combined with the development of the quality system;
  3. Realisation of cases concerning industrial waste water (process water), where the recovery of nutrient-rich products from the agri-food industry and SMEs is combined with the development of the quality system;
  4. Project management, stakeholder consultation and dissemination of the quality system and cases, involving relevant companies, governments (national, provincial, municipal, water boards) and other parties in the development of the quality system and the implementation of the cases.

The municipal waste-water cases are:

  • Valorisation of concentrated liquid fertilisers containing nitrogen;
  • Valorisation of solid mineral/phosphate fertilisers from municipal wastewater;
  • Valorisation of dewatered sludge and digestate from treated black water;
  • Valorisation of source separated decentralised sanitation (urine, possibly black water and organic waste);
  • Circular agriculture with recycled fertiliser from wastewater in the Flevoland region.

The cases for industrial wastewater are:

  • Sustainable use of valuable nutrients from the agri-food industry;
  • Valorisation of digestate from processed food waste;
  • Circular greenhouse horticulture with fertiliser from wastewater;
  • Valorisation of valuable nutrients from brewery and dairy effluent wastewater.

The outcome of this project consists of the following components:

  • An elaborated quality system for recycled products and fertilisers from municipal and industrial wastewater, with special attention to challenges in legislation and regulations at Dutch and EU level [Work Package 1];
  • Up-to-date insight into the largest leakages of (macro)nutrients from the Dutch nutrient system [WP1];
  • A variety of cases where nutrients from municipal and industrial wastewater are recovered and reused in a centralised and decentralised way, in interaction with the development of quality systems [WP2, WP3];
  • Detailed information on the agricultural value, quality and safety of individual recycled fertilisers [WP1, WP2, WP3];
  • Support of relevant parties for the quality system and implementation of cases during and after the project with regard to authorities, companies and knowledge institutions [WP4];
  • Listing of existing barriers in legislation and regulations that prevent optimal valorisation of nutrient-rich residue streams [WP1, WP2, WP3, WP4].

The project fills the gap to achieve the ambitions and goals of reusing nutrients from the wastewater system, using (locally) available raw materials as much as possible. The underlying objectives are:

  • Reduce as much as possible the input of 'fossil' nutrients, including feed and fertiliser imports;
  • To create added value by recycling and valorising nutrients from wastewater;
  • Reduce/shorten nutrient loops in the food system as much as possible and close them as locally as possible;
  • Remove and control contaminants in the closed-loop wastewater system to enable safe reuse of products;
  • Reduce emissions to land, water and air at source.


The consortium includes parties from all relevant sectors:

  • (Waste)watersector: AquaMinerals, Slibverwerking Noord-Brabant (SNB), HVC, Waterschap Vallei en Veluwe, Waterschap De Dommel, Waterschap Rijn en IJssel, Waterschap Zuiderzeeland, Wetterskip Fryslân, Hoogheemraadschap van Rijnland, Waterschap Brabantse Delta, Waterschapsbedrijf Limburg;
  • Agriculture and horticulture: LTO Noord, LTO Noord Flevoland, Flevolands Agrarisch Collectief, Glastuinbouw Nederland, Stichting Kennis In Je Kas, SIGN (Foundation for Innovation in Horticulture);
  • Agri-food industry: Cosun, Lamb Weston/Meijer, Avebe, Peka Kroef, Vereniging voor de Aardappelverwerkende Industrie (VAVI), Heineken, FrieslandCampina;
  • Fertiliser industry: Van der Knaap, ICL Fertilizers, Stelt
  • Agronomic advice: Agrifirm;
  • Technology suppliers: Pure Water Group, SusPhos, Circ, Desah, Colsen, DIXI Sanitary Services, Laufen Bathrooms;
  • Laboratories: Eurofins Agro;
  • Knowledge institutions and organisations: Wageningen University & Research, LeAF, KWR Water Research Institute (KWR), Boerderij van de Toekomst, Nationale Proeftuin Precisielandbouw, Witteveen+Bos, Aeres Hogeschool Dronten, Hogeschool Van Hall Larenstein, ISPT Facinating Programma;
  • Network organisations: Nutrient Platform, Water Stewardship Academy / Nederlands Consortium Antibiotica- en Medicijnresten uit Water, Waterlab Flevoland, Platform Circulair Flevoland;
  • Provinces: Flevoland, Friesland;
  • Municipalities: Almere;
  • Citizen collectives (decentralised sanitation): woonwijk Noorderhoek (Sneek), woonproject Arneco (Arnhem)
  • Nature organisations: Noardlike Fryske Wâlden.