Closing the Cycle of Nutrients from Wastewater and Process Water (KNAP)

In this cross-sectoral project within TKI Water Technology and TKI Agri & Food, research partners WUR/WENR, KWR and LeAF are working together with a wide range of public- and private-sector partners on closing the cycles of nutrients from municipal wastewater and industrial process water treatments. In nine highly diverse cases (five of which municipal and four industrial), work is being conducted to map out (quantitatively and qualitatively) the recyclable fertilisers, their agricultural values, and their possible disposal routes. Overarching work is also being done on a quality system with criteria which could provide a basis for assessing recycled fertilisers.

Problem definition

The PPS project, Closing the Cycle of Nutrients from Wastewater and Process Water (‘KNAP’ in the Dutch abbreviation), focuses on the integrated closure of nutrient loops from municipal and industrial wastewater systems, closing nutrient cycles both in concept development and in operational practice. The aim is to take nutrient recovery and reuse from wastewater to agriculture (or beyond) to a higher level.

Challenge and solution

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 cycles. Despite various ambitions and targets (over the last 10 years), in practice nutrients are still hardly recovered and reused from wastewater. The development and rollout 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 project focuses on the integrated closure of the loops of the macronutrients nitrogen (N), phosphorus (P), potassium (K), and, when appropriate, other nutrients from the municipal and industrial wastewater cycle. The aim is to take nutrient recovery and reuse from wastewater to a higher level, so that Water Authorities, fertiliser producers and vendors, agriculture, the agri-food industry, and other relevant actors are in a position to actually close nutrient cycles together. The recovered nutrients might possibly offer an answer to the potentially increased demand for nutrients resulting from current discussions about livestock farming, concerning the livestock, manure production and derogation. The project’s overall objective is to develop applied knowledge and expertise for the safe and sustainable application of wastewater products in a circular agriculture-food-sanitation system.

Intended result

Besides a variety of cases in which nutrients from municipal and industrial wastewater are, centrally and decentrally, recovered and reused, we want this project to provide the following:

  • As the core, an elaborated quality system for recycled products and fertilisers from municipal and industrial wastewater.
  • Up-to-date insight into the largest leakages of macronutrients from the Dutch nutrient system.
  • Detailed information on the agricultural value, quality and safety of individual recycled fertilisers from the various cases.
  • And, at the end of the project, a clear idea of the existing barriers in legislation and regulations that prevent optimal valorisation of the nutrient-rich residual streams, and also proposed solutions in this regard.

It is important that there be support on the part of public authorities, companies and knowledge institutions for the quality system and the implementation of cases during and after the project.