Building bio-based fertilisers from wastewater and brine
The world’s growing population is exerting intense pressure on agriculture to increase food production. To support European agriculture, the fertiliser action plan(opens in new window) will help farmers by investing in domestic production of bio-based fertilisers. In alignment with the European Urban Wastewater Treatment Directive(opens in new window), the EU-funded WalNUT(opens in new window) project addressed the challenge of sustainable food production by lab testing several nutrient recovery technologies and selecting five of the most promising to test at the project’s pilot sites.
Nutrient recovery technologies for bio-based fertilisers
Water treatment is a costly process, and the traditional linear approach does not return recovered resources to the value chain. Nutrient recovery changes that. Fertilisers rely on an assortment of nutrients present in waste streams, including nitrogen, phosphorus, potassium, magnesium and calcium. The WalNUT project used a tailored decision-making tool to select promising physicochemical, electrochemical and biological recovery technologies from a broad portfolio. The approaches tested included microalgae cultivation, high-rate activated sludge treatment(opens in new window), ion exchange or adsorption, liquid and solid fermentation, and nanofiltration.
Valorisation of wastewater and brine
The project targeted diverse wastewater streams when testing nutrient recovery technologies. “The strength of the project was that we did not focus on a single ideal stream,” says project coordinator Francisco Corona. “We worked with urban wastewater, sewage sludge, industrial wastewater, food-industry effluents and brine, because each one represents a real nutrient-recovery opportunity but also a different operational challenge.” Pilot sites brought together research institutes, industrial partners and technology providers involved in wastewater management. The pilot site in Belgium studied municipal wastewater and concentrated on nitrogen recovery. In Greece, the pilot focused on desalination brine and recovered potassium, magnesium and other micronutrients. Acid whey, an effluent from cheese processing, was used to recover phosphorous, calcium and other nutrients in Hungary. Pilots in Spain tested industrial wastewater and recovered nitrogen, phosphorus and ammonium nitrate. The pilot plants were very successful, with demonstrated recovery rates close to 95 %. With an eye towards the valorisation of recycled nutrients, according to Corona, “Field trials demonstrated that several recovered products can partially or fully replace conventional mineral fertilisers when application rates and timing are adapted to crop requirements.”
Centring collaboration in nutrient recycling
Sharing ideas and building intersectoral networks were key to the WalNUT approach. The project developed the WalNUT Platform to connect different players along the nutrient recovery value chain. “The WalNUT Platform is a web-based matchmaking and knowledge-exchange tool. It links wastewater producers, aggregators, technology providers, consultants and end-users, using information on nutrient quality, nutrient quantity and geographical distance to suggest matches,” explains Corona. By the end of the project, there were 119 registered users and 72 matches. In addition, WalNUT collaborated with related projects. In particular, WalNUT shared technical knowledge and experiences from agronomic trials with a cluster of sister projects(opens in new window) also working on bio-based fertilisers. A broader collection of projects, Biorefine Cluster Europe(opens in new window), was instrumental in expanding the project’s outreach. “Collaboration with related initiatives was essential because nutrient recovery is not only a technological challenge; it also involves regulation, agriculture, market uptake and stakeholder acceptance,” shares Corona. In addition to scientific and technological solutions, WalNUT offers policy recommendations(opens in new window) for defining bio-based fertilisers, ensuring their circularity and reinforcing the bio-based fertiliser value chain. There are many hurdles to ensuring food security and reducing Europe’s dependence on imported synthetic fertilisers. But with WalNUT’s multifaceted approach, the entry of bio-based fertilisers into the circular economy is within reach.
