Background Diffuse pollution affects 90% of river basin districts, 50% of surface water bodies and 33% of groundwater bodies across the EU. Manure nutrients, especially nitrogen (N) and phosphorous (P) are among the main pollution sources, especially in high-density farming areas. Agriculture and livestock (especially manure) are responsible for over 50% of the total nitrogen discharged into surface waters. This contributes to eutrophication, a key threat preventing good ecological status for EU surface waters under the Water Framework Directive. The Nitrates Directive was created to protect water against nitrate pollution from agricultural sources. To this end, a number of technologies have been developed to solve the problem of excess of N and P in manure but they are often high energy and/or chemical demanding processes. Duckweed (Lemnaceae) is a small floating macrophyte with a high capacity for removing dissolved nutrients from water, especially nitrogen and phosphorous. It produces biomass with high nutritional value. Duckweed has been used for the uptake of nutrients from non-agricultural waste, but it has yet to be applied to animal manure on an industrial scale in the EU. Laboratory-scale tests have shown promising results, and an industrial-scale demonstration is now needed, particularly as a complement to anaerobic digestion. Objectives The main objective of the LIFE LEMNA project is to demonstrate the feasibility of an innovative nitrogen and phosphorous recovery technology, to improve nutrient management and reduce the environmental impact of animal farming. This biological, energy-efficient system will involve the sustainable treatment of anaerobically digested manure through a duckweed (aquatic plant) production system. Duckweed biomass will be processed to obtain new bio-based products for local consumption, mainly bio-fertilisers and animal feed; and it will also feed an existing biogas plant in the same location, which will allow the system to run 100% on green energy. The new technology will be tested in a 250 m2 duckweed production prototype with a treatment capacity of 3 m3/day, which will be installed and operated over a period of 21 months on a pig farm in Castilla-La Mancha (Spain). Specific objectives are to: Reduce manure nutrient pollution of water bodies in farming areas by implementing an innovative and resource-efficient duckweed-based technology to help farmers achieve integrated nutrient management; Demonstrate the efficiency and sustainability of the technology to achieve high rates of nutrient recovery, including N and P, in comparison with existing technologies; Reduce the carbon footprint and other environmental problems of animal protein production, by treating manure via anaerobic digestion with reduced greenhouse gas emissions, by producing duckweed from liquid digested manure to reduce nutrient pollution, and by replacing traditional fossil products with bio-fertilisers and feed; and Improve resource efficiency and close mineral cycles in animal farming systems by integrating duckweed production and bio-based related products within a low-input value chain inspired by the circular economy concept. Expected results: Duckweed-based technology to show 95-100% nutrient (N and P) recovery efficiency rates from anaerobically digested pig manure; Demonstrated advantages (i.e. in terms of sustainability and resource-efficiency) thanks to i) low energy consumption and being 100% renewable and self-sufficient (due to biogas production), ii) low water usage for growing duckweed, as the liquid manure already has a high water content, and iii) no requirements for CO2, chemicals reagents or other resources; At least two duckweed strains selected for their high growth rate and nutrient recovery efficiency in digested manure liquid. These will be validated during full-scale demonstration trials. Selection will be made from a collection of 25 duckweed strains of three species native to Europe representing different climatic areas: Lemna minor, Lemna gibba and Spirodela polyrrhiza. The selected strains will be characterised and preserved for replicating the technology in other EU regions; New duckweed products obtained, including a nitrogen and phosphorous rich bio-fertiliser (> 6% aminoacids) to replace traditional products, and safe, high-quality sustainable animal feedstock to replace soya or other vegetable protein products; Animal protein produced at the demonstration farm in Castilla-La Mancha, showing at least a 20% reduction in carbon footprint; An assessment of the socio-economic benefits for the local economy; and Methodologies and an electronic tool to enable future replication.