Residue-based multilayer-filters reused as amendment after capturing pig slurry gases

Agriculture faces the challenge of reducing farm emissions and adopting circular economy strategies. This study assessed the formulation of three multilayer filters (MLFs) based on waste-derived materials from different industries. The study objectives were to (1) capture greenhouse gases and ammonia (NH₃) and volatile sulfide compounds (VSC) from pig slurry and (2) assess the potential reuse of the most effective MLF as a soil amendment. Firstly, MLFs were designed and their efficacy to capture gases emitted from pig slurry (N₂O, NO₂, NH₃, CH₄ and CO₂) evaluated. Secondly, MLF3 was used as a soil amendment (with and without previous exposure to pig slurry emissions) to evaluate its agronomic performance and environmental impact. For this, a soil was amended, introducing the variables sown (with Lolium perenne) or not-sown and with or without the nitrification inhibitor dicyandiamide. All MLFs captured > 75% of total N emitted from pig slurry and up to 95% of NO₂ and NH₃ emissions. The MLFs captured significant amounts of nitrogen, carbon and sulfur during the experiments, with maximum values of 4.4 g N kg^-1 for MLF3 and 27 g C kg^-1 and 2.5 g S kg^-1 for MLF1. When MLF3 was amended to soil, the germination rate of Lolium perenne and root biomass increased, but above ground biomass was reduced. In addition, the loss of water soluble oxidized-N forms was reduced when soil was amended with MLF3. These results demonstrate the multifunctionality of MLFs in livestock manure management systems, as emission capture and nutrient recycling technology.