Biodegradable electrospun fibers enriched with struvite crystal seeds for the recovery of phosphorous and nitrogen

One of the greatest global challenges of the 21st century is facing the depletion of phosphorous reserves, widely used in fertilizers. One possibility is to recover the phosphorous discharged in the water by human activities, with the consequent additional benefit of improving water quality by limiting eutrophication. In this work, biodegradable poly(L-lactic acid) (PLLA) nonwovens produced by electrospinning are proposed as highly porous fibrous materials characterized by high surface-to-volume ratio for promoting the crystallization of struvite crystals as a means to recover both phosphorus and nitrogen from a nutrient rich solution. To this aim, PLLA fibers were intentionally loaded with a small amount of struvite crystals (3,7 wt%) by applying different preparation procedures, including sonication steps, single-nozzle and coaxial electrospinning. PLLA fibers containing struvite crystals were immersed in a synthetic solution of suitable ions to investigate the occurrence of struvite accumulation through the analysis of the soaked nonwovens with several techniques, i.e. Scanning and Transmission Electron Microscopy, Wide Angle X-Ray Diffraction, Thermogravimetric analysis and Atomic Emission Spectrometry. We demonstrated that struvite loaded in the PLLA fibers successfully acted as crystal seeds and enabled the precipitation of struvite crystals firmly attached to fiber surface. Results showed that the quality of crystal seeds dispersion in PLLA fibers as well as their location along the fiber section heavily affect struvite recovery. Prospectively, these materials can be directly used, after being in contact with wastewater and enriched with struvite, as ready-to-use fertilizers.