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We report an advanced treatment method for phosphoric acid recovery from leached sewage sludge ash. Layer-by-layer (LbL) polyelectrolyte deposition has been used as a tool to modify and convert a hollow ultrafiltration membrane into a nanofiltration (NF) LbL membrane for H 3 PO 4 recovery. To build the LbL membrane, poly(styrenesulfonate) PSS was chosen as polyanion, while three different polycations were used: a permanently charged polyelectrolyte, poly(diallyldimethylammonium chloride), PDADMAC; a pH-dependent charged polyelectrolyte poly(allylamine hydrochloride), PAH; and a PAH modified with guanidinium groups (PAH-Gu). Based on detailed surface characterizations (AFM, XPS and Zeta-potential) it was concluded that both charge density and pH-responsiveness of the polycations are key parameters to control the final membrane surface structure and transport properties. The surface properties of LbL-coated membranes were correlated with the membrane filtration performance, when exposed to the real leached sewage sludge ash solution. The highest permeability was recorded for (PDADMAC/PSS) 6 , a result that was rationalized on its loose, and possibly less interpenetrated, structure, followed by (PAH-Gu/PSS) 6 characterized by a more dense, compact layer. H 3 PO 4 recovery was the highest in the case of (PDADMAC/PSS) 6 , but the retention of multivalent metals (Fe3+ and Mg2+) was low, leading to a more contaminated permeate. The opposite trend was observed for (PAH-Gu/PSS) 6, resulting in a less metal-contaminated, but also a less H 3 PO 4 -concentrated permeate. Our LbL-modified membranes were found to improve the permeability and H 3 PO 4 recovery compared to a commercially available acid-resistant NF membrane. Image 1 • Layer-by-layer NF membranes recover H 3 PO 4 from leachate sewage sludge ash. • Permeability: LbL-coated membranes > commercial acid-resistant NF membranes. • Type of polycation in LbL coatings affects separation properties. • Largest H 3 PO 4 recovery for permanent polycation, but low Fe3+ and Mg2+ retention. • Weaker polycation with guanidinium moiety: less metal and less H 3 PO 4 in permeate. [ABSTRACT FROM AUTHOR]

• Poly(l -lactic acid) electrospun fibers loaded with struvite crystals were prepared. • PLLA fibers loaded with struvite can recover nutrients (N and P) from solution. • Struvite dispersion and location along the fiber section affect nutrient recovery. • The biodegradable nanostructured mat can be employed as ready-to-use fertilizer. 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. [ABSTRACT FROM AUTHOR]