Paltrinieri, Laura, Remmen, Kirsten, Müller, Barbara, Chu, Liangyong, Köser, Joachim, Wintgens, Thomas, Wessling, Matthias, de Smet, Louis C.P.M., and Sudhölter, Ernst J.R.
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]