Recovery of phosphate using multilayer polyelectrolyte nanofiltration membranes

✍ Scribed by Seong Uk Hong; Lu Ouyang; Merlin L. Bruening

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 204 KB
• Volume: 327
• Category: Article
• ISSN: 0376-7388
• DOI: 10.1016/j.memsci.2008.11.035

✦ Synopsis

Nanofiltration (NF) is an attractive technique for selective recovery of phosphate from waste waters. This work examines the potential of NF membranes prepared by alternating layer-by-layer deposition of polycations and polyanions on porous substrates for selective recovery of phosphate from chloridecontaining solutions. These membranes are attractive because they contain a high surface charge, and the minimal thickness of the polyelectrolyte skins allows a high flux. In the best case we examined, at pH 8.4 poly(styrene sulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) films deposited on a porous alumina support showed a 98% rejection of phosphate, a chloride/phosphate selectivity of 48, and a solution flux of 2.4 m 3 /m 2 -day at 4.8 bar. By way of comparison, commercial NF 90 membranes exhibited low chloride/phosphate selectivity with more than 97% rejection for both chloride and phosphate at a solution flux of only 1.2 m 3 /m 2 -day. The rejection of phosphate depends on the pH of the feed solution, with rejection decreasing at lower pH where a large fraction of phosphate is H 2 PO 4

-. Even at pH 5.6, however, phosphate rejection was 86% and chloride/phosphate selectivity was 6 when using (PSS/PDADMAC) 4 PSScoated membranes. The selectivity of PSS/PDADMAC membranes varies significantly with the number of deposited layers, confirming that NF properties are very sensitive to film structure.