(557e) Polyelectrolyte Multilayer Membranes for Nutrient Recovery from Concentrated Wastewater

This talk will describe a novel nanofiltration technique for selectively recovering nutrients (ammonium and potassium) from concentrated wastewater. Global demand for fertilizer production is expanding substantially to meet the excess food demand with an increased world population. Anaerobic digestate (AD) of different concentrated wastewater systems contain considerable amounts of ammonium (NH₄⁺) (300-700 mg/L) and potassium (K⁺) (13-120 mg/L)-based nutrients. In addition to reducing energy costs and CO₂ emissions compared to conventional fertilizer manufacturing, recovering nutrients from these waste streams can aid with problems like eutrophication, which otherwise costs billions of dollars to US economy annually. However, apart from nutrients, wastewater streams also contain excessive amounts of organic contaminants (TOC) (250-750 mg/L). This work thereby aims to design selective membranes for nutrient recovery while excluding organic contaminants. In this work, surface-modification of commercial nanofiltration (NF) membranes have been utilized to observe NH₄⁺ + K⁺/TOC selectivities by using both synthetic and real wastewater. Surface-modification of NF membrane was done by utilizing layer-by-layer (LBL) deposition of two oppositely charged polyelectrolytes and a range of polyelectrolyte multilayer (PEM) membranes were fabricated by tuning variety of LBL parameters such as polymer types, pH adjustments, addition of salt (NaCl) within polylectrolytes, polymeric cross-linking, etc. Both the surface charge and size-exclusion mechanism were found to be important for achieving high NH₄⁺ + K⁺/TOC selectivity. PEM membranes modified by a strong polyelectrolyte system of poly diallyl dimethyl ammonium chloride (PDAC) and poly sodium-4 styrene sulfonate (SPS), through a charge-exclusion mechanism, can achieve >2X NH₄⁺ + K⁺/TOC selectivity compared to commercial NF270 membranes and permeates more NH₄⁺ and K⁺. While PEM membrane with relatively weaker polyelectrolyte system of polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA), through a size-based exclusion mechanism, were able to provide ~2X NH₄⁺ + K⁺/TOC selectivities compared to NF270 by rejecting higher organics.