Closing the nutrient loop by recovering P and N from wastewater is crucial for protecting aquatic environments from pollutants and producing sufficient fertilizer to support growing populations. The high concentrations of phosphate and ammonia in source-separated urine offer propitious opportunities for using membrane technologies to remove P and N as contaminants and capture these nutrients as fertilizer products. Firstly, by the principle of Donnan dialysis, HPO4- in a fresh urine feed can exchange with Cl- from an aqueous NaCl stream, across an anion-exchange membrane for P separation and recovery. Donnan dialysis drives anion-exchange via an electrochemical potential gradient set-up between the urine and inexpensive/waste receiver solution containing Cl-, such as seawater, reverse osmosis brine, and water softening recharge waste. Through application of simulated seawater and reverse osmosis brine as draw-solutions ~93% and ~95% phosphate recoveries from simulated fresh-urine were achieved, respectively. Furthermore, by increasing the feed and draw solution volume ratio to 2 and 4, phosphate can be enriched in the product stream ~1.4 and 2.5?, respectively, relative to the initial feed. Then, phosphate minerals can be precipitated from the enriched draw solution and applied as fertilizer; alternatively, draw solutions containing beneficial nutrients and micronutrients (KCl, MgCl2, and CaCl2), such as water softening recharge waste, can be applied to capture phosphate as a liquid fertilizer source. The second technology, membrane distillation (MD), can recover volatile NH3 from hydrolyzed urine, but conventional operation suffers from the simultaneous permeation of H2O vapor that results in poor selectivity for NH3 transport and high energy demand. To overcome the limitations of conventional MD, we present isothermal membrane distillation with acidic collector (IMD-AC). The innovative isothermal operation, i.e., same feed and collector temperatures, effectively suppressed water vapor permeation while maintaining ammonia vapor flux and, thus, significantly improved selectivity for NH3 transport. Against a total ammoniacal nitrogen concentration gradient, i.e., uphill transport, ammonia recovery of ~60% was attained, highlighting the prospect of the technology for high-yield recovery. Critically, IMD-AC achieved approximately 95% savings in vaporization energy consumption relative to conventional MD by practically eliminating the evaporation of H2O. This study shows the promising potential of an integrated Donnan dialysis and IMD-AC system for the selective and energy-efficient recovery of phosphate and ammonia from source-separated urine.
This presentation is available to AMTA Members only.
- Stephanie McCartney
- Columbia Univeristy
- AMTA Fellowship Recipients: Advancements in Membrane Research - Part 2, Online
- AMTA Fellowship Recipients Series
- Nutrient Recovery, Donnan Dialysis, Membrane Distillation