Ligand-Enabled Donnan Dialysis for Phosphorus Recovery from Alum-Laden Waste Activated Sludge

Abstract

While many nutrient recovery technologies target liquid waste streams, new strategies are required for effective phosphorus recovery from solid waste. This study reports an innovative ligand-enabled Donnan dialysis process to recover orthophosphate (P(V)) from alum-laden waste activated sludge (WAS). Four ligands, namely acetate, citrate, ethylenediaminetetraacetate (EDTA), and oxalate, were evaluated for P(V) release from a synthetic sludge containing 5 mM P(V) and 25 mM Al(III) and a real, alum-laden WAS with similar contents. Citrate and EDTA released more than 95% of P(V) at doses of 30 mM, outperforming acetate and oxalate. The ligand-based solubilization strategy was coupled with Donnan dialysis to recover P(V) into a clean sodium chloride draw solution. After Donnan dialysis with the synthetic sludge, the P(V) recovery's order was as follows: EDTA (54.4%) > citrate (41.7%) > oxalate (4.3%). The P(V) recovery efficiencies were slightly lower for Donnan dialysis with real, alum-laden WAS, namely 45.1% and 25.2% for EDTA and citrate addition, respectively, due to competitive effects exerted by other dissolved species. These promising results successfully demonstrated the proof-of-concept for ligand-enabled Donnan dialysis.

Ion exchange enabled selective separation from decontamination to desalination to decarbonization: recent advances and opportunities

“…Ion exchange membranes have limited ion storage capacity compared to resins, thus enabling ion separation through ion transport across the membrane without much retention or storage. A biological nitrate-selective ion exchange process (BIO-NIX) 62 and an ion exchange membrane-enabled Donnan dialysis process 99 have demonstrated the feasibility of minimizing/eliminating ion exchange regeneration via process design. The BIO-NIX process combines a fixed-bed biological denitrification (BIO) column with a nitrate-selective ion exchange (NIX) column in sequence.…”

“…As a result, the BIO-NIX system achieved resilient nitrate removal for over two months without any intermittent resin regeneration. 62 The ion exchange membrane-enabled Donnan dialysis process 99 leverages electrochemical potential as the driving force to transport phosphate ions from one side (wastewater) to another side (draw solution) of an anion exchange membrane. The use of an ion exchange membrane eliminated the regeneration process when using resins.…”

“…The use of an ion exchange membrane eliminated the regeneration process when using resins. Several recent advances of Donnan dialysis include using ligands to enable extracting phosphate from alum-laden waste activated sludge instead of wastewater, 99 using tubular anion- and cation-exchange membranes to simultaneously recover ammonium and phosphate from urine as struvite, 100 and more. 101 While these new processes are promising to minimize or eliminate regeneration, more work is needed beyond proof-of-concept demonstration to facilitate field implementations.…”

Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

“…With the use of proper technologies, approximately 90% of P that enters a municipal wastewater treatment plant (WWTP) is removed and incorporated into wastewater sludge, which can be a promising source for P recovery . Whole digestate, a slurry produced from anaerobic digestion of wastewater sludge, is typically enriched with inorganic orthophosphate (IP) in both aqueous and solid phases. − Direct land applications of digestate can be subject to restrictions due to the concerns over high concentrations of ammonium and salinity, recalcitrant compounds, and heavy metals. , To maximize P recovery from whole digestate, various treatments including strong acid and base, complexing agents, ozonation, ultrasonication, thermal, and electrochemical treatment have been applied to leach P out of the solid phase. − Electrochemical treatment, which relies on water electrolysis to mobilize solid P, is of particular interest with potential benefits such as reduced handling of corrosive chemicals, flexible operation, and relatively low environmental impact.…”