(557c) Electro-Driven Membrane Processes for Selective Recovery of Ammonia from Wastewater

Ammonia in wastewater can potentially displace high value fertilizer if recovered properly. Electro-driven membrane processes provide a compelling platform to separate and recover ammonia. Our group focuses on two major pathways to achieve this goal: (1) selective transport of ammonium through an ammonium-selective membrane and (2) electrochemically mediated conversion of ammonium into ammonia coupled with membrane stripping. The first approach is enabled by the use of ammonium-selective adsorbents introduced at the membrane/solution interface. In particular, we tested Prussian blue analogue that was directly deposited at the membrane surface, which showed an improved selectivity towards ammonium against sodium in synthetic and domestic wastewaters. The second approach is based on bipolar membrane electrodialysis, wherein bipolar membranes produce acid and base for selective ammonia recovery by membrane stripping. Ammonium is first separated from wastewater containing high a total ammonia nitrogen concentration (e.g., sidestream) through a cation exchange membrane. The separated ammonium is converted to ammonia at an elevated pH by hydroxide production from the bipolar membrane. Then, ammonia selectively captured by an acid solution produced also by the bipolar membrane in a membrane contactor. These two approaches demonstrate how electro-driven, selective membrane separations can be a critical first step towards circular economy.