Efficient ammonia recovery from wastewater using electrically conducting gas stripping membranes

Abstract

Recovery of nutrients, such as ammonia, from wastewater offers an attractive approach to increase the overall sustainability of waste management practices. Conventional wastewater treatment processes require significant energy input, and the useful form of nitrogen (ammonia), is usually lost. Ammonia, a major component of fertilizers, is conventionally manufactured using the Haber–Bosch process, which accounts for approximately 2% of worldwide energy demand. A better approach would efficiently capture ammonia directly from the wastewater. In this study, ammonia is recovered directly by using an electrically conducting gas-stripping membrane that is immersed into a wastewater reactor. Under cathodic potentials, these membranes were used to facilitate conversion of ammonium (NH₄⁺) into ammonia (NH₃), which was then extracted by either circulating an acid solution or by applying a vacuum on the back side of the membrane. The mechanism involves water electrolysis, which generates OH⁻, and transforms ammonium to ammonia that is stripped through the membrane. By engineering the surface and transport properties of the membrane 68.8 ± 8.0 g N per m² d⁻¹ of ammonia was recovered, with an energy consumption of 7.1 ± 1.1 kW h kg⁻¹ N.