Recovery of ammonia from simulated membrane contactor effluent using bipolar membrane electrodialysis

Abundant in municipal, agricultural, and industrial wastewaters, ammonia is a versatile chemical, which can be used as fertilizer or as a hydrogen carrier for the hydrogen economy. Membrane contactors (MCs)are an effective membrane process for selectively recovering ammonia from a wastewater stream, but the system's continuous acid consumption and the residual acidity in the produced stream remain a major hurdle. In this study, we propose a chemical-free, electrified process that combines MC with bipolar membrane electrodialysis (BMED)to produce ammonia as a gas from wastewater. We devise three different BMED configurations, and identify the most suitable configuration by examining the impact of different operating conditions including pH, initial ammonia concentration, and relative volume ratios on the ammonia recovery and BMED energy consumption. We demonstrate up to ?68 percent recovery of theoretically recoverable ammonia, and attribute the unrecovered fraction primarily to the diffusion of neutral ammonia through membranes. While the system is sub-optimal, the relative energy consumption of the system is comparable to the Haber-Bosch process for conventional ammonia production, with potentially lower energy consumption and higher ammonia recovery through higher initial ammonia concentrations, higher relative volume ratios or alternate BMED configurations.