Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein

Abstract

A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.