Livestock wastewater (LW) typically contains a substantial amount of NH4+ that can potentially be recovered and used in fertilizers or chemicals. In an attempt to recover NH4+ from LW, a novel electrochemical approach using a gas diffusion electrode (GDE) was developed and its efficacy was demonstrated in this study. The GDE-based electrochemical device, when operated at an air-flow rate of 20 mL/min, was free of back-diffusion flux, which is a fatal drawback of any membrane-based NH4+ separation approach. Continuous operation resulted in a nitrogen flux of 890 g N/m2d with synthetic LW and 770 g N/m2d with real LW at a current density of 10 mA/cm2. The electrochemical energy input was 7.42 kWh/kg N with synthetic LW and 9.44 kWh/kg N with real LW. Compared with the traditional stripping method, the GDE-based electrochemical system has a certain potential to be competitive, in terms of energy consumption. For instance, a rough-cost estimate based only on operating costs regarding chemical usage, air blowing, and water pumping revealed that the system consumed 13.44 kWh/kg N, whereas the conventional stripper required 27.6 kWh/kg N. This analysis showed that an electrochemical approach such as our GDE-based method can recover NH3, (particularly in gaseous form) from LW. In addition, with the future development of a smart operation method, as proposed and demonstrated in this study, the cost-effective implementation of a GDE-based method is feasible.
Keywords: Ammonia recovery; Ammonia stripping; Electrochemical system; Gas diffusion electrode; Livestock wastewater.
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