Hydrogen Gas Recycling for Energy Efficient Ammonia Recovery in Electrochemical Systems

Recycling of hydrogen gas (H₂) produced at the cathode to the anode in an electrochemical system allows for energy efficient TAN (Total Ammonia Nitrogen) recovery. Using a H₂ recycling electrochemical system (HRES) we achieved high TAN transport rates at low energy input. At a current density of 20 A m^-2, TAN removal rate from the influent was 151 g_N m^-2 d^-1 at an energy demand of 26.1 kJ g_N^-1. The maximum TAN transport rate of 335 g_N m^-2 d^-1 was achieved at a current density of 50 A m^-2 and an energy demand of 56.3 kJ g_N^-1. High TAN removal efficiency (73-82%) and recovery (60-73%) were reached in all experiments. Therefore, our HRES is a promising alternative for electrochemical and bioelectrochemical TAN recovery. Advantages are the lower energy input and lower risk of chloride oxidation compared to electrochemical technologies and high rates and independence of organic matter compared to bioelectrochemical systems.