Development of a novel electrochemical system based on gas-diffusion-electrode for selective ammonia recovery

Abstract

Nowadays, nitrogen compounds in wastewater, especially ammonia (NH3), which is produced during the decomposition of organic nitrogen, are commonly treated by denitrifying bacteria, converting it to dinitrogen gas. However, recent trend related with NH3 treatment is to recover as a resource, rather than remove it. One of the most representative technologies is ammonia stripping, but it always requires extremely high energy to adjust solution pH and temperature. To solve the aforementioned issue, electrochemical approach based on electrochemical dialysis (ED), which can be operated without chemical addition and temperature control, was developed. Although ED has an apparent advantage regarding energy aspect, additional process such as NH3 stripping always have to be implemented for pure NH3 recovery and for utilization. This problem can be avoided if a gas-diffusion-electrode based electrochemical system (GDE-ES), which is the integrative system of ED and post-treatment process, is adopted. The unique feature of this system is supplying air both for ammonia stripping and lowering operation energy. Even though energy-efficient ammonia recovery could be achieved with GDE-ES, there was back-diffusion issue, which is one of the most fatal issues regarding membrane-based techniques. Therefore, in this study, inhibition of back-diffusion was carried out by increasing flowrate or temperature of the supplied air. GDE-ES was not limited to the recovery of NH3 in wastewater

an experiment was also conducted with a solution containing a ferrous ethylenediaminetetraacetic acid (EDTA), which is the selective NO absorbent. Oxidation of ferrous EDTA dramatically lowered total electrochemical energy consumption as well as efficient NH3 separation. The novel electrochemical approach (GDE-ES), developed in this dissertation, is one of the most energy-efficient methods to recover NH3 in waste

therefore, it has the potential to become the most effective technology for waste resource recovery.