Nutrient pollution has a detrimental effect for the ecosystems, caused by the excessive loss of nutrients to the air, soil and water. Nitrogen-based compounds are one of the pollution contributors. When found in excess, nitrogen-based compounds provoke adverse effects in water bodies, known as eutrophication. These effects include the algal bloom, depletion of dissolved oxygen and ecosystem unbalance, which could cause the death of animals living in it.[1]
Nitrogen excess is usually removed in wastewater treatment plants by several biological treatment steps. However, space and economic constrains prevent the full implementation of these processes for the required discharge limits in some plants. Due to the need of managing nitrogen pollution in a more sustainable and efficient way, this project aimed to reduce nitrogen excess and recover energy in the form of hydrogen using an alternative non-biological process. A photoelectrochemical process was studied for the oxidation of nitrogen compounds. These compounds are oxidized by the photoexcited holes generated by the incoming irradiation at the photo-anode. Consequently, the photoexcited electrons are driven to the cathode by the external circuit that connects the two electrodes to produce hydrogen. This study is focused on the oxidation of two of the nitrogen species commonly found in wastewater: ammonia and urea. A photoelectrochemical cell was used with an immobilized TiO2 semiconductor as photo-anode and a Pt metal cathode. Due to the pH-controlled equilibrium that exits between ammonia and its ionic form ammonium in water, the ammonia oxidation study was carried out over a range of different pH.
Keywords: Photoelectrochemical oxidation, Urea, Ammonia, Hydrogen
Acknowledgement: The authors would like to acknowledge the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement N ͦ 812574.
[1] EPA. Aquatic Life Ambient Water Quality Criteria for Ammonia – Freshwater. United States Environmental Protection Agency (2013).