# Electrodegradation of Selected Water Contaminants: Efficacy and Transformation Products
## 1 Introduction
### Benzotriazoles  
Benzotriazoles are polar organic heterocyclic compounds which, due to their chemical structure and properties, find applications as corrosion inhibitors, coolants and hydraulic fluids, de-icing/anti-icing fluids, coating materials, dishwasher detergents, radioprotectors and photostabilizers in the production of plastics, rubber, and chemical fibres [15; 16]. Approximately 9000 tonnes of \(1H\)-benzotriazole (BTA) and its derivatives are produced worldwide annually [17], some of which are released into the environment through various human activities. BTA is currently under substance evaluation by the European Chemicals Agency (ECHA) within the Community Rolling Action Plan due to its suspected endocrine disrupting properties and ongoing assessment as a persistent, bioaccumulative, and toxic substance [6] and because of that, benzotriazoles are considered environmental pollutants of particular concern.  
Six main methodologies are used for the removal or degradation of emerging pollutants [7], of which a number of methods have been applied for the removal of BTA. However, the use of conventional processes for the removal of BTA has generally resulted in low efficiencies [18]. Therefore, efforts are being made to find more efficient technologies for removing this pollutant, and in this regard, electrochemical advanced oxidation processes (AOPs) are being investigated, either independently or in combination with other processes. The EO process, as a method for removing BTA from model wastewaters, has been applied in various studies. The results of these studies have shown that the efficiency of BTA removal depends on the material of the electrodes, the current density, the duration of the treatment, and the electrolyte used [19]. An examination of the influence of electrolytes (Na\({}_{2}\)SO\({}_{4}\)+NaNO\({}_{3}\) and Na\({}_{2}\)SO\({}_{4}\)+NaCl) on the formation of active sulphate species that lead to the degradation of BTA resulted in the highest degree of degradation, mineralization, and synergism of BTA degradation and the lowest energy consumption using an electrolyte in which the ratio of Na\({}_{2}\)SO\({}_{4}\) vs. NaCl was 10:1 [20]. During the electrochemical degradation of BTA, a significant decrease in oral lethal dose (LD\({}_{50}\)) values and bioaccumulation factors in rats was observed [18]. Other research has shown applicability and synergism in BTA removal by a UV-C (ultraviolet-C spectrum) process combined with electrogenerated H\({}_{2}\)O\({}_{2}\) using a carbon-based gas diffusion electrode [16]. For the removal of BTA and other organic compounds from model water used in cooling towers, the application of vertical flow constructed wetland (VFCW) and EO was tested, independently and in combination. The EO process after VFCW treatment contributed to the increase in the removal of organic compounds. In the case where the EO process was applied first, the removal efficiency was 100% using the BDD anode, and 75% using the mixed metal oxide (MMO) anode [21]. Paper [22] presents the results of applying the photo-electro-peroxon/zero-valent iron hybrid process for the degradation of methanyl yellow as a sample containing various organic pollutants, including benzotriazole. This process enabled the complete degradation of BTA and a TOC removal efficiency of 84.2% from a model solution. A more detailed literature review of these studies can be found in the Supplementary Materials (S1, Table S1b) [16; 19; 20; 21; 22].