# Electrodegradation of Selected Water Contaminants: Efficacy and Transformation Products
## 1 Introduction
### Triton X-100 (t-Octylphenoxy[poly(ethoxy)] Ethanol)  
Alkylphenol polyoxyethylene ethers (APPE) are non-ionic surfactants used as emulsifiers, dispersants, antioxidants, wetting agents, etc., in numerous industrial processes and products [23]. The consequence of such a wide application is the continuous release of APPE into the environment or into wastewater treatment plants. Their biodegradation and degradation in wastewater treatment plants leads to the formation of stable metabolites that represent a much greater ecotoxicological problem than APPEs themselves [24; 25; 26]. From this group of surfactants, nonylphenol polyethoxylates (NPPE) have the largest commercial presence, more than 80%, which is why they have attracted the most attention of the professional and scientific public so far. The rest are mainly octylphenol polyethoxylates (OPPE) with a small share of dodecylphenol polyethoxylates and dinonylphenol polyoxylates, only about 1% [27]. NPPE and OPPE are recognized as endocrine disruptors, which is why they are classified as Substances of Very High Concern [6] and as priority hazardous substances in the European Water Framework Directive (2013/39/CE), and their use is limited and controlled. Despite strict restrictions, APPEs are still detected in numerous biotic and abiotic matrices, as well as in industrial effluents [28; 29]. Previous research has shown a very effective application of electrochemical processes, such as electro-Fenton, photoelectrooxidation, and a combination of electrodeposition and with ozonation and other chemical oxidants, in the degradation of NPPE in aqueous solutions [30; 31; 32; 33]. Although OPPE degradation products are significantly more soluble than NPPE degradation products, which is why they have been found in numerous biotic and abiotic matrices, the EO potential for the degradation of these compounds has not been sufficiently investigated so far. An overview of research on electrochemical treatments of OPPE is given in the Supplementary Materials (S1, Table S1c) [34; 35; 36; 37; 38]. In the present paper, we addressed the electrooxidation of three important environmental contaminants, namely, anticorrosive \(1H\)-benzotriazole, plasticizer dibutyl phthalate,and non-ionic surfactant Triton X-100. These are structurally very different high-production chemicals with a wide range of applications. Their common denominator is their frequent detection in environmental water bodies, making them important water contaminants with adverse effects on aquatic organisms. They were selected based on their regulatory relevance and hazardous classification under the EU's chemicals legislation (ECHA). Except for DBP, EO is seldom studied as a possible AOP to improve the elimination of these contaminants from wastewaters, which are their important emission source into the environment. This study systematically compares the degradation efficiency and transformation of three structurally distinct yet regulatory-relevant (SVHC or under evaluation) contaminants. Using identical EO conditions enabled the assessment of the influence of chemical structure on the electrochemical degradation, which is an important topic because the real wastewater always contains several structurally different contaminants. Furthermore, the study introduces a comparative analysis of kinetic and energy consumption aspects of EO in different supporting electrolytes. The main TPs were identified using a combination of analytical techniques, providing a deeper understanding of the potential secondary toxicity. TP identification is rarely encountered in the papers dealing with electrodeposition, but it is equally important because the TPs are not necessarily less problematic than the parent pollutant. Practical insights regarding the choice of electrolyte and the use of a commercially available BDD anode add to the practical value of the study in the context of industrial wastewater treatment.