Multi-layer anode for saline wastewater treatment: Manipulating oxidant generation pathway by TiO_2 thin film deposition

Nowadays, both developed and developing countries are suffering from water scarcity due to the rapid urbanization and global climate change. The on-site reuse of water is a possible soln., which calls for the development of various decentralized wastewater treatment techniques. Electrochem. oxidn. is a promising candidate due to its modular design, convenient operation, and small carbon footprint. In the past decades, the IrO_x based DSA electrode showed excellent performance on saline wastewater treatment. However, the high cost and low energy efficiency impede the widespread application. In this study, uniform TiO_2 thin film was deposited onto the IrO_x electrode by novel spray- pyrolysis process. Instead of acting as catalyst, the IrO_x interlayer is served as ohmic contact to facilitate the electron transfer from TiO_2 top layer to the bottom Ti metal plate. Hence the required loading is significantly decreased. Interfacial electrochem. reaction in saline water can be manipulated by this approach. The pristine IrO_x electrode is active for both oxygen and chlorine evolution. After TiO_2 deposition, chlorine evolution prevails. Further increasing the thickness of TiO_2 film or inducing SnO_2 dopant provide addnl. active sites for the generation of stronger oxidants such as Cl• and Cl•. The optimized TiO/IrO electrodes were integrated into the solar-powered electrochem. reactor to treat black water. Rapid COD and total nitrogen removal as well as disinfection can be achieved after 4 h with energy cost of 100-200 kWh/kg COD. Phosphate, Ca^(2+), and Mg^(2+) can be simultaneously removed in the form of cathodic ppt. The treated water meets the criteria for water reuse