Electrodes and reactor design optimization for electrochemical water treatment

Electrochemical advanced oxidation processes (EAOP) represent a very promising alternative for the treatment of drinking water, which consists in the electro-generation of oxidizing substances in a sustainable, green and chemical-free way. The aim of this Master Thesis is to study the feasibility of utilize an EAOP system, powered by renewable energy, for the disinfection of low conductive water. Therefore, a preliminary design of the reactor is proposed, estimating the sizing and the power required to power it and discussing possible solutions for system improvement. This work is part of the TrAcqua project, done in collaboration with ACDA, which provided the technical specifications that the reactor must meet. Furthermore, an experimental work has been carried out for the study of a promising and performant anode material, based on the antimony doped-tin oxide (ATO) electrocatalyst, identifying an innovative, sustainable and scalable method for the electrode manufacturing. The objective of this experimental work is to optimize the parameters for the electrode preparation and the operating conditions, thus evaluating the activity of these innovative electrodes towards the oxidation of phenol, which was chosen as model target molecule. The results on the reactor design study showed difficulties in operating with non-conductive water, while remaining below the power that can be supplied by the renewable energy system (~1 kW). An extremely high number of electrolytic cells would be required to treat the design flow rate of 0,5 L/s, with an energy consumption of about 5-10 kW, a too high value even considering the flow rate reduced to 0,1 L/s. Consequently, it has been proposed a configuration achievable through the addition of a small amount of chlorine, in the form of NaCl, to increase the performance of the cell and decrease its energy consumption and the required number of electrodes for the electro-chlorination process. In this way, it is possible to propose a reactor design characterized by a feasible number of cells, equipped with about 50 electrodes of 100 cm2 and a sustainable energy consumption of 0,5 kW for the reduced flow rate, remaining well below the recommended limits for the presence of chlorine in water. The experimental work has identified the technique of spray deposition of ATO powder on carbon-based substrates a potential alternative technique to the classic ATO electrodeposition on titanium. The latter is an effective process, but entails some drawbacks such as long preparation time (including the substrate cleaning), difficult to reproduce and standardize, and a low sustainability as it involves the disposal of acidic and metallic wastes. Therefore, the production process of spray-deposited electrodes has been optimized in terms of catalyst loading and optimal antimony doping, obtaining the most effective configuration at 2 mg/cm2 and 11%Sb. Subsequently, the optimal operating conditions were optimized, also performing comparison tests with commercial electrodes and obtaining comparable results. Finally, exploiting literature correlations, the activity of the prepared ATO electrodes towards the phenol oxidation was used to evaluate the potential activity of the same materials towards the water disinfection, proving to be effective for bacteria removal. From these correlations, a log-2 bacteria removal in 25 minutes is expected, as will need to be verified in future system developments.