Scale-up of an electro-oxidation process for natural sources water treatment

Water is the most important resource for life on earth. In particular, humans need clean and safe water to prosper. Drinkable water availability has always represented an issue, thus nowadays more effort is devoted to developing modern techniques for water purification. The most implemented and adopted water treatments involve chlorine compounds such as hypochlorite, chloramines and chlorine dioxide, which are highly active in killing bacteria. Inevitably, those processes cause changes in the organoleptic features of the treated water because of the used chemicals. Other technologies with no added compounds, i.e. UV light disinfection, ozone treatment and electrochemical advanced oxidation processes (EAOP) could be an alternative. The electrochemical technology for water purification is still developing and represents a valid alternative to chlorination as it does not require any added chemical to the water and the energy supply needed for the disinfection activity can be produced by renewable sources. This work focuses on the scale-up of an electro-oxidation process for natural sources water treatment and it is part of the regional call PRISM-E about industrial research and development. This Thesis also includes the study of novel catalysts designed for Oxygen Evolution Reaction (OER) and their electrodisinfection activity. The catalyst used, designed by the CREST group, is antimony-doped tin oxide (ATO) electrodeposited on Ti. The electrodeposition technique was scaled-up by using a 2-electrodes cell, using pre-treated Ti sheets as support. Aqueous solutions of the metal precursors were used to obtain a layer-by-layer coating, then annealing is required to form the tin oxide active phase. The electrochemical reactor was put in operation at the site of Sampeyre and its bacteria abatement activity was observed analysing some samples of the treated water at the outlet of the reactor. A short-term measure was conducted to ensure the correct reactor functioning, then a long-term measure was carried out to confirm both the catalyst coating stability and the disinfection activity. The long-term test enlightened a high disinfection activity for the lowest flow rate (98% conversion). Also, the concentration of the catalyst metals in the outlet stream was below law limits, suggesting a stable coating. OER and EAOP are 2 sides of the same coin, thus manganese-based catalysts and pristine cobalt antimonate, synthesized for the OER, were also tested for EAOP. Electrochemical tests were conducted using phenol as a probe molecule for the oxidation mechanism. Among all, the most active was manganese oxychloride, which exhibited 85% conversion, even higher than the ATO. Such material can be proposed as a substitute of the ATO catalyst in a further scale-up of the bacteria disinfection reactor, being more active and secure from the toxicity point of view. Additionally, X-Ray diffraction analysis confirmed the catalyst stability and did not point out a loss in the chlorinated phase. Instead, all the catalysts tested towards OER showed similar activity, except for the platinum-doped cobalt antimonate obtained by solid-state reaction, which stands out among the proposed materials for the OER in acidic media, having 84.1% Faradaic efficiency and one of the lowest overpotentials of 1180 mV. Finally, this Master Thesis confirms that catalysts showing an activity towards water and phenol oxidation have the potential to be used in bacteria disinfection for water treatment.