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My Ph.D. activity developed along four lines of research dealing with non-thermal plasma (NTP) induced chemical processes for water remediation and biomedical applications. Specifically, I studied the effectiveness of atmospheric air plasma treatment in decomposing emerging organic contaminants (EOCs). The experimental setup used was a dielectric barrier discharge (DBD) reactor, a prototype developed in collaboration with the Department of Industrial Engineering of the University of Padova. Among EOCs, I chose six different contaminants, notably sulfamethoxazole, a veterinary antibiotic, triclosan, an antibacterial agent, perfluorooctanoic acid (PFOA), a perfluorinated organic contaminant, and the herbicides irgarol, metolachlor and mesotrione. Kinetics of their removal by plasma, intermediates of oxidation, possible degradation pathways and conversion to CO2 were evaluated. The achievement of more than 93% of conversion was observed for all the contaminants used at the initial concentration of 5 μM, except for PFOA (42%). An important advancement in my research involved the assessment of residual toxicity of plasma treated water samples. For this purpose, in collaboration with Prof. Giovanni Libralato (University of Naples), we tested the efficiency of plasma treatment in producing water free from ecotoxicological effects due to potentially toxic by-product residues. We tested one of the pollutants mentioned above, sulfamethoxazole (SMZ), an antibiotic listed among the most important emerging organic contaminants. A battery of acute and chronic toxicological test were employed: Daphnia magna, Raphidocaeilis Subcapitata and Vibrio Fischeri. It was found that toxicity of SMZ 5×10-4 M is minimized (V.fischeri) or reduced to zero (D. magna, R. Subcapitata) after 4 h of plasma treatment. To improve the efficiency of our DBD reactor, we tested the effect of addition of a photocatalyst, TiO2. We compared the kinetics of degradation of Irgarol in photocatalytic plasma process with those obtained when TiO2 was not included. The results obtained suggest that the effect of photoactivation by titanium dioxide in our reactor was negligible under the conditions employed. Possible reciprocal effects of different organic pollutants dissolved in water subjected to plasma induced advanced oxidation in our dielectric barrier discharge (DBD) reactor were then evaluated. As case study for this investigation, I chose the herbicides S-metolachlor and mesotrione, which are commonly applied in mixture. Results revealed that metolachlor does not affect mesotrione kinetics and viceversa when they are in solution, in 1:1 ratio. A new reactor was developed in our lab, in collaboration with Dr. Bosi from the Department of Industrial Engineering (University of Padova) with improved design and features with respect to the existing DBD reactor. The new reactor, operating in streamer discharge regime, was exhaustively characterized in collaboration with Dr. Gabriele Neretti (University of Bologna) and Dr. Barbara Zaniol (Consorzio RFX), and tested on phenol and metolachlor. Finally, during a four-month stage at the University of Bochum (Germany) I had the opportunity to work on a project dealing with plasma applications in the biomedical field under the supervision of Profs. Julia Bandow and Jan Benedikt. In particular, the effects of two plasma sources were tested in vitro on glyceraldehyde 3-phosphate dehydrogenase and E. coli. The results obtained for the enzyme suggest the importance of oxidation of the thiol group of the active site in plasma mode of action. The same approach was applied to assess the effect of ionic components of plasma by a new source developed by Prof. Benedikt (University of Bochum). The study of inactivation of the enzyme via plasma, with and without ions, showed a synergic effect between radicals and ions.

A new bench-top reactor employing a streamer discharge in air was developed and tested for potential use in an advanced oxidation stage in water treatment processes. The complex heterogeneous system and the ensuing chemical processes were characterized using an integrated approach to map the morphology of the plasma/gas/liquid interface, identify the plasma short-lived excited species, determine the oxidants in solution and monitor the organic pollutants degradation. Three model pollutants were used in these experiments, rhodamine B, phenol and metolachlor. The first two are common standards used to evaluate the performance of advanced oxidation processes. Metolachlor is a widely used herbicide listed among the most important recalcitrant emerging organic pollutants. Energy efficiency, kinetics and products of our tests show a good performance of the reactor. Specifically, mineralization appears feasible also in the case of metolachlor.