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Non-thermal plasma (NTP) is gaining increasing attention as a promising approach for advanced water treatment to degrade persistent organic pollutants. Aqueous solutions of sulfamethoxazole (4-amino-N-(5-methylisoxazol-3-yl)-benzensulfonamide, SMZ), an antibiotic largely employed for humans and animals and a widespread persistent pollutant of waters and wastewaters, were subjected to air NTP treatment in a dielectric barrier discharge (DBD) reactor. The effects of SMZ initial concentration and of the solution pH on SMZ decomposition kinetics and transformation products were investigated. Efficient degradation was achieved, resulting in the complete removal of SMZ (10 µM initial concentration) in less than 25 min treatments, in the exhaustive mineralization (a result never reported before in plasma treatments and seldom reached also with other advanced oxidation processes) of all organic carbon in 6 h and in an energy efficiency of 6.4 g/kWh at 50% conversion. By means of HPLC-UV/Vis and LC-ESI-MSn analyses, a number of organic transformation products was identified along the path to SMZ mineralization, all present always in very small amounts and in turn decomposed at short treatment times. The effect of the solution pH on the genesis and decay of transformation products was also investigated. Based on comparisons with literature data and on previous findings obtained with the DBD reactor used in this work, it is concluded that the major reactive species involved in the degradation of SMZ are the hydroxyl radical and ozone. Finally, toxicological analyses of water initially containing 0.5 mMSMZ and subjected to 4 h NTP treatment showed that the by-products are not toxic to Raphidocelis subcapitata and Daphnia magna, while residual toxicity was detected by Aliivibrio fischeri. [ABSTRACT FROM AUTHOR]

Atmospheric pressure mass spectrometry (APCI-MS) was used to investigate the positive ions in air containing acetone (A), methanol (M) and mixtures thereof (A + M), subjected to +dc corona discharges. The results of experiments with isotopically labelled analogues, perdeuterated acetone Adeu and methanol Mdeu, and relevant thermochemical data found in the literature allowed us to identify the main ionic reactions occurring in single component systems (A or M) and in binary mixtures (A + M). It is concluded that, thanks to its significantly higher proton affinity, A is very efficient in quenching M-derived ions at atmospheric pressure. These conclusions provide a rationale for interpreting the results of a parallel investigation on the reciprocal effects of M and A when treated together in air at atmospheric pressure with +dc corona in a non-thermal plasma reactor developed previously in our laboratory. Specifically, we observed a marked drop in the degradation efficiency of methanol when it was treated in the presence of an equivalent amount of acetone. This effect is attributed to acetone interfering with ion-initiated degradation processes of methanol, and supports the conclusion that ions and ionic reactions are important in dc+ corona induced oxidation of volatile organic pollutants in air. [ABSTRACT FROM AUTHOR]

• DBD in air achieves complete mineralization of herbicides in water. • Mechanisms of mesotrione and metolachlor advanced oxidation by non-thermal plasma. • No reciprocal influence of mesotrione and metolachlor in atmospheric plasma treatment. The goals of this research were to i) test the ability of air non-thermal plasma to promote the degradation in water of two widespread herbicides, mesotrione and metolachlor, ii) determine the process efficiency and products for each herbicide treated individually, iii) detect and investigate any possible reciprocal effects when the two herbicides, which are often used in combination, are treated together in the same solution. The experiments were carried out using a dielectric barrier discharge (DBD) reactor to generate a strongly oxidizing non-thermal plasma above the liquid surface and induce the advanced oxidation of dissolved organic chemicals. The results of extensive HPLC (UV, MS and MS/MS) and TOC analyses show that air non-thermal plasma efficiently decomposes both herbicides, that mesotrione is considerably more reactive than metolachlor and that complete mineralization of both is achieved at sufficiently long treatment times. Treatment of metolachlor was also performed in tap water, a closer model for environmental systems, achieving the same results as found in deionized water. Detailed product and kinetic studies failed to reveal any effect attributable to reciprocal influence of mesotrione and metolachlor when treated together in the same solution. [ABSTRACT FROM AUTHOR]

Abstract The herbicide 2-(methylthio)-4-(tert -butylamino)-6-(cyclopropylamino)- s -triazine (tradename Irgarol 1051, abbreviated here as Irg), widely used in antifouling paints as biocide inhibiting seaweeds growth, is found in coastal waters in the vicinity of ports and harbors. In this work, Irg was subjected to air non-thermal plasma (NTP) treatment, alone and in the presence of TiO 2. A dielectric barrier discharge reactor was used, powered by AC voltage (18 kV, 50 Hz) to produce air-NTP directly above the surface of the aqueous Irg solution to be treated. Due to the very fast degradation of Irg occurring under the experimental conditions used, the results of kinetic experiments failed to detect any rate enhancement due to titania induced photodegradation. We show, however, that pre-adsorption of Irg on titania provides a means to significantly increase Irg NTP-induced degradation throughput, a result which might have useful practical consequences. It is concluded that this phenomenon is due to the acidic character of TiO 2 which brings more Irg in solution by increasing the value of the ionization ratio, [IrgH + ]/[Irg]. Product analysis, performed by LC/ESI-MSn, allowed us to detect and identify numerous intermediates of Irg degradation and to propose different competing reaction pathways for the investigated NTP induced Irg advanced oxidation process. The extent of mineralization to CO 2 was assessed by Total Carbon analysis. It was found to reach 95% after 5 h treatment of Irg solutions with an initial concentration of 5·10−6 M. These results confirm the capability of our NTP prototype reactor to mineralize persistent organic pollutants. Graphical abstract Image 1 Highlights • Pre-adsorption of Irgarol on TiO 2 increases throughput of plasma induced degradation. • Acidic character of TiO 2 brings more Irgarol in solution by protonation. • The intermediate products formed from plasma degradation of Irgarol are characterized. • Almost total conversion of Irgarol to CO 2 was achieved by plasma degradation. [ABSTRACT FROM AUTHOR]

Verapamil, a drug widely used to treat cardiovascular disorders and an important water pollutant, has been subjected for the first time to advanced oxidation by air non-thermal plasma (NTP) in a previously described DBD reactor. Product analysis was performed to assess the extent of mineralization to CO 2 , quantified by FT-IR analysis, and to detect and identify oxidation intermediates by LC/ESI-MS/MS. Many intermediates form and their time profile was monitored during the treatment. Thorough mass spectrometric analysis and comparison with literature data on the oxidation of the functional groups of verapamil by the reactive species present in the air plasma allowed us to identify most of the intermediates formed by non-thermal plasma activation. The majority of the identified compounds can be attributed to reactions of verapamil with ozone, one of the major oxidizing species in our DBD reactor. A few intermediates, though, appear to form following direct attack by hydroxyl radicals, whereas there is no evidence of any byproduct attributable to reaction with reactive nitrogen species. When treated at low initial concentration verapamil is almost completely mineralized (98%), as determined by total carbon analysis. [ABSTRACT FROM AUTHOR]