In recent years, accumulation of pharmaceutical compounds in the environment has been an issue of growing concern. Conventional wastewater treatment has limited effectiveness with many pharmaceuticals at concentrations of ppb or ppt scale. An intuitive solution would be to treat the pharmaceuticals-contaminated wastewaters at the source sites before dilution in sewer networks. Health institutions with concentrated drug consumption provide logical point 2 sources for pharmaceuticals entering the sewage. This paper describes the pilot-scale removal of a wide range of pharmaceuticals from real wastewaters via gas-phase pulsed corona discharge oxidation. The process was studied for raw sewage from a public hospital and for biologically treated wastewater of a health-care institute. The non-selective oxidation of the observed pharmaceuticals (32 compounds) was effective at reasonable energy cost: 87-% reduction in residual pharmaceuticals (excluding biodegradable caffeine) from raw sewage was attained with 1 kWh m-3 from the raw sewage and 100% removal was achieved for biologically treated wastewater at only 0.5 kWh m-3. The impact for affected aquatic environments upon the present solution would be a dramatically reduced load of pharmaceutical accumulation. Keywords Non-thermal plasma, Micropollutant, Drug, Hydroxyl radical, Ozone Highlights A plasma pilot system is used for drugs abatement from point source wastewaters An extensive range of 57 aqueous pharmaceuticals was monitored in plasma oxidation Substantial reduction of residual medicines was achieved at feasible energy cost
Water treatment by gas-phase pulsed corona discharge (PCD) relies mainly on utilization of ozone and OH radicals as oxidizing agents. In a configuration where the treated solution is showered through the plasma zone, the gas−liquid contact surface is the primary OH-radical formation site and the interface in the mass transfer of ozone. Its significance to overall process efficiency is therefore notable. In this study, the effect of varying contact surface area at different discharge powers was investigated from the perspective of efficient utilization of the two prime oxidants in slow reaction with oxalate. It is seen that increasing the area of the contact surface improves OH-radical utilization up to the point where the pollutant oxidation efficiency abruptly decreases presumably because of unfavorable pulse energy distribution in the gas−liquid mixture. The existence of an optimal area for a given power has implications for future studies in the design of pulsed plasma applications for water treatment.
The highly energetic electrons in non-thermal plasma generated by gas phase pulsed corona discharge (PCD) produce hydroxyl (OH) radicals via collision reactions with water molecules. Previous work has established that OH radicals are formed at the plasma-liquid interface, making it an important location for the oxidation of aqueous pollutants. Here, by contacting water as aerosol with PCD plasma, it is shown that OH radicals are produced on the gas side of the interface, and not in the liquid phase. It is also demonstrated that the gas-liquid interfacial boundary poses a barrier for the OH radicals, one they need to cross for reactive affinity with dissolved components, and that this process requires a gaseous atomic H scavenger. For gaseous oxidation, a scavenger, oxygen in common cases, is an advantage but not a requirement. OH radical efficiency in liquid phase reactions is strongly temperature dependent as radical termination reaction rates increase with temperature.
The anti-epileptic drug carbamazepine (CBZ) receives growing attention due to slow biodegradation and inherent accumulation in the aquatic environment. The application of a gas-phase pulsed corona discharge (PCD) was investigated to remove CBZ from synthetic solutions and spiked wastewater effluent from a municipal wastewater treatment facility. The treated water was showered between high voltage (HV) wires and grounded plate electrodes, to which ultra-short HV pulses were applied. CBZ was readily oxidized and 1-(2-benzaldehyde)-4-hydroquinazoline-2-one (BQM) and 1-(2-benzaldehyde)-4-hydro-quinazoline-2,4-dione (BQD) were identified as the most abundant primary transformation products, which, contrary to CBZ ozonation data available in the literature, were further easily oxidized with PCD: BQM and BQD attributed to only a minor portion of the target compound oxidized. In concentrations commonly found in wastewater treatment plant effluents (around 5 µg L(-1)), up to 97% reduction in CBZ concentration was achieved at mere 0.3 kW h m(-3) energy consumption, and over 99.9% was removed at 1 kW h m(-3). The PCD application proved to be efficient in the removal of both the parent substance and its known transformation products, even with the competing reactions in the complex composition of wastewater.
Palladium nanoparticles are widely used in catalysis, sensors, coatings and hydrogen storage devices. This paper reports the one-pot photochemical reduction of Pd(II) alcohol solutions into Pd0 nanoparticle suspensions. The synthesis involves the reduction of [PdCl4][Formula: see text] dissolved in EtOH/2-PrOH mixtures by the ketyl radicals (Me)2(HO)C[Formula: see text] generated from 254[Formula: see text]nm irradiation, in the absence of other chemical reducing agents. Clusters of [Formula: see text][Formula: see text]nm Pd0 particles thus produced could be separated from their suspensions by microfiltration. Preliminary tests are reported on the catalytic potential of such particles for the thermal dehydrogenation of alcohols.
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