Robert Banaschik

Decomposition of Pharmaceuticals by Pulsed Corona Discharges in Water Depending on Streamer Length

Pulsed corona discharges generated in water provide a possibility for the abatement of even stable organic compounds. Decomposition efficacy correlates with the length of streamers, which in turn depends on water conductivity and applied voltage. We investigated the relation between conductivities from 25 to 500 μS/cm, pulse duration, and visible streamer length for applied peak voltages of 70 and 82 kV. Streamer development for an initially applied peak voltage of 70 kV was related to the decomposition rates of the pharmaceutical carbamazepine that was dissolved in solutions with conductivities in the same range.

Comparison of pulsed corona plasma and pulsed electric fields for the decontamination of water containing Legionella pneumophila as model organism

Pulsed corona plasma and pulsed electric fields were assessed for their capacity to kill Legionella pneumophila in water. Electrical parameters such as in particular dissipated energy were equal for both treatments. This was accomplished by changing the polarity of the applied high voltage pulses in a coaxial electrode geometry resulting in the generation of corona plasma or an electric field. For corona plasma, generated by high voltage pulses with peak voltages of +80kV, Legionella were completely killed, corresponding to a log-reduction of 5.4 (CFU/ml) after a treatment time of 12.5min. For the application of pulsed electric fields from peak voltages of -80kV a survival of log 2.54 (CFU/ml) was still detectable after this treatment time. Scanning electron microscopy images of L. pneumophila showed rupture of cells after plasma treatment. In contrast, the morphology of bacteria seems to be intact after application of pulsed electric fields. The more efficient killing for the same energy input observed for pulsed corona plasma is likely due to induced chemical processes and the generation of reactive species as indicated by the evolution of hydrogen peroxide. This suggests that the higher efficacy and efficiency of pulsed corona plasma is primarily associated with the combined effect of the applied electric fields and the promoted reaction chemistry.

Degradation and intermediates of diclofenac as instructive example for decomposition of recalcitrant pharmaceuticals by hydroxyl radicals generated with pulsed corona plasma in water

Seven recalcitrant pharmaceutical residues (diclofenac, 17α-ethinylestradiol, carbamazepine, ibuprofen, trimethoprim, diazepam, diatrizoate) were decomposed by pulsed corona plasma generated directly in water. The detailed degradation pathway was investigated for diclofenac and 21 intermediates could be identified in the degradation cascade. Hydroxyl radicals have been found primarily responsible for decomposition steps. By spin trap enhanced electron paramagnetic resonance spectroscopy (EPR), OH-adducts and superoxide anion radical adducts were detected and could be distinguished applying BMPO as a spin trap. The increase of concentrations of adducts follows qualitatively the increase of hydrogen peroxide concentrations. Hydrogen peroxide is eventually consumed in Fenton-like processes but the concentration is continuously increasing to about 2mM for a plasma treatment of 70min. Degradation of diclofenac is inversely following hydrogen peroxide concentrations. No qualitative differences between byproducts formed during plasma treatment or due to degradation via Fenton-induced processes were observed. Findings on degradation kinetics of diclofenac provide an instructive understanding of decomposition rates for recalcitrant pharmaceuticals with respect to their chemical structure. Accordingly, conclusions can be drawn for further development and a first risk assessment of the method which can also be applied towards other AOPs that rely on the generation of hydroxyl radicals.

Degradation of pharmaceutical residues in water by pulsed corona discharges — Investigation of reaction mechanism

The steady increase of concentrations of pharmaceutical residues in water reservoirs is of growing concern. Abatement strategies, such as filtration and biodegradation, which are used in conventional water treatment procedures, have only limited success for removal.

Degradation of selected pharmaceuticals with pulsed corona discharges generated in water

Summary form only given. Highly industrialized societies are facing growing problems with pollution of drinking water by chemically and biologically inert contaminants. In particular pharmaceutically active compounds (PhACs) are withstanding destruction by conventional means and can be found in increasing concentrations [1]. Advanced oxidation processes (AOPs), including plasmas that are generated at atmospheric pressure, can provide a solution for water decontamination. In particular the generation of reactive species like hydroxyl radicals offers a possibility to break up even recalcitrant substances. We developed a plasma source with a coaxial geometry to create large volume corona discharges directly in water. For diagnostic reasons, The reaction chamber was made of a glass tube with the length of 150 mm and a diameter of 45 mm, hence holding a treatment volume of about 240 ml. Discharges were generated by applying positive high voltage pulses from a 6-stage Marx-bank generator. Streamers were forming around a thin tungsten wire (diameter of 50 μm) which was fixed in the center of the tube. Repetition rates of 20 Hz and peak voltages up to 80 kV were investigated. To evaluate the efficacy of the setup we decomposed 6 selected pharmaceuticals: carbamazepine (anti-epileptic), diatrizoate (x-ray contrast agent), diazepam (hypnotic, anticonvulsant), ethinylestradiol (hormone), diclofenac and ibuprofen (analgesics, anti-inflammatories), which are known to be ecologically problematic or in general may cause problems for water purification. Solutions of 0.5 mg/l for each substance were prepared and treated with up to 80,000 discharges. Concentrations after the treatment were determined with HPLC-MS. Depending on the recalcitrance of the selected pharmaceuticals, we achieved degradation rates of 45 % (diatrizoate) to 99 % (diclofenac). During the treatment pH-values stayed almost constant, but concentrations of dissolved oxygen doubled. Experiments in pure water showed that the amount of nitrate and nitrite that was created was insignificant and far below legal limits for drinking water. Experiments on the reaction pathways and kinetics that are responsible for the observed degradation are underway.