22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Decomposition of fluorocarbons and medical compounds in water by means of
open plasma processes
J.P. Barz1, H. Schikora1, M. Haupt1 and C. Oehr1
1
Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, Stuttgart, Germany
Abstract: In this paper, we present results on the removal of several critical
contaminations from water by plasma processes. Several different plasmas were applied,
differing e.g. in the gas composition, in order to identify the most promising routes for
specific contaminations.
Keywords: water purification, advanced oxidation process, open plasma
1. Introduction
Today, the supply with pure drinking water is
threatened by many hazardous artificial compounds.
These contaminants are compounds which were
synthesized to fulfil certain demands concerning their
function and stability, but as they are not found in nature,
hardly any biological process is capable of removing
them. Amongst these substances, perfluorinated acids and
pharmaceuticals are two prominent examples.
Perfluorinated compounds (PFC), amongst them
perfluorinated surfactants, are widely used in several
industrial branches like the galvanic industry, but can also
occur as a side-product from telomerisation of
fluorocarbon textile finishes. They are highly stable and
quite inert. In particular long-chain PFCs have raised
several environmental concerns because of their biopersistance and toxicity levels.
Pharmaceuticals pose another danger to the safety of
drinking water. During the “design” of a medicament,
commonly only its function is considered, but
biodegradability is hardly of interest. This is partially
owed to the fact that degradation products formed in the
patient’s body would also need to be tested for negative
side effects – in such a way, high product stability
increases the product safety. But as a result, agents like
painkillers, anticonvulsants, psychopharmaca, betablockers or antibiotics can be even found in drinking
water.
In order to remove these non-biobased substances in
waste-water treatment plants, char-coal filtering and other
absorption techniques can be applied along with advanced
oxidation processes (AOP) as quaternary treatment step.
Amongst UV-treatment with admixture of oxidative
compounds, ozonisation and other standard AOPs, the
direct plasma treatment of water is a recent and very
promising approach for the removal of chemically stable
contaminations.
As an example, several advanced oxidation processes
using OH radicals only are inefficient in decomposing
PFCs such as perfluorohexanoic acid (PFHxA),
perfluorooctanoic
acid
(PFOA)
and
perfluorooctanesulfonic acid (PFOS) whereas this aim can
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be achieved by direct plasma treatments. In this study, we
demonstrate the decomposition of these compounds in a
DBD reactor. In addition to that, the removal of several
pharmaceuticals such as Carbamazepin and Diclophenac
will be shown as well.
2. Experimental setup and methodology
A reactor used in the experiments is depicted in Fig. 1.
It has been previously used to efficiently remove cyanide,
atrazine and other hazardous substances from
contaminated water [1, 2].
Fig. 1. Scheme of the coaxial thin-film dielectric barrier
discharge plasma reactor.
The fluorocarbon contaminants are depicted in Fig. 2 A-C
along with their numbering for NMR.
Fig. 2. Structures and labelling for PFHxA (A), PFOA
(B) and PFOS (B). Right: assignment of the 19F NMR
signals to the carbon atoms.
1
The structure of Carbamazepin is shown in Fig. 3 below.
Fig. 3. Molecular structure of Carbamazepin.
Solutions with different initial concentrations were
circulated with a gear pump through the plasma zone.
Here, hydrogen and oxygen were used as plasma process
gases.
For the fluorocarbon compounds, samples were taken at
different times and the residual amount of fluorocarbons
was determined by 19F NMR and TOC analysis
(TOC=total organic carbon).
The reduction of carbamazepine was measured by
chromatography (HPLC-UV).
3. Results and Discussion
The results of the NMR and TOC analysis for the
treatment of perfluorinated acids are depicted in Fig. 4
and Fig. 5, respectively.
Fig. 4. Removal of organic fluorine in oxygen and
hydrogen plasmas, determined by 19F NMR.
plasmas. Concerning the removal of organic carbon
(which occurs apparently slower compared with the
fluorine removal), oxygen plasmas are slightly more
efficient (Fig. 5). Ion chromatography indicates the
formation of fluorine salts (not shown here). The
mechanisms are under investigation.
For Carbamazepin, the removal of the specific groups is
seen in the UV spectra already after one minute of
treatment time. Several products are formed; the
assignment is still in progress.
The results on Diclophenac will be shown as well.
4. Conclusion and Outlook
The decomposition of PFHxA, PFOA and PFOA was
confirmed by 19F NMR and TOC measurements. The
NMR data reveals differences in the product compositions
which will be used to determine degradation routes and to
further optimize the processes.
The oxidation of Carbamazepin occurs within one
minute and is therefore very fast. A more detailed analysis
on the products formed will reveal if the decomposition
achieved after this time is sufficient or if products need to
be removed by further oxidation.
5. References
[1] Hijosa-Valsero, M., Molina, R., Schikora, H., Müller,
M. and Bayona, J. M.: Removal of priority pollutants
from water by means of dielectric barrier discharge
atmospheric plasma; Journal of Hazardous Materials 262,
664-673 (2013).
[2] Hijosa-Valsero, M., Molina, R., Schikora, H., Müller,
M. and Bayona, J. M.: Removal of cyanide from water by
means of plasma discharge technology; Water Research
47 (4), 1701-1707 (2013).
[3] Liu, Z., Goddard , J. D.: Predictions of the Fluorine
NMR Chemical Shifts of Perfluorinated Carboxylic
Acids, C n F 2n+1 COOH (n = 6−8); J. Phys. Chem. A,113
(50), 13921–13931 (2009).
[4] Ellis, D. A., Denkenberger, K. A., Burrow, T. E.,
Mabury, S. A.: The Use of 19F NMR to Interpret the
Structural Properties of Perfluorocarboxylate Acids: A
Possible Correlation with Their Environmental
Disposition, J. Phys. Chem. A, 108, 10099-10106 (2004).
[5] Vyas, S. M., Kania-Korwel, I., Lehmler, H.-J.:
Differences
in
the
isomer
composition
of
perfluoroctanesulfonyl (PFOS) derivatives; Journal of
Environmental Science and Health Part A, 42, 249–255
(2007).
Fig. 5. Removal of carbon.
As can be seen in Fig. 4, hydrogen plasma is more
efficient in removing organic fluorine than oxygen
2
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