Accepted Manuscript

PVC degradation by Fenton reaction and biological decomposition

Tomáš Mackuľak, Alžbeta Takáčová, Miroslav Gál, Jozef Ryba

PII: S0141-3910(15)30036-7

DOI: 10.1016/j.polymdegradstab.2015.07.005

Reference: PDST 7693

To appear in: Polymer Degradation and Stability

Received Date: 20 March 2015

Revised Date: 30 June 2015

Accepted Date: 6 July 2015

Please cite this article as: Mackuľak T, Takáčová A, Gál M, Ryba J, PVC degradation by Fentonreaction and biological decomposition, Polymer Degradation and Stability (2015), doi: 10.1016/j.polymdegradstab.2015.07.005.

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PVC degradation by Fenton reaction and biological decomposition

Tomáš Mackuľaka, Alžbeta Takáčováa, Miroslav Gálb, Jozef Rybac

aDepartment of Environmental Engineering, Faculty of Chemical and Food Technology, Slovak

University of Technology, Radlinského 9, 812 37 Bratislava, Slovakia

bDepartment of Inorganic Technology, Faculty of Chemical and Food Technology, Slovak

University of Technology, Radlinského 9, 812 37 Bratislava, Slovakia

cDepartment of Fibres and Textile Chemistry, Faculty of Chemical and Food Technology, Slovak

University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic.

Corresponding author. Tel.: +421 2 59325577

E-mail address: jozef.ryba@stuba.sk

Abstract

The possibility of the degradation of the recalcitrant polymer polyvinylchloride (PVC) was the

object of our study. For this purpose the Fenton reaction with subsequent biodecomposition step

was successfully used. Molecular degradation fragments were determined by HPLC and GC-FID

method. After the first step - degradation of PVC by the Fenton reaction, the formation of trans-1,2-

dichloroethene, cis-1,2-dichloroethene, trichloroethene and tetrachloroethene was observed. Also

more complex molecules such as benzene, ethylbenzene and o-xylene were identified. Probably

these chemical compounds are the products of phthalates decomposition. The resulted mixture was

in the second step used as a substrate for anaerobic biogas production. Biological degradation of

used COD was α = 67.3% and F/I = 0.004 [gCOD g-1 VS]. The decomposition of other compounds

such as trans-1,2-dichlorethylene (60 %), cis -1,2-dichlorethylene (70 %) was also observed.

Moreover, benzene, ethylbenzene and o-xylene were completely removed during the biological

decomposition step. It is possible to assume that Fenton pretreatment improves the degradation of

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PVC and, by this way the low molecular weight fragments are formed. Subsequently degradation

products of PVC by GC-FID were identified. In next steps, the digestion of these fragments by

anaerobic microorganisms was observed. It was also found that in anaerobic sludge the degradation

of low molecular weight fragments is carried out. One can conclude that these small fragments are

used by microorganisms as biological substrate.

Keywords

Fenton reaction, polyvinylchloride, biodegradation, hydroxyl radicals, biogas

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1. INTRODUCTION

PVC belongs to group of synthetic polymers with wide industrial application. The properties

of these materials allowed them to substitute wood and concrete. PVC production is cheap, but

there is a concern about its effect on environment. This article is focused on the possibility of the

degradation of artificial substances such as polyvinylchloride (PVC), which belongs to slowly

degradable substances by natural processes; however the world production of these substances is

very high. Its combustion produces e.g. dioxins that belong to the most toxic compounds [1]. The

monomeric unit of PVC, vinyl chloride, is classified as a human carcinogen. Final polymer have

high stiffness because plasticizers such as di(2-ethylhexyl)phthalate (DEHP), di-isodecylphthalate

(DIDP) a di-isononyl phthalate (DINP) causing better flexibility are added [2]. The release of the

DEHP from PVC was proved. This could be dangerous because toys and medical products are made

also from PVC. Phthalates are suspicion to cause scleroderma, cholangiosarcoma, angiosarcoma,

brain carcinoma or acroosteolysis [3]. These compounds are serious environmental load because of

their presence in foodstuffs, surface waters or sludge [4]. The production of PVC is connected with

a formation of high carcinogenic intermediates such as ethyl dichlorine, vinylchlorine, and

hexachlorine benzene. During this process several types of hazardous additives e.g plasticizers,

stabilizers, and fire-retardants are also used [5, 6].

Only a few publications dealt with the biological decomposition of PVC. The use of various

species of white rot fungi in PVC degradation was studied in this work [7]. In this paper the

usability of the enzymatic mixture is described. The results predict the possible biological ways of

artificial polymer degradation in natural environment. Utilization of degradation products as

biological substrates for aerobic and anaerobic microorganisms is also discussed. An analysis of

gases from waste dumps predicts the possibility of chlorinated polymers degradations in nature

environment [8]. Various chlorinated organic compounds are present in sediments and percolating

waters. Their source is probably the dissociative PVC waste. In the work of Hata et al. [9] the

degradation of cis-1,2-dichloroethene and vinylchloride in the landfill leachate by Clostridium

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saccarobutylicum was observed. The study of Leahy and Shreve [10] describes the presence of

dehalogenation of tetrachloroethylene (PCE) in landfill leachates by anaerobic microorganisms.

For the PVC elimination Advanced Oxidation Processes (AOP) resulting in low molecular

weight and, therefore, easier biologically degradable substances can be used [11]. Fenton reaction,

ozonization and ultrasonic treatment belong to the group of the most used AOPs. All of these

processes are able to degrade wide spectra of organic species namely chlorinated compounds,

antibiotics, endocrinic disruptors, and polymers that are present mainly in sediments and landfill

leachate [12-14].

Fenton reaction (H2O2/Fe2+) is a catalytic process based on the electron-transfer between metal

cation and H2O2 [12, 15]. This radical reaction is also a part of metabolic processes used by bio-

systems in Nature [15]. It may be used for degradation of different types of polymers (P-H).

Fe2+ + H2O2 → Fe3+ + HO– + HO• (1)

P-H + HO• → P• + H2O (2)

P• + O2 → POO• → PO• (3)

POO•(PO•) + PH → POOH (POH) + P• (4)

One of the examples is water soluble polyethyleneglycols degradation [16]. Feng at el. [17] dealt

with the photo-assisted Fenton reaction with UV irradiation for polystyrene splitting with efficiency

of 99 %. Authors assumed that cation-exchange mechanism of Fe3+ ions as a background of

heterogenic degradation process. Fenton reaction is also present in various biochemical and

biological processes; e.g. brown rot fungi use this reaction to split lignocellulose materials into

easier metabolizable compounds. These fungi use catechol-driven Fenton reaction instead of

enzymes for this purpose [18, 19]. An example, where these degradation processes can be observed

in a great scale are waste landfills where biotic and abiotic processes occur simultaneously in

aerobic and anaerobic conditions [12, 20].

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Similarly ozone can be used for the degradation of polymers, e.g. 1,4-trans-polychloroprene

or polyethylene [21]. In the work of Wang et al. [14] ultrasonic treatment was successfully used for

the degradation of ammonia pollution and COD. Gonze E et al. [22] described the decomposition of

chlorinated compounds via hydroxyl radicals produced by ultrasound. Ultrasound was also used for

polyvinylacetate (PVAC) and polyethyleneoxide (PEO) degradation [13]. Except chemical

procedures considerable part of scientific research is focused on the biodegradation of PCE, TCE

and DCE by genus Dehalococcoides [23, 24].

Our study is focused on the environmental aspects of raw PVC materials disintegration in

natural environments. This work is aimed on two-step PVC material degradation: the first one is

common Fenton reaction and in the next one degradation products by Fenton reaction are used as a

substrate for anaerobic fermentation. Our results will show the ability of anaerobic sludge to

decompose the degradation products of PVC (lower biogas production). The Fenton reaction and

subsequent bacterial digestion were chosen as possible biological processes of raw PVC materials

degradation that can occur in the landfills during anaerobic and anoxic conditions and produce low

molecular chlorinated compounds. Moreover, biogas production will be used to monitor the

digestion progress.

2. EXPERIMENTAL PART

2.1 Chemicals and reagents

In our experiments, all the reagents were analytical grade and used without further purification.

Hydrogen peroxide (H2O2, 30 %, w/w), sulfuric acid (H2SO4, 5 %, w/w ), sodium hydroxide

(NaOH, 20 %, w/w), ferrous sulfate hepta hydrate (FeSO4.7H2O, purity 98% min) were purchased

from Lachema (Brno, Czech Republic), The solutions were prepared using double-distilled

deionized water with resistivity above 18 MΩcm. All pH values were measured with pH meter

Model 215 (Denver Instrument, USA), which was calibrated with standard buffer solutions.

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2.2 Procedures

For a degradation study of PVC (SLOVIPLAST® TG 7008, ChZ Nováky, Slovakia; granulate with

diameter 4±2 mm, density 1430±50 kg m-3, thermal stability at 180 °C 180 min without mechanical

impurities) following procedure was used: Into Erlenmeyer flask 300 mL of deionized water and

0.5g of PVC material was added. Then pH of water was adjusted by 5 % solution of sulfuric acid to

pH = 3. Into a suspension calculated amount of 0.264 g of FeSO4.7 H2O and 0.80 mL (ratio 875:500

mg L-1, marked as X) or 1.60 mL (ratio 875:1000 mg L-1, marked as Y) of H2O2 was added [16].

Suspension was stirred for 20 minutes at 300 rpm and 16 °C and then was 5 minutes kept without

shaking. Subsequently, the suspension was neutralized with sodium hydroxide solution (30 %) to

stop the Fenton process and let to sediment for 15 minutes. Solution was analyzed by HPLC and

GC-FID method. Chemical oxygen demand (CODCr) was specified by spectrophotometric

dichromatic semimicro method. Released chlorine ions were determined by combined selective

chloride electrode (Sentek C1-ISE, UK).

2.3 Product analyses of PVC degradation by GC-FID instrumentation

Degradation products after the Fenton reaction were analyzed using Purge-and-trap technique

(Tekmar 3000, USA). A 5 mL of the sample was placed into a small vial and kept under a stream of

the nitrogen at a flow rate of 40 mL min-1. After that the nitrogen passed through a stainless steel

adsorption tube Carbopack C. The purge-and-trap device was coupled with a gas chromatograph

(Varian 3400 CX ,USA), column CP Select 624 CB (Varian USA) with dimensions D(30 m) x ID

(0,53 mm) x OD(30 m) and a temperature program: 50 ºC (hold 1 min), 5 ºC min−1 to 100 °C, 50 ºC

min−1 to 220 ºC (hold 2 min), injector (Varian) and detector (FID) temperature was 100 °C and

300 °C, respectively.

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2.4 Biological degradation of decomposition products of PVC in anaerobic sludge

In the second part of the experiment methane batch tests were realized. The reactor (0.65 L) for

biogas production was filled with anaerobic sludge from wastewater treatment plant unit in

Devínska Nová Ves (Slovakia) and was not adapted for decomposition of investigated compounds.

The initial values of sludge were: dry matter 16.5 g L-1, anneal loss 60 % and pH = 7.35. The

reactor temperature was 37-38 °C. Anaerobic semi-continual mixed reactors were filled with

300 mL of anaerobic stabilized sludge and 100 mL of mixture created by Fenton reaction (X,Y).

Biogas production was measured for 7 days by Micro-Oxymax device. The progress of the

degradation of PVC decomposition products was controlled by HPLC and GC-FID.

2.5 Samples analyses by HPLC method

Chemical analyses of sludge water were also performed by HPLC equipped with PDA detector

(Young Lin 9100). Mobile phase: 1 mL min-1 of methanol:water mixture, gradient 10:90 to 90:10,

16 minutes, temperature 25 °C, column GraceSmart, RP-18, length 150 mm, 4.6 mm ID, PDA

detector (wavelength used 200, 210, 222, and 235 nm).

2.6 Measuring of biogas production via Micro-Oxymax device (Columbus Instruments, USA)

This equipment for measuring of biogas composition consists of detectors for methane, oxygen,

carbon dioxide, hydrogen, hydrosulphide and water. This equipment is fully automatized system for

continual measuring of gas concentration in hermetic flasks. It’s used for testing of material

biodegradeability under aerobic or anaerobic conditions. Obtained data are evaluated by Micro-

Oxymax software. Obtained results represent the cumulative production and consumption of CO2,

CH4.

2.7. Scanning electron microscopy

The influence of the Fenton reaction on the PVC in the heterogeneous mixture was also analyzed by

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SEM microscope JEOL 7500F operated at 5 or 10 kV with SEI detector. The sample was firstly

dried in the oven at 40 °C for at least two hours. Then the sample was stacked at Si plate and

analyzed in the vacuum (10-4 Pa).

3. RESULTS AND DISCUSSION

PVC itself is biologically resistant and the products of its degradation may be quite toxic.

Fig. 1. HPLC analysis of PVC degradation by the FR (Y).

Figure 1 shows the chromatogram of PVC degradation using the Fenton reaction (Y). Main, low

molecular degradation products are found between 1.7 and 2.5 min. Except low molecular

fragments more complex structures benzene (retention time 6.04 min) and ethylbenzene (retention

time 7.77 min.) were also observed. We assume that these compounds are the degradation products

of the present phthalates. Another interesting point is that at the beginning of the PVC degradation

by FR higher concentration of Cl- ions (22 mg L-1) compare to 4 mg L-1 at the end of the

degradation process was observed. We think that the decrease of Cl- ions concentration at the end of

the degradation process is caused by the presence of OH• radicals. Chlorine anions react with OH•

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radicals and formed Cl• radicals. This leads to the formation of different chlorinated compounds

(see Fig.2). Direct reaction between Cl- ions and OH• radicals during PVC degradation decreases

the Fenton reaction efficiency.

Fig. 2. GC-FID analysis of PVC degradation products by the Fenton reaction (Y)

The presence of chlorinated degradation products were proved by the gas chromatography. Trans-

1,2-dichlorethylene, cis-1,2-dichlorethylene, trichloroethylene, and tetrachlorethylene were

identified by GC-FID (see Table 1, Fig. 2). These products belong to persistent pollutants of

environment. Other degradation products such as ethylbenzene (9.06 min) and o-xylene (10.22 min)

were also observed. We assume that molecules with benzene core can be formed by the

decomposition of released phthalates from PVC. COD value can be considerably influenced by

decomposition of present stabilizers and fire retardants.

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Table 1 The concentration of PVC decomposition products by Fenton reaction (X,Y) after 20

minutes determined by GC-FID method.

compound c (mg L-1)

retention time (min) X Y

trans-1,2-dichlorethylene 0.112 0.277 2.41

cis -1,2-dichlorethylene 0.198 0.442 2.94

trichlorethylene 0.010 0.024 4.44

tetrachlorethylene 0.012 0.019 6.96

ethylbenzene 0.009 0.013 9.06

o-xylene 0.010 0.014 10.22

From Table 1 one can see that FR (X) exhibits lower degradation efficiency compare to the FR (Y).

Under anaerobic conditions the degradation of PVC products is realized mainly by abiotic ways.

The important factors are H2S, FeS and Fe2+ ions which dechlorinized these substances. Also the

presence of zinc and iron are able to speed up this process. In anaerobic sludge the biotic

degradation can be carried out with the help of sulphate-reduction bacteria [25].

In the next Fig. 3 SEM micrographs of PVC before and after the Fenton reaction Y can be seen.

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A

B

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Fig. 3. SEM micrographs of PVC material before the Fenton reaction Y (A), after the Fenton

reaction Y (B), zoom of the selected section of B (C).

In Fig. 3 the differences in the structure (morphology) of PVC material before (A) and after (B) the

Fenton reaction Y are clearly visible. After the Fenton reaction Y is applied, PVC is fragmented

which is probably caused by the radicals formed during the Fenton process. Moreover, after the

attack of radicals defects in the PVC material structure are formed (C). Fragmentation of PVC

material observed by SEM microscopy was also confirmed by weight loss measurements of PVC

material before and after the Fenton processes. The highest weight losses of 10±2 % were detected

in the case of Fenton Y process.

Almost all above mention degradation products are potentially harmful for environment. Therefore

in the next part of our work we focused on utilization of these compounds as biological substrate in

anaerobic sludge[26]. The process of biodegradation in anaerobic sludge was controlled by HPLC

and GC-FID analyze. Production of biogas was also monitored.

During methane tests the decrease of organic compounds concentration formed during FR was

observed.

C

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Fig. 4. HPLC analyses of PVC degradation products by Fenton reaction in sludge 0 day.

Fig. 5. HPLC analyses of PVC degradation products by Fenton reaction in sludge after 7 days.

The significant decrease of the concentration of low molecular compounds released after PVC

degradation was observed in sludge water after seven days (Fig.4, Fig.5, Table 2).

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Table 2 Concentration of the selected compounds at the beginning (0 day) and at the end (7th day)

of the biological step determined by GC-FID method.

compound c (mg L-1)

retention time (min) 0 day 7th day

trans-1,2-dichlorethylene 0.088 0.035 2.41

cis -1,2-dichlorethylene 0.105 0.031 2.94

trichlorethylene 0.011 0.005 4.44

tetrachlorethylene 0.013 0.009 6.96

ethylbenzene 0.007 < DL 9.06

o-xylene 0.006 < DL 10.22

The concentration of the selected organic compounds at the beginning (0 day) and at the end (7th

day) of the biological step in anaerobic sludge condition is summarized in Table 2. Measured results

by GC-FID method exhibit partial decomposition of chlorinated low-molecular compounds. The

highest efficiency of the degradation was reached in the case of trans-1,2-dichlorethylene and cis -

1,2-dichlorethylene, respectively. The concentration of these compounds is influenced by the

decomposition of trichlorethylene and tetrachlorethylene during reductive dechlorination. Total

decomposition of benzene, etylbenzene, and o-xylene was observed at the end of the digestion

process. In general, the number of compounds with retention time under 2 minutes is lower at the

end of the anaerobic digestion (7th day) compare to the state immediately after the FR (0 day).

During the experiment the formation of oxalic (1.80 min) and formic acid (2.29 min) was also

observed. The first source of these compounds is probably the decomposition of chlorinated

compounds by enzymatic degradation by microorganisms and the second one is probably the

degradation of present phthalates. TCE can be degraded by reductive dechlorination and also by

aerobic and anaerobic degradation through the use of co-metabolism. Little et al. [27] describe the

process of the enzymatic degradation of TCE using various enzymatic substrates. Some

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microorganisms are able use TCE as a carbon and an energetic source. Some genuses of

methanotrophic organisms are able to degrade TCE by a nonspecific enzymatic activity (methane

monooxygenase) as a secondary substrate. These microorganisms consequently produce epoxide by

enzymatic degradation and exclude it from the cell. Epoxide is decomposed to dichloroacetic and

glyoxylic acids and one-carbon products.

To better control the progress of an anaerobic digestion of PVC decomposition products

after FR, biogas production was also monitored.

0 1 2 3 4 5 6 70

2

4

6

8

10

12

14

16

18

Pro

duct

ion

biog

as (

ml)

Time (day)

inocullum

pre-treated substrate PVC

Fig. 6. Cumulative biogas yield during the anaerobic digestion experiment.

Figure 6 shows production of biogas during 7 days test in anaerobic conditions. An elevated amount

of produced biogas in comparison with production of biogas from the sludge without substrate was

observed. Single sludge cumulates 7.7 mL of biogas with composition of 29 wt. % of methane and

71 wt. % of carbon dioxide during 7 days. This production is caused by decomposition processes in

the sludge. The sludge with concentration of 11.5 mg of COD of substrate and feed/inoculum ratio

F/I = 0 004 [gCOD g-1VS] accumulate ca twice more biogas with content of 26 wt. % of methane and

74 wt. % of carbon dioxide. Efficiency of used COD of biological decomposition is α = 67.3 %. It is

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possible to assume that biological decomposable after adaptation will be higher. Production of

methane after the addition of decomposition products of PVC after FR is influenced by many

factors. Decomposition of organic compounds to carbon dioxide is caused by the inhibition of

methanogenic germs in presence of TCE and VC. These compounds can inhibit the growth of

methanogenic germs and, consequently, the production of biogas itself. Young et al. [28] investigate

biodegradation of trichloroethene (TCE) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by anaerobic

sludge. They observed that anaerobic sludge itself was not able to degrade TCE. Therefore, germs cultures

adapted for TCE were used. Higher efficiency of the degradation was reached and decomposition products

were identified as cis-dichloroethene and other chlorinated metabolites. Increased concentration of CO2 in

produced biogas can be also influenced by mechanism of decomposition of TCE and DCE [29].

Some dehalorespiring organisms are able to efficiently degrade PCE, TCE, DCE, VC to less toxic

compounds. Subsequently TCE can be degraded under anaerobic condition by reductive

dechlorination to carbon dioxide[28, 29].

Because the Fenton reaction is widely spread in natural environment, the measured PVC

degradation results show the possibility of its decomposition in natural environments not only by

chemical ways but also by biological processes in aerobic and anaerobic conditions. Decomposed

PVC materials can be a source of small chlorinated molecules like trans-1,2-dichloroethene, cis-1,2-

dichloroethene, trichloroethene and tetrachloroethene [8, 10]. These products were already

identified in landfill gas and sediment leachate [8, 9] what supports the assumption, that the Fenton

reaction is able to degrade chlorinated polymer materials in an environment and like this, partly

supports the self-cleaning of an environment. A very important fact that come out of our

experiments and greatly influences the efficiency of the degradation processes in the environment is

a combination of biotic and abiotic processes in aerobic and anaerobic conditions [10]. It should be

stressed that the processes that lead to the presence of these toxic chlorinated compounds and their

presence in landfill gas and sediment leachate it is not yet fully understood.

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4. CONCLUSION

The aim of this work was to prove the possibility of the degradation of commercially

available synthetic polymer PVC by the Fenton reaction and subsequent anaerobic digestion in the

sludge water. Results obtained by HPLC and GC-FID confirm the formation of low molecular

organic compounds. During degradation process of PVC chlorinated products such as trans-1,2-

dichlorethylene, cis -1,2-dichlorethylene, trichlorethylene and tetrachlorethylene were identified.

Benzene, etylbenzene, and o-xylene were also found. Various ratios between Fenton reagents

FeSO4.7 H2O and H2O2 was tested. In the next step, under the anaerobic conditions, these

compounds undergo a dechlorination and further decomposition. We observed that the products of

the FR degradation serve as a source of carbon for anaerobic bacteria. After addition of 11.5 mg

COD anaerobic sludge F/I = 0.004 [gCOD g-1 VS] produced ca 14 mL of biogas with content of

26 wt. % of methane and 74 wt. % of carbon dioxide with efficiency of α = 67.3 %. Also high

efficiency of the decomposition of selected organic compounds such as trans-1,2-dichlorethylene

60 %, and cis-1,2-dichlorethylene 70 % was observed. On the other side, trichlorethylene and

tetrachlorethylene were degraded with lower efficiency. It is possible to assume that Fenton

pretreatment improves the degradation of PVC and, by this way the low molecular weight

fragments are formed. Subsequently we identified degradation products of PVC by GC-FID. In next

steps, the degradation of these fragments by anaerobic microorganisms was observed. It was also

found that in anaerobic sludge the degradation of low molecular weight fragments is carried out.

One can conclude that these small fragments are used by microorganisms as biological substrate.

We also proved that investigated reactions are able to participate on processes of degradation of

waste from chlorinated polymers in the environment.

Acknowledgement

This work was supported by the Slovak Research and Development Agency under the contract No.

APVV-0122-12.

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