(14h) Treatment of OIL Produced Water Using Advanced Oxidative Processes: Heterogeneous-Photocatalysis and Photo-Fenton

TREATMENT OF OIL PRODUCED WATER
USING ADVANCED OXIDATIVE PROCESSES: HETEROGENEOUS PHOTOCATALYSIS AND
PHOTO-FENTON.

SILVA
PC¹, FERRAZ NP¹, PERPETUO EA¹, ASENCIOS YJO¹*

¹ Instituto do Mar, Universidade
Federal de São Paulo, Campus Baixada Santista yvan.jesus@unifesp.br

The treatment of contaminants
present in the oil-produced water must be carried out before the disposal
according to the legislation. This paper presents the use of Advanced Oxidative
Processes in the degradation of phenol in sea water, and in treatment of a real
sample of oil-produced water (OPW). Two catalysts were used: TiO₂ for
photocatalysis-heterogeneous, and FeSO₄.7H₂O for the
Photo-Fenton process. The pH variation of the effluent (in acid, neutral and alkaline)
and the addition of traces of hydrogen peroxide, were evaluated. The results
obtained show an efficiency in the removal of the phenolic compound in sea
water in about 96%, under an hour of experiment, having the best behavior when
the solution is in pH 3. Regarding to the real sample of OPW, it was observed that
larger reductions of the absorption bands  relative to organic matter, in both
processes proposed in pH 3.

INTRODUCTION

Water that reaches the surface
during oil extraction is called oil-produced water (OPW) and is defined as a
mixture of salts, suspended solids, heavy metals, microorganisms and oil droplets
dispersed in the water. The treatment of OPW is necessary due to the high
volumes of this water that are generated during the production of crude oil specially
in Offshore processes. When OPW is not treated causes problems to the
environment and to the equipment.  In this work, phenol was used as the model
molecule (representing the soluble aromatic fraction of the crude oil) in
seawater. The choice of sea water was made in order to simulate the conditions
of the water produced, since the high content of salts is similar to OPW, but
in different concentrations. In addition, the composition of organic compounds
in the OPW has  benzene, toluene, ethylbenzene and xylene (BTEX), naphthalene,
phenanthrene, dibenzothiophene (NFD), polyaromatic hydrocarbons (HPA), phenols,
gases and heavy metals [Neff, 2002].

2. METHODOLOGY

Characterization: The crystalline
phases of the catalysts used in this study were analyzed in a Rigaku miniflex
diffractometer (30Kv-10mA). The compounds formed were identified by comparison
with the JCPDS - International Center of Difraction Data.

The phenol concentration during
the processes was monitored through: High Performance Liquid Chromatography
(HPLC) and by colorimetric Method (EPA 9065). In the case of OPW, the photodegradation
tests were accompanied by UV/Vis Spectrophometry in the scanning mode.

Catalytic test: Phenol
degradation was performed with two different catalysts: TiO₂ (for
Photocatalysis-Heterogeneous, Synth 99.99% P.A.) and FeSO₄.7H₂O
(for Photo-Fenton, Synth 99.99% P.A.). The tests were carried out using a
solution of 43 ppm phenol prepared in sea water (previously filtered). In the
case of Photocatalysis-heterogeneous the TiO₂ dosage was 1g.L^-1
and H₂O₂ (in the proportion 0.3% v/v) for 25 mL of
effluent. In the case of the Fenton process 4.2 mg of FeSO₄.7H₂O
(for 25 mL of effluent) was used, with a ratio of catalyst/H₂O₂
of 1:10. For both processes, the pHs of the phenol solution were varied in: 3,
7 and 10. UV radiation (254 nm) was used for the catalytic degradation assays.
The same procedures were applied treatment of OPW extracted from the Rio Grande
do Norte Basin, Brazil.

3. RESULTS AND DISCUSSION

In the X-ray diffraction
analysis, it was possible to identify a single crystalline phase present in the
FeSO₄.7H₂O sample, having unit cell parameters indicating
pure monoclinic phase (JCPDS 25-0409) with a = 7.624 Å, b = 7.648
Å and c = 7,123 Å. The TiO₂ diffractogram presents purely the
Anatase phase (JCPDS 21-1272), with unit cell parameters of the tetrahedral
phase of a = b = 3.73 Å and c = 9.37 Å. Diffusse
reflectance spectroscopy (DRS) analyzes showed that band-gap energy for each
material was 2.87 eV (TiO₂) and 1.98 eV (FeSO₄.7H₂O),
respectively.

Photocatalytic degradation of
Phenol in seawater by Photocatalysis-heterogeneous with TiO₂

In the test performed without
addition of H₂O₂, the more favorable condition was at
initial pH 3, where a decrease in 19 ppm of phenol from the initial solution
was reported. On the other hand, no significant removal was observed when the
initial pH was 7 and 10, indicating that the pH strongly influences in this
process. Similar results were seen by [Seftel et al. 2014; Moraes 2003] which
studied the removal of phenol from distilled water. In the tests in presence of
traces of H₂O₂, it was observed that in pH 3 and 7 there
were almost the total reduction in the concentration of phenol reaching 5.8 ppm
and 2,7 ppm (as final concentration), respectively. In addition, it was
observed by chromatographic analysis the marked formation of an intermediate
organic compound similar to that already present in sea water, this could be
associated to the formation of organic acids. Curiously, a slight increase in
the final pH of the solution was observed after the photocatalytic test carried
out at pHs 3 and 7, which can be explained by the formation of organic acids in
the ionic form (formed by the degradation of phenol example: acetates), and
which are in equilibrium. This could be related to the higher formation of
intermediate compounds observed in the chromatogram at these pHs. The tests
also showed that the reaction reaches equilibrium in 1 hour exposure to UV
light.

Photocatalytic degradation of
Phenol in sea water by Photo-Fenton with FeSO₄.7H₂O

In these assays it was noted that
the different pHs influenced the process similarly to that reported in the photocatalysis-heterogeneous.
The pH 3 and 7 assays obtained a complete removal of the phenol, quantified at
0 ppm by HPLC. The process was less efficient at pH 10. This is a fact that
proves the Photo-Fenton is favored at acidic pH, due to the stability of the Fe
ions in acid pH and its interaction with hydrogen peroxide. Wang et al.[2014]
found an 85% reduction of phenol content for Photo-Fenton tests performed at pH
3;  the similar finding was reported by  Kuo et al. [1992] and Kiwi and
Nadtochenko [2000]; according to them the hydroxyl radical is the most active
species in the degradation of phenol at this condition. There was, however, a
very marked formation of organic acids (intermediates compound) produced during
Photo-fenton process, which have similar chemical behavior as those compounds present
in sea-water. The kinetics assay demonstrated that 1 hour was sufficient to
achieve equilibrium in the assays at three differrent pHs.

Photocatalysis-heterogeneous and
Photo-fenton with a real sample of OPW

In this spectrophotometric analyzes
the decharacterization of the absorption band of dissolved organic compounds, after
the photocatalysis, indicates the occurrence of degradation processes [Tambani
2011]. The spectral scan of OPW has a single wide band below 400 nm with
maximum intensity around 250 nm. Considering that pHs 3 and 7 are of more interest,
the photocatalysis-heterogeneous and photo-fenton tests were performed at these
pHs for 3 hours. The results showed a marked decharacterization of the spectral
scan of OPW, in comparison to the same sample before photocatalysis; thus
indicating degradation of part of the organic compounds dissolved in OPW. The
decharacterization of the water profile produced was more marked in the Photo-fenton
assays indicating a greater efficiency of this process in comparison to
heterogeneous photocatalysis.

4. CONCLUSIONS

In the
photocatalysis-heterogeneous and Photo-fenton processes for degradation of phenol
in sea water, it was found that phenol removal is favored at low pHs (3 or 7).
The degradation efficiency for phenol reached about 96% for Photo-fenton, which
is very high considering the high content of salts in sea water. In the tests
with a real sample of  OPW it was identified that for the two catalytic
processes, the best working pH is in acidic of neutral pH (3 or 7). Both
processes are good for Treatment of OPW, Photo-fenton performed better that heterogeneous-phootcatalysis,
however it forms a sludge at the final of the reaction.

5. ACKNOWLEDGMENTS

The authors thank the São
Paulo Research Foundation (FAPESP) for the financial support (process Nº: 2014/24940-5), and to CEPEMA of
Poli-USP for the analyzes by Liquid Chromatography.

 

6. REFERENCES

Neff
J.M. Bioaccumulation in Marine Organisms Effect of Contaminants From Oil
Well Produced Water, (Ed.), Amsterdam, Elsevier Science, (2002)

 E.M.Seftel.
M.C.Puscasu, M.Mertens, P.Cool, G.Carja. Assemblies of Nanoparticles of CeO₂
–Znti – Ldhs And Their Derived Mixed Oxides As Novel Photocatalytic System For
Phenol Degradation. Applied
Catalysis B: Environmental, 150 (2014) 157-166.

J.E.F.
Moraes, Aplicação do Processo Foto-Fenton na Degradação De Efluentes
Industriais Contendo Poluentes Orgânicos. Tese de Doutorado. Universidade de
São Paulo, Brasil, 2003.

Wang
C., Zhang S., Zhang Z., Zeng M., Yuji S. Optimization and Interpretation of
Fenton and UV/Fenton Processes for Degradation of Syringyl Lignin. J Environ Anal Chem 1:
(2014) 115-119. doi:10.4172/JREAC.1000115

J.
Kiwi, V. Nadtochenko. Mechanism and kinetics of the oh-radical intervention
during fenton oxidation in the presence of a significant amount of radical
Scavenger (cl–). Environmental
science & technology,
34 (2000) 2162-2168.

P.C.
Tambani, Estudo da Degradação do Fenol e Sais Intermediários Pelo Processo
UV/H₂O₂, Universidade de São Paulo, Brasil,
2011, 115.