Environmental Engineering and Management Journal September 2014, Vol.13, No.
9, 2395-2399
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
ELECTROCHEMICAL RECLAMATION OF WASTEWATER
RESULTED FROM PETROLEUM TANKER TRUCK CLEANING
Konstantinos Dermentzis1, Dimitrios Marmanis1, Achilleas Christoforidis1,
Konstantinos Ouzounis2
1
Eastern Macedonia and Thrace Institute of Technology, Department of Petroleum and Mechanical Engineering, 65404 Agios
Loucas, Kavala, Greece
2
Democritus University of Thrace, Department of Environmental Engineering, 67100 Xanthi, Greece
Abstract
Petroleum tanker trucks are integral vehicles for delivering fuel and other petrochemical products from place to place and must be
cleaned regularly. Pressure washing with hot or cold water serving to remove oil and filth from the tanker truck container,
produces oily waste water with an oil concentration of about 300-500 mg L-1 which, according to environmental standards and
regulations worldwide, must be disposed of and treated properly. In the present paper an integrated electrochemical treatment for
oily wastewater reclamation is presented comprising a) the electrocoagulation process with sacrificial iron and aluminum
electrodes, b) the electrooxidation process with platinized titanium (Ti/Pt) and boron doped diamond (BDD) electrodes and c) the
electro-Fenton process with iron electrodes and added hydrogen hydroxide. A simulated oil tanker truck washing wastewater was
prepared by mixing heating oil with fresh water and separating the aqueous from the oily phase in a separation funnel. The COD
of the obtained oily wastewater was 456 mg L-1. The effect of crucial parameters on oil removal, such as pH, applied current
density, initial oil concentration and electro-processing time was explored. During the electrocoagulation treatment at the current
density of 5 mA cm2 using iron and aluminum electrodes, COD was only partially removed by 8 and 11% respectively. The COD
removal could drastically be increased exceeding 80 % by performing the electrocoagulation process after initial addition of the
surfactant sodium dodecyle sulfate. The electro-oxidation process with platinized titanium (Ti/Pt) and boron doped diamond
(BDD) electrodes at the applied current density of 20 mA/cm2 reduces COD to 15 and 36 % at 25 0C and to 28 and >98 % at 60
0
C respectively. Finally the electro-Fenton process with Fe electrodes and supplied H2O2 in acidic solution at the applied current
densities of 5 and 10 mA cm2, led to a COD reduction beyond 90% in only a few minutes of electro-processing time.
Key words: electrocoagulation, electro-Fenton, electro-oxidation, oily wastewater, surfactant
Received: March, 2014; Revised final: August, 2014; Accepted: September, 2014
1. Introduction products from place to place and must be cleaned
regularly. Pressure washing with hot or cold water is
Oily wastewater can exist in three forms: free used to remove oil and filth from the tanker truck
floating, dispersed and emulsified. Large quantities container. The produced oily wastewater with an oil
of oil contaminated water are produced throughout in concentration of about 300-500 mg L-1 should be
the industry. Oil fields, oil refineries, automobile gathered and taken to a wastewater chemical plant to
industries, aircraft plants, machine shops, car be disposed of and treated properly according to
washing stations, cargo ships and oil tanker truck environmental standards and regulations. Several
washing plants produce large amounts of oil-in-water methods are applied to remove or decompose oil
emulsions. Petroleum tanker trucks are integral from oily water, such as biological treatment (Gasim
vehicles for delivering fuel and other petrochemical et al., 2012), photo-degradation (Stepnowski et al.,
Author to whom all correspondence should be addressed: email: demerz@otenet.gr, Phone: +302510245133
Dermentzis et al./Environmental Engineering and Management Journal 13 (2014), 9, 2395-2399
2002), Fenton and photo-Fenton processes (Coelho et aluminum and two iron plates respectively were used
al., 2006), flocculation (Zhong et al., 2003), chemical with an effective area of 30 cm2 each. Further details
coagulation (Canizares et al., 2008), precoat filtration on the experimental tools are provided in
(Meeroff and Engelhardt, 2001), ultrafiltration Stergiopoulos et al. (2014).
(Waite et al., 1999), reverse osmosis (Salahi et al.,
2010) and electrochemical methods. 2.3. Experimental procedures
Electrochemical methods such as direct or
indirect anodic oxidation (Dermentzis et al., 2013; The experiments were carried out in a
Motoc et al., 2013; Stergiopoulos et al., 2013; cylindrical glass electrochemical reactor of 500 ml
Zanbotto Ramalho et al., 2010), electro-Fenton and an inter-electrode distance of 1 cm. The
(Yavuz et al., 2010) and electrocoagulation (Biswas concentrations of the supporting electrolytes Na2SO4
and Lazarescu, 1991; Fouad et al., 2009; Yang, 2007) and NaCl were 2 and 0.5 g/L respectively. The
have been attracting great attention for the last applied current density was 5 and 10 mA/cm2. The
decades in treating various types of wastewater, as wastewater pH of 6.5 was not adjusted. A brief
they are easily operated, require relatively low description of the three electrochemical processes
investment cost and are amenable to automation can be found in our previous works (Dermentzis et
(Yavuz et al., 2010). In spite of abundant applications al., 2011; Stergiopoulos et al., 2013).
of electrochemical processes for the treatment of
various kinds of wastewater, their use for the 3. Results and discussion
treatment of petroleum wastewater is scarce in
literature. 3.1. Electrocoagulation with and without addition of
The present paper discusses an integrated surfactant
electrochemical treatment for reclamation of oily
wastewater from oil tanker truck washing plants, The remediation treatment of the wastewater
which comprises electrocoagulation, elctro-oxidation was investigated by electrocoagulation using iron and
and advanced electrochemical oxidation using the aluminum electrodes as anode and cathode at a
electro-Fenton process. The three electrochemical current density of 5 mA/cm2 and NaCl (2.5 g/L) as
processes are compared and their efficiencies supporting electrolyte. The initial solution pH of 6.5
evaluated. needed no adjustment as it lies in the optimum near
neutral region. Every 10 minutes samples from the
2. Materials and methods treated solution were taken, which were allowed to
settle for 24 hours, filtered using Whatman filters
2.1. Chemicals (0.45 μm) and afterwards COD was measured.
For the iron and aluminum electrocoagulation,
Sodium dodecyle sulfate (SDS), NaCl, the initial COD of 456 mg/L decreased only slightly
Na2SO4 and H2O2 were of analytical grade. The pH to 420 and 405 mg/L in 80 minutes of electrolysis
value was adjusted with 0.1 M solutions of H2SO4 time, showing a reduction of about 8 and 11%
and NaOH as required. respectively (Fig. 1a,b). Based on the experimental
results, it can be concluded that the
2.2. Apparatus electrocoagulation treatment of the aqueous oil
dispersion was inefficient even at higher current
A DC power supply (Agilent E3612A, USA) densities and more prolonged time of electro-
was used for measuring the electrode potential and processing.
current. The experiments were conducted at room Performing the electrocoagulation treatment
temperature. Conductivity was measured by means of after addition of the surfactant SDS, the wastewater
a conductometer (WTW). The pH value and COD could more drastically be decreased. Surfactant
temperature were determined using a pH-meter molecules, as known, enclose the oil droplets
(Hanna) connected to a combined electrode forming oil-surfactant aggregates and micelles.
comprising a temperature sensor. Surfactants show higher affinity for adsorption on the
The progress of the electrochemical treatment coagulants Fe(OH)3 or Al(OH)3 and so do the oil-
was followed by measurement of chemical oxygen surfactant aggregates. Therefore, the oil molecules
demand (COD). COD was analyzed using a COD are swept by the surfactant molecules and removed
reactor (Thermoreaktor TR 420, MERCK) and a together from the treated solution. By adding 450
direct reading spectrophotometer (Spectroquant mg/L of the surfactant SDS the solution COD of 456
Pharo100, MERCK). Electrolyses were conducted at mg/L initially increases to 1300 mg/L. However, fast
room temperature in a cylindrical glass cell of 500 ml and effective removal of the total COD occurs. In 80
and the solution was rigorously stirred with a minutes of electro-processing at the applied current
magnetic bar at 500 rpm. The electrodes used for density of 5 mA/cm2, the total COD of 1300 mg/L
electro-oxidation were two platinized titanium plates (originated from oil and added surfactant) decreased
(Ti/Pt) and two Boron Doped Diamond electrodes, to 205 and 193 mg/L, showing a reduction of about
BDD, (DiaCCom, Germany) while for the 84 and 85% using iron and aluminum electrodes
electrocoagulation and electro-Fenton treatment two respectively (Fig. 1a,b).
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Electrochemical reclamation of wastewater resulted from petroleum tanker truck cleaning
Fig. 1. Electrocoagulation treatment of oily wastewater with and without surfactant using a) iron and b) aluminum electrodes
Further electrocoagulation experiments, under achieve higher COD removal from treated petroleum
the same experimental conditions, with an aqueous wastewater the temperature was elevated from 25 to
solution only of the surfactant (without oil) of same 60 0C. As reported by Rocha et al. (2012), an
initial COD (1300mg/L) led to a COD value of 112 increase of temperature favors organic oxidation due
mg/L (Stergiopoulos et al., 2014). Based on the to an increase of the indirect reaction of organics
experimental results, it can indirectly be concluded with electro-generated oxidizing agents from
that the initial oil COD of 456 mg/L decreased to electrolyte solution.
205-112 = 93 and 193-112 = 81 mg/L, showing a
reduction of about 80 and 82 % for the surfactant
aided iron and aluminum electrocoagulation
respectively. During the electrocoagulation process
the petroleum hydrocarbons are not oxidized or
destructed. They are adsorbed and relocated as a
whole in the electro-generated Al(OH)3 or Fe(OH)3
precipitate or rise to the surface by electro-flotation,
due to the electrochemically in situ generated
hydrogen bubbles.
The electrical energy consumption for the
SDS surfactant aided electrocoagulation process at
the applied current density of 5 mA/cm2 amounts to
3.6 kWh/m3 of treated oily wastewater
(Stergiopoulos et al., 2014). Fig. 2. Electro-oxidation at 250C using Ti/Pt and BDD
electrodes
3.2. Electro-oxidation with Ti/Pt and BDD electrodes
Electrolysis at higher temperatures in aqueous
The degradation of hydrocarbons from solutions containing chloride or sulfate ions
wastewater was investigated by direct electro- generates chlorine, peroxodisulfate, hydroxyl radicals
oxidation at Ti/Pt and BBD electrodes. The and hydrogen peroxide according to the reactions
supporting electrolyte was a mixture of 2 g/L Na2SO4 (Eqs. 1-4):
and 0.5 g/L NaCl to increase the solution
conductivity and therefore reduce the resistance and 2Cl- Cl2 + 2e (1)
the electrical energy consumption. The wastewater
4 S2 O 8 + 2e
2SO 2-
pH of 6.5 was not adjusted and the electro-oxidation 2-
(2)
treatment was conducted at room temperature (25
0
C). The applied current density was held at H 2O OH* + H + + e (3)
20 mA/cm2. Fig. 2 shows the decrease of COD of the
treated wastewater during electro-oxidation at Ti/Pt
and BDD electrodes respectively. After two hours of
2OH* H 2 O 2 (4)
electro-processing, the initial COD of 456 mg/L
Performing the electrooxidation treatment at
decreased only slightly to 388 mg/L using the Ti/Pt
60 0C, higher COD removal percentage could be
electrodes showing a COD elimination of about 15
obtained. Namely COD was reduced to 28% with
%. Under the same conditions at BDD electrodes
Ti/Pt, while it was almost quantitatively (>98 %)
COD could be more effectively decreased i.e. to 292
eliminated with BDD electrodes (Fig. 3).
mg/L achieving a COD elimination of about 36 %.
The most powerful oxidant in water is the
In order to increase the efficacy of anodic
hydroxyl radical with a redox potential of 2.8NHE.
oxidation at both, Ti/Pt and BDD electrodes and
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Dermentzis et al./Environmental Engineering and Management Journal 13 (2014), 9, 2395-2399
Chemical Advanced Oxidation Processes (AOPs) and of H2O2 (Boye et al., 2003; Dermentzis et al., 2011).
Electrochemical Advanced Oxidation Processes The oily wastewater was acidified with H2SO4 until it
(EAOPs), therefore, are characterized by the reached pH 3. The applied current densities were 5
production and use of these hydroxyl radicals for and 10 mA/cm2. The solution pH was monitored and
oxidative destruction of organic substances. BDD adjusted with dilute H2SO4. Fig. 4 shows that for the
electrodes show the largest overvoltage for oxygen two given applied current densities, the initial COD
production and the widest potential window in water of 456 mg/L was almost quantitatively eliminated by
ever found for an electrode material (Kraft et al., about 90% in 60 and 40 minutes of electrolysis time
2003, Troster et al., 2002). These electrodes are also respectively. The electro-Fenton process seems to be
chemically and mechanically stable. Therefore, BDD faster than the electro-oxidation with Ti/Pt and BDD
electrodes, compared to Ti/Pt are more suited for electrodes due to the ease of formation of OH*
producing free OH* radicals and performing EAOPs radicals and their fast reaction with the oily
with very high current efficiencies (Chatzisymeon et compounds.
al., 2006, Kraft et al., 2003).
During the electrooxidation treatment pH was
slightly rising from 6.5 to 8.25. The COD reduction
ratio is greater at the beginning and diminishes by the
end of electro-processing. This can be explained by
side reactions of the OH* radicals. Due to lower
concentration of organic compounds at the end of
treatment, the highly reactive hydroxyl radicals react
with scavenger substances or undergo recombination
of two OH* to form H2O2, according to reaction (4).
Hydrogen peroxide is further anodically oxidized to
molecular oxygen, according to reaction (Eq. 5):
Fig. 4. Residual COD versus time during the electro-
H 2O2 O2 2 H 2e (5) Fenton treatment at different current densities
The electrical energy consumption for the
petroleum wastewater cleanup after 60 and
40 minutes of electrolysis time at the applied current
densities of 5 and 10 mA/cm2 are 3.1 and
7.6 kWh/m3 of treated wastewater respectively.
4. Conclusions
The electrocoagulation process without
addition of surfactants is not an efficient method for
reducing COD from the treated petroleum
wastewater as the process reduces it to only 8 and 11
Fig. 3. Electrooxidation at 60 0C using Ti/Pt and BDD % when aluminum and iron electrodes respectively
electrodes are used. The surfactant aided electrocoagulation
process becomes effective by addition of sodium
The electrical energy consumption for the dodecyle sulfate and emulsification of the oily
electro-oxidation treatment with BDD electrodes at droplets. The electrical energy consumption for
60 0C and the applied current density of 20 mA/cm2 treatment with iron electrodes was 3.6 kWh/m3 of
amounts to 15.2 kWh/m3 of treated wastewater. treated oily wastewater.
The electro-oxidation process using Ti/Pt
3.3. Electro-Fenton with sacrificial iron anode and electrodes in acidic medium at the applied current
added H2O2 density of 20 mA/cm3 and Na2SO4 /NaCl as
supporting electrolyte leads to a COD reduction of
The very reactive free hydroxyl radicals, about 15 % in 120 minutes of electro-processing
OH*, as known, are produced between ferrous ions time. The electro-oxidation process was improved
and hydrogen peroxide in acidic media with optimum reaching about 36 % of COD reduction by
pH 3, according to the classical Fenton reaction (Eq. substituting Ti/Pt with BDD electrodes and using the
6): same Na2SO4/NaCl supporting electrolyte. Higher
COD removal percentage to 28 and >98 % with Ti/Pt
Fe 2 H 2 O2 Fe 3 OH OH (6) and BDD electrodes respectively was reached when
the electrooxidation process was performed at the
The Fenton reaction can be carried out also elevated temperature of 60 0C, due to increased
electrochemically with sacrificial Fe anode, which reaction rate between the organic oily contents of the
supplies Fe2+ ions to the solution and added amounts treated wastewater and the anodically generated
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Electrochemical reclamation of wastewater resulted from petroleum tanker truck cleaning
powerful oxidants, such as hydroxyl radicals, Gasim H.A., Kutty S.R.M., Isa M.H., Isa M.P.M., (2012),
peroxodisulfate and chlorine. The electrical energy Treatment of petroleum refinery wastewater by using
consumption for treatment with BDD electrodes is UASB reactors, World Academy of Science,
15.2 kWh/m3 of treated wastewater. Engineering and Technology, 62, 176-179.
Kraft A., Stadelmann M., Blaschke M., (2003), Anodic
The electro-Fenton process with Fe oxidation with doped diamond electrodes: a new
electrodes and supplied H2O2 in acidic solution is a advanced oxidation process, Journal of Hazardous
more efficient method for reclamation of oily Materials, B103, 247-261.
wastewater of this type. 90% degradation of the oil Meeroff D., Engelhardt J., (2001), Precoat filtration and
content was achieved 60 and 40 minutes when ultrafiltration of emulsified bitumen from water,
current densities of 5 and 10 mA/cm2 respectively Journal of Environmental Engineering, 127, 46-53.
were applied. The corresponding energy Motoc S., Manea F., Pop A., Baciu A., Burtica G., Pode R.,
consumptions were 3.1 and 7.6 kWh/m3 of treated (2013), Electrochemical mineralization of reactive red
147 on boron doped diamond electrodes,
wastewater.
Environmental Engineering and Management Journal,
It can be concluded that the proposed 12, 509-516.
electrochemical treatment is a safe and efficient Rocha J.H.B., Soares Gomes M.M., Fernandes N.S.,
process for remediation of wastewater from oil tanker Ribeiro da Silva D., Martinez-Huitla C.A., (2012),
truck washing plants. The process efficiency Application of electrochemical oxidation as alternative
increases when a suitable surfactant is added treatment of produced water generated by Brazilian
(electrocoagulation) and when free hydroxyl radicals petrochemical industry, Fuel Processing Technology,
are generated (electro-Fenton and electrooxidation at 96, 80-87.
BDD electrodes). Salahi A., Mohammadi T., Rekabdar F., Mahdavi H.,
(2010), Reverse osmosis of refinery oily wastewater
effluents, Iranian Journal of Environmental Health
References Science and Engineering, 7, 413-422.
Stepnowski P., Siedlecka E.M., Behrend P., Jastorff B.,
Biswas N., Lazarescu G., (1991), Removal of oil from (2002), Enhanced photo-degradation of contaminants
emulsions using electrocoagulation, International in petroleum refinery wastewater, Water Research, 36,
Journal of Environmental Studies, 38, 65-75. 2167-2172.
Canizares P., Martinez F., Jimenez C., Saez C., Rodrigo Stergiopoulos D., Dermentzis K., Giannakoudakis P.,
M.A., (2008), Coagulation and electrocoagulation of Sotiropoulos S., (2014), Electrochemical Degradation
oil-in-water emulsions, Journal of Hazardous and Removal of Indigo Carmine Textile Dye From
Materials, 151, 44-51. Wastewater, Global NEST Journal, 16, 499-506.
Chatzisymeon E., Xekoukoulotakis N.P., Coz A., Troster I., Fryda M., Herrmann D., Schafer L., Hanni W.,
Kalogerakis N., Mantzavinos D., (2006), Perret A., Blaschke M., Kraft A., Stadelmann M.,
Electrochemical treatment of textile dyes and (2002), Electrochemical advanced oxidation process
dyehouse effluents, Journal of Hazardous Materials for water treatment using DiaChemR eledtrodes,
B137, 998-1007. Diamond and Related Materials, 11, 640-645.
Coelho A., Castro A.V., Dezotti M., Sant’ Anna Jr., (2006), Waite T.D., Schafer A.I. Fane A.G., Heur A., (1999),
Treatment of petroleum refinery sourwater by Colloidal fouling of ultrafiltration membranes: impact
advanced oxidation process, Journal of Hazardous of aggregate structure and size, Journal of Colloid and
Materials, B137, 178-184. Interface, Science, 212, 264-274.
Dermentzis K., Marmanis D., Valsamidou E., Yang C.-L., (2007), Electrochemical coagulation for oily
Christoforidis A., Ouzounis K., (2011), water demulsification, Separation and Purification
Electrochemical decolorization treatment of nickel Technology, 54, 388-395.
phthalocyanine reactive dye wastewater, Yavuz Y., Koparal A.S., Ogutveren U.B., (2010),
Environmental Engineering and Management Journal, Treatment of petroleum refinery wastewater by
10, 1703-1709. electrochemical methods, Desalination, 256, 201-205.
Dermentzis K., Valsamidou E., Chatzichristou C., Zanbotto Ramalho A.M., Martinez-Huitle C.A., Riberio da
Mitkidou S., (2013), Decolorization treatment of Silva D., (2010), Application of electrochemical
copper phthalocyanine textile dye wastewater by technology for removing petroleum hydrocarbons
electrochemical methods, Journal of Engineering from produced water using a DSA-type at different
Science and Technology Review, 6, 33-37. flow rates, Fuel, 89, 531-534.
Fouad Y.O.A., Konsowa A.H., Farag H.A., Sedahmed Zhong J., Sun X., Wang C., (2003), Treatment of oily
G.H., (2009), Performance of an electrocoagulation wastewater produced from refinery processes using
cell with horizontally oriented electrodes in oil flocculation and ceramic membrane filtration,
separation compared to a cell with vertical electrodes, Separation and Purification Technology, 32, 93-98.
Chemical Engineering Journal, 145, 436-440.
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