Science and Technology Indonesia
e-ISSN:2580-4391 p-ISSN:2580-4405
Vol. 7, No. 3, July 2022
Research Paper

Electro-adsorption as a Hybrid Processing to Removed Oil from Synthetic Oily Solution
by Using Activated Carbon and Iron Electrodes
Lia Cundari1 *, Bazlina Dawami Afrah1 , Suci Dwijayanti2 , Alvina Suryadinata1 , Aldi Ramadhani1
1 Chemical Engineering Department, Faculty of Engineering, Universitas Sriwijaya, Palembang, 30128, Indonesia
2 Electrical Engineering Department, Faculty of Engineering, Universitas Sriwijaya, Palembang, 30128, Indonesia
*Corresponding author: liacundari@ft.unsri.ac.id

Abstract
Biosolar contains oil, fatty acids, emulsifiers, bactericides, and other chemicals. If the oil contents are mixed with water, it will become
hazardous waste and affect drinking water sources, endanger human health, air pollution, affect agricultural production, and damage
the natural landscape, so the oil content must be processed to reduce its hazardous content. One of the methods used in treating
oily solutions is adsorption. The adsorption method for oily solution treatment is ineffective because it requires several stages, so the
required capital is relatively larger and takes longer. Electro-adsorption is one of the methods that is being developed for treating oily
solutions. Electro-adsorption is a hybrid separation technology to break down oil emulsions in wastewater and some other organic
content. The purpose of this study is to characterize the activated carbon and determine the effect of voltage and time on synthetic
oily solution treatment in terms of COD value and oil-fat content. A synthetic oily solution is made by mixing 1 g of biosolar/B30 into
the water from the Musi River to a volume of 1 L. The application of the electro-adsorption method uses commercially activated
carbon as an adsorbent and iron as an electrode. Variations given to the process with voltage 0, 5, 10, 15 V and time 0, 5, 10, 15,
20, and 25 minutes. The characteristic of activated carbon showed a size change in the pore size from 2.58 µm to 1.98 µm and a
reduction of surface area from 740 (±180) m2 /g to 730 (±120) m2 /g. The electro-adsorption method was effective in treating oily
solutions. The decrease of COD reaches the maximum level at a voltage 10 V for 25 minutes, which was 75.92% from 62.33 mg/L
to 15 mg/L initially, while the concentration of oil-fat obtains the maximum level at a voltage of 5 V for 5 minutes that is equal to
99.65%, initially 303.19 mg/L to 1.05 mg/L. The optimum condition of the electro-adsorption process in synthetic oily solution was
at the voltage of 5 V and a time of 5 minutes. The electro-adsorption process is an effective method to treat synthetic oily solutions.
Keywords
Activated Carbon, Electro-Adsorption, Hybrid Technology, Iron Electrode, Synthetic Oily Solution
Received: 28 December 2021, Accepted: 1 April 2022

https://doi.org/10.26554/sti.2022.7.3.344-352

1. INTRODUCTION
The oil and gas industry is vital because it produces products
that people need in their daily lives. High demand for products
requires factories to continue to produce products in large
quantities. The conducted process of producing products will
also form waste. The oil and gas industry is an industry that
produces hazardous and toxic waste. One of the industrial
wastes is an oily liquid waste. Other industries that produce
oily liquid waste are metallurgical, food, leather, and metal
industries (Coca-Prados and Gutiérrez-Cervelló, 2010) . Oily
liquid waste cannot be directly discharged into the environment
because it can affect drinking water sources, endanger human
health, air pollution, affect agricultural production, and damage
the natural landscape (Poulopoulos et al., 2005) . It means that
the waste must be treated first before being discharged into the

environment. Oily liquid waste contains oil (mineral, vegetable,
or synthetic oil), fatty acids, emulsifiers, bactericides, and other
chemicals (Gryta et al., 2001) .
The present oily wastewater treatment takes a long period
and is inefficient. Therefore, a new method that is shorter,
efficient, and able to process large waste at a time considering the large amount of waste produced due to the large mass
production of oil in the oil and gas industry. Many methods
can be used as a treatment process for oily wastewater. One
of the methods is electro-adsorption which is a hybrid process of a combination of two methods between adsorption and
electrolysis.
According to the United States Environmental Protection
Agency (USEPA) that the adsorption process by utilizing activated carbon is one of the best environmental treatment tech-

Cundari et. al.

nologies (Sivakumar et al., 2012) . Activated carbon adsorbent
is widely used because it has a high adsorption rate, high specific
surface area, and even distribution of pores. In addition, it can
adsorb up to 50% of the mass of the carbon itself (Khairunisa,
2008) .
The adsorption and electrolysis methods each have an excellent ability to carry out the process. The adsorption method
with the addition of voltage in the process can increase the
ability of the adsorbent to adsorb unwanted substances. Combining the two methods can be seen in its ability in the research
of Xie et al. (2018) , which used electrochemical adsorption and
succeeded in adsorbing solid particles with sizes below 10 m
with an efficiency rate of more than 90%. Research conducted
by Ziati et al. (2017) showed a high reduction rate using the
electro-adsorption method to reduce chromium with the result
reaching 96%.
Electrolysis is alternative energy used to produce hydrogen
by breaking down water components into clean and pollutantfree hydrogen and oxygen (Saputra, 2018) . The water electrolysis process is also considered to have high effectiveness in
producing hydrogen, reaching more than 70% (Barbir, 2005) .
The adsorption and electrolysis methods each have an excellent
ability to carry out the process. The adsorption method with
the addition of voltage in the process can increase the ability of
the adsorbent to adsorb unwanted substances.
The electrolysis method for doing its reaction process requires electrodes. Electrodes are a carrier consisting of electrolyte carriers and ionic carriers (Rivai, 1995) . The materials
which can and are often used ad electrodes are graphite, platinum, and gold. Other materials or electrodes that have been
used for many research are carbon, iron, aluminum, copper,
and stainless steel.
In this study, the electrode that will be used are iron electrodes. Iron is widely used as an electrode because iron is one
of the materials with high durability and has a lower cost compared to aluminum (Casillas et al., 2007) . The availability of
iron electrode material is also abundant and its use has proven
effective (Larue et al., 2003) . Iron is also an excellent material
to use at the anode because it is a trivalent ion. Trivalent ions
have a higher ability to adsorb particles in water than bivalent
ions due to their higher density (Koren and Syversen, 1995) .
The research of Mohammed et al. (2011) , treats oily liquid
waste by adsorption method. The adsorbents used in his research were activated carbon and zeolite with expanded beds
as a tool for adsorption. The sample used was corn oil which
was prepared by mixing corn oil in distilled water. The best
adsorption results from the two adsorbents were shown by activated carbon. The result can be seen from the oil concentration
of the research results. By using an adsorbent weighing 2-8
grams for 20 minutes at a temperature of 30◦ C, activated carbon reduced the residual oil concentration from 20,000 ppm
to zero ppm while in the zeolite adsorbent, the final oil residue
concentration was 10,000 ppm.
Activated carbon is a combination of carbon atoms with a
vast surface area obtained from the activation of the carbon.
© 2022 The Authors.

Science and Technology Indonesia, 7 (2022) 344-352

Activation is the treatment of charcoal or carbon to enlarge the
pores. This activation is carried out by breaking the hydrocarbon bonds or by oxidizing the molecules from the surface
until carbon change’s physical and chemical properties. These
changes are shown by increasing the size of the carbon surface
and will affect the adsorption power (Sembiring and Sinaga,
2003) . One gram of activated carbon that has been activated
will be equivalent to a material having a surface area of 500m2 .
The purpose of activation is usually to enlarge the carbon pores,
but some of the activations are associated with increasing the
adsorption power of activated carbon (Idrus et al., 2013) .
Xie et al. (2018) used the electrochemical adsorption method on drilling fluids waste from domestic oilfields. The adsorbent used in his research is in the form of bentonite. The study
was conducted by the electro-adsorption plate with a distance
between plates of 5 cm, and the voltage used was 1.3 V and 1.6
V for 5 minutes. Electrosorption carried out aims to adsorb
and remove solid particles with a size below 10 microns. This
research obtained the efficiency of removing solid particles
measuring 1-10 m up to more than 90% by using the single
factor experiment.
The research that has been mentioned above focused on
adsorption or electrolysis only. The combination of adsorption
and electrolysis named electro-adsorption was done by Xie
et al. (2018) and Ziati et al. (2017) also didn’t focus on oily
treatment by using activated carbon and iron electrodes. The
adsorption method with activated carbon as an adsorbent is
known to have a high level of oil adsorption in the waste. The
combined method with the electrolysis process can also increase
the oil absorption rate compared to without electrolysis. The
advantages of both methods encourage the search for research
on electro-adsorption. The research that will be carried out
this time uses the electro-adsorption method using activated
carbon adsorbents and iron electrodes to process synthetic oily
solutions as a substitute for oily wastewater.
This study aims to determine changes in the characteristics of activated carbon and the effect of voltage and time on
the electro-adsorption method on the synthetic oily solution
as a replacement for the oily wastewater treatment process,
which is resistant to COD levels and oil-fat content. The adsorbent used is commercial activated carbon. The activated
carbon wrapping container used a type of spunbond fabric
made from polypropylene. The electrode used in this study
is iron electrodes. Synthetic oily solution treatment using the
electro-adsorption method is expected to provide a better percentage of absorption than using only the electrolysis method
or only adsorption method.
2. EXPERIMENTAL SECTION
2.1 Materials
The materials used for this research are the synthetic oily solution (using biodiesel/B30), commercial activated carbon in
granular shape, Musi River water, and aquadest. The tools
used are a 2 liters glass beaker, iron electrode plates with size

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Cundari et. al.

Table 1. The COD and Oil-Fat Content of Synthetic Oily

Solution After Electro-Adsorption Process
Time
(minutes)
5

10

15

20

25

Voltage COD
(V)
(mg/L)
0
5
10
15
0
5
10
15
0
5
10
15
0
5
10
15
0
5
10
15

23.5
18
19
19
26.5
20
21
20
23
18
21
18
23
18
18
18
24.5
17
15
18

Oil-fat
(mg/L)
7.99
1.05
1.15
1.64
7.57
1.82
2.03
1.89
7.71
2.04
1.78
2.03
7.85
1.73
1.89
1.77
7.98
1.31
2.04
1.97

17×5×0.1 cm, a power supply, a spunbond cloth made of
polypropylene with size 12×8 cm, and a stopwatch.
The synthetic liquid solution used in this study was made
by mixing the Musi River water and biodiesel (B30) into one
vessel. A synthetic oily solution is made by mixing 1 g of
biosolar/B30 with water from the Musi River to a volume of 1
L. The Musi River was used because this is the main source of
water for Palembang society and this synthetic oily solution is
analogous to biosolar/B30 spills to the river. The COD and
oil-fat content of synthetic oily solution before the process is
analyzed to obtain the initial characteristic to be compared later
with the processed or final synthetic oily solution.
The activated carbon used in this research is commercial
activated carbon. Activated carbon received from the seller still
contains a lot of impurities, so the activated carbon needs to
be washed before its utilization (Sahara et al., 2017) . The activated carbon was first washed with water from the Palembang
Regional Drinking Water Company then followed by doubled
aquadest washing to remove dust and other impurities. The
washed adsorbent was then dried in an oven at 110◦ C for 1
hour. The dried activated carbon as much as 50 g was placed
into a spunbond bag made of polypropylene.
The research was conducted by applying an electric potential to the electrodes of 5, 10, and 15 V with specific time
intervals (5, 10, 15, 20, and 25 minutes). As a comparison, a
test was also carried out without using an electrode (voltage 0 V).
The research procedure started when 1 mg/L of the synthetic

© 2022 The Authors.

Figure 1. Schematic of Electro-Adsorption Equipment

oily solution is filled into the beaker glass with the electrode
plates placed on the right and left sides in it. The electrodes
are connected to the power supply. Then, the wrapped activated carbon is set in the middle of the electrodes. After all,
the components are set in each of their places, turned on the
power supply with the appropriate voltage, and countdown the
time of the process, as seen in Figure 1. At the end of the
process, turned off the power supply, took the adsorbent out,
and analyzed the lean solution.
The activated carbon characterized by using Scanning Electron Microscope (SEM) and Fourier Transform Infra-Red
(FTIR). The electro-adsorption process results are analyzed
for COD levels based on SNI 6989.2:2019 and oil-fat concentrations based on SNI 06-6989.10-2004. The percentage
reduction in COD and oil-fat concentrations are calculated
using Equation (1), where C0 is the initial COD/oil-fat concentration and Ct is the COD/oil-fat concentration at time
t.

% Removal =

C0 − Ct
C0

(1)

3. RESULTS AND DISCUSSION
The synthetic oily solution used in this study was made by mixing Musi River water and biodiesel (B30). The initial sample
of the synthetic liquid solution was tested to be used as an iniPage 346 of 352

Cundari et. al.

tial sample characteristic before conducting research using the
electro-adsorption method on the sample. The initial COD
was 62.33 mg/L and the oil-fat content was 303.19 mg/L.
The maximum permissible level based on the Regulation of
the Minister of the Environment No. 19 the year of 2010
concerning the quality standard for the disposal of process
wastewater from petroleum processing activities for COD was
160 mg/L and oil-fat was 20 mg/L. Based on that regulation
the oil-fat content of the sample was 15 times more than the
maximum permissible level.
The synthetic oily solution is then electroadsorbed with the
variation of voltages of 0, 5, 10, and 15 V for 5, 10, 15, 20, and
25 minutes. The electroadsorbed oily solution was analyzed
with COD and oil-fat parameters. The results of COD and oilfat content of oily solution samples after the electro-adsorption
process can be seen in Table 1.
Table 1 showed the results of the analysis with a big difference from the initial value. The oil-fat concentration in Table 1
ranged from 1.05 mg/L to 2.04 mg/L. That means the electroadsorption process was effective to reduce the oil-fat content
to a value that is lower than the permissible point of oil-fat
content on the regulation of The Minister of Environment No.
19 the year of 2010. Similar results also occurred for COD
values, that ranged from 15-21 mg/L. The results indicate that
the electro-adsorption process has an influence on the analyzed
parameter namely COD and oil-fat content which the effect
explained later. At the voltage 0 volts which can be called as
adsorption process only, the COD and oil-fat content resulted
in 23-26.5 mg/L and 7.57-7.99 mg/L respectively.
3.1 Activated Carbon Characteristic
The activated carbon used in this research is commercial activated carbon. The activated carbon was prepared with the
procedure explained in section 2. Characterization methods
to determine the morphology and functional group in the activated carbon were Scanning Electron Microscope (SEM) and
Fourier Transform Infra-Red (FTIR) respectively. Analysis of
the activated carbon characteristics was carried out on activated
carbon before and after the electro-adsorption process. The
adsorbent samples to be tested were the highest oil-fat electroadsorption results (at an operating voltage of 5 V for 5 minutes)
to see the changes that occurred in it. SEM analysis results
of activated carbon before and after the electro-adsorption
process can be seen in Figure 2 and Figure 3.
The initial and final activated carbon presented in Figures
2 and 3 were characterized using SEM at a magnification of
5000×. Figure 2 showed rough topography (surface texture)
and morphology, irregular porosity, and uneven pore size diameter. The pore size diameter ranged from 1.64 to 4.77 𝜇m,
with an average pore diameter of 2.58 𝜇m.
In contrast, the pore diameter after the electro-adsorption
process reduced, as seen in Figure 3. The shortest and the
longest pore diameter were 1.16 𝜇m and 2.92 𝜇m respectively,
with an average pore size diameter was 1.98 𝜇m. The topography, morphology, and porosity were similar to Figure 2. This
© 2022 The Authors.

Science and Technology Indonesia, 7 (2022) 344-352

Figure 2. SEM Analysis of Initial Activated Carbon (Before

Electro-Adsorption Process)

indicated the adsorption of oil molecules onto the activated
carbon that stuck and covered the pore. The result of this activation was the degradation of the pore size diameter of the
activated carbon. At the beginning of the process, the active site
of the carbon was still empty so the adsorption process occurred
in the fast stage. As time goes by, the oil molecules began to
fill the active site of the carbon which causes the adsorption
process to enter a slow stage. This matter is also supported by
FTIR results that can be seen in Figure 4.
Based on analysis results using BET analyzer, the surface
area of activated carbon before and after the electro-adsorption
are 740 (±180) m2 /g and 730 (±120) m2 /g respectively. The
reduction in surface area after electro-adsorption process indicates the presence of substances that are absorbed by the
activated carbon.
Figure 4 showed the analysis results using FTIR before and
after the electro-adsorption process. The green line in Figure
4, which was the FTIR result for activated carbon before the
electro-adsorption process, did not show any peaks formed,
that indicated no oily molecules adsorbed. The red line in
Figure 4, the FTIR result of activated carbon after the electroadsorption process, showed the peak of the wave, although not
very sharp. The first peak formed at wavenumber 3700 - 3000
cm−1 , the wide wavenumber pointed the absorbance activity of
the double bond with the H-OH hydroxyl group (3570-3200
cm−1 ); the second peak formed at wavenumber 2150-2000

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Science and Technology Indonesia, 7 (2022) 344-352

Figure 4. FTIR Analysis of Activated Carbon (Before and After

Electro-Adsorption Process)

Figure 3. SEM Analysis of Final Activated Carbon (After

Electro-Adsorption Process)

cm−1 showed the wavelength region of the triple bond; and
the third peak formed that the smallest peak at wavenumber
1700-1500 cm−1 indicated the absorbance of the group with
varying double bonds (Nandiyanto et al., 2019) . This indicated
the presence of a group of biosolar (B30) that adsorbed into
the activated carbon.
3.2 Effect of Voltage and Time Variations on COD Levels
Chemical Oxygen Demand (COD) is the amount of oxygen
needed to chemically oxidize organic and inorganic materials
in water (Riyanti et al., 2019) . The higher the COD number
indicates the reduced dissolved oxygen content in the water
so that water pollution is high. The effect of voltage and time
variations on decreasing COD levels in synthetic oily solution
samples was shown in Figure 5.
Figure 5 showed the results of COD level analysis ranging
from 15 to 21 mg/L. The maximum reduction in COD level
was 75.92% at a voltage of 10 V for 25 minutes, that reduced
from 62.33 mg/L to 15 mg/L. A very drastic decrease in COD
levels in the treatment of oily solution was shown in the first 5
minutes of the processing that pointed fast electro-adsorption,
this result similar to Okiel et al. (2011) and (Ramli and Ghazi,
2020) . In the next minutes, the changes that occurred were not
as significant anymore, that showed slow electro-adsorption.
The optimum condition for all of the voltage variations happened at contact time at 5 minutes. This showed the equilib-

© 2022 The Authors.

rium condition of the electro-adsorption process. This was
because the pores in the activated carbon had been filled with
oil molecules that affected the adsorbent ability to degrade the
COD level (Ramli and Ghazi, 2020) .
According to Siregar et al. (2015) , the longer the operation
time, the ability of activated carbon to remove COD levels
decreased which caused degradation of efficiency. The ability
of activated carbon to adsorb is reduced due to the saturated
pores of the activated carbon. As a comparison to see the effect
of time on the COD levels reduction, a sample was time-tested
at a voltage of 15 V for 75 minutes and obtained a final COD
level of 20 mg/L. This value was still within the range of COD
produced for 0-25 minutes.
Based on research conducted by Hamid et al. (2017) , the
addition of voltage to the process decreased the COD levels.
Based on Figure 6, the average value of COD levels at various voltages of 5, 10, and 15 V were 18.2, 18.8, and 18.6
mg/L respectively. This showed that the addition of voltage
had no significant effect on decreasing COD levels in electroabsorption of synthetic oily solution. This happened because
if the voltage used was too high, a decomposition reaction will
occur, which will affect the results of reducing the COD of oily
solution (Xie et al., 2018) .
Figure 6 described the percentage of COD removal ranged
from 57.46% to 75.92%. This value was greater than the study
conducted by Hamid et al. (2017) but lower than Yan et al.
(2011) . Hamid et al. (2017) reduced COD levels in domestic wastewater treatment using the electrolysis method from
192.96 mg/L to 85.92 mg/L or 55% COD removal. Yan et al.
(2011) also researched the electrolysis method of petrochemical waste treatment using graphite type electrodes, get the best
results at 60 minutes and 12 V, namely a reduction in COD
levels from 1027 to 80.89 mg/L or 93.1%.
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Figure 5. The Effect of Voltage and Time Variability of

Electro-Adsorption Process on COD Levels

Science and Technology Indonesia, 7 (2022) 344-352

Figure 7. Comparison of Percentage of COD Removal with
Various Methods

content of the synthetic oily solution was shown in Figure 8.

Figure 6. Percentage of COD Removal of Synthetic Oily
Solution by Using an Electro-Adsorption Process

Figure 7 showed a comparison result of the percentage
of COD removal using electrolysis, adsorption, and electroadsorption methods. The average value for each process sequence was 50.24%, 61.32%, and 70.14%. COD removal by
electro-adsorption method has the highest percentage. These
results indicated that applying voltages to the adsorption process can increase the adsorption rate of COD from synthetic
oily solutions.
3.3 Effect of Voltage and Time Variations on Oil-Fat Content
Oil and fat content are included in one of the water quality
measurement parameters. High levels of oil and fat in wastewater indicate the amount of oil contained. The more oil content
in the water showed a high level of water pollution by oil. The
wastewater could not be directly discharged into the environment. The effect of voltage and time variations on the oil-fat
© 2022 The Authors.

Figure 8. The Effect of Voltage and Time Variability of

Electro-Adsorption Process on Oil-Fat Content
Figure 8 showed a drastic reduction in oil-fat content in
the first 5 minutes of application. In the next minutes, there
were no significant differences in the oil-fat data. The analysis results of the oil-fat content after the electro-adsorption
method ranged from 1.05 mg/L to 2.04 mg/L. These values
are appropriated with the Regulation of the Minister of the
Environment No. 19 of 2010. The oil-fat and COD data
showed a similar trend, where fast electro-adsorption occurred
at the beginning of 5 minutes and slow electro-adsorption at
the rest of the time applied (Ramli and Ghazi, 2020) .
The oil-fat content in the sample was influenced by the duration of processing time. The longer the contact time between
the adsorbent and the waste, the lower the oil-fat content (Okiel

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Table 2. Comparison with Another Researcher that Focused on Oily Wastewater Treatment

Researcher

Process

Result

This research

Electro-adsorption

Mohammed et al.,
2011

Adsorption

Okiel et al., 2011

Adsorption

Xie et al., 2018

Electrochemical adsorption

Ziati et al., 2017

Electrosorption

Ramli and Ghazi,
2020

Adsorption

Ulucan and Kurt,
2015

Electrocoagulation /
electroflotation and
Electrofenton

Bhagawan et al.,
2018

Electrocoagulation

By using activated carbon and iron electrodes, the
COD removal resulted from 57.46% to 75.92% and the
oil-fat removal resulted from 99.33% to 99.65%.
Final oil concentration with adsorbent weight 2-8 g for
20 minutes from 20,000 ppm is 0 ppm (100%
removal) for activated carbon and 10,000 ppm (50%)
for zeolite
The oil removal percentage using powdered activated
carbon obtained 82.6% for oil concentration 836 mg/L
and 72.5% for oil concentration that increased to 1613
mg/L
Waste water-based treatment using electrochemical
adsorption is a treatment without the potential
environmental hazard
The application of potential had a significant result.
The adsorption without potential obtained 33.7%,
whereas with the application of -0.7 and -1.4 V
potential, the adsorption of chromium up to 90% and
96%
The results of maximum oil removal resulted from
99.89% at 1 mL/min flowrate with an oil concentration
5%w/v
The results using an iron electrode in
electrocoagulation process and electrofenton, for COD
removal, resulted from 36.2% and 71%, for oil-grease
removal resulted from 12.5% and 68.8%
The maximum COD removal using iron electrode
obtained 60% in 40 minutes

et al., 2011) . The highest reduction in oil-fat levels in synthetic
oily solution reached 99.65%, and occurred at a voltage of 5
V for 5 minutes from the initial condition of 303.19 mg/L to
1.05 mg/L. The optimum condition for all of the voltage variations on oil-fat content is similar to COD, which happened
at a contact time of 5 minutes. This showed the equilibrium
condition of the electro-adsorption process. The pores of the
adsorbent had been covered with oil molecules, thus inhibiting
the next electro-adsorption process.
Experiments using a voltage of 0 V (with no electrodes
applied), the process that took place only adsorption, showed
that the oil-fat content ranged from 7.57-7.99 mg/L. These
values were higher than the 5, 10, and 15 V electro-adsorption
processes which have values ranging from 1.05-2.04 mg/L.
These results explained that the application of voltages in the
electro-adsorption process affected the absorption of synthetic
oily solution in terms of oil-fat content.
Figure 9 showed the percentage of oil removal in synthetic
oily solution ranged from 99.33% to 99.65%. These results are
better than the research of Okiel et al. (2011) on activated carbon adsorbents, which succeeded in removing 82.6% and 72.5%

© 2022 The Authors.

oil-fat with initial oil concentrations of 836 mg/L and 1613
mg/L, respectively. Based on the research that had been done,
the phenomenon of the electro-adsorption process occurred in
the early minutes of the study; in the following minutes, there
was no significant change. The same trend also occurred in the
research of Ramli and Ghazi (2020) , namely the oil-fat content
with a concentration of 10% oil, which can be removed 99.87%
in 2 hours. However, after 24 hours of application, it decreased
to 73.04% due to the saturation level of activated carbon.
Figure 10 showed the comparison of the percentage of oilfat removal using electrolysis, adsorption, and electro-adsorption
methods. The average percentages for each process sequentially were 92.13%, 97.42%, and 99.39%. The graph pointed to
the highest oil-fat removal reached by the electro-adsorption
method. These results were not much different from the adsorption method, which successfully adsorbed oil-fat of 97.42%.
These results indicated that the addition of voltage in the adsorption process could increase the efficiency of oil-fat adsorption from synthetic oily solutions. Another researcher that
focused on oily wastewater treatment and the result comparison showed in Table 2.

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Cundari et. al.

of electro-adsorption process in synthetic oily solution was
at voltage of 5 V and time of 5 minutes. After the first 5
minutes, the process reached equilibrium condition. It could
be concluded that electro-adsorption process is an effective
method to treat synthetic oily solution.
5. ACKNOWLEDGMENT
The author would like to thank the Environmental Research
Center of Universitas Sriwijaya for providing the laboratory
supports and facilities during the research and activities.
REFERENCES

Figure 9. Percentage of Oil-Fat Removal of Synthetic Oily
Solution by Using Electro-Adsorption Process

Figure 10. Comparison of Percentage of Oil-Fat Removal with
Various Methods

4. CONCLUSIONS
Characteristics of activated carbon showed rough topography
(surface texture) and morphology, irregular porosity, uneven
pore size diameter. The average pore size changed from 2.58
𝜇m to 1.98 𝜇m. The surface area reduced from 740 (±180)
m2 /g to 730 (±120) m2 /g. The changes occured due to the
presence of COD components and the oil-fat content of synthetic oily solution that adsorbed onto the activated carbon.
The highest reduction in COD levels was produced at a
voltage of 10 V for 25 minutes, which was 75.94% from 62.33
mg/L to 15 mg/L. The highest reduction in oil-fat content
was produced at a voltage of 5 V for 5 minutes of 99.65%
from 303.19 mg/L to 1.05 mg/L. The oil-fat and COD data
showed a similar trend, where fast electro-adsorption occurred
at the beginning of 5 minutes and slow electro-adsorption at
the rest of time applied. That indicated the optimum condition
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