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8
Coagulation/flocculation and
electrocoagulation methods for
oily wastewater treatment
J. Trevin
˜o-Rese
´ndez
1
, A. Medel
1
, P. Mijaylova
2
and Y. Meas
1
1
Department of Water and Environment Research, Centre for Research and
Technological Development in Electrochemistry, Santiago de Quere
´taro,
Me
´xico
2
Department of Wastewater Treatment and Reuse, Mexican Institute
of Water Technology, Morelos, Me
´xico
8.1 Introduction
Water use in oil refineries can be classified into four main
groups: boiler-feed (16%), cooling systems makeup (56%), pro-
duction processes (19%), and auxiliary operations (9%) [1].The
refining of crude oil into primary products involves a large num-
ber of processes (desalting, distillation, hydrotreating, catalytic
cracking, hydrocracking, etc.), in which the primary function of
water is to provide adequate cooling of equipment and products
at the outlet of the processes. Therefore cooling systems are the
largest consumers since they require significant amounts of
makeup water due to water losses in the system [2]. According to
an analysis of 58 European oil refineries, Barthe et al. [3] reported
that an average of 5.89 m
3
of water is used per ton of refined
crude oil (maximum of 149 m
3
/ton), which is equivalent to
39 Mm
3
/year on average (maximum of 842 Mm
3
/year).
In general, liquid wastes or oily wastewater streams are gen-
erated from water used for [4]:
1. Process purposes or washwater in direct contact with either
crude oil or the different fractions of hydrocarbons.
2. Washwater or steam used to clean and purge systems for
maintenance.
3. Water separated and removed from crude oil, intermediates,
and product tanks.
On the other hand, offshore and onshore oil and gas extraction
activities also generated significant quantities of wastewater with
specific particular characteristics [5,6]. Typical physicochemical
173
Advanced Technologies in Wastewater Treatment. DOI: https://doi.org/10.1016/B978-0-323-99916-8.00013-4
©2023 Elsevier Inc. All rights reserved.
characteristics of oily wastewater are high content of oils and
grease (O&G), polyaromatic hydrocarbons (PAHs), phenols, sul-
fides (S
22
), ammonia, cyanides, heavy metals, suspended solids,
and dissolved salts [7,8].
Coagulation/flocculation (C/F) and electrocoagulation (EC) are
physicochemical processes for removing colloidal and suspended
particles, O&G, and organic matter in water and wastewater by
dosing coagulating agents. However, they differ in the dosing
method, which implies different phenomena to destabilize and
remove pollutants [9]. Therefore they are suitable for carrying out
the primary treatment of oil refinery wastewater, contributing sig-
nificantly to the depuration of these effluents for compliance with
the maximum permissible discharge limits or reuse in different
activities. For this reason, this chapter presents the fundamental
principles of the C/F and EC processes, and some results reported
in the literature or obtained in our research group.
8.2 Principles and fundamentals of the
coagulation/flocculation process
C/F is one of the most used processes for oily wastewater
treatment due to its effectiveness and maturity [10]. Commonly,
this process is implemented as a secondary oil/water separation
stage of the primary treatment, to improve the dispersed oil
droplets, emulsified oil, and suspended solids removal after the
American Petroleum Institute (API) separators, where the
floatable free oil portion is recovered. The effluent from API
separators is mainly composed of suspended oil droplets inter-
spersed with solid particles and dissolved compounds, each
having different molecular weights and electrical charges. These
electrical charges can be measured as the zeta potential and
tend to keep them physically interacting with each other.
Electrical charges tend to form a semistable emulsion, which is
difficult to separate to the level of treatment required. Therefore
appropriate primary treatment is important to ensure second-
ary biological processes’ efficient and prolonged operation [11].
In general terms, the C/F process involves adding a floc-forming
chemical reagent (coagulant and flocculant) to wastewater to break
the emulsions and remove particulate material in suspended or col-
loidal form. The most commonly used inorganic coagulants are alu-
minum or iron salts (aluminum sulfate (AS), ferric sulfate, ferric
chloride, and ferrous sulfate) due to their low cost and ease of use.
However, polymeric flocculants (long-chain organic compounds)
have been used in conjunction with, or instead of, inorganic salts to
174 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
enhance the performance of the process [12]. The coagulation pro-
cess involves the destabilization of particles (chemical conditioning)
by modifying their superficial charges (typically negative) to promote
their neutralization [10]. The flocculation stage aims to promote
interparticle contact by appropriate mixing, forming agglomerates or
flocs of the destabilized particles with a greater weight and size [13].
The agglomeration of oil droplets, nonsettling colloidal solids, and
slow-settling suspended solids produces rapid-settling floc and oil
flotation. The flouted oil and the resulting flocs (also called waste
sludge) can then be removed from the treated water by sedimenta-
tion, flotation, and filtration processes [14].Fig. 8.1 shows a typical
process flow diagram, including the C/F process.
As can be observed in Fig. 8.1, the coagulation performed
during the rapid-mix: it is the stage where the coagulant is dis-
persed, the emulsion is broken, and small particles are formed.
During the flocculation stage, chemical reagents called floccu-
lants or precipitant-aid chemicals can be added to improve the
emulsion breaking and floc formation. For this, the coagulated
wastewater is gently stirred in a flocculation basin. In addition,
conventional or lamellar sedimentation tanks, flotation units
such as dissolved air flotation (DAF) or induced air flotation
(IAF), or sand filtration are physical methods that can be used
to clarify the coagulated water [15].
8.2.1 Coagulation/flocculation theory
When particles (suspended and colloidal) are dispersed in
water, ions of opposite charge (known as counterions) to the
Figure 8.1 Process flow diagram of effluent treatment plant with C/F process.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 175
surface charge accumulate enclosing its surface held by electro-
static and van der Waals forces. This accumulation of ions is
opposite to the tendency of the ions to diffuse and is known as
the Stern layer. A second layer of ions can be formed, where
ions of both electrical charges are attracted (but coions of the
primary charge predominate), known as the diffused layer [16].
This cloud of ions surrounding the particle can extend up to
30 nm. This is known as the electric double layer [17]. A layer
of the surrounding liquid (water) remains attached to the parti-
cle. The boundary of this layer is known as the shear plane,
and the electric potential of the shear plane is called zeta poten-
tial [18]. It is an important indicator of the colloidal system’s
stability or the coagulation process’s effectiveness [12]. A zeta
potential between 25 and 240 mV has been reported for col-
loids in water [19].
Generally, the particles and oil droplet destabilization
mechanisms can be categorized as the following kinds:
1. Counterions adsorption/charge neutralization.Thismecha-
nism can be accomplished by adding a coagulant having a
positive charge. The counterions from the coagulant can then
be adsorbed onto the particle’s surface, causing the neutrali-
zation of the negative net charge. Consequently, destabilized
particles can come closer, forming agglomerates as flocs [12].
2. Adsorption and interparticle bridging. When high molecular
and low charge density polymers are used as flocculants, col-
loids adsorb on polymer’s structure at one or more sites.
Long-chain flocculants connect the fine flocs to aggregate
into the large one.
3. Charge patching. It occurs when polymers of low molecular
weight are positively charged adsorbed oil droplets or col-
loids with negative charges [20].
4. Entrapment. This type of destabilization mechanism is also
termed sweep-floc coagulation. The entrapment occurs when a
high dose of metal coagulant is added and hydrolyzes into its
hydroxide form (M(OH)
n
). These hydroxides are highly insolu-
ble in water. Then, as the hydroxide precipitate, the particles
become entrapped or enmeshed in the amorphous floc struc-
ture. This mechanism is based on inorganic coagulants [21].
In this sense, the wastewater composition, the use of different
coagulating or flocculating products, and the operating parameters
influence the coagulation mechanisms, the efficiency of the particle
destabilization, and emulsion breaking processes. Therefore select-
ing the best chemicals and operating parameters is an essential
stage of the C/F study. For example, metal salts (mainly iron and
176 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
aluminum) may destabilize colloids by three basic mechanisms:
double-layer compression, adsorption/charge neutralization, and
sweep-floc. Polymeric flocculants function by one or more of three
basic mechanisms: charge neutralization, charge-patch destabiliza-
tion, or interparticle bridging. Adsorption onto the flocculated
aggregates might remove some of the dissolved organic com-
pounds usually found in oily wastewater and could present possi-
ble difficulties in the subsequent biological treatment process.
8.2.2 Effect of the operating parameters on
coagulation/flocculation
The efficient performance of the C/F process depends on sev-
eral factors, such as the type and dosage of coagulant/flocculant,
physicochemical characteristics of the wastewater, hydrodynamic
conditions of the coagulation and flocculation stages, reaction
time, and settling time. The most important parameters for pro-
cess optimization are briefly summarized below.
8.2.2.1 Coagulant/flocculant dosage
Zeng et al. [22] reported that the oil removal efficiency is directly
related to the doses of coagulant and flocculant. When charge neu-
tralization is the main mechanism, low doses of coagulant and floc-
culant may be insufficient to achieve destabilization of colloidal
particles [21,23]. However, excessive doses can cause a restabiliza-
tion of the particles, reducing the efficiency of the process [24].A
similar effect has also been observed in oil separation [25].Onthe
other hand, during bridging flocculation, it is essential to have suffi-
cient unoccupied adsorption sites on the oil colloids [26].
Furthermore, the dosage of inorganic salts is typically lower than
for polymeric flocculants because of their higher electron density.
Therefore it requires a lower dosage for charge neutralization [10].
8.2.2.2 Wastewater pH
The pH is another operating parameter that influences the C/F
efficiency. For oily wastewater treatment, the various coagulants/
flocculants differ in their pH dependencies. For inorganic coagu-
lants such as aluminum or iron salts, the predominance of a par-
ticular hydrolysis species during destabilization largely depends on
the pH value [13]. Most inorganic coagulants perform in pH rang-
ing from 3 to 9 [16]. Nevertheless, an appropriate pH adjustment
must be performed where the most effective hydrolysis species of
the coagulant is formed to ensure optimum coagulation [27].
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 177
8.2.2.3 Initial concentration
The physicochemical characteristics and the pollutants load of
oily effluents are very variable, affecting the performance of the
treatment, as well as optimal coagulant and flocculant dosages.
Therefore the appropriate initial concentration range is of impor-
tance. Almojjly et al. [28] compare different AS dosages to obtain a
removal efficiency of 90% in samples with oil concentrations vary-
ing from 200 to 1000 mg/L. It was necessary to increase the AS
dosage from 17 to 68 mg/L sequentially in each sample to obtain
the required performance.
8.2.2.4 Temperature
Temperature also affects the efficiency of the C/F treatment. In
general, the optimum dose of coagulant and flocculant is higher as
the temperature diminishes within a certain range. Firstly, the viscos-
ity of water increases with decreasing temperature, which negatively
affects floc formation [29,30]. In addition, the collision frequency of
colloidal particles (Brownian motion) is also affected by decreasing
temperature [31]. Therefore only small flocs are formed. On the other
h
and,hydrolysisofinorganicsaltsisanendothermicreaction,
impacting coagulation kinetics at low temperatures [32,33].
Consequently, the coagulant and flocculantdosagemustbeadjusted
dynamically according to the ambient temperature [10].
8.2.2.5 Mixing
The mixing conditions are also important parameters that require
optimization during the C/F process to produce a good quality trea-
ted water. Mechanical or hydraulic mixing in a basin causes circula-
tion and shearing of the water. In the rapid mixing stage, where the
inorganic coagulant is first mixed into the raw water, the destabiliza-
tion step occurs in some seconds. Flocculation is a transport step
that brings the collisions of the destabilized particles/oil droplets
needed to form larger flocs that can be removed rapidly by settling or
flotation. This step requires slow mixing. The power input per unit
volume of liquid can be used as a proxy measure of mixing efficiency,
based on the reasoning that more input power creates more turbu-
lence, resulting in better mixing. Controlling the velocity gradient
involves determining the degree of agitation. Camp and Stein devel-
oped the following equitation (Eq. 8.1)topresenttheeffectofvelocity
gradient in C/F basins [34].
G5ffiffiffiffiffiffiffi
P
Vμ
sð8:1Þ
178 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
where Gis the average velocity gradient (s
21
), Pis the power
requirement (W ), Vis the basin volume (m
3
), and μis the abso-
lute viscosity of water (N s/m
2
).
The physicochemical parameters (pH and coagulant/floccu-
lant doses) are obtained with the standard jar test technique (as
demonstrated in Fig. 8.2), and the subsequent step is to obtain
the optimal values for rapid and slow mixing stages intensity
(velocity gradient) and the mixing time.
On the other hand, optimum operating conditions and effi-
ciencies of reported studies in the literature on C/F process for
oily wastewater are presented in Table 8.1.
8.3 Application of coagulation/flocculation
process for oily wastewater treatment
This section presents two studies for the implementation of
C/F systems performed in Mexican refineries to obtain higher
wastewater treatment efficiencies and improve their quality for
reuse. Each refinery has different collection systems, depending
on the production processes, effluent composition, and the
point of the wastewater generation. However, one of the most
polluted effluents is always the oily wastewater.
8.3.1 Wastewater characteristics and current
pretreatment systems
The first refinery (R1) uses an average of 384 L/s of fresh water
and generates 99 619 L/s of oily wastewater. There are two oily
drainages denoted as D1 and D2, respectively. D1 is the discharge
Figure 8.2 Experimental setup of C/F at laboratory scale for jar test technique.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 179
Table 8.1 Optimum operating conditions and efficiencies of reported studies on C/F process in oily wastewater.
Petroleum industry
wastewater type
Coagulant
(dosage)
Flocculant or
precipitant-aid
(dosage)
pH Process conditions Removal efficiency
and sludge generation
References
Oil refinery effluent FeSO
4
7H
2
O
(60 mg/L)
Ca(OH)
2
(100 mg/L) 8.8 120 rpm (1 min),
40 rpm (30 min),
sedimentation (90 min)
99.4% S
22
, 69% COD [35]
Petrochemical effluent
(purified terephthalic
acid production)
FeCl
3
(3000 mg/L) Cationic polyacrylamide
(175 mg/L)
5.6 200 rpm (5 min),
10 rpm (15 min),
sedimentation (30 min)
75.5% COD [36]
WWTP influent PAX-18, 17%
Al
2
O
3
(28.6 mg/L)
National Aluminate
Corporation 71,408
(4.5 mg/L)
7.15 Continuous operation,
t512 min (2.4 L/h)
85.3% COD, 82.4% TOC,
81.4% turbidity,
235 mL/L
[37]
Wastes from a floating
tank of an oil costal
deposit
Al
2
(SO
4
)
3
18H
2
O
(70 mg/L)
Anionic polyelectrolyte
A57(2.5 mg/L)
7 200 rpm (1 min),
30 rpm (20 min),
sedimentation (180 min)
75% COD, 80% TOC,
80% turbidity, 65% TPH
[38]
Synthetic solution
(lubricant oil and Tween
80)
Al
2
(SO
4
)
3
16H
2
O
(50 mg/L) 4 Coagulation and mechanical IAF,
600 rpm (3 min), t
flotation
510 min,
Q
air
54.51 L/min, 1000 rpm
93% TPH [39]
API separator effluent Scrap iron
shavings 8.5 Photo-Fenton 1C/F: 2070 rpm
(30 min)
C/F stage: 26.6% COD [40]
Flowback and produced
water from fracking
well
FeCl
3
6H
2
O
(900 mg/L) 6.1 Coagulation 1ultrafiltration 1
nanofiltration:
300 rpm (1 min),
40 rpm (20 min),
sedimentation (30 min)
C/F stage: 34.7% COD,
98.6% turbidity
[41]
Al
2
(SO
4
)
3
18H
2
O
(600 mg/L) 6.75 C/F stage: 42% COD, 95.4%
turbidity
Wastes from tankers for
transporting petroleum
products
Al
2
(SO
4
)
3
18H
2
O
(90 mg/L)
Anionic polyelectrolyte
A57 (1 mg/L)
7.9 500 s
21
(1 min),
50 s
21
(30 min),
Sedimentation/flotation (120 min)
90% COD, 98% TOC,
90% TSS, 100% TPH
[42]
(Continued )
Table 8.1 (Continued)
Petroleum industry
wastewater type
Coagulant
(dosage)
Flocculant or
precipitant-aid
(dosage)
pH Process conditions Removal efficiency
and sludge generation
References
Electric desalting
effluent
Al
2
(SO
4
)
3
18H
2
O
(500 mg/L)
APAM (2.5 mg/L) 8.6 400 rpm (0.5 min),
100 rpm (1 min),
sedimentation (30 min)
94%99% TSS, 84%99%
turbidity, 35%85% COD,
decrease of the acute
biotoxicity and improved the
biodegradability
[43]
Lubricating oil
wastewater
Polyaluminum
ferric silicate
(396 mg/L)
Poly(acrylamide-co-
diallyldimethylammonium
chloride) (0.08%)
6.9 200 rpm (3 min),
60 rpm (7 min),
sedimentation (60 min)
99.7% turbidity, 94.5% COD,
77.7% TN
[44]
Synthetic solution
(crude oil, dodecyl
benzene sulfonate, and
APAM)
Hydrophobically
modified
polyaluminum
sulfate
(polyaluminum
silicate sulfate-
based coagulant,
1%) (140 mg/L)
6.83 200 rpm (1 min),
40 rpm (12 min),
sedimentation (20 min)
95% oil, 98.8% turbidity [45]
APAM, Anionic polyacrylamide; TPH, total petroleum hydrocarbon.
with the highest O&G concentration (11,455 mg/L on average),
and it passes through the first stage of API separator (S1).
Subsequently, the effluent from S1 is mixed with D2 (O&G content
of 7880 mg/L on average). This mixture passes through the second
(S2) and third (S3) separation stages. The physicochemical charac-
terization of the different oily effluents is presented in Tab le 8 . 2.
The oily wastewater showed a pH of 7.20 60.12.
As it can be seen, S1 allowed average removals of 73%, 53%, and
80% for chemical oxygen demand (COD), total suspended solids
(TSS), and O&G, respectively. On the other hand, S2 showed higher
O&G removal, reaching a concentration of 69 mg/L. COD and TSS
removals were only 69% and 32%, respectively. It was observed a sig-
nificant contribution on O&G, COD, and TSS removals by the third
stage separator, yielding 61%, 68%, and 86%, respectively. This per-
formance is related to the high hydraulic retention time (HRT) in
this unit (37 h), which allowed an excellent performance of the sepa-
ration process. The long HRT in the separators could also contribute
to the desorption of sulfides. Conversely, S1 showed low O&G
removals, attributed to oil and sludge separation equipment defi-
ciencies. Phenols were partially removed in each stage. The main
Table 8.2 Physicochemical characterization of the oily effluents in refinery R1.
Parameter Oily discharge
D1
Oily discharge
D2
Effluent from
S1
Effluent from
S2
Effluent from
S3
O&G (mg/L) 11,455 65230 7880 64870 2291 61350 69 672765
COD (mg/L) 8316 62980 6806 61990 2245 61105 1390 6228 448 681
TSS (mg/L) 496 678 376 665 233 645 207 622 28 69
TDS (mg/L) 964 6248 1390 6295 894 6196 1160 6220 1138 6206
Sulfates
(SO
422
, mg/L)
255 638 424 649 243 632 319 639 280 635
Chlorides
(Cl
2
, mg/L)
249 647 119 622 229 634 230 637 228 633
Sulfides
(S
22
, mg/L)
37 622 59 634 36 620 37 611 6 65
Phenols (mg/L) 0.40 60.44 1.63 60.85 0.37 60.25 0.51 60.32 0.22 60.21
Ammonium
(NH
4
-N, mg/L)
7.0 66.5 15.3 63.4 6.9 65.1 12.4 65.5 12.3 66.6
TKN (mg/L) 12.4 67.9 28.0 69.2 11.2 66.1 20.4 68.5 20.3 67.4
Total hardness
(mg/L as CaCO
3
)
337 645 532 626 330 634 412 644 347 632
Temperature (C) 37 663665366535643464
182 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
problem identified in the effluent of the primary treatment of refin-
ery R1 was the high COD concentration, with an average of
448 681 mg/L. This organic load could represent a problem for the
subsequent biological treatment. For this reason, it is proposed an
additional destabilization method to reduce the COD concentration.
The second refinery (R2) uses 467 L/s of fresh water and gen-
erates 224 6127 L/s of oily wastewater. It has two oily drai-
nages, also denoted as D1 and D2, respectively. The refinery R2
is equipped with two API separators, one for each discharge of
oily wastewater. In the second separation stage, corrugated
plate separators (CPS) are used. The characteristics of the oily
discharges and the effluents of the separation stages are pre-
sented in Table 8.3. The oily effluents had a pH of 7.13 60.34.
R2 discharges showed lower O&G and COD concentrations than
the discharges of R1, with values between 400 and 600 mg/L on
average for both parameters. Chlorides and total Kjeldahl
Table 8.3 Physicochemical characterization of the oily effluents in refinery R2.
Parameter Oily discharge
D1
Oily discharge
D2
Effluent
from API
discharge 1
Effluent
from API
discharge 2
Effluent from
the final CPS
O&G (mg/L) 624 6728 474 6464 55 654 40 621 48 640
COD (mg/L) 586 6212 591 6214 311 673 318 656 314 661
Soluble chemical
oxygen demand
(mg/L)
217 663 159 648 192 652 141 645 167 646
BOD
5
(mg/L) 144 654 146 684 108 626 102 660 105 652
TSS (mg/L) 185 665 195 664 24 6242624 33 66
TDS (mg/L) 1583 6250 828 6167 1076 6155 733 6109 883 6165
SO
422
(mg/L) 111 68 253 652 98 614 214 688 164 677
Cl
2
(mg/L) 782 639 241 686 545 683 222 689 388 685
S
22
(mg/L) 50 637 18 6940633 14 6527618
Phenols (mg/L) 0.95 60.65 1.29 60.82 0.82 60.61 1.21 60.90 1.01 60.72
NH
4
-N (mg/L) 28 622 35 632 25 621 33 636 29 623
TKN (mg/L) 49 625 67 629 36 624 58 638 46 631
Total phosphorus
(mg/L)
0.70 60.17 0.87 60.22 0.63 60.16 0.72 60.13 0.66 60.15
Total hardness
(mg/L as CaCO
3
)
389 6126 224 635 249 638 207 645 225 634
Temperature (C) 44 673262416432613863
BOD
5
, Biochemical oxygen demand.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 183
nitrogen (TKN) were higher for R2, which is related to the oil
desalination effluents.
The physicochemical characterization showed important O&G
(90%) and TSS ( 80%) removals in both API separators. COD
removals were 50%70%, as observed in R1. Slight removals for
hardness, total dissolved solids (TDS), and chloride were observed
in the API separator D1, which can be attributed to precipitation
due to the high water temperature. Phenol and sulfides were also
partially removed in this treatment. Some operational problems
related to oily sludge saturation in the CPS were also observed,
and a complicated task for the cleaning and removal of the sludge.
These results indicated that the refinery R2 also needs to enhance
the primary treatment. Hence, emulsion destabilization was also
proposed after the API treatment, followed by DAF process.
8.3.2 Coagulation/flocculation tests
Jar tests were performed to study the destabilization of
oilwater emulsions and the removal of suspended and dissolved
pollutants by using different coagulants and polymeric flocculants.
For the essays with oily effluent from refinery R1, it was used a
sample from the second stage of API separators. This effluent
showed O&G and COD of 69 67 and 1390 6228 mg/L, respectively.
The evaluated products were: AS, polyaluminum chloride
(PAX- XL19, PAX-260XL S, PAX-16 S, PAX-XL60S, and POLYCAT ), ferric
chloride (PIX-111), and ferric sulfate (PIX-145 and Ferrix-3). In
addition, the coagulants were tested individually and in combina-
tion with some anionic and cationic polymers with different
molecular weight and charge density. The assessed anionic poly-
mers were: OPTIFLOC A-1638 and AE-1488, SUPERFLOC
A-100 HMW, and PHENOLPOL A-305. Regarding cationic polymers,
the following products were tested: SUPERFLOC C-1288, C-1392,
C-1781, C-498, LACKFLOC-C-5100, and ECOFLOC 432.
Preliminary tests were performed with the samples taken
from the second API separator stage of the refinery R1. The
dose that corresponds to the formation of the first floccules was
determined for each product. Tests were then carried out by
applying doses three times higher. The results of the prelimi-
nary selection of the best products are presented in Fig. 8.3.
It is important to mention that sedimentation of the flocs was
observed in the experiments in which only coagulant was added,
but oily flocs floated in the trials in which coagulant
flocculant combinations were used. The addition of the cationic
polymers in relatively low doses, 0.41.2 mg/L, allowed for
achieving a quick and effective emulsion breakdown. The flocs
184 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
were light and, after stopping the mixing, floated to the surface,
forming an oily layer thinner than the one obtained with coagu-
lantflocculant combinations. Tests performed to verify the pH
effect on the efficiency of the polymers indicated that they can
work properly in a wide pH range. Also, these assays with coagu-
lants indicated no significant difference between the results
obtained at different pH values. For this reason, the following
tests were performed at the original pH of 7.4 60.3. COD and
O&G removals determined in the preliminary tests are presented
in Fig. 8.4. The best results were obtained with the combinations
of the coagulants AS and ferric chloride with the cationic poly-
mers, as well as with the cationic polymers applied individually.
POLYCAT, PAX-XL60S, ferric sulfate (Ferrix-3), and some of
their combinations with cationic polymers also allowed for obtain-
ing removals greater than 80%; however, higher doses of the pro-
ducts were necessary. That is why it was decided to continue
the study only with AS, ferric chloride, and their combinations
with cationic polymers, as well as testing individually the cationic
polymers C-1288, C-1781, and ECOFLOC 432. The anionic poly-
mer A-1638 applied individually did not work well; combined with
coagulants, it caused good flocculation but did not contribute to
COD removal.
The jar tests performed for the best doses of the coagulants AS
and ferric chloride are illustrated in Fig. 8.4A and the tests with
flocculants in Fig. 8.4B. The optimal AS dose was 50 mg/L and the
optimal ferric chloride (PIX-111) dose was 45 mg/L. Also, tests
applying the coagulants in optimal doses in combination with the
Figure 8.3 Results of the preliminary tests for the selection of the best reagents. Experimental conditions: rapid
mixing (100 rpm and 5 min), slow mixing (30 rpm and 25 min), settling (25 min).
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 185
polymers were carried out. The results of the combinations of AS
with the polymers can be seen in Fig. 8.4C and the results of the
combinations of ferric chloride (PIX-111) with the same polymers
in Fig. 8.4D.Tab l e 8. 4 presents a summary of the results of the
destabilization tests. The blends of AS with polymers allowed to
Figure 8.4 Results of the jar tests for the determination of the best dose of coagulant and flocculant. (A) jar tests
with aluminum sulfate (AS) and ferric chloride coagulants; (B) jar tests with flocculants; (C) jar tests with AS and
flocculants; (D) jar tests with ferric chloride and flocculants. Experimental conditions: rapid mixing (100 rpm and
5 min), slow mixing (30 rpm and 25 min), settling (25 min).
186 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
obtain a complete removal of O&G, 90.8%92.7% COD removal,
and 96.1%97.4% turbidity removal, been the reagent costs of
0.670.68 USD/m
3
treated water. Good removals were also
obtained with the combinations of ferric chloride with the poly-
mers: 99.5%99.9% of O&G, 90.2%94.2% of COD, and 93.9%
95.1% of turbidity. The cost of treatment, in this case, was
0.480.51 USD/m
3
of treated water. The best combination was
ferric chloride with C-1288. The results of the three cationic poly-
mers applied individually indicated that they can remove 98.2%
99.8% O&G, 89.1%90.6% COD, and 84.8%92.0% turbidity.
Based on the performed jar test using the effluent of the sec-
ond stage API separator in refinery R1, it can be concluded that
the combination of C/F separation processes allows achieving
O&G and COD removals of more than 99% and 91%, respec-
tively. Furthermore, emulsion breaking was satisfactorily
obtained using combinations of inorganic coagulants (AS or fer-
ric chloride) and polymers, as well as applying cationic poly-
mers of high molecular weight.
Table 8.4 Doses, efficiencies, and costs of the jar tests using different coagulants and
flocculants for treating refinery R1 effluent.
Coagulation Flocculation Sludge
(mL/L)
Removal (%) Cost (USD/m
3
treated water)
Coagulant
type
Dose
(mg/L)
Flocculant
type
Dose
(mg/L)
O&G COD Turbidity Coagulation Flocculation Total
Aluminum
sulfate
50 Slow
settling
99.9 91.9 97.7 0.65 0.65
Aluminum
sulfate
50 C-1288 0.6 14 100 90.8 97.4 0.65 0.03 0.68
Aluminum
sulfate
50 C-1781 0.4 17 100 92.3 96.1 0.65 0.02 0.67
Aluminum
sulfate
50 ECOFLOC 0.6 15 100 92.7 97.1 0.65 0.03 0.68
Ferric
chloride
45 21 98.1 92.8 92.0 0.48 0.48
Ferric
chloride
45 C-1288 0.4 11 99.9 94.2 95.1 0.48 0.03 0.51
Ferric
chloride
45 C-1781 0.4 14 99.5 90.2 94.9 0.48 0.02 0.50
Ferric
chloride
45 ECOFLOC 0.6 13 99.6 92.7 93.9 0.48 0.03 0.51
C-1288 1.0 7 98.2 89.1 84.8 0.32 0.32
C-1781 1.0 7 99.0 90.5 87.2 0.24 0.24
ECOFLOC 1.0 7 99.8 90.6 92.0 0.33 0.33
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 187
Regarding the jar tests with the effluents from refinery R2, they
were performed using samples from the effluent of the API
separators (D1 and D2). These effluents presented O&G and COD
concentrations on average of 45 and 315 mg/L, respectively. The
laboratory tests were performed at the following conditions:
150 rpm and 3 min for rapid mixing, 20 rpm and 15 min for slow
mixing, and 30 min for separation. The removal efficiencies
obtained with different coagulants are summarized in Table 8 . 5 .
The results in Table 8. 5 show that the iron-based coagulants
(PIX-111 and PIX-145) permit slightly higher O&G removals, reach-
ing 75%79% for both effluents. Nevertheless, COD removals were
of the same magnitude as all the coagulants, obtaining 60%70%.
Suspended solids were also successfully removed using PAX-16S,
PIX-111, and PIX-145 coagulants, almost reaching 90% efficiency.
However, poor clarification was observed, mainly forming small flocs
with slow-settling velocity. Hence, it was evaluated the combination
of coagulants with different polymers. Tab l e 8. 6 shows the removal
efficiencies of the jar tests using different coagulants and flocculants.
For these tests, it was only added 70% of the optimal doses
determined in the last essays with different coagulants. As can be
observed in Tab l e 8 .6 , higher O&G, COD, and TSS removals were
obtained compared to tests with only coagulant. O&G and COD
removals were greater than 90% for both oily samples. These
results indicate that despite the lower dose of coagulant, the addi-
tion of flocculant improved the removal of all parameters. The
combination of ferric sulfate (PIX-145) and the cationic flocculant
SUPEFLOC C-498 showed the best performance.
Table 8.5 Removals of O&G, COD, and TSS obtained using only coagulants in both API
effluents of the refinery R2.
Coagulant Optimal doses
(as mg/L of
chemical product)
Removal efficiencies (%)
R2-effluent API-D1 R2-effluent API-D2
O&G COD TSS O&G COD TSS
Aluminum sulfate (AS) 50 62 63 69 61 62 76
PAX-260XLS 30 64 66 80 66 67 78
PAX-16S 30 66 70 86 67 68 77
PAX-XL19 40
Ferric chloride (PIX-111) 15 75 66 85 78 65 77
Ferric sulfate (PIX-145) 20 77 62 85 79 64 79
API-D1, API’s effluent from drainages 1; API-D2, API’s effluent from drainages 2.
188 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
Additionally, jar tests were performed only with the addition of
cationic polymers. Tabl e 8 . 7 summarizes the obtained removals
and the optimum pH values for these tests.
The application of only cationic flocculants resulted in excel-
lent O&G removals, higher than 90%, except for the ECOFLOC
polymer. In general, all the polymers showed good efficiencies
of organic matter, suspended solids, and oils, similar to those
obtained with coagulant and flocculant tests.
Table 8.6 Removals of O&G, COD, and TSS obtained using coagulants and flocculants in the
different API effluents.
Coagulant Optimal doses
(as mg/L of
chemical
product)
Flocculant Optimal doses
(as mg/L of
chemical
product)
Removal efficiencies (%)
R2-effluent
API-D1
R2-effluent
API-D2
O&G COD TSS O&G COD TSS
PAX-16S 31 C-1392 0.3 96 94 85 93 92 84
PAX-XL19 35 C-1288 0.3 95 90 83 94 89 83
Ferric chloride
(PIX-111)
11 C-1288 1.0 93 95 81 93 93 83
Ferric sulfate
(PIX-145)
14 C-498 1.1 96 95 90 94 93 88
Table 8.7 Removals of O&G, COD, and TSS obtained using different cationic polymers and the
optimum pH values in the different API effluents of refinery R2.
Coagulant Optimal doses
(as mg/L of
chemical product)
Optimal pH Removal efficiencies (%)
R2-Effluent API-D1 R2-Effluent API-D2
O&G COD TSS O&G COD TSS
C-1288 25 7.0 96 84 82 93 83 83
C-498 25 7.2 93 84 88 92 82 87
C-1781 35 7.2 92 83 95 90 80 91
C-1392 35 7.0 91 83 88 89 81 90
C-5100 34 7.6 95 94 91 92 90 92
ECOFLOC 50 7.2 83 81 78 82 82 80
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 189
Based on the results obtained during the oily effluents treat-
ment tests, the application of inorganic coagulants (AS and fer-
ric chloride) and polymers permit the breaking and separation
of emulsions of the phase oil/water and the removal of organic
matter and suspended solids. In addition, it also allowed for low
sludge production, with good settling and compaction charac-
teristics. Furthermore, by using only cationic polymers of high
charge density and molecular weight, significant removals of
contaminants were also achieved.
8.4 Principles and fundamentals of the
electrocoagulation process
EC process has emerged as an efficient, cost-effective, and
versatile technology for the depuration of many industrial efflu-
ents [46], such as slaughterhouse and dairy [47], textile [48], air-
craft [49],oily[50], and so on. The theory for destabilizing and
removing pollutants in the EC and the conventional C/F pro-
cesses is basically the same. Nevertheless, EC presents some
operational and performance advantages over C/F. In addition,
it is worth noting, the EC process offers an in-site generation
and chemical dosing approach, making it a suitable and attrac-
tive technology for its application in wastewater treatment.
A basic EC unit (as shown in Fig. 8.5) consists of an electro-
lytic cell with metal electrodes (commonly Al or Fe) as anodes
and cathodes, which are immersed in the polluted water and
connected externally to a power supply (direct or alternating
current) [51]. The electric current provides the potential differ-
ence that causes the redox reactions at the electrodes, promot-
ing the electrodissolution of metal ions, which are hydrolyzed,
generating metal polyhydroxides or oxyhydroxides. These spe-
cies act as coagulants or destabilizing agents, helping to sepa-
rate contaminants from wastewater [52]. Subsequently, the flocs
formed in the electrochemical process are separated from the
treated water in a sedimentation unit (e.g., lamellar settler),
obtaining an effluent with low O&G and solids concentration.
Nevertheless, sand filtration system can be also implemented to
enhance solids removal. The waste sludge can be stabilized and
dewatered (e.g., filter press) for final disposal at a suitable site.
8.4.1 Electrocoagulation theory
In general, the following steps can occur in the EC process
during the generation of coagulants and other byproducts for
190 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
oily wastewater treatment. Also, Fig. 8.6 shows a scheme of the
main chemical and electrochemical reactions and destabiliza-
tion and removal mechanisms in the EC process.
1. Generation of different ionic species (M
n1
) due to electrodis-
solution of the anode, depending on electrode material, pH,
and applied potential [5355] (Eqs. 8.28.4). By using the
Pourbaix diagrams of Fe and Al, the possible thermodynami-
cally stable species can be elucidated, helping to understand
the reaction mechanism [56]:
Iron anode:
Fe-Fe2112e2;E520:44 V vs SHE ð8:2Þ
Fe-Fe3113e2;E520:037 V vs SHE ð8:3Þ
Aluminum anode:
Al-Al3113e2;E521:66 V vs SHE ð8:4Þ
2. Anodic side reactions, such as oxygen or chlorine evolution
reaction (if Cl
2
are present in the solution) at sufficiently
high overpotentials (Eqs. 8.58.6)[57]:
2H2O-O2ðgÞ14H112e2;E51:23 V vs SHE ð8:5Þ
2Cl2
-Cl2ðgÞ12e2;E51:36 V vs SHE ð8:6Þ
Figure 8.5 Process flow diagram of effluent treatment plant with EC reactor.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 191
3. Cathodic generation of hydroxide ions (OH
2
) and hydrogen
evolution reaction, resulting in an increase in the pH of the
solution [55] (Eq. 8.7).
2H2O12e2
-H2ðgÞ12OH2ð8:7Þ
4. Spontaneous hydrolysis of the metal ions in the liquid, generating
polyhydroxides or oxyhydroxides of the metal (Eqs. 8.88.10)
[53,58].
Iron anode:
Fe 12H2O-FeðOHÞ2ðsÞ1H2ðgÞð8:8Þ
4Fe21110H2O1O2ðgÞ-4FeðOHÞ3ðsÞ18H1ð8:9Þ
Aluminum anode:
Al 13H2O-AlðOHÞ3ðsÞ13
2H2ðgÞð8:10Þ
Figure 8.6 Schematic diagram of typical reactions and pollutant removal mechanisms in the EC process.
192 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
5. Destabilization of dissolved contaminants (inorganic and
organic), colloids, and suspended solids by different mechan-
isms: charge neutralization, entrapment, adsorption, and com-
plexation. Colloidal particle destabilization is a well-known
process where several mechanisms can contribute to their
removal, such as adsorption/charge neutralization, adsorption/
interparticle bridging, and entrapment of the particles in the
precipitate [56,59]. For inorganic dissolved contaminants, it has
been shown that the main mechanisms contributing to the
removal of cationic contaminants (Ca
21
,Mg
21
,etc.)andheavy
metals (Pb
21
,Cd
21
,Zn
21
,Cu
21
,Ni
21
, etc.) are surface com-
plexation and adsorption. The surface complexation mechan-
isms (Eqs. 8.118.14) consider that cations or heavy metals
(Me
1
) could act as ligands to form a bond with the hydrous
moiety of the coagulant flocs (FeO(OH) or AlO(OH)).
FeðOHÞ3-FeOðOHÞðsÞ1H2Oð8:11Þ
Me11FeO OHðÞ
ðsÞ-M2FeOðsÞ1H2Oð8:12Þ
AlðOHÞ3-AlOðOHÞðsÞ1H2Oð8:13Þ
Me11AlO OHðÞ
ðsÞ-M2AlO 1H2Oð8:14Þ
On the other hand, the adsorption mechanism considers the
attraction by electrostatic forces and charge neutralization
between the pollutant and the flocs [60,61]. Likewise, some
anionic or oxoanionic contaminants can also be removed by
precipitation, such as S
22
with Fe
21
or Al
13
(Eqs. 8.158.16)
[62], or complexation such as fluorides (F
2
)(Eq. 8.17)[63].The
chemical substitution reaction between F
2
and OH
2
from Al
(OH)
3
flocs is another mechanism proposed for F
2
removal in
the EC process [64].
Fe211S22
-FeSðsÞð8:15Þ
2Al3113S22
-Al2S3ðsÞð8:16Þ
F21FeO OHðÞ-F22FeO 1H2Oð8:17Þ
Although studies are still underway to understand the
mechanisms and different factors that influence the removal
of organic matter in the EC process [65], chemical
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 193
coagulation studies suggest that natural organic matter is
removed through a combination of charge neutralization,
entrapment, and complexation mechanisms with metallic
coagulants in insoluble particulate aggregates [66].
6. Formation of aggregates of the destabilized phases (floccula-
tion), flotation, and sedimentation [67]. The evolution of O
2(g)
and H
2(g)
due to water electrolysis promote oil droplets and
solids adhesion with the gases rising to the surface of the
reactor, where can be skimmed off as foam [68].Inaddition,
the heavy flocs are settled, accumulating at the bottom of the
reactor or in the subsequent sedimentation stage.
7. Metals cathodic electrodeposition. It occurs if the appropri-
ate cathodic overpotential is reached [69].
Mex11xe2
-Me0ðsÞð8:18Þ
8.4.2 Factors affecting the performance of
electrocoagulation
There are some important factors to consider when imple-
menting or optimizing. Additional to the reactor design, the
physicochemical characteristics of the raw wastewater must
also be taken into account.
8.4.2.1 Electrode material
In an electrolytic cell, the anodes are the positive electrodes
where oxidation reactions are performed; the cathodes are the
negative electrodes where reduction reactions are carried out. In
the EC process, iron [70] or aluminum [71] electrodes are com-
monly used individually or as a combination of them [72] due to
the coagulating properties of multivalent ions (Fe
21
,Fe
31
,orAl
31
)
[61]. Alternatively, other electrodematerials, such as zinc (Zn) [73]
and magnesium (Mg) [74] have been evaluated.
8.4.2.2 Current density and potential difference
The current density (j) controls the rate at which electro-
chemical reactions take place and depends on the applied cur-
rent (I) and the surface area of the electrodes (A). Therefore this
parameter can be used to manage the electrogenerated dose of
coagulant [75,76]. Typically, current densities in the range of
140 mA/cm
2
(10400 A/m
2
) are applied to treat effluents from
the oil industry. On the other hand, the potential difference or
cell potential (E
cell
) provides the electromotive force for specific
redox reactions at the electrodes.
194 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
8.4.2.3 Electrolysis time
The electrolysis time (t
e
), also called reaction time, has a great
influence on the efficiency of the electrochemical treatment.
Usually, the longer the electrolysis time, the higher the efficiency
of the process. Together with jor E
cell
, they are parameters that
must be appropriately selected and controlled, since the energy
consumption of the process depends on them, as well as the
amount of waste sludge produced. In addition, the presence of
eletrogenerated metal ions (Fe
21
,Fe
31
,orAl
31
) in the treated
water (caused by electrodissolution of the anode) also depends on
these parameters. Therefore short (from 5 to 30 min) or instanta-
neous (in the order of seconds) times are preferable to reduce the
energy consumption of the process [68].
8.4.2.4 Wastewater pH
The performance of the EC process is highly influenced by this
parameter, as the presence of the different coagulant species
(ionic species, monomeric, and polymeric hydroxide complexes)
in equilibrium depends on the pH of the solution. Therefore pre-
dominance zone diagrams can be used to observe the distribution
of these species as a function of pH, helping to elucidate the pos-
sible interactions that could occur during the EC process at a spe-
cific pH. The EC process has generally shown higher efficiencies
at slightly acidic to alkaline pH (5.58.5) due to the lower solubil-
ity of metal hydroxides in this range [61,77].
8.4.2.5 Reactor design
The reactor design refers to selecting the number of electro-
des, the distance between electrodes, the electrical configuration
of the electrodes (monopolar or bipolar), and the definition of
the hydrodynamics and geometry of the electrochemical reactor.
Recently, computational fluid dynamics simulations have been
used to study the hydrodynamic behavior, mass transport, and
current distribution of electrochemical reactors. This approach
allows the optimization of the main operating variables, as well
as the reactor geometry in a theoretical way, to be subsequently
demonstrated and evaluated in experimental studies [78].
8.5 Application of electrocoagulation process
for oily wastewater treatment
This section presents an overview of recent academic applica-
tions of EC for the treatment of different types of oily wastewater.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 195
The EC process was one of the first electrochemical technologies
invented for water treatment. Although it was patented by several
researchers in the late 19th and early 20th centuries [79,80],itisa
developing technology with certain limitations that do not allow
its full implementation on an industrial scale. Most of the research
on the EC process has been carried out at the laboratory scale,
with a few papers addressing the treatment of effluents from the
oil industry on a pilot scale. Therefore in terms of technology
readiness level, the EC process is at a level between 5 and 6, which
implies that the process has been validated, demonstrated, and
prototype systems already exist [81].
El-Naas et al. [82] evaluated a pilot plant (1 m
3
/h) for the
treatment of highly contaminated oil refinery wastewater to
comply with the national discharge limits (150 mg/L COD and
phenols of 0.1 mg/L). The refinery effluent had a COD between
3900 and 4800 mg/L, TDS ranging from 3.8 to 6.2 g/L, a phenol
content of 10 mg/L, and various cresols (5070 mg/L). The pilot
plant consisted of an EC unit fabricated by Powell Water
Systems (maximum capacity of 1.48 m
3
/h
1
), housing 73 electro-
des made of either aluminum or iron. The waste sludge was
separated into a settling tank, where the treated water was
pumped into the biological process. As a secondary treatment,
a 1.7 m
3
spouted bed bioreactor inoculated with Pseudomonas
putida immobilized inside gel particles. The polishing treatment
step consisted of an adsorption column with granular activated
carbon with a total bed volume of 0.5 m
3
. The removal of COD
in the pilot EC unit was around 35%, with minimal phenol
removal. The low performance of the EC unit was associated with
the corrosion/erosion of the electrodes, which diminished the pro-
cess efficiency. Nevertheless, the integrated pilot plant proved
effective, reaching 96% COD removal and complete removal of
phenols and cresols after up to 8 h of continuous operation.
Another interesting semipilot scale study was conducted by
Mohd et al. [83]. An EC unit of 60 L/h maximum flow rate was
assessed. The operating parameters investigated were the applied
current and material electrodes (aluminum and stainless steel). In
addition, the electrochemical treatment was tested with two sam-
ples from oil-based companies in Malaysia. The former was char-
acterized by a high organic matter content, with a COD of
16,000 mg/L. According to their results, the best-operating condi-
tions for COD removal were 5 min of electrolysis and 2 A, reducing
COD to 1900, equivalent to an efficiency of 88%. The second
196 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
sample presented a lower COD, with a value of 330 mg/L. In this
case, the aluminum electrodes also allowed the highest COD
removal, decreasing its concentration to 89 mg/L with 5 min elec-
trolysis and 2 A, with an efficiency of 73%. COD removal with SS
electrodes was comparable to that with aluminum electrodes only
at 20 min and 2 A, obtaining an efficiency of 69%.
Moreover, an innovative laboratory-scale approach is the
internal loop split-plate airlift EC reactor implemented by
Ammar et al. [84]. This design could offer a better mixing and
distribution of coagulants and flocs without mechanical stirring,
improving the removal of suspended solids, oils, and other pol-
lutants. The EC unit consisted of one reactor with two split-
plates with two aluminum electrodes (120 cm
2
) in the middle.
In the lower part was located a diffuser connected to an air
compressor for air injection. Their results revealed a good per-
formance for treating an oil refinery wastewater, reaching a
removal for COD, oils, and TSS of 93%, 99%, and 90% at 30 min
of electrolysis, 0.8 L/min of air, and 11.3 mA/cm
2
.Table 8.8
shows the main operating parameters and removal efficiencies
of some studies at a laboratory scale applying the EC process
for the treatment of different oil industry effluents.
8.5.1 Photo-electrocoagulation study
It has been conducted some studies of the EC process at a
laboratory scale for the degradation/removal of the main con-
taminants in oil refinery effluents, using synthetic solutions and
real effluents. With the objective to enhance the pollutants
removal and promote some degradation mechanisms in the EC
process, it is typically combined with other advanced oxidation
processes such as ultrasonic radiation, ozone (O
3
), hydrogen per-
oxide (H
2
O
2
), photolysis, or the simultaneous combination of
them [61].Also,theoccurrenceofindirectoxidationviaactive
chlorine species (reported concentrations in the order of ppb) in
the EC process can contribute to the degradation of the contami-
nants [9496]. In this context, a coupled photo-electrocoagulation
(photo-EC) system (UV 254 nm) with aluminum electrodes was
evaluated to demonstrate the hydroxyl radicals (
•
OH) generation
via active chlorine (presented in Fig. 8.7). Furthermore, phenol
degradation experiments were performed to assess the synergistic
effect [97]. Using fluorescence spectrophotometry and coumarin
as probe compound, it was determined an
•
OH radical
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 197
Table 8.8 Optimum operating conditions and efficiencies of reported laboratory studies of EC process in oily wastewater.
Petroleum industry
wastewater type
Anode/
cathode
Electrodes
configuration/
connections
Current density, current
applied, or cell potential
Process
conditions
Removal efficiency References
WWTP influent Al/Al Monopolar/parallel 13 mA/cm
2
pH 58,
t560 min
70% COD,
90% SO
422
[14]
Synthetic solution
(gasoline and diesel)
Al/Al Monopolar/parallel 28 mA/cm
2
pH 58,
t5100 min,
2 g/L NaCl
100% benzene, toluene,
ethylbenzene, and xylene,
100% PAHs
[85]
Sulfidic spent caustic
wastes
Fe/Fe Monopolar/parallel 21.2 mA/cm
2
pH 59,
t530 min
84.7% COD, 95% heavy metals
(Cd, Cu, Pb, Ni, Zn, Cr), 83.8%
S
22
[86]
API separator effluent Mild
steel/SS
Monopolar/parallel 9 mA/cm
2
pH 58,
t540 min
87% COD [87]
Oil refinery effluent Al/Al Monopolar/parallel 3 mA/cm
2
(100 mA) Q510 mL/min
1
46% COD, 33.6% phenols, 14.7%
cresols
[88]
Synthetic solution
(petroleum and lubricant
oil)
Al/Al Monopolar/parallel 55.5 A/m
2
Direct current,
pH 56.9,
t56 min
97%98% COD, 99.5% turbidity [89]
Fe/Fe 92%96% COD, 99.5% turbidity
Oil refinery effluent Fe/Fe Monopolar/parallel 40 mA/cm
2
pH 57,
t520 min,
155 rpm
52.4% phenols, 42.3% TOC [90]
WWTP influent Fe/Fe Bipolar 30 V pH 56,
t590 min, 10
electrodes
66.9% COD [91]
Flowback and produced
waters from fracking
well
Fe/Fe Monopolar/parallel 25 mA/cm
2
t520 min, 4
electrodes
37.4% COD, 87.8% turbidity, 54%
dissolved organic carbon
[92]
Natural gas refinery
effluent
Al/SS316 Monopolar/parallel 35 mA/cm
2
t5120 min,
pH 56
90% COD, 94% turbidity [93]
production of 1.403 μM/h at constant pH of 3 and 5.5 mA/cm
2
.In
conclusion, it was deduced that the synergistic participation of
active chlorine species and UV irradiation in the photo-EC process
increased phenol mineralization up to 20.1% of total organic car-
bon (TOC) removal, which is larger than the additive removal of
EC (2.8% TOC removal) and photolysis processes (7.9% TOC
removal) [97].
8.5.2 Electrocoagulation tests
Another approach in investigation by our workgroup is the
applying of the EC process as primary treatment to enhance the
secondary treatment performance and reach an effluent water
quality for cooling tower reuse. EC treatability tests were carried
out with an oily effluent, comparing the performance of Fe and
Al electrodes. The sample used in this work was taken from the
influent of the wastewater treatment plant (WWTP) of an oil
refinery (a mix of the different liquid waste streams from the
refining processes). Table 8.9 presents the physicochemical
characterization of the oil refinery wastewater sample. As shown
in Table 8.9, the biodegradability index is ,0.5, indicating the
presence of recalcitrant compounds, which would make their
treatment by biological processes not very efficient [98]. On the
other hand, it also presented a significant concentration of
Figure 8.7 Photo-electrocoagulation mechanism for
•
OH radical’s generation.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 199
phenol and sulfides, which explains the toxic and biorefractory
character of the effluent. Furthermore, this wastewater stream
presented a relevant concentration of dissolved salts (1172 mg/L
as TDS) and relatively high conductivity (2.41 mS/cm), so it com-
plies with the necessary characteristics to be treated electrochemi-
cally. It is also important to highlight the presence of a wide range
of metals and nonmetals (not presented here), such as Li
1
,B
31
,
As
31
,Ba
21
,Sr
21
,Ni
21
,V
31
,Zn
21
,andF
2
, making the EC process
a suitable technology for their precipitation [86,92,99102].
Fig. 8.8 shows the comparison in the removals of organic
matter (measured as COD), TH, CH, and silica using Fe and Al
electrodes. In addition, Table 8.10 presents the specific energy
consumption (SEC) with respect to the volume of treated water
and pollutant removal, the amount of sludge generated (mea-
sured as total solids [TS]), and the sludge volume index (SVI). It
Table 8.9 Physicochemical characterization of the oil refinery wastewater sample.
Parameter WWTP influent
BOD
5
(mg/L) 146
COD (mg/L) 419.78
BOD
5
/COD 0.34
Phenol (mg/L) 15.06
S
22
(mg/L) 31.31
Silica (mg/L as SiO
2
)74
SO
422
(mg/L) 717
Fluorides (F
2
, mg/L) 14
Total nitrogen (TN, mg/L) 45.88
O&G (mg/L) 35.90
TSS (mg/L) 425
TDS (mg/L) 1172
Total hardness (TH, mg/L as CaCO
3
) 584.7
Calcium hardness (CH, mg/L as CaCO
3
) 378.34
Alkalinity (mg/L as CaCO
3
) 299.30
Cl
2
(mg/L) 500
Color (U Pt-Co) 3400
pH 8.18
Electrical conductivity (mS/cm) 2.41
200 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
Figure 8.8 Results of EC tests as primary treatment.
Table 8.10 Specific energy consumption and sludge characteristics of the EC treatability tests.
Parameter EC—Al EC—Fe
SEC (kWh/m
3
) 0.30.4 0.30.4
SEC-COD (kWh/kg) 4.87 4.74
SEC-SiO
2
(kWh/kg) 6.05 7.75
SEC-TH (kWh/kg) 3.92 3.75
SEC-CH (kWh/kg) 5.76 5.45
TS (g/L) 0.23 0.30
SVI (mL/g) 304 200
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 201
was observed that a relatively short electrolysis time (12 min)
and current density (5.5 mA/cm
2
) can contribute significantly to
silica and organic matter removal and slight hardness removal.
Based on Fig. 8.8, Al electrodes allowed the highest silica
removal, obtaining an effluent with 21 mg/L, an appropriate
concentration for reuse in cooling towers [103]. On the other
hand, organic matter abatement resulted in almost 45% COD
removal, obtaining an effluent with 230 mg/L. TH and CH
decreased to 500 and 325 mg/L, respectively. In this regard, ade-
quate secondary and tertiary treatment could make it possible
to achieve the quality of makeup water for cooling towers.
Moreover, low energy consumptions in the order of
0.30.4 kWh/m
3
were obtained in the EC experiments with
both electrodes. Typically, energy consumptions between 0.5
and 15 kWh/m
3
are reported in the literature, depending on
water quality, effluent conductivity, and electrolysis time [104].
During the EC tests, sludge generation was very similar with
both types of electrodes, producing an average of 70 mL/L (TS
of 230 mg/L as dry sludge) with Al electrodes and 60 mL/L (TS
of 300 mg/L as dry sludge) with Fe electrodes. These results are
equivalent to an SVI of 304 and 200 mL/g for Al and Fe, respec-
tively, indicating that the EC process with Fe electrodes pro-
duces a more compact and heavier sludge due to the smaller
volume occupied by one gram of sludge. Similar settling sludge
characteristics have been reported in the EC process with Fe
and Al electrodes in the treatment of other types of industrial
effluents [105,106].
8.6 Coagulation/flocculation versus
electrocoagulation
Considering the C/F process with conventional inorganic
coagulants such asAS or ferric sulfate and the EC process with
Fe or Al electrodes, the following differences can be listed in
Table 8.11 [10,104,107].
202 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
8.7 Conclusions and future trends
This chapter presents an overview of the principles and fun-
damentals of the C/F and EC processes emphasizing the applica-
tion of these technologies in the treatment of oily wastewater. In
addition, some results have been presented regarding the C/F
treatment tests of two oily effluents from Mexican refineries,
demonstrating the technical feasibility of the process for the
removal of different pollutants presented in this type of wastewa-
ter. In conclusion, the characteristics of oily wastewater may be
different in each refinery. Therefore selecting the best chemical
products and determining the optimal doses and pH are crucial
for the process’s success. On the other hand, a developing tech-
nology such as EC process was approached at a laboratory scale
to elucidate its capacity to remove suspended and dissolved pol-
lutants from oily effluents, which could contribute to the depura-
tion of these effluents in the WWTPs of oil refineries.
Table 8.11 Comparison of the main characteristics of C/F and EC processes.
Feature Coagulation/flocculation Electrocoagulation
Dosing
approach
External In-site
Chemical
storage
Necessary Not necessary
COD removal Low to medium (higher COD removals can be
obtained with the use of flocculant or precipitant-
aid)
Low to medium (high COD removals can be
reached at long electrolysis time, increasing
the operating cost)
Oil removal high high
TSS and
turbidity
removal
high high
Hardness and
silica removal
Low (the use of polymeric flocculants or
precipitant-aid could enhance its removal)
Low to medium (depending on the electrodes
material, electrolysis time, and current
density)
Sludge
generation
Low to medium (the use of polymeric flocculants
could diminish its generation)
Low to medium (depending on the electrolysis
time and current applied)
Energy
consumption
Low to medium Medium to high (depending on the
electrolysis time, cell potential, and current
applied)
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 203
List of abbreviations
APAM Anionic polyacrylamide
API American Petroleum Institute
API-D1 API’s effluent from drainages 1
API-D2 API’s effluent from drainages 2
BOD
5
Biochemical oxygen demand
CH Calcium hardness
COD Chemical oxygen demand
CPS Corrugated plate separators
C/F Coagulation/flocculation
DAF Dissolved air flotation
EC Electrocoagulation
HRT Hydraulic retention time
IAF Induced air flotation
O&G Oils and grease
PAHs Polyaromatic hydrocarbons
PAX Polyaluminum chloride-based coagulant
POLYCAT Cationic polymer flocculant
PIX Ferric chloride or sulfate-based coagulant
rpm Revolutions per minute
R1 Oil refinery 1
R2 Oil refinery 2
AS Aluminum sulfate coagulant
SEC Specific energy consumption
SS316 Stainless steel 316
SVI Sludge volume index
TDS Total dissolved solids
TH Total hardness
TKN Total Kjeldahl nitrogen
TOC Total organic carbon
TPH Total petroleum hydrocarbon
TS Total solids
TSS Total suspended solids
WWTP Wastewater treatment plant
ASurface area of the electrodes (m
2
)
E
cell
Cell potential (V )
GAverage velocity gradient (s
21
)
IApplied current (A)
JCurrent density (A/m
2
)
PPower requirement (W)
pH Potential hydrogen
t
e
Electrolysis time (min)
VBasin volume (m
3
)
μAbsolute viscosity of water (N s/m
2
).
References
[1] P. Mijaylova, Water management in the petroleum refining industry, in: M.
Jha (Ed.), Water Conservation, InTech, 2011, pp. 106128. Available from:
http://doi.org/10.5772/31018.
[2] V.L. dos Santos, A.A. Veiga, R.S. Mendonc¸ a, A.L. Alves, S. Pagnin, V.M.J.
Santiago, Reuse of refinery’s tertiary-treated wastewater in cooling towers:
204 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
microbiological monitoring, Environ. Sci. Pollut. Res. 22 (2015) 29452955.
Available from: https://doi.org/10.1007/s11356-014-3555-7.
[
3] P.Barthe,M.Chaugny,S.Roudier,L.DelgadoSancho,BestAvailable
Techniques (BAT ) Reference Document for the Refining of Mineral Oil and
Gas: Industrial Emissions Directive 2010/75/EU Integrated Pollution
Prevention and Control, 2015. Available from: https://doi.org/10.2791/010758.
[4] S. Jafarinejad, Pollutions and wastes from the petroleum industry, in:
S. Jafarinejad (Ed.), Petroleum Waste Treatment and Pollution Control, first
ed., Butterworth-Heinemann, 2017, pp. 1983. Available from: https://doi.
org/10.1016/B978-0-12-809243-9.00002-X.
[5] M.A. Al-Ghouti, M.A. Al-Kaabi, M.Y. Ashfaq, D. Adel, Produced water
characteristics, treatment and reuse: a review, J. Water Process. Eng. 28
(2019) 222239. Available from: https://doi.org/10.1016/j.
jwpe.2019.02.001.
[6] E. Mohammad-Pajooh, D. Weichgrebe, G. Cuff, B. Mohamadpour, K. Rosenwinkel,
On-site treatment of flowback and produced water from shale gas hydraulic
fracturing: a review and economic evaluation, Chemosphere 212 (2018)
898914. Available from: https://doi.org/10.1016/j.chemosphere.2018.08.145.
[7] B. Hasan, W. Mohd, A. Wan, A.R.A. Aziz, Treatment technologies for
petroleum refinery effluents: a review, Process. Saf. Environ. Prot. 89 (2011)
95105. Available from: https://doi.org/10.1016/j.psep.2010.11.003.
[8] A. Medel, F. Lugo, Y. Meas, Application of electrochemical processes for
treating effluents from hydrocarbon industries, in: C.A. Martı
´nez-Huitle,
M.A. Rodrigo, O. Scialdone (Eds.), Electrochemical Water and Wastewater
Treatment, first ed., Elsevier, 2018, pp. 365392. Available from: http://doi.
org/10.1016/b978-0-12-813160-2.00014-6.
[9] T. Harif, M. Khai, A. Adin, Electrocoagulation versus chemical coagulation:
coagulation/flocculation mechanisms and resulting floc characteristics,
Water Res. 46 (2012) 31773188. Available from: https://doi.org/10.1016/j.
watres.2012.03.034.
[10] C. Zhao, J. Zhou, Y. Yan, L. Yang, G. Xing, H. Li,et al., Application of coagulation/
flocculation in oily wastewater treatment: a review, Sci. Total Environ. 765 (2021)
142795. Available from: https://doi.org/10.1016/j.scitotenv.2020.142795.
[11] S. Singh, Shikha, Treatment and recycling of wastewater from oil refinery/
petroleum industry, in: R.L. Singh, R.P. Singh (Eds.), Advances in Biological
Treatment of Industrial Waste Water and Their Recycling for a Sustainable
Future, Springer, Singapore, 2019, pp. 303332. Available from: http://doi.
org/10.1007/978-981-13-1468-1_10.
[12] S.R. Qasim, E.M. Motley, G. Zhu, Coagulation, flocculation, and
precipitation, Water Works Engineering: Planning, Desing and Operation,
first ed., Prentice-Hall, 2000, pp. 229294.
[13] J. Bratby, Coagulation and Flocculation in Water and Wastewater
Treatment, second ed., IWA Publishing, UK, 2006.
[14] M.H. El-Naas, S. Al-Zuhair, A. Al-Lobaney, S. Makhlouf, Assessment of
electrocoagulation for the treatment of petroleum refinery wastewater, J.
Environ. Manage. 91 (2009) 180185. Available from: https://doi.org/
10.1016/j.jenvman.2009.08.003.
[15] S. Jafarinejad, Treatment of oily wastewater, in: S. Jafarinejad (Ed.),
Petroleum Waste Treatment and Pollution Control, Butterworth-
Heinemann, 2017, pp. 185267. Available from: https://doi.org/10.1016/
B978-0-12-809243-9.00006-7.
[16] C.Y. Teh, P.M. Budiman, K.P.Y. Shak, T.Y. Wu, Recent advancement of
coagulationflocculation and its application in wastewater treatment, Ind.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 205
Eng. Chem. Res. 55 (2016) 43634389. Available from: https://doi.org/
10.1021/acs.iecr.5b04703.
[17] K.J. Howe, D.W. Hand, J.C. Crittenden, R.R. Trussel, G. Tchobanoglous,
Coagulation and flocculation, Principles of Water Treatment, third ed., John
Wiley & Sons, USA, 2012, pp. 140190.
[18] S.-J. Park, M.-K. Seo, Chapter 1—Intermolecular force, in: S.-J. Park, M.-K.
Seo (Eds.), Interface Science and Composites, Elsevier, 2011, pp. 157.
Available from: https://doi.org/10.1016/B978-0-12-375049-5.00001-3.
[19] S.A. Parsons, B. Jefferson, Coagulation and flocculation, Introduction to
Potable Water Treatment Processes, Blackwell, 2006, pp. 2642. Available
from: https://doi.org/10.1002/9781444305470.ch3.
[20] B. Cerff, D. Key, B. Bladergroen, A review of the processes associated with
the removal of oil in water pollution, Sustainability 13 (2021). Available
from: https://doi.org/10.3390/su132212339.
[21] R. Yang, H. Li, M. Huang, H. Yang, A. Li, A review on chitosan-based
flocculants and their applications in water treatment, Water Res. 95 (2016)
5989. Available from: https://doi.org/10.1016/j.watres.2016.02.068.
[22] Y. Zeng, C. Yang, J. Zhang, W. Pu, Feasibility investigation of oily wastewater
treatment by combination of zinc and PAM in coagulation/flocculation, J.
Hazard. Mater. 147 (2007) 991996. Available from: https://doi.org/
10.1016/j.jhazmat.2007.01.129.
[23] M.L.S. Welz, N. Baloyi, D.A. Deglon, Oil removal from industrial wastewater
using flotation in a mechanically agitated flotation cell, Water SA 33 (2007)
453458. Available from: https://doi.org/10.4314/wsa.v33i4.52939.
[24] A.L. Ahmad, S. Sumathi, B.H. Hameed, Coagulation of residue oil and
suspended solid in palm oil mill effluent by chitosan, alum and PAC,
Chem. Eng. J. 118 (2006) 99105. Available from: https://doi.org/10.1016/j.
cej.2006.02.001.
[25] T. Lu
¨, H. Zhao, D. Qi, Y. Chen, Synthesis of a novel amphiphilic and
cationic chitosan-based flocculant for efficient treatment of oily
wastewater, Adv. Polym. Technol. 34 (2015). Available from: https://doi.org/
10.1002/adv.21502.
[26] N.A. Oladoja, Advances in the quest for substitute for synthetic organic
polyelectrolytes as coagulant aid in water and wastewater treatment
operations, Sustain. Chem. Pharm. 3 (2016) 4758. Available from: https://
doi.org/10.1016/j.scp.2016.04.001.
[27] A.P. Black, C. Chen, Electrophoretic studies of coagulation and flocculation of
river sediment suspensions with aluminum sulfate, J. AWWA 57 (1965)
354362. Available from: https://doi.org/10.1002/j.1551-8833.1965.tb01410.x.
[28] A. Almojjly, D. Johnson, D.L. Oatley-Radcliffe, N. Hilal, Removal of oil from
oil-water emulsion by hybrid coagulation/sand filter as pre-treatment, J.
Water Process. Eng. 26 (2018) 1727. Available from: https://doi.org/
10.1016/j.jwpe.2018.09.004.
[29] X. Liu, H. Yin, J. Zhao, Z. Guo, Z. Liu, Y. Sang, Understanding the
coagulation mechanism and floc properties induced by Fe(VI) and FeCl
3
:
population balance modeling, Water Sci. Technol. 83 (2021) 23772388.
Available from: https://doi.org/10.2166/wst.2021.150.
[30] Y. Sun, S. Zhou, P.-C. Chiang, K.J. Shah, Evaluation and optimization of
enhanced coagulation process: water and energy nexus, Water-Energy Nexus 2
(2019) 2536. Available from: https://doi.org/10.1016/j.wen.2020.01.001.
[31] T.R. Camp, D.A. Root, B.V. Bhoota, Effects of temperature on rate of floc
formation, J. Am. Water Work. Assoc. 32 (1940) 19131927. Available from:
http://www.jstor.org/stable/41232359.
206 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
[32] F. Xiao, J.-C.H. Huang, B. Zhang, C. Cui, Effects of low temperature on
coagulation kinetics and floc surface morphology using alum, Desalination.
237 (2009) 201213. Available from: https://doi.org/10.1016/j.
desal.2007.12.033.
[33] P. Zhang, L. Liao, G. Zhu, Performance of PATC-PDMDAAC composite
coagulants in low-temperature and low-turbidity water treatment,
Materials 12 (2019). Available from: https://doi.org/10.3390/ma12172824.
[34] Metcalf & Eddy, Wastewater Engineering: Treatment and Resource
Recovery, fifth ed., Metcalf & Eddy, New York, 2014.
[35] L. Alta¸s, H. Bu
¨yu
¨kgu
¨ngo
¨r, Sulfide removal in petroleum refinery wastewater
by chemical precipitation, J. Hazard. Mater. 153 (2008) 462469. Available
from: https://doi.org/10.1016/j.jhazmat.2007.08.076.
[36] S. Verma, B. Prasad, I.M. Mishra, Pretreatment of petrochemical wastewater
by coagulation and flocculation and the sludge characteristics, J. Hazard.
Mater. 178 (2010) 10551064. Available from: https://doi.org/10.1016/j.
jhazmat.2010.02.047.
[37] C.E. Santo, V.J.P. Vilar, C.M.S. Botelho, A. Bhatnagar, E. Kumar, R.A.R.
Boaventura, Optimization of coagulationflocculation and flotation
parameters for the treatment of a petroleum refinery effluent from a
Portuguese plant, Chem. Eng. J. 183 (2012) 117123. Available from:
https://doi.org/10.1016/j.cej.2011.12.041.
[38] G. Di Bella, M.G. Giustra, G. Freni, Optimisation of coagulation/flocculation
for pre-treatment of high strength and saline wastewater: performance
analysis with different coagulant doses, Chem. Eng. J. 254 (2014) 283292.
Available from: https://doi.org/10.1016/j.cej.2014.05.115.
[39] S.M. Hoseini, M.M. Salarirad, M.R. Alavi Moghaddam, TPH removal from
oily wastewater by combined coagulation pretreatment and mechanically
induced air flotation, Desalin. Water Treat. 53 (2015) 300308. Available
from: https://doi.org/10.1080/19443994.2013.846522.
[40] A. Saber, S. Mortazavian, D.E. James, H. Hasheminejad, Optimization of
collaborative photo-Fenton oxidation and coagulation for the treatment of
petroleum refinery wastewater with scrap iron, Water Air Soil Pollut. 228
(2017) 312. Available from: https://doi.org/10.1007/s11270-017-3494-2.
[41] H. Chang, B. Liu, B. Yang, X. Yang, C. Guo, Q. He, et al., An integrated
coagulation-ultrafiltration-nanofiltration process for internal reuse of shale
gas flowback and produced water, Sep. Purif. Technol. 211 (2019) 310321.
Available from: https://doi.org/10.1016/j.seppur.2018.09.081.
[42] P. Bruno, R. Campo, M.G. Giustra, M. De Marchis, G. Di Bella, Bench scale
continuous coagulation-flocculation of saline industrial wastewater
contaminated by hydrocarbons, J. Water Process. Eng. 34 (2020) 101156.
Available from: https://doi.org/10.1016/j.jwpe.2020.101156.
[43] H. Ye, L. Chen, Y. Kou, Z.T. How, P. Chelme-Ayala, Q. Wang, et al.,
Influences of coagulation pretreatment on the characteristics of crude oil
electric desalting wastewaters, Chemosphere. 264 (2021) 128531. Available
from: https://doi.org/10.1016/j.chemosphere.2020.128531.
[44] H. Zhang, H. Lin, Q. Li, C. Cheng, H. Shen, Z. Zhang, et al., Removal of
refractory organics in wastewater by coagulation/flocculation with green
chlorine-free coagulants, Sci. Total Environ. 787 (2021) 147654. Available
from: https://doi.org/10.1016/j.scitotenv.2021.147654.
[45] H. Zhang, H. Yu, C. Sun, Y. Tong, J. Deng, L. Wu, et al., Evaluation of new
hydrophobic association inorganic composite material as coagulant for
oilfield wastewater treatment, Sep. Purif. Technol. 275 (2021) 119126.
Available from: https://doi.org/10.1016/j.seppur.2021.119126.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 207
[46] A. Shahedi, A.K. Darban, F. Taghipour, A. Jamshidi-Zanjani, A review on
industrial wastewater treatment via electrocoagulation processes, Curr.
Opin. Electrochem. 22 (2020) 154169. Available from: https://doi.org/
10.1016/j.coelec.2020.05.009.
[47] M.A. Sandoval, R. Salazar, Electrochemical treatment of slaughterhouse and
dairy wastewater: toward making a sustainable process, Curr. Opin.
Electrochem. 26 (2021) 100662. Available from: https://doi.org/10.1016/j.
coelec.2020.100662.
[48] V. Khandegar, A.K. Saroha, Electrocoagulation for the treatment of textile
industry effluent—a review, J. Environ. Manage. 128 (2013) 949963.
Available from: https://doi.org/10.1016/j.jenvman.2013.06.043.
[49] Y. Meas, J.A. Ramirez, M.A. Villalon, T.W. Chapman, Industrial
wastewaters treated by electrocoagulation, Electrochim. Acta 55 (2010)
81658171. Available from: https://doi.org/10.1016/j.electacta.
2010.05.018.
[50] J.D.J. Trevin
˜o-Rese
´ndez, A. Medel, Y. Meas, Electrochemical technologies
for treating petroleum industry wastewater, Curr. Opin. Electrochem. 27
(2021) 100690. Available from: https://doi.org/10.1016/j.coelec.2021.100690.
[51] O. Sahu, B. Mazumdar, P.K. Chaudhari, Treatment of wastewater by
electrocoagulation: a review, Environ. Sci. Pollut. Res. 21 (2014) 23972413.
Available from: https://doi.org/10.1007/s11356-013-2208-6.
[52] J. Gregory, J. Duan, Hydrolyzing metal salts as coagulants, Pure Appl.
Chem. 73 (2007) 20172026. Available from: https://doi.org/10.1351/
pac200173122017.
[53] M. Mechelhoff, G.H. Kelsall, N.J.D. Graham, Electrochemical behaviour of
aluminium in electrocoagulation processes, Chem. Eng. Sci. 95 (2013)
301312. Available from: https://doi.org/10.1016/j.ces.2013.03.010.
[54] C.H.A. Moreno, D.L. Cocke, J.A.G. Gomes, P. Morkovsky, J.R. Parga,
E. Peterson, et al., Electrochemistry behind electrocoagulation using iron
electrodes, ECS Trans 6 (2007) 115. Available from: https://doi.org/
10.1149/1.2790397.
[55] D. Lakshmanan, D.A. Clifford, G. Samanta, Ferrous and ferric ion
generation during iron electrocoagulation, Environ. Sci. Technol. 43 (2009)
38533859. Available from: https://doi.org/10.1021/es8036669.
[56] D.T. Moussa, M.H. El-Naas, M. Nasser, M.J. Al-Marri, A comprehensive
review of electrocoagulation for water treatment: potentials and challenges,
J. Environ. Manage. 186 (2017) 2441. Available from: https://doi.org/
10.1016/j.jenvman.2016.10.032.
[57] M. Ingelsson, N. Yasri, E.P.L. Roberts, Electrode passivation, faradaic
efficiency, and performance enhancement strategies in
electrocoagulation—a review, Water Res. 187 (2020) 116433. Available from:
https://doi.org/10.1016/j.watres.2020.116433.
[58] H.A. Moreno C, D.L. Cocke, J.A.G. Gomes, P. Morkovsky, J.R. Parga, E. Peterson,
et al., Electrochemical reactions for electrocoagulation using iron electrodes,
Ind. Eng. Chem. Res. 48 (2009) 22752282. Available from: https://doi.org/
10.1021/ie8013007.
[59] D. Ghernaout, Advanced oxidation phenomena in electrocoagulation
process: a myth or a reality? Desalin. Water Treat. 51 (2013) 75367554.
Available from: https://doi.org/10.1080/19443994.2013.792520.
[60] I.D. Tegladza, Q. Xu, K. Xu, G. Lv, J. Lu, Electrocoagulation processes: a
general review about role of electro-generated flocs in pollutant removal,
Process. Saf. Environ. Prot. 146 (2021) 169189. Available from: https://doi.
org/10.1016/j.psep.2020.08.048.
208 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
[61] S. Garcia-Segura, M.M.S.G. Eiband, J.V. de Melo, C.A. Martı
´nez-Huitle,
Electrocoagulation and advanced electrocoagulation processes: a general
review about the fundamentals, emerging applications and its association
with other technologies, J. Electroanal. Chem. 801 (2017) 267299.
Available from: https://doi.org/10.1016/j.jelechem.2017.07.047.
[62] M. Murugananthan, G.B. Raju, S. Prabhakar, Removal of sulfide, sulfate and
sulfite ions by electro coagulation, J. Hazard. Mater. 109 (2004) 3744.
Available from: https://doi.org/10.1016/j.jhazmat.2003.12.009.
[63] L.F. Castan
˜eda, J.F. Rodrı
´guez, J.L. Nava, Electrocoagulation as an affordable
technology for decontamination of drinking water containing fluoride: a
critical review, Chem. Eng. J. 413 (2021) 127529. Available from: https://doi.
org/10.1016/j.cej.2020.127529.
[64] M.A. Sandoval, R. Fuentes, J.L. Nava, I. Rodrı
´guez, Fluoride removal
from drinking water by electrocoagulation in a continuous filter press reactor
coupled to a flocculator and clarifier, Sep. Purif. Technol. 134 (2014) 163170.
Available fro m: https://doi.org/10.1016/j.seppur.2014.07.034.
[65] H.A. Moreno-Casillas, D.L. Cocke, J.A.G. Gomes, P. Morkovsky, J.R. Parga,
E. Peterson, Electrocoagulation mechanism for COD removal, Sep. Purif.
Technol. 56 (2007) 204211. Available from: https://doi.org/10.1016/j.
seppur.2007.01.031.
[66] P. Jarvis, B. Jefferson, S.A. Parsons, Characterising natural organic matter
flocs, Water Supply 4 (2004) 7987. Available from: https://doi.org/10.2166/
ws.2004.0064.
[67] Y. Liu, X. Zhang, W.M. Jiang, M.R. Wu, Z.H. Li, Comprehensive review of
floc growth and structure using electrocoagulation: characterization,
measurement, and influencing factors, Chem. Eng. J. 417 (2021) 129310.
Available from: https://doi.org/10.1016/j.cej.2021.129310.
[68] C. An, G. Huang, Y. Yao, S. Zhao, Emerging usage of electrocoagulation
technology for oil removal from wastewater: a review, Sci. Total Environ.
579 (2017) 537556. Available from: https://doi.org/10.1016/j.
scitotenv.2016.11.062.
[69] A.A. Al-Raad, M.M. Hanafiah, Removal of inorganic pollutants using
electrocoagulation technology: a review of emerging applications and
mechanisms, J. Environ. Manage. 300 (2021) 113696. Available from:
https://doi.org/10.1016/j.jenvman.2021.113696.
[70] Y. Yavuz, A.S. Koparal, U
¨.B. O
¨˘
gu
¨tveren, Treatment of petroleum refinery
wastewater by electrochemical methods, Desalination 258 (2010) 201205.
Available from: https://doi.org/10.1016/j.desal.2010.03.013.
[71] K. Sardari, P. Fyfe, D. Lincicome, S.R. Wickramasinghe, Aluminum
electrocoagulation followed by forward osmosis for treating hydraulic
fracturing produced waters, Desalination 428 (2018) 172181. Available
from: https://doi.org/10.1016/j.desal.2017.11.030.
[72] S. Safari, M. Azadi Aghdam, H.-R. Kariminia, Electrocoagulation for COD
and diesel removal from oily wastewater, Int. J. Environ. Sci. Technol. 13
(2016) 231242. Available from: https://doi.org/10.1007/s13762-015-0863-5.
[73] A.S. Fajardo, R.F. Rodrigues, R.C. Martins, L.M. Castro, R.M. Quinta-Ferreira,
Phenolic wastewaters treatment by electrocoagulation process using Zn
anode, Chem. Eng. J. 275 (2015) 331341. Available from: https://doi.org/
10.1016/j.cej.2015.03.116.
[74] T.R. Devlin, M.S. Kowalski, E. Pagaduan, X. Zhang, V. Wei, J.A. Oleszkiewicz,
Electrocoagulation of wastewater using aluminum, iron, and magnesium
electrodes, J. Hazard. Mater. 368 (2019) 862868. Available from: https://
doi.org/10.1016/j.jhazmat.2018.10.017.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 209
[75] C. Jime
´nez, C. Sa
´ez, F. Martı
´nez, P. Can
˜izares, M.A. Rodrigo, Electrochemical
dosing of iron and aluminum in continuous processes: a key step to
explain electro-coagulation processes, Sep. Purif. Technol. 98 (2012)
102108. Available from: https://doi.org/10.1016/j.seppur.2012.07.005.
[76] S.L.G. Santiago, S.P. Castrejo
´n, A.M. Domı
´nguez, A.M. Brito, I.E.V. Mendoza,
Current density as a master variable in designing reactors, Proc. Chem. 12
(2014) 6672. Available from: https://doi.org/10.1016/j.proche.2014.12.043.
[77] M. Bajpai, S.S. Katoch, A. Kadier, A. Singh, A review on electrocoagulation
process for the removal of emerging contaminants: theory, fundamentals,
and applications, Environ. Sci. Pollut. Res. (2022). Available from: https://
doi.org/10.1007/s11356-021-18348-8.
[78] L.F. Catan
˜eda, F.F. Rivera, T. Pe
´rez, J.L. Nava, Mathematical modeling and
simulation of the reaction environment in electrochemical reactors, Curr.
Opin. Electrochem. 16 (2019) 7582. Available from: https://doi.org/
10.1016/j.coelec.2019.04.025.
[79] E.A. Vik, D.A. Carlson, A.S. Eikum, E.T. Gjessing, Electrocoagulation of
potable water, Water Res. 18 (1984) 13551360. Available from: https://doi.
org/10.1016/0043-1354(84)90003-4.
[80] G. Chen, Y.-T. Hung, Electrochemical wastewater treatment processes, in:
L.K. Wang, Y.-T. Hung, N.K. Shammas (Eds.), Advanced Physicochemical
Treatment Technologies, Humana Press, Totowa, NJ, 2007, pp. 57106.
Available from: http://doi.org/10.1007/978-1-59745-173-4_2.
[81] E. Lacasa, S. Cotillas, C. Saez, J. Lobato, P. Can
˜izares, M.A. Rodrigo,
Environmental applications of electrochemical technology. What is needed
to enable full-scale applications? Curr. Opin. Electrochem. 16 (2019)
149156. Available from: https://doi.org/10.1016/j.coelec.2019.07.002.
[82] M.H. El-Naas, R. Surkatti, S. Al-Zuhair, Petroleum refinery wastewater
treatment: a pilot scale study, J. Water Process. Eng. 14 (2016) 7176.
Available from: https://doi.org/10.1016/j.jwpe.2016.10.005.
[83] F.A. Mohd, A.A. Mohd, M.N. Abu, A.S. Abdul, T. Tajuddin, S. Nurdin, Treatment
of petroleum-based industrial wastewater using electrocoagulation, Advances
in Waste Processing Technology, Springer, 2020, pp. 4959. Available from:
https://doi.org/10.1007/978-981-15-4821-5_4.
[84] S.H. Ammar, N.N. Ismail, A.D. Ali, W.M. Abbas, Electrocoagulation
technique for refinery wastewater treatment in an internal loop split-plate
airlift reactor, J. Environ. Chem. Eng. 7 (2019) 103489. Available from:
https://doi.org/10.1016/j.jece.2019.103489.
[85] Y. AlSalka, F. Karabet, S. Hashem, Evaluation of electrochemical processes
for the removal of several target aromatic hydrocarbons from petroleum
contaminated water, J. Environ. Monit. 13 (2011) 605613. Available from:
https://doi.org/10.1039/C0EM00450B.
[86] I. Ben Hariz, A. Halleb, N. Adhoum, L. Monser, Treatment of petroleum
refinery sulfidic spent caustic wastes by electrocoagulation, Sep. Purif.
Technol. 107 (2013) 150157. Available from: https://doi.org/10.1016/j.
seppur.2013.01.051.
[87] D.S. Ibrahim, M. Lathalakshmi, A. Muthukrishnaraj, N. Balasubramanian,
An alternative treatment process for upgrade of petroleum refinery
wastewater using electrocoagulation, Pet. Sci. 10 (2013) 421430. Available
from: https://doi.org/10.1007/s12182-013-0291-4.
[88] M.H. El-Naas, M.A. Alhaija, S. Al-Zuhair, Evaluation of a three-step
process for the treatment of petroleum refinery wastewater, J. Environ.
Chem. Eng. 2 (2014) 5662. Available from: https://doi.org/10.1016/j.
jece.2013.11.024.
210 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
[89] J.R.P. da Silva, F. Merc¸on, L.F. da Silva, A. Andrade Cerqueira, P. Braz
Ximango, M.R. da Costa Marques, Evaluation of electrocoagulation as pre-
treatment of oil emulsions, followed by reverse osmosis, J. Water Process.
Eng. 8 (2015) 126135. Available from: https://doi.org/10.1016/j.
jwpe.2015.09.009.
[90] E. Herna
´ndez-Francisco, J. Peral, L.M. Blanco-Jerez, Removal of phenolic
compounds from oil refinery wastewater by electrocoagulation and
Fenton/photo-Fenton processes, J. Water Process. Eng. 19 (2017) 96100.
Available from: https://doi.org/10.1016/j.jwpe.2017.07.010.
[91] T. Shahriari, A.R. Karbassi, M. Reyhani, Treatment of oil refinery
wastewater by electrocoagulationflocculation (Case Study: Shazand Oil
Refinery of Arak), Int. J. Environ. Sci. Technol. (2018) 18. Available from:
https://doi.org/10.1007/s13762-018-1810-z.
[92] K.A. Sitterley, J. Rosenblum, B. Ruyle, R. Keliher, K.G. Linden, Factors
impacting electrocoagulation treatment of hydraulic fracturing fluids and
removal of common fluid additives and scaling ions, J. Environ. Chem. Eng.
8 (2020) 103728. Available from: https://doi.org/10.1016/j.jece.2020.103728.
[93] M. Moussavi, A. Pendashteh, H. Alinia, Treatment of a natural gas refinery
effluents by electrocoagulation, Environ. Challenges. 3 (2021) 100036.
Available from: https://doi.org/10.1016/j.envc.2021.100036.
[94] E. Bocos, E. Brillas, M.A
´. Sanroma
´n, I. Sire
´s, Electrocoagulation: simply a
phase separation technology? The case of bronopol compared to its
treatment by EAOPs, Environ. Sci. Technol. 50 (2016) 76797686. Available
from: https://doi.org/10.1021/acs.est.6b02057.
[95] S. Gao, M. Du, J. Tian, J. Yang, J. Yang, F. Ma, et al., Effects of chloride ions
on electro-coagulation-flotation process with aluminum electrodes for
algae removal, J. Hazard. Mater. 182 (2010) 827834. Available from:
https://doi.org/10.1016/j.jhazmat.2010.06.114.
[96] C.T. Tanneru, N. Jothikumar, V.R. Hill, S. Chellam, Relative insignificance
of virus inactivation during aluminum electrocoagulation of saline waters,
Environ. Sci. Technol. 48 (2014) 1459014598. Available from: https://doi.
org/10.1021/es504381f.
[97] J. Trevin
˜o-Rese
´ndez, A. Medel, P. Mijaylova, I. Robles, F. Rodrı
´guez-
Valadez, L.A. Godı
´nez, et al., Insight into the generation of hydroxyl
radicals by photo-electrocoagulation process via active chlorine, Int. J.
Environ. Sci. Technol. 19 (2021) 29132924. Available from: https://doi.
org/10.1007/s13762-021-03351-w.
[98] R. Saravanathamizhan, V.T. Perarasu, Improvement of biodegradability index of
industrial wastewater using different pretreatment techniques, in: M.P. Shah,
A. Sarkar, S. Mandal (Eds.), Wastewater Treatment: Cutting-Edge Molecular
Tools, Techniques, and Application Aspects, Elsevier, 2021, pp. 103136.
Avail ab le from : https://doi.org/10.1016/B978-0-12-821881-5.00006-4.
[99] M.A. Sari, S. Chellam, Mechanisms of boron removal from hydraulic fracturing
wastewater by aluminum electrocoagulation, J. Colloid Interface Sci. 458
(2015) 103111. Available from: https://doi.org/10.1016/j.jcis.2015.07.035.
[100] H.K. Hansen, S. Franco, C. Gutie
´rrez, A. Lazo, P. Lazo, L.M. Ottosen,
Selenium removal from petroleum refinery wastewater using an
electrocoagulation technique, J. Hazard. Mater. 364 (2019) 7881.
Available from: https://doi.org/10.1016/j.jhazmat.2018.09.090.
[101] S.B. Kausley, C.P. Malhotra, A.B. Pandit, Treatment and reuse of shale gas
wastewater: electrocoagulation system for enhanced removal of organic
contamination and scale causing divalent cations, J. Water Process. Eng. 16
(2017) 149162. Available from: https://doi.org/10.1016/j.jwpe.2016.11.003.
Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment 211
[102] E.M. Nigri, A.L.A. Santos, S.D.F. Rocha, Removal of organic compounds,
calcium and strontium from petroleum industry effluent by simultaneous
electrocoagulation and adsorption, J. Water Process. Eng. 37 (2020)
101442. Available from: https://doi.org/10.1016/j.jwpe.2020.101442.
[103] U.S. EPA, Guidelines for Water Reuse, Washington, DC, 1992.
[104] N. Yasri, J. Hu, M.G. Kibria, E.P.L. Roberts, Electrocoagulation separation
processes, Multidisciplinary Advances in Efficient Separation Processes,
American Chemical Society, 2020, pp. 167203. SE6. Available from:
https://doi.org/10.1021/bk-2020-1348.ch006.
[105] S. Zodi, J.-N. Louvet, C. Michon, O. Potier, M.-N. Pons, F. Lapicque, et al.,
Electrocoagulation as a tertiary treatment for paper mill wastewater:
removal of non-biodegradable organic pollution and arsenic, Sep. Purif.
Technol. 81 (2011) 6268. Available from: https://doi.org/10.1016/j.
seppur.2011.07.002.
[106] P.V. Nidheesh, A. Kumar, D. Syam Babu, J. Scaria, M. Suresh Kumar,
Treatment of mixed industrial wastewater by electrocoagulation and
indirect electrochemical oxidation, Chemosphere 251 (2020) 126437.
Available from: https://doi.org/10.1016/j.chemosphere.2020.126437.
[107] M. Vepsa
¨la
¨inen, M. Sillanpa
¨a
¨, Chapter 1—Electrocoagulation in the
treatment of industrial waters and wastewaters, in: M. Sillanpa
¨a
¨(Ed.),
Advanced Water Treatment: Electrochemical Methods, Elsevier, 2020,
pp. 178. Available from: https://doi.org/10.1016/B978-0-12-819227-
6.00001-2.
212 Chapter 8 Coagulation/flocculation and electrocoagulation methods for oily wastewater treatment
