Advances in Chemical Engi neering and Science , 2011, 1, 245-251
doi:10.4236/aces.2011.14035 Published Online October 2011 (
Copyright © 2011 SciRes. ACES
Pretreatment of Wa stewater Streams from
Petroleum/Petrochemical Industries Using Coagulation
Hossam Altaher*, Emad ElQada, Waid Omar
Chemical Engi neeri n g Techn ol o gy Dep art m e nt, Yanbu Industrial College, Saudi Arabia
E-mail: * (or
Received June 27, 2011; revised July 19, 2011; accepted August 12, 2011
Coagulation-flocculation processes using different types of conventional coagulants, namely, ferric chloride
(FeCl3), aluminum sulfate (AL2(SO4)3·18H2O), lime and ferrous sulfate (FeSO4) were investigated using the
Jar-test technique. A further aim is to determine the optimum conditions for the treatment of industrial
wastewater effluents i.e. coagulant dosage, mixing rate, temperature and pH control. Under optimal condi-
tion of process parameters, coagulation/flocculation process was able to lower the turbidity well below the
permissible level (1.8 NTU). The results indicate that ferric chloride had superior efficiency compared with
other coagulants with efficient dose of 800 mg/l. The optimal initial pH of the effluents that enhanced the
turbidity removal was 8.6. The temperature showed no significant effect on the turbidity removal.
Keywords: Ferric Chloride, Coagulation, Wastewater, Petrochemicals, Pretreatment
1. Introduction
This template, Yanbu Industrial City, at the Red Sea
Coast of Saudi Arabia, is considered as one of the major
industrial cities in the Kingdom of Saudi Arabia. The
city accommodates several large refining and petro-
chemical plants as well as a broad range of other manu-
facturing and support enterprises [1]. This inexorable
growth in the scale of the petrochemical industries and
oil refinery was largely responsible for the remarkable
ecological problems at Yanbu Industrial City .
This forces the Saudi government to issue strict legis-
lation concerning the quality of industrial wastewater
effluents and the industries are not allowed to discharge
any treated or untreated effluent in open channels and
even after treatment, the reclaimed water must have to
comply with direct discharge standards before discharge
to the sea [2]. So the entire industrial sectors send their
wastewater effluents to a local wastewater treatment
plant to treat their waste effluents to an increasingly high
standard. Actually, the treatment system consisting of
physical, chemical, and biological units is not enough in
its current state to reach the permissible levels of dis-
charge especially for turbidity. However, the focus of
this paper is the enhancement of coagulation process in
an attempt to comply with turbidity standards for obvi-
ous health issues.
Coagulation, adsorption on activated carbon, precipi-
tation, evaporation, ion-exchange, oxidation, and bio-
degradation and membrane filtration are known as an
industrial pollution prevention technology and used for
the decontamination of contaminated water and waste-
water [3]. According to Renault et al. [3], complete
treatment will clearly require several steps and it is o ften
appropriate to combine several methods of purification
before maximal efficiency is obtained.
Coagulation/flocculation is a widely-used process in
the primary purification of water and in industrial
wastewater treatment [3-5]. This method has a prefer-
ence in the primary purification processes mainly due to
the ease of operation, high efficiency, cost effective Also,
it uses less energy than alternative treatment [5-7].
Coagulants, both inorganic and organic such as alu-
minum sulfate (alum), ferrous sulfate, ferric chloride and
ferric chloro-sulfate are widely used as coagulants in
water and wastewater treatment for removing a broad
range of impurities from effluent, including organic mat-
ter, turbidity, color, microorganism, colloidal particles
and dissolved organic substances [4,5,8-10]
Wang et al [11] demonstrated that many factors can
influence the efficiency of coagulation-flocculation pro-
cess such as the type and dosage of coagulant/ floccu-
lant, pH, mixing speed and time, temperature and reten-
tion time. An appropriate combination of these factors is
desirable to obtain a high efficiency of treatment.
Dosta et al [9] and Franceschi et al [12] illustrated the
role of the pH in determining the electrical charge of
organic and inorganic colloids and considered it as a
major factor in the hydrolysis of aluminum salts.
The process usually consists of the rapid dispersal of a
coagulant into the wastewater containing solid particles
followed by an intense agitation commonly defined as
rapid mixing [13]. The coagulant aggregates the particles
into small flocs that slowly settle by charge neutraliza-
tion in negatively charged colloids by cationic hydrolysis
products and incorporation of impurities in an amor-
phous hydroxide precipitate (sweep flocculation), there-
by facilitating their removal in subsequent sedimentation,
floatation and filtration stages [5,6]. Zheng et al. [10]
reported that the basic prerequisites for an effect- tive
coagulant are the charge neutralization capacity and the
bridge-aggregation ability.
The aim of this systematic study was to optimize the
coagulation-flocculation process and investigate the ef-
fect of wastewater initial pH, affects the type of coagu-
lant and coagulant dosage, Temperature and mixing con-
ditions in order to enhance the efficiency of the coagula-
tion—flocculation process especially focusing on the
optimal turbidity removal.
2. Materials and Methods
2.1. Wastewater Samples
Wastewater was obtained from the wastewater treatment
facility in Yanbu Industrial City. This wastewater is a
mixture of industrial wastewater from all the industrial
facilities in Yanbu Industrial City. However, most of
these industrial facilities are petrochemical companies
and refineries. The wastewater was collected from the
influent collection well and sent directly to our lab.
Wastewater was stored at 4˚C and was equilibrated to
room temperature before use. The main characteristics of
the wastewater are presented in Table 1.
2.2. Preparation of Coagulants
Ferric chloride (FeCl3) was obtained from Loba Chemie
(India), Aluminum sulfate (Al2(SO4)3·18H2O) was ob-
tained from Panreac Quimica SA (Spain), Ferrous sulfate
(FeSO4) was obtained from TechnoPharmChem (india).
The solutions were prepared by dissolving 10g of each
substance in distilled water and the solution volumes
were increased to 1 liter. Each 1 ml of these stock solu-
tions was equivalent to 20 mg/l when added to 500 ml of
wastewater to be tested.
Table 1. Main characteristics of wastewater.
mg/lit TSS2
mg/lit TDS3
mg/lit TS4
mg/lit Total hardness
mg/lit as CaCO3
57.5 22172323 4545 190
1After 1/10 dilution; 2TSS: Total suspended solids; 3TDS: Total dissolved
solids; 4TS: total solids.
2.3. Comparison of Different Coagulants
Coagulation and flocculation tests were performed in a
standard jar test apparatus (SOLTEQ flocculation test
unit, Mode TR 10) consisting of six paddles and
equipped with 6 beakers of 1 liter volume. Each beaker
was filled with 500 ml of wastewater sample. The per-
formance of the coagulants was compared by adding 50
ml of each one to 500 ml of wastewater without adjust-
ing pHs of the samples. The samples were agitated at a
flash mixing speed of 300 rpm for 3 minutes followed by
slow mixing speed of 50 rpm for 15 minutes. At the end
of the stirring period the flocs were allowed to settle
down for 20 minutes. The samples were taken by im-
mersing a pipette 2 cm below the surface of the water.
Turbidity, total dissolved solids, and pH were measured
using Hach 2100 AN turbidimeter, SevenEasy conduc-
tivity meter from Metler Toledo, and pH501 EuTech
Instrument, respectively. All the equipment were cali-
brated before use.
2.4. Effect of pH
To measure the effect of initial pH 7, 1-liter beakers were
filled with 500 ml of the wastewater. The pH of each of
sample was adjusted at different value using 1 N of sul-
furic acid or sodium hydroxide solutions. The pHs tested
covered the range from 3 up to 11.5. To each beaker 50
ml of FeCl3 were added. The mixture were rapidly mixed
at 300 rpm for 3 minutes, slow mixed for 15 minutes at
50 rpm and allowed to settle for 20 minutes. Samples to
be analyzed were taken from the supernatant 2 cm below
the level of the liquid.
2.5. Effect of Coagulant Dose
The optimum dose of the selected coagulant was deter-
mined by placing different volumes of coagulant (5, 10,
20, 30, 40, 50, 70 ml) in conical flasks. The volume was
adjusted to 70 ml in each flask by adding distilled water
(65, 60, 50. 40, 30, 20, 0 ml, respectively). This proce-
dure was applied to keep the total volume of the treated
samples at the same value. The rapid stirring speed was
300 rpm for 3 minutes and the slow stirring speed was 50
rpm for 15 minutes, followed by 20 minutes of settling.
The effect of coagulant dose on pH of solution was
Copyright © 2011 SciRes. ACES
measure by adding different doses of coagulant to 500 ml
aliquot of the wastewater, stirring for 2 minutes and then
measuring the pH of the different solutions. The effects
of rapid and slow mixing speed were studied similarly.
The rapid mixing speed was varied from 100 to 350 rpm
keeping the slow mixing at a constant value of 50 rpm.
The slow mixing effect was studied by varying the speed
from 45 rpm to 100 rpm keeping the rapid mixing at a
value of 30 0 rpm.
2.6. 30-Minutes Settling Tests
This experiment as usual with a jar test protocol. Two
beakers were filled with 500 ml aliquot of wastewater.
40 ml of FeCl3 were added to each beaker. The mixtures
were rapidly stirred at 300 rpm for 3 minutes, followed
by slow stirring at 50 rpm for 15 minutes. The two sam-
ples were placed in 1-liter cylinder and allowed to settle
down without disturbance. The volume of the sludge in
the cylinder was observed with time. All the above men-
tioned tests were performed at room temperature.
2.7. Effect of Temperature
The effect of temperature was tested by adjusting the
temperatures of three wastewater samples (500ml each)
at three different temperatures (13˚C, 22˚C and 43˚C).
To each sampl e 40 ml of FeCl3 were added. The mixture
were stirred rapidly for 3 minutes at 300 rpm, slow-
stirred at 50 rpm for 15 minutes, and allowed to settle for
20 minutes. The final temperature was measured to take
into account the effect of any change that may have oc-
3. Results and Discussion
3.1. Comparison of Different Coagulants
The objective of this experiment was to determine the
best coagulan t that can be used to reduce tu rbidity to the
permissible level for such wastewater. It is well known
that the behavior of coagulant may change from waste-
water to another according to many factors including
alkalinity, pH, and different constituents of wastewater
[11, 12]. Figure 1 depicts the removal efficiencies for
different coagulants. It was found that ferric chloride had
superior efficiency in removing turbidity compared with
other coagulants at the sp ecified conditions.
Final turbidity of 1.8 NTU is well below the permissi-
ble level set by governmental agencies in Yanbu Indus-
trial City (15 NTU) for such parameter. Ferrous sulfate at
these conditions increased the turbidity of the sample,
while lime has negligible effect on turbidity removal.
Figure 1. Effect of different coagulants on turbidity removal.
Alum was found to have comparable removal efficiency
to FeCl3, but the later was chosen to avoid the hazardous
effect of alum .
3.2. Effect of pH on Treatment Process
The pH value is a very important factor in the coagula-
tion process. The optimum value of pH depends essen-
tially on the properties of the water treated, type of the
coagulant used and its concentration. Abdulaziz et al. [14]
attributed the effect of pH on coagulation process as a
balance of two competitive forces; (1) forces between H+
and metal hydrolysis products for interaction with or-
ganic ligands that may be present in water, and (2) forces
between hydroxide ions and organic anions for interact-
tion with metal hydrolysis products. The effect of pH can
be explained by the study of the reactions involved with
the coagulants as depicted below [15]:
332 32
2FeCl3Ca(HCO )2Fe(OH) ()3CaCl6CO
32 3
2FeCl3Ca(OH)2Fe(OH) ()3CaCl
It is clear that the increase of the concentration of al-
kalinity will shift the reaction to the right direction
(product side), i.e. enhancing the coagulation/ floccula-
tion process. It can be depicted from Figure 2 that the
optimum initial pH for turbidity removal is 7 and 8.6
giving removal efficiencies of 95.9% and 95.2%, re-
spectively. The later pH was selected for further tests for
two reasons. First, it was the initial pH of the raw
wastewater. So, no need for adding chemicals to adjust
the pH. Second, as illustrated by Figure 3, the coagulan t
dose will lead to a decrease in pH of the solution until it
reaches an acidic value, which is not required during
coagulation. By the addition of iron chloride (FeCl36H2O)
as coagulant, the suspended negatively charged solid
particles are destabilized.
The removal of solids in water by settling or filtration
of the solid particles must be incorporated as flocks and
Copyright © 2011 SciRes. ACES
Figure 2. Effect of initial pH on turbidity removal.
Figure 3. Effect of coagulant dose on solution pH.
these flocks are formed after dosing of the coagulant.
The addition of FeCl36H2O, as coagulant, to water
will result in formation of Fe(OH)3 which dissociates to
form different positively charged ions and negatively
charged ions which are produced due to the following
hydrolysis reactions [16]:
 
 
 
2Fe4H OFe(OH)2H O
As the above reactions indicate, in addition to iron hy-
droxide, the following hydrolyses products of Fe3+ are
also formed: Fe(OH)2+, Fe(OH)2+, Fe(OH)–4. The con-
centration of each ion depends on the pH, dose concen-
tration and equilibrium constant for each reaction which
is temperature dependant. The calculated dependence of
the concentration of each hydrolysis product over wide
pH range and different dose concentrations is depicted in
Figure 4.
The results obtained indicated that the best turbidity
removal was achieved at dose concentration of 800 mg/l
and pH range between 7 and 8.6 as indicated in Figures
Figure 4. Effect of initial pH on turbidity removal.
2 and 5, respectively. By referring to Figure 4, these
operating conditions are located in the above dark rec-
tangle. In this region, large amounts of precipitated
Fe(OH)3 are formed with the absence of positively
charged particles. This is evidence that at these optimum
conditions a precipitation coagulation, or sweep coagula-
tion, is the dominant mechanism where colloids are in-
corporated into neutral (iron) hydroxide flocs.
The measurements presented in Figure 2 showed that
the pH value of water decreases by increasing the dose
concentration of FeCl36H2O.
As a result of the dosing of iron chloride, OH- ions are
removed and the pH will decrease. The magnitude of the
pH drop depends on the buffering capacity of the water.
The higher the buffering capacity, the smaller the pH
drop is. When the pH drop is too large, pH will be in-
creased by dosing a base, such as caustic soda.
It is worthy to notice that, by examining Figure 4, the
pH value influences the solid particles stabilization in
two counter currently directions. At low dosage concen-
tration, increasing the pH leads to an increase in the
negatively charged ions (stabilization effect) and a de-
crease in the concentration of the positively charged ions
(destabilization effect). The achieved maximum turbidity
removal at high dose concentration over the optimum pH
range between 7 and 9 can be explained through the en-
hancement of precipitation of Fe(OH)3. This forces the
sweep coagulation process. This process cannot occur in
strongly basic medium or strongly acidic medium.
The observed drop in turbidity removal in strongly ba-
sic medium is due to the increased concentration of the
negatively charged ions which contributes negatively in
the coagulation process by its stabilization effects.
3.3. Effect of Coagulant Dose
As illustrated by Figure 5, the highest efficiency of tur-
bidity removal to such wastewater was achieved using
800 mg/l of ferric chloride. This dose resulted in turbid-
ity removal efficiency of 97.5% equivalent to a final tur-
bidity of 2.2 NTU. This high dose can be decreased to
half its value (400 mg/l) to produce turbidity removal
Copyright © 2011 SciRes. ACES
Figure 5. Effect of Coagulant Dose on turbidity removal.
efficiency of 93% (equivalent to final turbidity of 5.9
NTU). This later value can be accepted from a pretreat-
ment process for such wastewater taking into considera-
tion it would go through more treatment processes (two
biological treatment processes followed by sand filtra-
3.4. Effect of Mixing and Settling Rates
The effect of agitation rate on the turbidity removal effi-
ciency is illustrated by Figures 6 and 7. The highest tur-
bidity removal (98.1%) was achieved at 200 rpm of rapid
mixing. However, the other rates produced comparable
results. The lowest removal efficiency was obtained at a
stirring rate of 350 rpm (95.6%). The next one was at
100 rpm (96.55%). Comparing the later value obtained at
the lowest speed with the rate that produced the highest
removal efficiency (98.1% at a rate of 200 rpm), it is
clear that the negligible difference in removal efficiency
suggests the use of the lowest velocity that will save en-
ergy. Similar results were obtained for the slow mixing
rates. All the tested rates gave comparable removal effi-
ciencies ranging from 98.2% up to 98.7%. These re-
moval efficiencies are equivalent to final turbidities less
than 2 NTU. So, the lowest velocity (45 rpm) can be
used for a slow mixing step. Figure 8 illustrates the set-
tling process after flocculation/ coagulation. The solid
volume reached a value of 13% of its initial value after
90 minutes. The sludge volume index for the produced
sludge was calculated to be 190 which is an acceptable
3.5. Effect of Temperature
The temperature of Saudi Arabia may reach 50 Degrees
Celsius. This high temperature in Saudi Arabia is very
common. The average temperature during the winter
season is roughly around 8 to 20 degrees Celsius.
However, even in the summers, the nights are really
chilly as the desert tends to become cold once the sun
Figure 6. Effect of Rate of Rabid Mixing on turbidity re-
Figure 7. Effect of Rate of slow Mixing on turbidity removal.
Figure 8. Settling rate of the sludge.
sets down. The effect of temperature on the coagulation
process was studied at three different temperatures as
illustrated by Figure 9. It is clear that the temperature
does not have a considerable effect within the studied
temperature range (13 up to 43˚C). Slight differences
were noticed due to this temperature effect. Removal
efficient obtained at room temperature 22˚C (96.3%) was
the highest compared to 95.4% and 95.8% achieved at 13
and 43˚C, respectively.
Copyright © 2011 SciRes. ACES
Figure 9. Effect of Temperature on turbidity removal.
4. Conclusions
The focus of this paper was to investigate the potential
use of coagulation-flocculation process for the removal
of turbidity from industrial wastewater influents using
aluminum sulfate and iron salts. The experiments con-
ducted confirm the significant effect of pH on coagula-
tion process.
Increasing pH form acidic range to alkaline range
promotes turbidity removal indicating the significant role
played by pH in imparting surface charge of organic and
inorganic colloids. The optimum pH for the removal of
turbidity from industrial effluents under the experimental
conditions used in this work was = 8.6.
Under optimal conditions of process parameters, a
coagulant dose of 400 mg/l was efficient to remove 93%
of the effluents’ turbidity.
Rate of mixing range used in this work showed negli-
gible differences in the turbidity removal efficiencies and
this suggests that the lowest mixing rate can be used to
save energy.
Coagulation-flocculation process has proved an effi-
cient process to remove turbidity from industrial waste-
water effluents.
5. Acknowledgement
The authors gratefully acknowledge the financial support
provided through the Planning and Development De-
partment of Yanbu I ndustrial College.
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