Slaughterhouse wastewater treatment by combined chemical coagulation and electrocoagulation process.
ABSTRACT Slaughterhouse wastewater contains various and high amounts of organic matter (e.g., proteins, blood, fat and lard). In order to produce an effluent suitable for stream discharge, chemical coagulation and electrocoagulation techniques have been particularly explored at the laboratory pilot scale for organic compounds removal from slaughterhouse effluent. The purpose of this work was to investigate the feasibility of treating cattle-slaughterhouse wastewater by combined chemical coagulation and electrocoagulation process to achieve the required standards. The influence of the operating variables such as coagulant dose, electrical potential and reaction time on the removal efficiencies of major pollutants was determined. The rate of removal of pollutants linearly increased with increasing doses of PACl and applied voltage. COD and BOD(5) removal of more than 99% was obtained by adding 100 mg/L PACl and applied voltage 40 V. The experiments demonstrated the effectiveness of chemical and electrochemical techniques for the treatment of slaughterhouse wastewaters. Consequently, combined processes are inferred to be superior to electrocoagulation alone for the removal of both organic and inorganic compounds from cattle-slaughterhouse wastewater.
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ABSTRACT: Slaughterhouse wastewater contains diluted blood, protein, fat, and suspended solids, as a result the organic and nutrient concentration in this wastewater is vary high and the residues are partially solubilized, leading to a highly contaminating effect in riverbeds and other water bodies if the same is let off untreated. The performance of a laboratory-scale Sequencing Batch Reactor (SBR) has been investigated in aerobic-anoxic sequential mode for simultaneous removal of organic carbon and nitrogen from slaughterhouse wastewater. The reactor was operated under three different variations of aerobic-anoxic sequence, namely, (4+4), (5+3), and (3+5) hr. of total react period with two different sets of influent soluble COD (SCOD) and ammonia nitrogen (NH4 (+)-N) level 1000 ± 50 mg/L, and 90 ± 10 mg/L, 1000 ± 50 mg/L and 180 ± 10 mg/L, respectively. It was observed that from 86 to 95% of SCOD removal is accomplished at the end of 8.0 hr of total react period. In case of (4+4) aerobic-anoxic operating cycle, a reasonable degree of nitrification 90.12 and 74.75% corresponding to initial NH4 (+)-N value of 96.58 and 176.85 mg/L, respectively, were achieved. The biokinetic coefficients (k, K s , Y, k d ) were also determined for performance evaluation of SBR for scaling full-scale reactor in future operation.BioMed research international. 01/2013; 2013:134872.
Slaughterhouse Wastewater Treatment by Combined
Chemical Coagulation and Electrocoagulation Process
Edris Bazrafshan1, Ferdos Kord Mostafapour1, Mehdi Farzadkia2, Kamal Aldin Ownagh1, Amir
1Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran, 2School of Public Health, Tehran University of Medical Sciences, Tehran, Iran,
3Center for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran, 4National Institute of Health Research, Tehran
University of Medical Sciences, Tehran, Iran
Slaughterhouse wastewater contains various and high amounts of organic matter (e.g., proteins, blood, fat and lard). In
order to produce an effluent suitable for stream discharge, chemical coagulation and electrocoagulation techniques have
been particularly explored at the laboratory pilot scale for organic compounds removal from slaughterhouse effluent. The
purpose of this work was to investigate the feasibility of treating cattle-slaughterhouse wastewater by combined chemical
coagulation and electrocoagulation process to achieve the required standards. The influence of the operating variables such
as coagulant dose, electrical potential and reaction time on the removal efficiencies of major pollutants was determined.
The rate of removal of pollutants linearly increased with increasing doses of PACl and applied voltage. COD and BOD5
removal of more than 99% was obtained by adding 100 mg/L PACl and applied voltage 40 V. The experiments
demonstrated the effectiveness of chemical and electrochemical techniques for the treatment of slaughterhouse
wastewaters. Consequently, combined processes are inferred to be superior to electrocoagulation alone for the removal of
both organic and inorganic compounds from cattle-slaughterhouse wastewater.
Citation: Bazrafshan E, Kord Mostafapour F, Farzadkia M, Ownagh KA, Mahvi AH (2012) Slaughterhouse Wastewater Treatment by Combined Chemical
Coagulation and Electrocoagulation Process. PLoS ONE 7(6): e40108. doi:10.1371/journal.pone.0040108
Editor: Andrew C. Marr, Queen’s University Belfast, United Kingdom
Received November 14, 2011; Accepted June 1, 2012; Published June 29, 2012
Copyright: ? 2012 Bazrafshan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The authors are grateful for the financial support of this project by the health research deputy of Zahedan University of Medical Sciences (Project No.
89-2147). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: firstname.lastname@example.org
Wastewater from a cattle slaughterhouse is a mixture of the
processing water from both the slaughtering line and the cleaning
of the guts, which causes a large variation in the concentration of
organic matter. The main pollutant in slaughterhouse effluents is
organic matter. The contributors of organic load to these effluents
are paunch, feces, fat and lard, grease, undigested food, blood,
suspended material, urine, loose meat, soluble proteins, excre-
ment, manure, grit and colloidal particles [1,2].
Untreated slaughterhouses waste entering into a municipal
sewage purification system may create severe problems, due to the
very high biological oxygen demand (BOD) and chemical oxygen
demand (COD) . Therefore treating of slaughterhouse waste-
water is very important for prevention of high organic loading to
municipal wastewater treatment plants. The most common
methods used for treating slaughterhouse wastewaters are fine
screening, sedimentation, coagulation– flocculation, trickling filters
and activated sludge processes.
The treatment of slaughterhouse wastewater by various
methods such as aerobic and anaerobic biological systems
[4,5,6,7] and hybrid systems  have been intensively studied.
Aerobic treatment processes are limited by their high energy
consumption needed for aeration and high sludge production.
Also, the anaerobic treatment of slaughterhouse wastewater is
often slowed or impaired due to the accumulation of suspended
solids and floating fats in the reactor which lead to a reduction in
the methanogenic activity and biomass wash-out. In addition, it is
also reported that anaerobic treatment is sensitive to high organic
loading rates, as a serious disadvantage . Even though biological
processes are effective and economical, both biological processes
require long hydraulic retention time and large reactor volumes,
high biomass concentration and controlling of sludge loss, to avoid
the wash-out of the sludge. Among physico-chemical processes,
dissolved air flotation (DAF) and coagulation–flocculation units
are widely used for the removal of total suspended solids (TSS),
colloids, and fats from slaughterhouse wastewaters .
Chemical coagulation of slaughterhouse wastewater has also
been studied by adding aluminum salts and polymer compounds,
and a maximum COD removal efficiency of 45–75% has been
reported [9,10]. Polyaluminum chloride (PACl) is commonly used
as the flocculant to coagulate small particles into larger flocs that
can be efficiently removed in the subsequent separation process of
sedimentation and/or filtration. Much attention has been paid to
PACl in recent years because of its higher efficiency and relatively
low costs compared with the traditional flocculants [11,12]. On
the other hand, PACl has become one of the most effective
coagulant agents in water and wastewater treatment facilities with
various applications, including removal of colloids and suspended
particles, organic matter, metal ions, phosphates, toxic metals and
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Recently, electrochemical methods such as electrooxidation
 and electrocoagulation have been widely used as an attractive
and suitable method for the treatment of various kinds of
wastewater such as poultry and cattle slaughterhouse wastewater
and wastewaters contain heavy metals, by virtue of various benefits
including environmental compatibility, adaptability, energy effi-
ciency, safety, selectivity, amenability to automation, and cost
effectiveness [15,16,17,18,19,20]. An examination of the chemical
reactions occurring in the electrocoagulation process shows that
the main reactions occurring at the electrodes (aluminum
In addition, Al3+and OH2ions generated at electrode surfaces
react in the bulk wastewater to form aluminum hydroxide:
The aluminum hydroxide flocs normally have large surface
areas which are beneficial for a rapid adsorption of soluble organic
compounds and trapping of colloidal particles [15,16,21]. Also,
these flocs polymerize further and are removed easily from
aqueous medium by sedimentation or/and flotation by hydrogen
Chemical coagulation using PACl and electrocoagulation
process with aluminum electrodes of wastewater from a cattle
slaughterhouse is described in this article. The purpose of this work
was to investigate the feasibility of treating cattle-slaughterhouse
wastewater by combined chemical coagulation and electrocoagu-
lation process separately to achieve the required legal direct-
discharge limit of COD and BOD5which is 60 and 30 mg/L in
Iran for the slaughterhouse industry effluents. The influence of the
operating variables such as coagulant dose, pH, applied voltage
and reaction time on the removal efficiencies of major pollutants
was also determined. Information regarding the electrical energy
consumption (EEC) is also included to provide an estimation of the
cost of pollutants removal by an electrocoagulation system.
Results and Discussion
Table 1 presents the slaughterhouse wastewater characteristics
prior to any treatment, after 24 h settling time and the guidelines
from Iran for effluent discharge in the sewage urban works. The
values of the pollution parameters were lowered after 24 h of
preliminary settling time. Also, the comparison of these values
showed that, the COD, BOD5,microbial indicators (Total and
Fecal Coliforms) and the concentration of Oil and grease were
very greater than those recommended by Iran. Consequently, the
slaughterhouse effluent needed to be treated before discharge.
Table 1. Characteristics of the experimental cattle slaughterhouse wastewater.
Mean ± S.D.
24 h settled wastewater
Mean ± S.D.
Permissive levels (Iran Standard
to surface waters)
Number of samples 4848–
Total COD (mg/L) 581764734159628160
Total BOD (mg/L)254363622204617730
Total Suspended Solids
Total Kjeldhal Nitrogen
Fat, oil, grease (mg/L)3469 3267 10
Figure 1. Effects of coagulant dose (PACl) on pollutants
removal efficiency at pilot scale coagulation process.
Slaughterhouse Wastewater Treatment
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Effect of preliminary settling time
Preliminary settling process is a natural treatment method that
requires no chemical addition. Although some workers realized the
importance of the natural settling process, there is little informa-
tion available in the literature on the effect of the preliminary
settling time on TSS removal capacity . Most studies carried
out on the treatment of slaughterhouse wastewater were based on
diluted pre-settled wastewater .
In this study, the raw slaughterhouse wastewater was allowed to
settle for 24 h in a preliminary settling tank before the addition of
a coagulant. The process had an effect on BOD5, COD, TSS,
TKN and coliform bacteria removals on the first 24 h. TKN
concentration reduced from 137612 to 92612 mg/L (on average
33% TKN removal efficiency), COD concentration reduced from
58176473 to 41596281 mg/L (approximately 28% COD
removal efficiency) whereas BOD5was reduced in the wastewater
from 25436362 to 22046177 mg/L (about 13% BOD5removal
efficiency). Furthermore, TSS concentration was reduced to
1172684 mg/L (approximately 64% TSS removal efficiency).
Similar results were reported by Amuda and Alade .
Also, data revealed that the effluent of the settling unit is
characterized by high load of organic matter. The ratio BOD5/
COD of approximately 0.5, indicates that 50% of the COD of this
wastewater is easily able to be degraded by biological treatment.
Nevertheless, the remainder COD is high, which indicates the
necessity of an efficient physicochemical treatment for this
Effect of coagulation process (first step)
Coagulation/flocculation experiments using PACl as coagulant
in the jar test were performed to investigate the effect of
coagulation process in the removal efficiencies of COD, BOD5,
TSS, TKN and coliform bacteria. Therefore, PACl was added to
the slaughterhouse wastewater to achieve particle instability and
increase in the particle size, consequently achieving effective
removal of organic substances present as COD and BOD5. The
doses of PACl as coagulant were varied between 0 and 100 mg/L
to determine the optimum dose of PACl for pollutants removal.
The results of jar-tests using the PACl individually are presented in
Table 2 and Figure 1. It is shown that at lower doses of the PACl
(25 mg/L), COD, BOD5, TSS and TKN removal efficiency
reached a maximum of 37%, 31%, 47% and 27%, respectively.
Aguilar et al.  reported TKN removal efficiency 50–60% by
using PACl as coagulant from slaughterhouse wastewater. Also,
Amuda and Alade  were reported maximum removal
efficiency 65% and 34% of COD and TSS using a 750 mg/L
dose of alum as coagulant in abattoir wastewater treatment.
As it shown in Figure 1, the efficiency of the process increased
with increasing dosages of coagulant (PACl). The curve obtained
with PACl points to a considerable increase in performance from
the lowest dose up to 100 mg/L. On the other hand in chemical
coagulation, as seen in Figure 1, an increase in COD, BOD5, TSS,
TKN and other pollutants removal efficiency is noted with
increasing PACl dosage, reaching nearly 40–60% for PACl dosage
of 100 mg/L. Al-Mutairi et al.  reported that suspended solids
and turbidity removal from slaughterhouse wastewater increased
substantially as the alum (as coagulant) dosage is increased. Also,
Table 2. Influence of PACl dosage on water quality parameters of coagulated mixed liquor (mean values).
Water quality parameters of treated effluent after chemical coagulation unit
COD (mg/L)BOD5(mg/L)TSS (mg/L)TKN (mg/L)TC (MPN/100mL) FC (MPN/100mL)
0 415922041172 1922.36109
252643 1534 6231392.86107
502228 1418 544130 1.66107
10017251217 470 116 1.66106
Figure 2. Effect of applied voltage on pollutants removal
efficiency (coagulant dose: 25 mg/L, reaction time: 60 min).
Figure 3. Effect of applied voltage on pollutants removal
efficiency (coagulant dose: 50 mg/L, reaction time: 60 min).
Slaughterhouse Wastewater Treatment
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Figure 1 shows that the TSS removal and COD and BOD5
reduction trends are similar to each other. This may be due to the
high organic contents of the suspended solid particles.
Maximum TC and FC removal efficiency of .99.9% (Table 2)
were obtained by using PACl at the dosage of 100 mg/L. The TC
and FC reduction, increase with increase in coagulant dosage.
TC indicator of effluent with coagulant dose 25 mg/L PACl was
reduced from 2.36109to 2.86107(MPN/100mL) (approximately
more than 98% TC removal efficiency), and by increasing the
coagulant dose to 100 mg/L, the TC indicator of effluent was
decreased was reduced from 1.76108to 1.66106(MPN/100mL)
(on average more than 99% TC removal efficiency) that is much
more than permissible level. A similar reduction trend was
determined for FC indicator. Similar results were obtained in
previous reports concerning the electrocoagulation of wastewater
from vegetable oil refinery wastewater using aluminum electrodes
(with adding PACl as coagulant aid) .
According the results of this study (Table 2) it can be concluded
that although the efficiency for removal of most parameters from
slaughterhouse wastewater are high, but the concentration of
pollutants in effluent of chemical coagulation process does not
meet the effluent discharge standards to the environment. Thus,
the effluent from conventional coagulation should be preceded by
another treatment process to be completed. For this purpose, in
this research, electrocoagulation was employed as a completion of
treatment process to obtain discharge standards.
Effect of electrocoagulation process (second step)
Electrocoagulation processes a direct current source between
metal electrodes immersed in wastewater. The electrical current
causes the dissolution of metal electrodes commonly iron and
aluminum into wastewater. The dissolved metal ions, at an
appropriate pH, can form wide ranges of coagulated species and
metal hydroxides that destabilize and aggregate the suspended
particles or precipitate and adsorb dissolved contaminants [25,26].
As be mentioned earlier, an examination of the chemical
reactions occurring in the electrocoagulation process shows that
the main reactions occurring at the aluminum electrodes are:
monomeric species such as Al(OH)2+, Al(OH)2+, Al2(OH)24+,
Al7(OH)174+, Al8(OH)204+, Al13O4(OH)247+, Al13(OH)345+are
formed during the electrocoagulation process [26,27]. The
aluminum hydroxide flocs act as adsorbents and/or traps for
pollutants and so eliminate them from the solution [28,29].
As mentioned earlier, the performances by the two pretreat-
ment, namely, preliminary settling and chemical coagulation, were
not carried out efficiently enough to satisfy the national guideline
of effluent qualities. Additional dosage of coagulant (PACl) and
longer time were needed to keep the national guideline of the
effluent qualities. Therefore, the electrocoagulation process was
employed as the final treatment step in this study. In adopting the
electrocoagulation process, it was intended to treat the pollutant
efficiently as well as economically.
The effects of applied voltage and reaction time on electroco-
agulation process of slaughterhouse wastewater treatment were
determined. The results of the effects of operating parameters on
pilot scale electrocoagulation process are shown in Table 3 and
Figures 2, 3, 4, and 5.
Effect of applied voltage
One of the most important parameter influencing the perfor-
mance and economy of the electrocoagulation process is the
applied voltage at the electrodes . To understand the effect of
applied voltage on the efficiency of electrocoagulation process in
treating of slaughterhouse wastewater, several voltages in the range
of 10 to 40 V were applied between the electrodes in the
electrocoagulation cell, and pollutants removal was determined at
the conditions given in Table 3.
The applied voltage is expected to exhibit a strong effect on
electrocoagulation, especially on the COD abatement: higher the
current (voltage), shorter the treatment. The supply of current to
the electrocoagulation system determines the amount of Al3+ion
released from the respective electrodes and the amount of resulting
coagulant. Thus, more Al3+ion get dissolved into the solution and
the formation rate of Al(OH)3is increased. Also, it is well-known
that electrical potential not only determines the coagulant dosage
rate but also the bubble production rate and size and the flocs
growth [31,32], which can influence the treatment efficiency of the
Figure 4. Effect of applied voltage on pollutants removal
efficiency (coagulant dose: 75 mg/L, reaction time: 60 min).
Figure 5. Effect of applied voltage on pollutants removal
efficiency (coagulant dose: 100 mg/L, reaction time: 60 min).
Slaughterhouse Wastewater Treatment
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As it can be seen from Table 3 and Figures 2, 3, 4, and 5, the
removal efficiency of pollutants is very high and as expected, it
appears that for a given time, the removal efficiency increased
significantly with increase of electrical potential. As the results
shown in Table 3 and Figures 2, 3, 4, and 5, the removal
efficiencies increased as the electrical potentials are increased. As
an example, COD concentration of chemical coagulation process
with 25 mg/L PACl has decreased from 2643 to 555 mg/L
(approximately 79% COD removal efficiency) after electrocoag-
ulation process with electrical potential of 10 V. Again, by
increasing electrical potential to 40 V, the COD concentration
in the effluent decreased to 108 mg/L in 60 min (approximately
96% COD removal efficiency). In addition, the COD of effluent
from chemical coagulation with 100 mg/L PACl, was decreased
to about 294 mg/L (approximately 83% COD removal efficiency)
by electrocoagulation process with electrical potential of 10 V, and
by increasing the electrical potential to 40 V, the COD of effluent
was decreased to less than 13 mg/L (on average more than 99%
COD removal efficiency) that is lower than permissible level.
According to the results of Table 3, and Figures 2, 3, 4, and 5,
TKN of chemical coagulation process with 25 mg/L PACl was
reduced to lower than 50 mg/L after electrocoagulation process
with electrical potential of 10 V (approximately 65% TKN
removal efficiency), and by increasing electrical potential to
40 V, the TKN concentration in the effluent decreased to
26 mg/L (about 81% TKN removal efficiency). Furthermore,
with increase in coagulant dose to 100 mg/L and increase of
applied voltage to 40 V, TKN concentration in effluent was
Table 3. Influence of electrocoagulation process using aluminum electrodes on effluent quality parameters (mean values).
Water quality parameters of treated effluent after electrocoagulation unit
2510 555 409331 49 67431274
20 267 223282 40 6437814
40 10879 245264139 634
50 10 452332270 416274 1347
20283218221 345712 712
30145 108 20928 4831 643
40 2921 156214376 473
75 10376 316 241395712 785
20 225174 210314833531
309674 14923 3157 375
401813 111152563 114
10010 294254199343652 437
20 153 125 153262715 364
305933 118 17 1864 153
401310 827 943 72
Figure 6. Electrical energy consumption during coagulation-
electrocoagulation process (kWh/L).
Figure 7. Electrode consumption during chemical coagulation-
Slaughterhouse Wastewater Treatment
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reduced to lower than 7 mg/L (on average 94% TKN removal
efficiency). A similar trend was seen for TSS and BOD5
Also, as can be seen from Table 3, the removal efficiency of
bacterial indicators (TC and FC) is very high and efficiency was
increased with increase in applied voltage from 10 to 40 V.
Maximum removal efficiency (.99.9%) was obtained in applied
voltage 40 V (coagulant dosage 100 mg/L), and thus the effluent
quality was reached to permissive levels (lower than 1000 and 400
for TC and FC, respectively) and hence discharge of this effluent
to environment is safe. Also, minimum removal efficiency
occurred in the lowest electrical potential (10 V). This is ascribed
to the fact that at high voltage, the amount of aluminum oxidized
increased, resulting in a greater amount of precipitate for the
removal of pollutants. In addition, it was demonstrated that
bubbles density increases and their size decreases with increasing
current density , resulting in a greater upwards flux and a
faster removal of pollutants and sludge flotation. As be mentioned
earlier, the main mechanisms for removal of pollutants in this
process are rapid adsorption of soluble organic compounds and
trapping of colloidal particles in ‘‘sweep flocs’’ (Al(OH)3).
Nevertheless, Bayar et al.  was reported that increase in the
current density does not cause an expected removal efficiency
increase; on the contrary, it can cause a relatively negative effect
on it. Also, a similar trend was seen in the study of Holt et al. .
Electrical energy and electrode consumption
Electrical energy consumption is a very important economical
parameter in the electrocoagulation process. Therefore, for the
same operating conditions, after 60 min of electrocoagulation,
consumption of energy and aluminum electrode is also represented
in Figures 6 and 7. The electrical energy consumption was
calculated using the related equations .
It can be understood from Figures 6 and 7 that electrical energy
and electrode consumption were found to increase with increasing
the applied voltage as would be expected in any other electrolytic
process. An increase in applied voltage from 10 to 40 V causes an
increase in energy consumption from about 0.001 to 0.08 kWh/L
and from 0.011 to approximately 0.09 kWh/L for 25 and
100 mg/L of coagulant dosage (PACl), respectively. A similar
trend was seen in the study of Bayar et al.  on Poultry
slaughterhouse wastewater treatment by electrocoagulation meth-
Also, as shown in Figure 7, an increase in applied voltage from
10 to 40 V causes an increase in electrode consumption from
about 0.41 to 1.23 g/L and 0.51 to 1.3 g/L of pollutants for 25
and 100 mg/L of PACl, respectively. This result is in agreement
with the results obtained by Bazrafshan et al. [36,37,38].
When the applied voltage was increased from 10 V to 40 V, the
COD and BOD5 removal efficiency increased appreciably, to
more than approximately 99%, whereas the corresponding specific
energy consumption increased only slightly. Therefore, in present
study, 40 V is chosen as optimum operating voltage for
In this study, chemical coagulation using Polyaluminum
chloride (PACl) and Electrocoagulation process using aluminum
electrodes of wastewater from a cattle slaughterhouse was
investigated. The effects of the different operational parameters
on the removal of pollutants analyzed. The following conclusions
can be reached from the results obtained in this work:
– The installation of a good fat separator prior to each biological
or chemical treatment unit seemed an appropriate alternative
to a chemical coagulation and electrocoagulation process.
– Preliminary settling time were investigated and found to be
important operational parameter for effective treatment of
– A preliminary settling time of 24 h had an effect on the BOD5,
COD, TSS and TKN with removal efficiency up to 14%, 29%,
64% and 33%, respectively.
– According to the results obtained from the present experi-
ments, the removal efficiencies increased by increasing the
coagulant dose and electrical potential. At the highest applied
voltage, the fastest treatment rate for pollutants (COD, BOD5,
TSS, TKN and microbial parameters) removal was obtained.
Moreover, the energy consumption increased by increasing the
applied electrical potential.
Figure 8. The schematic view of coagulation and electrocoagulation reactor.
Slaughterhouse Wastewater Treatment
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– Evaluation of the experimental results indicates that both
processes (chemical coagulation and Electrocoagulation) show
excellent efficiency at reducing of pollutants.
– Based on this study results, although the coagulation process
had high efficiency in removing organic and microbial
contaminants, but nevertheless it’s not able to meet discharge
standards, hence a supplemental process (such as electrocoag-
ulation process) is essential for enhance effluent quality.
– Finally according to the results of this study, it can be
concluded that the combined application of chemical coagu-
lation and electrocoagulation processes is able to meet effluent
standards for safe discharge to environment.
Materials and Methods
The effluent used throughout this study was taken from a local
cattle Slaughterhouse plant with 250 cows per day capacity,
located in Zahedan City in the province of Sistan and Baluchestan
province (Iran), producing approximately 60 m3of wastewater
daily. The cattle slaughterhouse effluent was sampled after the
screening of coarser solids using a filter having a pore size of
approximately 2.0 mm and sedimentation for 24 h. Samples were
collected in polypropylene bottles, shipped cold, and kept at 4uC
before use. The length of the storage before starting experiments
varied from one day to six weeks. The effluent has been sampled at
different times during this study and the initial characteristics
varied with time (Table 1). This effluent initially contained high
concentrations of soluble and undissolved organics (4159681 mg/
L COD, 2204677 mg/L BOD5).
Chemical treatment (coagulation) of slaughterhouse
All the chemicals used in the study were of analytical reagent
(AR) grade. Poly- aluminum chloride (PACl) Al12Cl12(OH)24was
chosen for this study because it has been used extensively at water
and wastewater treatment plants to remove solids and may
function as an effective and less expensive coagulant. PACl was
used in this study up to 100 mg/L (25, 50, 75 and 100 mg/L). A
six-beaker jar test (flocculator) was set up at room temperature for
each trial. Each of the beakers contained 2 L of settled wastewater.
The coagulants were added into the beakers, and the pH values
were immediately adjusted to the preset values (760.1) using
NaOH or H2SO4for pH-controlled experiments. Rapid stirring at
150 rpm for 2 min was followed by gentle mixing at 50 rpm for
20 min, and the solids formed were left to settle for 30 min.
Samples were taken from the water surface (supernatant) and
filtered through 0.45-mm membranes. After chemical coagulation,
electrocoagulation process with aluminum electrodes was per-
formed on the supernatant.
Electrochemical treatment of slaughterhouse effluent
In each run, wastewater (supernatant) after chemical coagula-
tion (first stage of treatment) was poured into the electrocoagu-
lation cell. All experiments were performed in a bipolar batch
reactor (Figure 8), with four aluminum electrode connected in
parallel. Only the outer electrodes were connected to the power
source, and anodic and cathodic reactions occurred on each
surface of the inner electrode when the current passed through the
15 Cm615 Cm625 Cm (width 6 length 6 depth) with an
effective volume of 2000 Cm3. The volume (V) of the solution of
each batch was 2 L. The active area of each electrode (plate) was
14620 Cm with a total area of 280 Cm2. The distance between
electrodes was 1.5 Cm. A power supply having an input of 220 V
and variable output of 0–40 V (10, 20, 30 and 40 V) with
maximum current of 5 ampere was used as direct current source.
The temperature of each system was maintained at 2561uC.
Different samples of 100 ml were taken at 15 min intervals for up
to 1 h and filtered before being analysed to determine BOD5,
COD, TSS and other parameters. During the runs, the reactor
unit was stirred at 150 rpm by a magnetic stirrer to allow the
chemical precipitate to grow large enough for removal. During
electrocoagulation, an oxide film formed at the anode. In order to
overcome electrode passivation at the anode, the electrodes were
rinsed in diluted HCl solution (5% v/v) after each experiment and
rinsed again with tap water and finally weighted. Also the
electrodes reweighted to calculate sacrificial electrode consump-
tions. These weights are used in the calculations of the total
operating cost. In addition, the electrical energy consumed per
unit volume of treated wastewater has been calculated for different
experimental conditions. All analyses were conducted in duplicate
for reproducibility of the experimental results, and all of the data
in the Figures and Tables were the average ones.
COD, BOD5, oil-grease, conductivity, pH, total solids (TS),
total suspended solids (TSS), and total Kjeldhal nitrogen (TKN)
determinations were determined according to the standard
methods . COD was measured using COD reactor and direct
reading spectrophotometer (DR/5000, HACH, USA). Five-day
biological oxygen demand (BOD5) was determined by the
manometric method with a respirometer (BSB-Controller Model
620 T (WTW)). Oil-grease was determined with hexane extrac-
tion. The pH and conductivity were adjusted to a desirable value
using NaOH or H2SO4, and NaCl, and measured using a pH
meter model E520 (Metrohm Herisau, Switzerland) and a
Conductivity Meter (Jenway Model 4200), respectively. Also the
most-probable-number technique was used for the enumeration of
total coliform (TC) and fecal coliform (FC) bacteria .
E. Bazrafshan gratefully acknowledges helpful comment from Dr. M.A.
Conceived and designed the experiments: EB AHM. Performed the
experiments: EB KAO. Analyzed the data: MF. Contributed reagents/
materials/analysis tools: FKM. Wrote the paper: EB AHM.
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