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LSST #1494744, VOL 00, ISS 00
Electrocoagulation/electroflotation of real printing wastewater using copperelectrodes: A comparative study with aluminum electrodesSafwat M. Safwat, Ahmed Hamed, and Ehab Rozaik
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Electrocoagulation/electroflotation of real printing wastewater using copper electrodes: A comparative study with aluminumelectrodesSafwat M. Safwat, Ahmed Hamed, and Ehab Rozaik
Electrocoagulation/electroflotation of real printing wastewater using copperelectrodes: A comparative study with aluminum electrodesSafwat M. Safwata, Ahmed Hamedb, and Ehab Rozaika
aSanitary & Environmental Engineering Division, Faculty of Engineering, Cairo University, Giza, Egypt; bPurchasing & Procurement5 Department, Rowad Modern Engineering, Cairo, EgyptQ1
ABSTRACTMost studies investigated electrocoagulation/electroflotation process (EC/EF) using either alumi-num or iron electrodes. The main aim of this study is to investigate the performance of EC/EF totreat printing wastewater under various experimental conditions using copper electrodes. The
10 effects of several variables, including different electrode materials (copper and aluminum), differ-ent current densities, electrolysis time, and spacing between electrodes on the removal efficiencyof various parameters were investigated. The results showed that the maximum removal efficien-cies for COD,TDS, and oil and grease were obtained when using a copper electrode. Themaximum removal efficiencies were obtained at a gap distance of 4 cm.
ARTICLE HISTORYReceived 27 April 2018Accepted 26 June 2018
KEYWORDSElectrocoagulation;electroflotation; copper;aluminum; wastewater
15 1. Introduction
Printing processes are used for several applicationssuch as printing books and newspapers, clothing, cir-cuit boards, and electrical appliances. Wastewater fromprinting can cause environmental risks due to the high
20 chemical oxygen demand (COD).[1Q2] Chemical coagula-
tion and biodegradation are among the conventionalprocesses used for treatment of printing wastewater.[2,3]
For chemical coagulation, large amounts of sludge willbe generated. Treatment of the sludge is expensive, and
25 secondary pollution may occur if it is not handledproperly.[1] Regarding the biodegradation treatment,microbial activity may be inhibited due to the presenceof toxic pollutants in the printing wastewater.[1,4,5]
Consequently, it is essential to treat printing wastewater30 through an innovative and efficient treatment
technology.Electrochemical wastewater treatment technologies
such as electrocoagulation, electro-oxidation, and elec-troflotation are found to be promising technologies for
35 wastewater treatment.[6,7] These technologies are envir-onmentally friendly options that produce low amountsof sludge, do not require chemical additives, and have aminimal footprint.[8,9] Electrocoagulation and electro-flotation can be a substitute for conventional coagula-
40 tion and flotation, respectively, in wastewater treatmentplants.[10] In electrocoagulation/electroflotation pro-cess, sacrificial anodes, such as aluminum, dissolve
due to an applied current, thus producing active coa-gulant compounds.[10] This technology combines the
45benefits of coagulation, flotation, and electrochemistry.-[8] Electrocoagulation/electroflotation (EC/EF) offersmany advantages over traditional coagulation/floccula-tion, such as higher efficiency, shorter retention time,prevention of secondary pollution caused by added
50chemicals, and simple operation.[11,12] Coagulation/flocculation uses chemical coagulants/flocculants suchas metal salts or polyelectrolytes, while EC/EF generatescoagulants in situ through electrolytic oxidation of asacrificial anode material which results in much less
55sludge production.[8] The theories behind coagulation/flocculation and EC/EF are basically the same.[13] Bothmethods remove particles from wastewater by destabi-lizing repulsive forces that keep the particles suspendedin water.[8] When the repulsive forces are destabilized,
60the suspended particles will form larger particles calledflocs that can settle.[8] In EC/EF, a direct current (DC)voltage is applied to an electrochemical cell with anodeand cathode metal electrodes, immersed in wastewateras the electrolyte.[12] There are three main processes
65that happen during the electrocoagulation/electroflota-tion process: (i) oxidation of the anode, (ii) generationof gas bubbles at the cathode, and (iii) flotation andsedimentation of the flocs formed.[14] When a currentis applied to the process, oxidation reactions take place
70on the sacrificial anode producing cations, and reduc-tion reactions that occur on the cathode.[11] Those
CONTACT Safwat M. Safwat [email protected] versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsst.
SEPARATION SCIENCE AND TECHNOLOGY2018, VOL. 00, NO. 00, 1–12https://doi.org/10.1080/01496395.2018.1494744
© 2018 Taylor & Francis
cations form metal hydroxides in aqueous media.[11]
Metal hydroxide species provide effective destabiliza-tion of suspended solids. At the cathode, hydrogen gas
75 is continuously generated. Flocculated particles areformed and pollutants are removed with the aid ofscouring and floating.[12] The removal mechanismcould be via adsorption, charge neutralization, orsweep coagulation.[11,15] In the EC/EF process, the elec-
80 trochemical reactions with metal M as electrodes are asfollows [10]:
At the anode : M ! Mnþ þ ne�; for coagulation
At the cathode : 2H2Oþ 2e�
! H2 þ 2OH�; for flotation
Various types of wastewater have been successfullytreated using EC/EF.[16,17] Previous studies haveshown that EC/EF is a successful treatment process
85 for treatment of industrial wastewater, especially thoseof high strength and toxic materials.[18,19] Onestudy showed that over 97% of heavy metal ions frommetal plating wastewater were removed usingelectrocoagulation.[20] Another study showed that the
90 maximum efficiencies of phenol removal from aqueoussolutions with aluminum and iron electrodes were94.72% and 98.0%, respectively.[21] Removal of phenolfrom oil refinery wastewater was also investigated usingelectrocoagulation with an aluminum screen anode,
95 and the removal efficiency of phenol reached 97%.[22]
In a study investigating the treatment of paper milleffluents using electrocoagulation, the removal efficien-cies using an aluminum electrode were 70% of bio-chemical oxygen demand, 98% of phenol, and 75% of
100 the COD after 7.5 min. While using an iron electrode,the removal efficiencies were 80%, 93%, and 55%,respectively.[23] During treatment of poultry slaughter-house wastewater by electrocoagulation, the removal ofthe COD reached 93% with aluminum electrodes, while
105 the maximum removal of oil and grease obtained was98% with iron electrodes.[24] Treatment of olive oilmill wastewater was also studied using electrocoagula-tion. Under a 30-min retention time, the removal effi-ciency of the COD was 52% and 42% when using
110 aluminum anode and iron anode, respectively.[25]
Electrocoagulation was used to investigate the removalof polycyclic aromatic hydrocarbons in a paper-makingwastewater, and the results showed that the processeffectively removed a total of 86% of polycyclic aro-
115 matic hydrocarbons by mass in the effluent.[26]
Moreover, the electrocoagulation process was able totreat fluoride by reducing its concentration from theinitial 6.0 mg/L to lower than 0.5 mg/L.[27] A group ofresearchers used electrocoagulation to treat baker’s
120yeast production wastewater. The results showed thatthe maximum removal efficiencies of the COD, totalorganic carbon, and turbidity under optimal operatingconditions were 71%, 53%, and 90% for the aluminumelectrode and 69%, 52%, and 56% for the iron electrode,
125respectively.[28] The EC/EF can be used as a pre-treat-ment step to reduce the contaminant loads of highstrength industrial wastewater, such as printing waste-water, prior to the following treatment steps.[8] It isworth noting that most studies investigated EC/EF
130using either aluminum electrodes or iron electrodes asthe sacrificial anode. Since other types of electrodes,such as copper electrodes, showed promising resultswhen used in EC/EF, it is essential to investigate thesetypes with real wastewater to show their performance
135compared to the most widely used electrodes (alumi-num or iron).[29–31] To the best of authors’ knowledge,EC/EF using a copper electrode has not been investi-gated yet in the treatment of printing wastewater.Hence using EC/EF process with copper electrodes
140can be regarded as a new and potential method fortreatment of printing wastewater. The main aim ofthis study is to investigate the performance of the EC/EF process using copper electrodes in batch operatingmode to treat real printing wastewater under various
145experimental conditions using copper electrodes. Theconfiguration of EC/EF process used in this study is thesimplest type mentioned in literature. The effects of theoperating variables, including different electrode mate-rials (copper and aluminum), different current densities
150(CDs), electrolysis time, and spacing between electro-des, on the removal efficiency of several parameterswere examined. These parameters were COD, totaldissolved solids (TDS), and oil and grease. The energyconsumption for the electrocoagulation cell was also
155calculated in this work.
2. Materials and methods
2.1. Characteristics of real printing wastewater
The wastewater used in this study was collected fromthe printing industry in Egypt. The characteristics of
160wastewater are shown in Table 1.
Table 1. Characteristics of wastewater.Parameter Unit Value
pH - 6.8COD mg/l 7150TDS mg/l 6800Total suspended solids (TSS) mg/l 72.5Oil and grease mg/l 385Color - Yellowish
2 S. M. SAFWAT ET AL.
2.2. Electrocoagulation system setup
The EC/EF unit is shown in Figure 1. Batch experi-ments were performed under a constant temperatureof 20°C ± 2°C for 90 min. The EC/EF unit consists
165 of an electrochemical reactor which was a one-literglass beaker with magnetic stirring. The unit con-tained two parallel electrodes connected externallyto a DC power supply. The cathode electrode wasstainless steel, and the anode electrode was either
170 copper (Cu) or aluminum (Al). The submerged sur-face area of each electrode was 28 cm2. The gapbetween the electrodes was 4 cm, but some experi-ments have been performed with 2 and 6 cm gaps.The stirring speed was kept low (100 rpm) to avoid
175 shearing of the flocs.[32] The electrolysis time wasmaintained in the range of 5– 90 min. Four CDs; 7,14, 21 and 28 mA/cm2, were examined. An ammeterand voltmeter were used to check the current inten-sity and the voltage during the EC/EF process.
180 Samples were periodically withdrawn then filteredto eliminate sludge formed during electrolysis forfurther analysis.
2.3. Analysis
Influent and effluent samples were collected for analy-185 sis. In addition, COD, TSS, and oil and grease were
measured according to the standard methods.[33] TheTDS and pH were measured using a multi-meter. Thepollutant removal efficiency (%) after treatment wascalculated using the following formula:
Removal efficiencyð%Þ ¼ ðC0 � CeÞ=C0 � 100
190 where Co and Ce are the influent and effluent con-centrations of pollutants, respectively. The sludgegenerated during the EC/EF process was analyzedusing a Fourier transform infrared (FTIR) spectro-meter. The morphologies of the anode electrodes
195were investigated using scanning electron micro-scopy (SEM). Chemical coagulation tests were con-ducted using the jar test. Copper sulfate andaluminum sulfate (Loba Chemie, India) were usedas coagulants to simulate copper and aluminum
200electrodes. Experiments of conventional coagulationincluded flash mixing for 1.5 min at 100 rpm andslow mixing for 20 min at 30 rpm, followed by a20 min settling period, after which the samples werecollected for further analysis.[34] All chemicals were
205of analytical grade. All experiments were run induplicate, and the results were reported as the aver-age of the measurements.
3. Results and discussion
3.1. Effect of current density on EC/EF
210In the EC/EF process, a CD that determines the rateof hydrogen bubble formation and the growth offlocs was applied between the two electrodes topromote the dissolution of the electrodes to formcoagulant species.[35] The effect of the CD was ana-
215lyzed for copper and aluminum electrodes between7 and 28 mA/cm2. Figures 2 and 3 show the removalefficiencies of the COD and TDS, respectively. Ascan be observed, the rate of removal of the COD forall CDs increased rapidly during the first 10 min.
220Then, the rate of removal efficiency of the CODdecreased due to the desorption phenomenon.[19]
Furthermore, oxidation reactions that promotedthe corrosion phenomena might lead to the forma-tion of stable oxide layers on the surface of anode
225electrodes. These layers caused passivation effects,so decreased the efficiency of EC/EF cell.[36] Themaximum values of the COD removal efficienciesafter 10 min were 60% and 49% for copper andaluminum electrode, respectively. The maximum
230values of the COD removal efficiency after 90 minwhen using copper electrode was around 67% andobtained at a CD of 28 mA/cm2. For the aluminumelectrode, the maximum value of the COD removalefficiency after 90 min was 55% and obtained at CD
235of 21 mA/cm2. At a CD of 28 mA/cm2, the removalefficiency of the COD was higher during the entireperiod when using the copper electrode, while theremoval efficiencies of the COD for CDs of 14 mA/cm2 and 21 mA/cm2 were very close.
240For the TDS removal efficiency, the performanceof the copper electrode was better than that of thealuminum electrode for all CDs. The maximumremoval efficiencies of the TDS after 90 min were24% and 7% for copper and aluminum electrodes,Figure 1. EC/EF unit.
SEPARATION SCIENCE AND TECHNOLOGY 3
245 respectively. During the EC/EF process, the waste-water remains yellowish in color when using thealuminum electrode, while the color changed fromyellowish to blue when using the copper electrode.The blue color was due to the dissociation of copper
250 into the wastewater. The number of ions released asCu2+ or Al3+ depends on the applied CD and deter-mines the amount of the resulting coagulant.Consequently, the rate of formation of metal hydro-xide increased as the amount of metal ions that
255 dissolved into the wastewater increased. Thisincreased the removal efficiencies of both the CODand TDS. Moreover, adsorption of pollutantsoccurred on the surface of metal oxides, hydroxides,and oxyhydroxides.[3,37] The reduction of pollutants
260 could also be due to the destabilization mechanismthat comprises three main steps: compression of thedouble layer, followed by charge neutralization, then
floc formation.[37] Moreover, the increase of CD ledto an increase in the generation of hydrogen bubbles
265and a decrease in their sizes. This results in theremoval of pollutants through flotation. In the caseof the aluminum electrode, the maximum removalefficiency of the COD was not obtained at the max-imum CD used. This might be because higher CDs
270increase the turbulence in the system. Increasing theturbulence can affect the coagulation processbecause the particles will not have enough time toagglomerate and remove the pollutants.
Figure 4 shows the change of pH values over time.275The pH increased for all values of CDs over time. This
might be due to the reactions occurring at the cathode.During the EC/EF process, water molecules receiveelectrons and dissociate into hydrogen bubbles andhydroxyl ions, causing an increase in pH values. The
280increase of pH values in the case of the copper
ab
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Figure 2. COD removal efficiencies over time at various current densities: a) Cu electrode, b) Al electrode.
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14 mA/cm2 7 mA/cm2
a b
Figure 3. TDS removal efficiencies over time at various current densities: a) Cu electrode, b) Al electrode.
4 S. M. SAFWAT ET AL.
electrode was more than those for the aluminum elec-trode for all CDs. This indicates that the amount ofdissociation of water molecules in the case of copperelectrode was more than that for the aluminum elec-
285 trode. The higher pH values were obtained for bothtypes of anodes at the higher CDs (21 and 28 mA/cm2),and this is because at high CDs, corrosion of the cath-ode occurs due to the intensive production of hydro-xide anions.[32] Copper is dissolved to produce divalent
290 ions Cu2+ ions, forming copper hydroxide, which ther-modynamically forms at 7.7.[38] For pH values between4 and 9.5, Al(OH)3 (s) predominates.[8] The increase inpH values during EC/EF process favors the formationof these hydroxides. These hydroxides trap the colloids/
295 pollutants in a sweep coagulation manner as they pre-cipitate leading to a higher COD removal.[12]
Figures 5 and 6 show the effluent TSS and oil andgrease when using copper and aluminum electrodes atdifferent CDs. The copper electrode provides the best
300removal efficiency for oil and grease. For oil and grease,intensive fine hydrogen bubbles were formed at a CDof 21 mA/cm2, which adhered to the oil droplets andraised them to the surface the of solution in a sweepingaction called sweep flocculation, as shown in
305Figure 7.[39] The number of flocs formed with thecopper electrode was more than that of the aluminumelectrode at all CDs, leading to more TSS in the effluentfor the copper electrode. Since a high removal of pol-lutants occurred at a CD of 21 mA/cm2, the next
310experiments for both types of electrodes were per-formed at this value of CD.
3.2. Effect of spacing between electrodes
It is known that the gap distance between electrodesaffects the ohmic potential of the EC/EF cell and the
315energy consumption.[9] The effects of spacingbetween electrodes were investigated at a CD of21 mA/cm2. Figures 8 and 9 show the removal
a b
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Time (min)
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14 mA/cm2 7 mA/cm2
Figure 4. pH over time at various current densities: a) Cu electrode, b) Al electrode.
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28 mA/cm2 21 mA/cm2 14 mA/cm2 7 mA/cm2
Efflu
en
t T
SS
(m
g/l)
Cu electrode Al electrode
Figure 5. Effluent TSS at various current densities: a) Cu electrode, b) Al electrode.
SEPARATION SCIENCE AND TECHNOLOGY 5
efficiencies of COD and TDS, respectively, for dif-ferent gap distances (2 cm, 4 cm, and 6 cm). The
320 maximum removal efficiencies were obtained at aspacing of 4 cm. Although decreasing the gap dis-tance leads to decreasing the resistance between theelectrodes and increasing the efficiency of the pol-lutant’ removal, this was not the case in this study.
325 When increasing the spacing to 6 cm or decreasingit to 2 cm, the pollutant removal efficienciesdecreased compared to those at spacing of 4 cm.This phenomenon might be due to the configurationof the system. The cross-section of the reactor was
330 circular, and the spacing of 4 cm between electrodeswas approximately equidistant between the two elec-trodes and between each electrode and the edge.This equidistance might lead to two results: i) uni-form distribution of flocs inside the reactor and ii)
335 minimization of the disturbance that could occur tothe flocs during mixing compared to the disturbance
when the electrodes are very close to each other orwhen they are very close to the edges. Moreover, thesmall gap distance between the electrodes led to a
340high electrostatic effect that hinders the particlecollision. More electrochemically generated gas bub-bles caused turbulence, while the big gap distancesignificantly decreased the formation of flocs.-[36,40,41] The behavior during the removal of pollu-
345tants was almost the same for all gap distances. Therate of removal of the pollutants was high duringthe first 10 min, then decreased until the end of theexperiments. The maximum efficiencies of the CODremoval when using the copper electrode for the gap
350distances of 2, 4, and 6 cm were 19%, 65%, and 15%,respectively. The maximum efficiencies of CODremoval when using the aluminum electrode forthe gap distances 2, 4, and 6 cm were 24%, 55%,and 15%, respectively. The maximum efficiencies of
355TDS removal when using the copper electrode forgap distances 2, 4, and 6 cm were 8%, 24%, and 5%,respectively. The maximum efficiencies of TDSremoval when using aluminum electrode for gapdistances 2, 4, and 6 cm were 7%, 3%, and 5%,
360respectively. Removal of the COD and TDS usingthe copper electrode were higher than those whenusing the aluminum electrode for all gap distances.The effluent values of oil and grease in the case ofthe copper electrode were less than those for the
365aluminum electrode as shown in Figure 10. Thevalues of TSS in effluent increased in the case ofthe copper electrode when compared to those valuesobtained from the aluminum electrode. This isbecause the number of flocs formed in the case of
370the copper was more than that formed in the case ofthe aluminum. This confirms that the EC/EF unit
Figure 7. Floatation at the end of EF/EF process using copperelectrode.
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il &
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ase
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Figure 6. Effluent Oil and grease at various current densities: a) Cu electrode, b) Al electrode.
6 S. M. SAFWAT ET AL.
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Co
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ntra
tio
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/l)
Effluent Oil & grease Effluent TSS
Figure 10. Effluent Oil and grease, and TSS at various gap distances.
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Figure 8. COD removal efficiencies over time at various gap distances a) Cu electrode, b) Al electrode.
a b
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Figure 9. TDS removal efficiencies over time at various gap distances a) Cu electrode, b) Al electrode.
SEPARATION SCIENCE AND TECHNOLOGY 7
with the copper electrode performs better than theEC/EF unit with the aluminum electrode.
3.3. Characterization of the by-products obtained375 from the EC/EF by FTIR
To characterize the by-products, FTIR analyses werecarried out. Figure 11 shows the characterizations ofthe sludge samples produced at 21 mA/cm2 using cop-per and aluminum electrodes. It can be observed that
380 FTIR spectra for sludge samples showed some spectro-scopic changes. The finger-prints of the two sludgesamples between 400 cm−1 and 1500 cm−1 were notidentical, confirming the presence of different compo-nents. These different components were due to the
385dissociation of either copper or aluminum electrodesduring the electrocoagulation process. The FTIR spec-tra of the two sludge samples showed a broad andintense band between 3000 cm−1 and 3700 cm−1, indi-cating the presence of an OH group. The presence of
390this group enhanced the adsorption of the counter ionsduring settling. This confirms that adsorption is one ofthe removal mechanisms of the EC/EF process.
3.4. Morphologies of electrodes
The morphologies of copper and aluminum electrodes395were investigated before and after electrocoagulation at
a CD of 21 mA/cm2. Figure 12 shows the SEM imagesof the electrodes before and after the treatment. Forboth the copper and aluminum electrodes, corrosionhappened to the anodes after the EC/EF experiment,
400confirming the occurrence of the treatment process.The surface of the copper electrode contained cracks,while that of the aluminum electrode was rough andcontained dents. The formation of a large number ofcracks and dents in anodes is attributed to the con-
405sumption of metal at active sites of electrodes due tothe generation of oxygen at the surfaces.[42] The corro-sion in the copper electrode was a uniform corrosion,while that for the aluminum electrode was a pittingcorrosion. Uniform corrosion is better than pitting
410corrosion, since it is easier to predict.
3.5. Electrical energy consumption
Key factors, such as energy cost, must be taken intoconsideration in the process optimization. The energyconsumptions required for the treatment of the print-
415ing wastewater versus the operating time at differentCDs is shown in Figure 13. The electrical energy
70
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100
40080012001600200024002800320036004000
Ab
so
rb
an
ce
%
Wave Number (cm-1)
Al Cu
Figure 11. FTIR spectra of by-products.
a b
c d
Figure 12. SEM images of electrodes: a) Cu electrode beforetreatment, b) Cu electrode after treatment, c) Al electrodebefore treatment, and d) Al electrode after treatment.
8 S. M. SAFWAT ET AL.
consumption (EEC) was calculated in terms of kwh/m3
of treated effluent using the following equation:
EEC kwh=m3� � ¼ UIt
V
where U is the average cell voltage (V), I is the current420 intensity (A), t is the time of electrocoagulation treat-
ment (h), and V is the volume of effluent to be treated(l). The results show that energy consumptionincreased with the CD. The values of energy consump-tion for the copper electrode were more than those for
425 the aluminum electrode. The maximum values forenergy consumption were 14 kwh/m3 and 13 kwh/m3
for the copper electrode and aluminum electrode,respectively. The values of the COD removal efficien-cies after 10 min with a CD of 21 mA/cm2 represented
430 more than 90% of the total COD removal efficienciesobtained after 90 min, as observed in Section 3.1. As aresult, 10 min can be considered the optimum condi-tion. The maximum values for energy consumption at aCD of 21 mA/cm2 were 0.86 kwh/m3 and 0.8 kwh/m3
435 for the copper electrode and aluminum electrode,respectively. These values are within the range of valuesmentioned in the literature for energy consumptionwith the electrocoagulation processes, lying between0.002 and 58 kwh/m3.[43] These observations show
440 that the copper anode is more energy demanding thanthe aluminum.
3.6. Performances of chemical coagulation
Copper sulfate and aluminum sulfate were used atdifferent dosages (10 g/l–160 g/l) to investigate the
445 difference in performance between chemical
coagulation and electrocoagulation, as shown inFigure 14. Figure 15 shows the removal efficiencies ofthe COD using chemical coagulants. The values of theCOD removal efficiencies increased with increasing
450coagulant doses. Aluminum sulfate gives better resultswhen compared to copper sulfate. The maximumremoval efficiencies of the COD were 14% and 28%for copper sulfate and aluminum sulfate, respectively.These values are much lower than those obtained using
455electrocoagulation, although the amount of coagulantused is practically very high (160 g/l). These resultsconfirm that the performance of electrocoagulation isbetter than that of chemical coagulation in treatingprinting wastewater.
4603.7. Limitations of the study
The lack of information about concentrations of copperand aluminum ions in the effluent is one of the limita-tions. These ions can cause environmental problems.The concentrations of these ions in effluent were not
0
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EE
C (
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CD= 21 mA/cm2 CD= 28 mA/cm2
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C (
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CD=7 mA/cm2 CD=14 mA/cm2
CD= 21 mA/cm2 CD= 28 mA/cm2
Figure 13. EEC over time at various current densities: a) Cu electrode, b) Al electrode.
Figure 14. Jar test using copper sulfate.
SEPARATION SCIENCE AND TECHNOLOGY 9
465 included in the present study, as the study focused onthe ability of EC/EF process in reducing influent pollu-tants of real printing wastewater. Another limitation isthe time period after which the anode electrodes willneed to be replaced due to dissociation in the solution
470 during treatment process.
4. Conclusion
This work studied the treatment of printing wastewaterusing the EC/EF process. Two different electrodes (cop-per and aluminum) were examined. The results showed
475 that the pollutant removal efficiencies when using thecopper electrode were better than those found whenusing the aluminum electrode. The maximum value ofthe COD removal efficiency was around 67%, obtained ata CD of 28 mA/cm2. For the aluminum electrode, the
480 maximum value of the COD removal efficiency was 55%,obtained at a CD of 21 mA/cm2. The values of pHincreased for all values of CD over time. The maximumremoval efficiencies of the TDS after 90 min were 24%and 7% for the copper and aluminum electrodes, respec-
485 tively. EC/EF process was not sufficient in removal ofcolor, so further treatment is needed to remove colorfrom effluent. The maximum removal efficiencies wereobtained at a gap distance of 4 cm. Characterizations ofthe sludge samples produced at 21 mA/cm2 were carried
490 out by FTIR. The finger-prints of the samples were notidentical, confirming the presence of different compo-nents. The morphologies of the copper and aluminumelectrodes were analyzed before and after electrocoagula-tion. For both copper and aluminum electrodes, corro-
495 sion happened to the anodes after the EC/EF processconfirming the occurrence of metal dissociation. Thecorrosion in the copper electrode was a uniform corro-sion, while that for the aluminum electrode was a pitting
corrosion. The results showed that energy consumption500increased with the CD. The performance of electrocoa-
gulation was better than that of the chemical coagulationin treating real printing wastewater.
Acknowledgments
The authors wish to thank the specialists at Micro Analytical505Center, Cairo University; National Research Center; and the
central laboratory of Egyptian mineral resources authority forhelp with the analyses. This research did not receive anyspecific grant from funding agencies in the public, commer-cial, or not-for-profit sectors.
510Disclosure statement
No potential conflict of interest was reported by the authors. Q3
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