Research Article The Application of a Surface Response

Hindawi Publishing CorporationInternational Journal of Chemical EngineeringVolume 2013 Article ID 393467 5 pageshttpdxdoiorg1011552013393467

Research ArticleThe Application of a Surface Response Methodology inthe SolarUV-Induced Degradation of Dairy Wastewater UsingImmobilized ZnO as a Semiconductor

Gisella R Lamas Samanamud12 Helcio J Izario Filho1 Carla C A Loures13

Ivy S Oliveira1 Andre L Souza1 Ana Paula B R de Freitas13 and Ruoting Pei2

1 Department of Chemical Engineering Engineering School of Lorena University of Sao Paulo (USP)Estrada Municipal do Campinho sn∘ Bairro do Campinho 126020-810 Lorena SP Brazil

2 Department of Civil and Environmental Engineering University of Texas at San Antonio (UTSA)One UTSA Circle San Antonio TX 78249 USA

3Departament of Production Engineering Sao Paulo State University (UNESP) 12516-410 Guaratingueta SP Brazil

Correspondence should be addressed to Gisella R Lamas Samanamud zeldalshotmailcom

Received 30 May 2013 Accepted 15 August 2013

Academic Editor Antonia Perez de los Rıos

Copyright copy 2013 Gisella R Lamas Samanamud et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

An Advanced Oxidation Process (AOPs) was carried out in this study with the use of immobilized ZnO and solarUV as an energysource to degrade dairy wastewater The semibatch reactor system consisted of metal plate of 800 times 250mm and a glass tank Thereaction timewas of 3 h for 3 L of dairy wastewater Experiments were performed based on a surface responsemethodology in orderto optimize the photocatalytic process Degradation was measured in percentage terms by total organic carbon (TOC) The entryvariables were ZnO coating thickness and pH using three levels of each variableThe optimized results showed a TOC degradationof 317 Optimal parameters were metal-plate coating of 100120583m of ZnO and pH of 80 Since solarUV is a constant and freeenergy source in most tropical countries this process tends to suggest an interesting contribution in dairy wastewater treatmentespecially as a pretreatment and the optimal conditions to guarantee a better efficiency of the process

1 Introduction

The use of ZnO as a semiconductor was studied for possibleapplication in a photo-excitation-initiated degradation of thecatalyst followed by the formation of a surface bandgap (see(1)) The oxidation potential (hVB

+) permits the formationof active intermediates by the direct oxidation of an organicmatter (see (2)) Many reactive hydroxyl radicals can beformed either by decomposition of water or by a bandgapreaction with OHminus (see (3) and (4)) The Hydroxyl radicalis a powerful nonselective oxidation agent leading to organicpollutants degradation [1ndash3] Consider that

ZnO + ℎ] 997888rarr ZnO (eCBminus

+ hVB+

) (1)

hVB+

+ organic matterminus

997888rarr oxidation products (intermediates)(2)

hVB+

+H2O 997888rarr H+ + ∙OH (3)

hVB+

+OHminus 997888rarr ∙OH (4)

The methodologies used in the design of experimentsallow a similar result as the one obtained from conventionalexperiments with the advantage of the use of fewer exper-iments Thus a good design of experiments can providesufficient results for an effective statistical analysis [4] Inorder to obtain the optimized variables for the study of

2 International Journal of Chemical Engineering

Pump

Sunlight

Effluent

Efflue

nt re

circ

ulat

ion

23∘

Figure 1 Schematic diagram of the solar reactor with ZnO photo-catalyst based on [8]

dairy wastewater photocatalytic treatment a surface responsemethodology was employed

Dairy wastewater does not generally contain inherentlytoxic chemical substances but it is composed of dissolvedorganic compounds that are not easily degradable by bio-logical treatment without a prior treatment In fact thislimitation affects the efficiency of the treatment through pH(depending on the type of dairy) overload of the system andsludge volume Moreover dairy wastewater also produces anunpleasant odor and consists of a liquid with a significantcolor if the organic load is high enough [5ndash7]

2 Materials and Methodology

21 Sampling and Conservation The dairy wastewater sam-ples used in this work were generously provided by Cooper-ativa de Laticınios de Guaratingueta state of Sao Paulo andrefrigerated at 4∘C while stored

22 Preparation of the ZnO Coating and Experiment Proce-dures The immobilization of ZnO particles was carried outby the application of a coating containing the photocatalyst[8] by DuPont do Brasil SA in Guarulhos Sao Paulo Twoidentical 800 times 250mm stainless steel plates with an areaof 200 cm2 were used each with a different thickness (50and 100 120583m) The coating containing ZnO was diluted untilobtaining a sliding viscosity as described in [8] Differencein thickness was obtained by applying an extra layer of theprepared ZnO paint to the 100120583m plate

The entire system was placed in a wooden structure thatpositioned the metal plate at 23∘ in relation to the Earthrsquosequatorial plane (Figure 1)

This angular position corresponds to the 23∘ southlatitude in order to enhance irradiation The solar reactorwas then placed to receive the solar UV responsible for thephotoexcitation of ZnO particles SolarUV was monitored

Table 1 Variables and levels based on the Surface responsemethodology (15 runs with replication) for the dairy wastewaterphotocatalytic process

Control variables Level minus1 Level 0 Level 1pH 60 80 100ZnO coating thickness (120583m) 0 50 100

by Radiometer ILT1400-A Figure 2 shows the scheme of UV-induced degradation when a semiconductor as ZnO is used

The preparation of samples was carried out according tothe surface response methodology designed for this studyand experiments were conducted as in [10] without the blankprocedure

23 Surface Response Methodology for the Dairy Wastewaterof This Study A design was developed using a surfaceresponse methodology with a central point as shown inTable 1 Response was measured in TOC percentage termsExperiments were conducted in pairs at the same time exceptthose with central levels that were conducted one at a timeThe advantage of using a surface response methodologyis that it is able to analyze three levels instead of two asit happens to other designs of experiments The surfaceresponsemethodology consisted of 2 factors in duplicate withthe base run of 15 a total of 30 experiments

24 Surface Response Matrix Procedure According to Table 1for the central point sample was adjusted to pH 80 withthe addition of NaOH 5molsdotLminus1 A metal plate with ZnOcoating thickness of 50120583m was used in the solar reactorThe first sample was collected before the beginning of theexperiment The last sample was collected after 3 h pH con-trol was constant either by addition of H

2SO4or NaOH The

procedure for the other experiments was analogous to the onedescribed previously and performed randomly to guaranteethe statistical significance of the experiments and avoid anybias The efficiency of the process was evaluated in terms ofTOC effective percentage degradation TOC determinationswere carried out in a Shimadzu Model TOC-VCPH analyzerusing catalytic oxidation in high temperatures and CO

2

determination by infrared spectroscopy

3 Results and Discussion

31 Characterization of the Dairy Wastewater Table 2 showsthe physical-chemical results obtained for the dairy wastew-ater before and after the photocatalytic process using immo-bilized ZnO and SolarUV

BOD chloride phosphorous ammonia TOC and tur-bidity showed a reduction range of 20ndash35While the param-eters color oils and total solids showed a more expressivereduction with the range of 45ndash63

The presence of chloride in the dairy wastewater samplesis mainly because chloride is present in the cleaning steps ofreactors in the dairy industry Its removal is then expressive

International Journal of Chemical Engineering 3

Semiconducting particle

CB

Organic pollutants

VB

O2

O2

minus

2eminus

2H+

2H2O

h

2OH∙+ 2H+

O2

minus or OH∙

CO2+ H2O

Figure 2 Schematic illustration of the UV-induced degradation of organic pollutants by semiconductors [9]

Table 2 Physical-chemical results for dairy effluent before and afterAOP treatment

Parameters Results Percentage119894119899 119899119886119905119906119903119886 After AOP

BOD5 (mg Lminus1) 22187 1775 20Chloride (mg Lminus1) 7935 526 337Color (Pt Co) 65235 3260 50N-NH3 (mg Lminus1) 1584 1267 20Oil and grease (mg Lminus1) 20021 750 625Phosphorus (mg Lminus1) 2085 1564 25TOC (mg Lminus1) 1010 690 317Total solids (mg Lminus1) 10720 5886 45Turbidity (NTU) 2786 1894 32Zinc (mg Lminus1) 50 50 mdash

and could improve the biodegradability of the wastewater ina biological system

The analysis of zinc before and after the treatment servesto verify the concentration of zinc as the process proceeds andshows the durability of the coated plate No further studieswere made to the coating plate in terms of longevity of theZnO on the plate nor were biological studies conducted toverify the growth of any type of bacteria on the surface of theplate

The results obtained indicate that the process is signifi-cantly more effective for the removal of color oils and solidsThus indications in this study show this process to be a validpretreatment

32 Optimization of the Photocatalytic Process by Using theSurface Response Methodology Experiments were analyzedin terms of TOC effective percentage degradation as shownin Table 3

Thus the highest percentage of TOC degradation was of316 for a ZnO coating thickness of 50120583m and a pH of 80corresponding to the central point of the matrix

It is possible to visualize the optimized parameters whenusing a surface response methodology through a 3D graphThis is shown in Figure 3

As it can be seen in Figure 3 (acquired by the softwareMinitab v 15) surface maximum peak leans towards pH 80

Table 3 Surface response methodology matrix using 2 factors and15 runs in duplicate and TOC effective percentage degradation of thedairy effluent after the AOP treatment

Experiments pH Thickness(120583m)

TOC effectivepercentage degradation

1 80 50 3162 100 100 543 60 100 574 60 0 795 100 0 1366 100 0 687 60 100 938 60 0 139 80 50 31510 100 100 10611 60 100 4612 60 0 0513 100 0 11714 100 100 7515 60 0 7216 100 100 13617 100 0 6618 80 50 26419 80 50 28720 60 100 5421 100 100 10522 80 50 26623 60 100 6124 60 0 2425 60 100 7126 80 50 25927 100 100 13928 100 0 4429 100 0 7530 60 0 44

as its optimal variable In terms of thickness Figure 2 showsan increase as thickness is raised Thus a coating of 100120583mseems to perform better results than a coating of 50 120583mThisdifference however is not as expressive as it is shown for pHThis can be due to the relative small difference in thickness


30

20

10

060

75 90 1050

50

100

pH ZnO thick

nessTOC

degr

adat

ion

perc

enta

ge

Figure 3 Surface Response graph in terms of TOC percentageremoval by ZnO coating thickness and pH

Table 4 ANOVA of surface response methodology for the photo-catalytic process of dairy wastewater

Coefficient SE Coefficient 119905-value 119875 valueConstant 29597 1377 21490 0000pH 1798 0746 2409 0025ZnO coating thickness 1283 0746 1719 0100pH lowast pH minus22639 1567 minus14452 0000pH lowast thickness 0072 0746 0097 0924Where S = 337352 Rsq = 9108 Rsqadj = 8945 Rsqpred = 8673

between both metal platesThe ANOVA of this methodologyis shown in Table 4

Themodel of this study can express 91 of TOC percent-age degradation Predicted value was 867 that correspondsto a difference of 5 from the model The adjusted value was895 and therefore it shows a difference of 18 from themodel value Thus values were not parameterized and thedata included are significant

Results showed that pH was significant (119875 lt 005) ZnOcoating thickness was less significant in the process (119875 = 01)and the interaction of both variables was not significant (119875 =093)

After statistical analysis the optimal conditions for theAOP using ZnO photoirradiated are pH 80 a value that wasmentioned in [11] and ZnO coating thickness higher than100 120583m

A new experiment was conducted with the optimizedparameters from this study and the ones found in [10] thatis pH of 80 ZnO coating thickness of 100 120583m reaction timeof 3 h effluent concentration in natura average radiation of5840120583Wcm2 reaction temperature of 31∘C and averageevaporation rate of 017 Lh The TOC percentage removalwas of 32 as obtained by [8 12 13] though the authorsemployed TiO

2with lower organic load

Something that must be taken into consideration is thecost of the process for 1 h of reaction For this experimentthe cost of reagents is not high since there is only pHcontrol during the whole process pH values however tendto remain constant during the process once it is adjusted atthe beginning of the process

The energy source chosen for this study requires sunexposition only preventing the use of lamps and henceminimizing the energy consumption of lamps

There is no water consumption during the processbecause the effluent is directly treated that is no dilutionsare required for the effluent of 1010mgsdotLminus1 in this study

4 Conclusion

Optimal values of the variables were pH 80 and a ZnOcoating thickness plate of 100120583m When optimized aneffective TOC degradation of 317 was obtained

Since solarUV is a constant and free energy source inmost tropical countries this process suggests an elevatedpotential contribution to dairy wastewater treatment espe-cially as a pretreatment

Subsequent studies may explore and enhance solarUVcollecting and diminished vaporization Results from thisstudy show that the photocatalytic degradation contributesto the organic load removal of effluents and studies relatedto economic viability may expand the process

In addition nanometric ZnO can be used not onlyfor dairy wastewater treatment but also for other types ofindustrial wastewater even to a scale-up level There was 50of color removal in the dairy effluent which can also be usedin the treatment of dye industry effluents

The AOP using ZnO photoirradiated can be associatedwith membranes and be an instrument in H

2O treatment

for industriesrsquo own water reuse especially those like dairyindustries in which water consumption is extremely high

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors thank Cooperativa de Laticınios de Guaratin-gueta in the state of Sao Paulo (CLG) for the dairy wastew-ater sample used in this work The authors also thank MarcoFernandes fromDuPont for preparing the ZnO-coated platesand Dr Messias Borges Silva from the University of SaoPaulo

References

[1] A A Khodja T Sehili J-F Pilichowski and P Boule ldquoPhoto-catalytic degradation of 2-phenylphenol on TiO

2

and ZnO inaqueous suspensionsrdquo Journal of Photochemistry and Photobiol-ogy A vol 141 no 2-3 pp 231ndash239 2001

[2] N Daneshvar D Salari and A R Khataee ldquoPhotocatalyticdegradation of azo dye acid red 14 in water on ZnO as analternative catalyst to TiO

2

rdquo Journal of Photochemistry andPhotobiology A vol 162 no 2-3 pp 317ndash322 2004

[3] M A Behnajady N Modirshahla and R Hamzavi ldquoKineticstudy on photocatalytic degradation of CI Acid Yellow 23 byZnOphotocatalystrdquo Journal ofHazardousMaterials vol 133 no1ndash3 pp 226ndash232 2006


[4] R E Bruns I S Scarminio and B B Neto Como FazerExperimentos Editora Unicampo Campinas Brazil 2003

[5] B Sarkar P P Chakrabarti A Vijaykumar and V KaleldquoWastewater treatment in dairy industriesmdashpossibility ofreuserdquo Desalination vol 195 no 1ndash3 pp 141ndash152 2006

[6] S Goblos P Portoro D Bordas M Kalman and I KissldquoComparison of the effectivities of two-phase and single-phaseanaerobic sequencing batch reactors during dairy wastewatertreatmentrdquo Renewable Energy vol 33 no 5 pp 960ndash965 2008

[7] W Janczukowicz M Zielinski and M Debowski ldquoBiodegrad-ability evaluation of dairy effluents originated in selectedsections of dairy productionrdquo Bioresource Technology vol 99no 10 pp 4199ndash4205 2008

[8] J S Carrocci R Y Mori O L C Guimaraes et al ldquoApplicationof heterogenous catalysis withTiO

2

photo irradiated by sunlightand latter activated sludge system for the reduction of vinasseorganic loadrdquo Engineering vol 4 pp 746ndash760 2012

[9] K S Choi Band Gap Tuning of Zinc Oxide Films ForSolar Energy Conversion A CASPiE Module Purdue Univer-sity West Lafayette Ind USA 2007 httppapadantonakiscomimages991Band Gap Modulepdf

[10] G R L Samanamud C C A Loures A L Souza et alldquoHeterogeneous photocatalytic degradation of dairy wastewaterusing immobilized ZnOrdquo ISRN Chemical Engineering vol 2012pp 1ndash8 2012

[11] NDaneshvarMH Rasoulifard A R Khataee and FHossein-zadeh ldquoRemoval of CI Acid Orange 7 from aqueous solutionby UV irradiation in the presence of ZnO nanopowderrdquo Journalof Hazardous Materials vol 143 no 1-2 pp 95ndash101 2007

[12] S Malato J Blanco D C Alarcon M I Maldonado PFernandez-Ibanez andW Gernjak ldquoPhotocatalytic decontam-ination and disinfection of water with solar collectorsrdquoCatalysisToday vol 122 no 1-2 pp 137ndash149 2007

[13] R F S Salazar J S Carrocci and H J I Filho ldquoEmploymentof factorial design to evaluate the organic loading and aerationof biological systems in the degradation of dairy wastewaterrdquoAmbiente amp Agua vol 6 no 3 pp 98ndash109 2011

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Pump

Sunlight

Effluent

Efflue

nt re

circ

ulat

ion

23∘

Figure 1 Schematic diagram of the solar reactor with ZnO photo-catalyst based on [8]

dairy wastewater photocatalytic treatment a surface responsemethodology was employed

Dairy wastewater does not generally contain inherentlytoxic chemical substances but it is composed of dissolvedorganic compounds that are not easily degradable by bio-logical treatment without a prior treatment In fact thislimitation affects the efficiency of the treatment through pH(depending on the type of dairy) overload of the system andsludge volume Moreover dairy wastewater also produces anunpleasant odor and consists of a liquid with a significantcolor if the organic load is high enough [5ndash7]

2 Materials and Methodology

21 Sampling and Conservation The dairy wastewater sam-ples used in this work were generously provided by Cooper-ativa de Laticınios de Guaratingueta state of Sao Paulo andrefrigerated at 4∘C while stored

22 Preparation of the ZnO Coating and Experiment Proce-dures The immobilization of ZnO particles was carried outby the application of a coating containing the photocatalyst[8] by DuPont do Brasil SA in Guarulhos Sao Paulo Twoidentical 800 times 250mm stainless steel plates with an areaof 200 cm2 were used each with a different thickness (50and 100 120583m) The coating containing ZnO was diluted untilobtaining a sliding viscosity as described in [8] Differencein thickness was obtained by applying an extra layer of theprepared ZnO paint to the 100120583m plate

The entire system was placed in a wooden structure thatpositioned the metal plate at 23∘ in relation to the Earthrsquosequatorial plane (Figure 1)

This angular position corresponds to the 23∘ southlatitude in order to enhance irradiation The solar reactorwas then placed to receive the solar UV responsible for thephotoexcitation of ZnO particles SolarUV was monitored

Table 1 Variables and levels based on the Surface responsemethodology (15 runs with replication) for the dairy wastewaterphotocatalytic process

Control variables Level minus1 Level 0 Level 1pH 60 80 100ZnO coating thickness (120583m) 0 50 100

by Radiometer ILT1400-A Figure 2 shows the scheme of UV-induced degradation when a semiconductor as ZnO is used

The preparation of samples was carried out according tothe surface response methodology designed for this studyand experiments were conducted as in [10] without the blankprocedure

23 Surface Response Methodology for the Dairy Wastewaterof This Study A design was developed using a surfaceresponse methodology with a central point as shown inTable 1 Response was measured in TOC percentage termsExperiments were conducted in pairs at the same time exceptthose with central levels that were conducted one at a timeThe advantage of using a surface response methodologyis that it is able to analyze three levels instead of two asit happens to other designs of experiments The surfaceresponsemethodology consisted of 2 factors in duplicate withthe base run of 15 a total of 30 experiments

24 Surface Response Matrix Procedure According to Table 1for the central point sample was adjusted to pH 80 withthe addition of NaOH 5molsdotLminus1 A metal plate with ZnOcoating thickness of 50120583m was used in the solar reactorThe first sample was collected before the beginning of theexperiment The last sample was collected after 3 h pH con-trol was constant either by addition of H

2SO4or NaOH The

procedure for the other experiments was analogous to the onedescribed previously and performed randomly to guaranteethe statistical significance of the experiments and avoid anybias The efficiency of the process was evaluated in terms ofTOC effective percentage degradation TOC determinationswere carried out in a Shimadzu Model TOC-VCPH analyzerusing catalytic oxidation in high temperatures and CO

2

determination by infrared spectroscopy

3 Results and Discussion

31 Characterization of the Dairy Wastewater Table 2 showsthe physical-chemical results obtained for the dairy wastew-ater before and after the photocatalytic process using immo-bilized ZnO and SolarUV

BOD chloride phosphorous ammonia TOC and tur-bidity showed a reduction range of 20ndash35While the param-eters color oils and total solids showed a more expressivereduction with the range of 45ndash63

The presence of chloride in the dairy wastewater samplesis mainly because chloride is present in the cleaning steps ofreactors in the dairy industry Its removal is then expressive



CB

Organic pollutants

VB

O2

O2

minus

2eminus

2H+

2H2O

h

2OH∙+ 2H+

O2

minus or OH∙

CO2+ H2O















1 80 50 3162 100 100 543 60 100 574 60 0 795 100 0 1366 100 0 687 60 100 938 60 0 139 80 50 31510 100 100 10611 60 100 4612 60 0 0513 100 0 11714 100 100 7515 60 0 7216 100 100 13617 100 0 6618 80 50 26419 80 50 28720 60 100 5421 100 100 10522 80 50 26623 60 100 6124 60 0 2425 60 100 7126 80 50 25927 100 100 13928 100 0 4429 100 0 7530 60 0 44



30

20

10

060

75 90 1050

50

100

pH ZnO thick

nessTOC

degr

adat

ion

perc

enta

ge













4 Conclusion






2O treatment




Acknowledgments


References


2



2









2









RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











CB

Organic pollutants

VB

O2

O2

minus

2eminus

2H+

2H2O

h

2OH∙+ 2H+

O2

minus or OH∙

CO2+ H2O















1 80 50 3162 100 100 543 60 100 574 60 0 795 100 0 1366 100 0 687 60 100 938 60 0 139 80 50 31510 100 100 10611 60 100 4612 60 0 0513 100 0 11714 100 100 7515 60 0 7216 100 100 13617 100 0 6618 80 50 26419 80 50 28720 60 100 5421 100 100 10522 80 50 26623 60 100 6124 60 0 2425 60 100 7126 80 50 25927 100 100 13928 100 0 4429 100 0 7530 60 0 44



30

20

10

060

75 90 1050

50

100

pH ZnO thick

nessTOC

degr

adat

ion

perc

enta

ge













4 Conclusion






2O treatment




Acknowledgments


References


2



2









2









RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










30

20

10

060

75 90 1050

50

100

pH ZnO thick

nessTOC

degr

adat

ion

perc

enta

ge













4 Conclusion






2O treatment




Acknowledgments


References


2



2









2









RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation















2









RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Documents

Research Article The Application of a Surface Response