Empirical Model of Electro-Fenton Process for SDS Surfactant Removal from Synthetic Acidic Wastewater

An Empirical Model of Electro-Fenton Process for

SDS Surfactant Removal from Synthetic Acidic Wastewater

Ghanim ANChemical Eng Dep Eng College Babylon

University

Introduction Surfactants are diversified chemicals that are

intended to have cleaning or solubilization properties They consisted mainly of three types anionic nonionic and cationic High applications of the surfactant increasing its discharge in the wastewater and enter into the water resources Thus the water treatment process is necessary in order to remove surfactants from domestic and industrial wastes to reduce its concentration undergroundSodium dodecyl sulfate (SDS) is classical emulsifier mainly used as anionic surfactant widely blended in household and industrial detergent it consist of a water-soluble (hydophilic) and a water-insoluble (hydrophobic) component

IntroductionAdvance oxidation processes (AOPs) based on classic Fenton processes are usually developed Fenton process using zero valence iron Fentonrsquos reagent a homogeneous catalytic system comprising hydrogen peroxide and a ferrous salt leads to the formation of OHbull and other reactive free radicals which are capable of oxidizing many organic pollutants and converting them to lower molecular weight compounds

and eventually to carbon dioxide and water In electro-Fenton process either H2O2 or ferrous ion is continuously generated or regenerated on the electrode and their accumulative concentrations in aqueous solution depend on a competition between their generation rate and consumption rate aqueous organic pollutants

IntroductionAdvanced Electrochemical Oxidation Processes (AEOPs)The sacrificial Fe anode which is electrodissolved supplying stoichiometric amounts of Fe2+ to the effluent The oxidation of a sacrificial Fe anodeFe rarr Fe2+ + 2 emacr (1)The electro-Fenton process is carried out with a conventional anode and the oxidation power of electrogenerated H2O2 is enhanced by addition of Fe2+ to the solution because hydroxyl radical OH is formed from the classical Fentonrsquos reaction between Fe2+ and H2O2 Fe2+ + H2O2 + H+ rarr Fe3+ + OH + H2O (2)RH + OH rarr R + H2O (3)The catalytic reaction (2) indicating the need for an acid environ-ment to produce the maximum amount of hydroxyl radicals

Materials and Method

Materials and MethodDOERSM was used for determining the amounts of SDS removal as a function of hydrogen peroxide concentrations current density and the initial pH of wastewater

Generalized (multiple regression polynomial) equation

β0 the constant coefficientthree first-order effects (terms in PE CD and pH)three interaction effects (terms in PECD PEpH and pHCD)three second-order effects (PE2 CD2 and pH2)

Materials and MethodBox-Behnken design as an experimental design of RSM was used to create a set of designed experiments by Design-Expert software

(version 703) A series of 17 experiments were designed of reliable measurement for SDS removal response with design of unblocked and 5 replicate

Results and DiscussionEffect of Fe2+ RegenerationIn AOPs the rapid depletion of Fe2+ usually terminates the production of hydroxyl radicalsthe rate constant of Fe2+ reaction with OH 32 times108 M-1 s-1 is approximately 10 times that of H2O2 reaction with OH 33 times107 M-1 s-1

H2O2 + OH rarr H2O + HObull2

Fe3+ + HObull2 rarr Fe2+ + H+ + O2

In AEOPs there is continuous generation of Fe2+ provided from sacrificial iron anodes that leads the generation of a powerful oxidant the hydroxyl radical (OH) which can react with most organic pollutants and then degrade them

Results and DiscussionModel Prediction and Development

SDS Removal = ndash 697862+ 6925PE + 69625pH + 16250CD ndash 6875PECD + 0237PEpH ndash 0044PE2 ndash 1166250CD2 ndash

7412pH2

Correlation coefficients R2 = 9962 Adj R2 = 9913 Pred R2 =9451

Where PE peroxide concentration (mgl) CD current density (mAcm2) and pH acidity

Results and Discussion Data Matrix of Box-Behnken Design

Run No Peroxide concentratio

n (mgl)

Current Density

(mAcm2)

Acidity of wastewate

rpH

SDSRemoval

Exp Pred

1 40 05 6 8200 8112

2 50 05 5 9400 9370

3 60 05 6 9050 9112

4 50 05 5 9300 9370

5 50 04 6 7150 7112

6 50 05 5 9400 9366

7 50 05 5 9395 93908 40 04 5 5850

59759 40 06 5 9000

902510 60 05 4 7700

778711 60 06 5 8300

817512 40 05 4 7800

773713 60 04 5 7900

793714 50 04 4 6200

613715 50 05 5 9375 9365

16 50 06 6 8600 8662

17 50 06 4 7900 7875

The predicated values approaches the experimental results

Results and DiscussionANOVA Source Statistical Parameters

Sum of Squares

DF F-value P-valueProbgtF

Model 194546 9 20379 lt 00001

Peroxide Conc (PE) 5512 1 51 97 00002

Current Density(CD)

56112 1 52901 lt 00001

Acidity (pH) 14450 1 13623 lt 00001

PECD 18906 1 17824 lt 00001

PEpH 2256 1 2127 00024

CDpH 156 1 147 02642

PE2 8198 1 7729 lt 00001

CD2 57269 1 53991 lt 00001

pH2 23135 1 21811 lt 00001

Data given in this table demonstrates that the model was significant at the 95 confidence level since p-values were less than 005

Results and DiscussionEffect of PE and CD on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign points above predicted valueDesign points below predicted value94

585

X1 = A PEX2 = B CD

Actual FactorC PH = 500

4000 4500

5000 5500

6000

040 045

050 055

060

58

675

77

865

96

SDS

Rem

oval

A PE B CD

Response surface shows elliptical peak started at the midlevel to the high level of current density while along the whole levels of peroxide concentration

Results and DiscussionEffect of PE and CD on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign Points94

585

X1 = A PEX2 = B CD

Actual FactorC PH = 500

4000 4500 5000 5500 6000

040

045

050

055

060 SDS Rem oval

A PE

B CD

656588715675 774763

833851

892938

892938

5

Results and DiscussionEffect of PE and pH on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign points above predicted valueDesign points below predicted value94

585

X1 = A PEX2 = C PH

Actual FactorB CD = 050

4000 4500

5000 5500

6000

400 450

500 550

600

77

815

86

905

95

SDS

Rem

oval

A PE C PH

For both variables peroxide concen and pH increasing the levels from their midlevel to the high the SDS removal percent increases to clearly sharp peak thereafter it starts to decrease

Results and DiscussionEffect of PE and pH on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign Points94

585

X1 = A PEX2 = C PH

Actual FactorB CD = 050

4000 4500 5000 5500 6000

400

450

500

550

600SDS Rem oval

A PE

C PH

803052 803052832353

861655

861655

890956

920258

5

Results and DiscussionEffect of CD and pH on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign points above predicted valueDesign points below predicted value94

585

X1 = B CDX2 = C PH

Actual FactorA PE = 5000

040 045

050 055

060

400 450

500 550

600

61

6975

785

8725

96

SDS

Rem

oval

B CD C PH

The response surface shows a clear peak started at pH of 45 to its high level and current density of midlevel to its high level

Results and DiscussionEffect of CD and pH on SDS Removal

Design-Expertreg Software

SDS Rem ovalDesign Points94

585

X1 = B CDX2 = C PH

Actual FactorA PE = 5000

040 045 050 055 060

400

450

500

550

600SDS Rem oval

B C D

C PH

671037

728324

785611

842898

900184

900184

5

Results and DiscussionOptimization Analysis

Design-Expertreg Software

SDS Rem oval94

585

X1 = A PEX2 = B CD

Actual FactorC PH = 510

4000 4500 5000 5500 6000

040

045

050

055

060SDS Rem oval

A PE

B CD

650287701564

752841 804118

855395

855395

906672

906672Prediction 917204

Response numerical optimization of Design-Expert software at minimum amount of peroxide addition and within the tested range of current density and acidity

Results and DiscussionOptimization Analysis

Design-Expertreg Software

Desirability1

0

X1 = A PEX2 = B CD

Actual FactorC PH = 510

4000 4500 5000 5500 6000

040

045

050

055

060Desirability

A PE

B CD

0161

0322

0322

0484

0645

0806

Prediction 0967

SDS removal of 9172 was determined at 0967 desirability

The optimum conditions

PE (40 mgl) CD(057 mAcm2) and initial acidity of wastewater (pH=510) depend upon the selected design range assumption

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