**10. Results and discussion**

TOC (Total Organic Carbon) analysis of the effluent was conducted according to relevant physical-chemical aspects; that is, parameters monitored by environmental agencies (Morais, 2005). Figure 5 illustrates the appearance of the effluent polyester resin *in natura.* 

Multivariate Analysis in Advanced Oxidation Process 73

UV Factor D

Replica 1: reduction of total organic carbon (%)

H2O2 Factor C

Experiment

Experiment

TOC of 7920mg / l.

reaction.

achieved significant values again.

pH Factor A

**Table 4.** L9 Taguchi Orthogonal Array with 4 factors and 3 levels each

TiO2 Factor B

oxidation process (Heterogeneous Photocatalysis).

pH Factor A

TiO2 Factor B

1 1 1 1 1 2 1 2 2 2 3 1 3 3 3 4 2 1 2 3 5 2 2 3 1 6 2 3 1 2 7 3 1 3 2 8 3 2 1 3 9 3 3 2 1

Table 5 shows the percentage change in COT response to experiments using experimental design L9. Experiments 3 and 4 had a higher percentage of TOC removal for the advanced

> H2O2 Factor C

Table 6 shows a replica of the experiment and the experimental conditions 3 and 4 that

Statistical analysis of Taguchi L9, on Figure 6, showed the most significant parameters for the degradation of organic matter in the wastewater, the latter reflecting of pH = 3, adjusted at a low level and factors set at a maximum level of: 182 g hydrogen peroxide and ultraviolet lamp power of 21 W. According to the plan performed, the level of titanium dioxide added to the process can be adjusted at low or medium level, i.e. with values 0.083g / L and 0.167g / L. According to Malik and Saha (2003), the influence of peroxide with temperature is related to the efficiency of ratio by using this compound and its rapid decomposition in the

1 1 1 1 1 31,970 2 1 2 2 2 34,981 3 1 3 3 3 39,489 4 2 1 2 3 37,216 5 2 2 3 1 29,962 6 2 3 1 2 30,095 7 3 1 3 2 30,549 8 3 2 1 3 33,504 9 3 3 2 1 28,182 **Table 5.** Results of the first replica of the percentage reduction obtained in experiments for an initial

UV Factor D

**Figure 5.** Effluent polyester resin *in natura*

The statistical planning performed is represented by Taguchi L9 orthogonal array to which the response variable was TOC and independent variables as factors proposed for this stage were: pH, titanium dioxide, hydrogen peroxide and UV radiation power. Table 3 shows the variables with treatment of levels with selected AOP.


\* [H2O2] = 30 % m/m

**Table 3.** Control variables and their levels

Initially, the mass of H2O2 (30% w / w) is calculated by a stoichiometric ratio that depended on the organic load of the effluent. This obtained a mass of H2O2 of 50 g per liter of effluent.

The amount of TOC of the effluent *in natura* had a mean value of 7920mg / L that was subjected to pre-treatment. For each experiment amount of TOC, a sample in a 60-minute reaction was determined. The percent reduction of TOC is calculated by equation 7.

$$\% \text{ reduction of TOC} = \frac{\text{TOC}\_{\text{in natura}} - \text{TOC}\_{\text{t=oo min}}}{\text{TOC}\_{\text{in natura}}} \tag{7}$$

Table 4 shows the arrangement of orthogonal Taguchi L9 for the treatment of effluent polyester resin using AOP.


**Table 4.** L9 Taguchi Orthogonal Array with 4 factors and 3 levels each

72 Multivariate Analysis in Management, Engineering and the Sciences

TOC (Total Organic Carbon) analysis of the effluent was conducted according to relevant physical-chemical aspects; that is, parameters monitored by environmental agencies (Morais, 2005). Figure 5 illustrates the appearance of the effluent polyester resin *in natura.* 

The statistical planning performed is represented by Taguchi L9 orthogonal array to which the response variable was TOC and independent variables as factors proposed for this stage were: pH, titanium dioxide, hydrogen peroxide and UV radiation power. Table 3 shows the

Control variables (factors) Level 1 Level 2 Level 3 A- pH 3,0 5,0 7,0 B- TiO2 [g/L] 0,083 0,167 0,250 C- H2O2\*[g] 120,0 151,0 182,0 D- UV [W] Sem 15 21

Initially, the mass of H2O2 (30% w / w) is calculated by a stoichiometric ratio that depended on the organic load of the effluent. This obtained a mass of H2O2 of 50 g per liter of effluent.

The amount of TOC of the effluent *in natura* had a mean value of 7920mg / L that was subjected to pre-treatment. For each experiment amount of TOC, a sample in a 60-minute

% reduction of TOC = ����� ������� ������� ���

Table 4 shows the arrangement of orthogonal Taguchi L9 for the treatment of effluent

����� ������

(7)

reaction was determined. The percent reduction of TOC is calculated by equation 7.

**10. Results and discussion** 

**Figure 5.** Effluent polyester resin *in natura*

**Table 3.** Control variables and their levels

polyester resin using AOP.

\* [H2O2] = 30 % m/m

variables with treatment of levels with selected AOP.

Table 5 shows the percentage change in COT response to experiments using experimental design L9. Experiments 3 and 4 had a higher percentage of TOC removal for the advanced oxidation process (Heterogeneous Photocatalysis).


**Table 5.** Results of the first replica of the percentage reduction obtained in experiments for an initial TOC of 7920mg / l.

Table 6 shows a replica of the experiment and the experimental conditions 3 and 4 that achieved significant values again.

Statistical analysis of Taguchi L9, on Figure 6, showed the most significant parameters for the degradation of organic matter in the wastewater, the latter reflecting of pH = 3, adjusted at a low level and factors set at a maximum level of: 182 g hydrogen peroxide and ultraviolet lamp power of 21 W. According to the plan performed, the level of titanium dioxide added to the process can be adjusted at low or medium level, i.e. with values 0.083g / L and 0.167g / L. According to Malik and Saha (2003), the influence of peroxide with temperature is related to the efficiency of ratio by using this compound and its rapid decomposition in the reaction.



Multivariate Analysis in Advanced Oxidation Process 75

with F of 60.65201 and a p-value less than 0.001%, and then the remaining factors are the pH (F = 30.11586; p-value = 0.10 %) and H2O2 (F = 4.67497; p-value = 4.053%). The values obtained by analysis of variance confirmed the significance shown in the graph of main

The analysis of variance (ANOVA) with F> 2 demonstrated that the factor TiO2 is significant for TOC removal. According to Phadke (1989), an F value statistically greater than 2 is considered as a significant effect (factor). The statistical significance factor in TOC reduction

Variation SQ GL SMQ F P-Value pH 53,0700 2,00 26,53499 30,11586 0,00010 TiO2 3,7711 2,00 1,88554 2,13999 0,17366 H2O2 8,2382 2,00 4,11909 4,67497 0,04053 UV 106,8806 2,00 53,44030 60,65201 <0,00001

Multiple linear regressions provide another statistical approach to evaluate variables in a quantitative approach. Significant parameters to the regression analysis are shown in Table 8, where pH, UV and H2O2 are relevant for the degradation process of the organic load of

Factor Coefficient t-value Coef. Beta Probability pH -1,04933 -4,573584 -0,542040 0,0003 TIO2 -5,73042 -1,042771 -0,123584 0,1580 H2O2 0,0266726 1,627560 0,192891 0,0638 UV 0,245688 5,791488 0,686380 0,0000

Multiple linear regression showed a coefficient of determination (R2) of 0.817404, which demonstrates the efficiency of the degradation of effluent using the polyester resin of the experimental design. An ANOVA (Table 9) was performed in order to validate the multiple linear regression equation. The significance of equation shown is for a level of significance

Sources of Variation GL SQ SMQ F P-Value Due to Regression 4 147,0425 36,76063 14,55 0,0001

Independent 13 32,84718 2,526706

in the effluent treatment was confirmed by ANOVA, as shown in Table7.

Error 7,9299 9,00 0,88110

**Table 7.** Analysis of variance Taguchi L16 orthogonal array obtained for TOC (%) removal

effects.

Source of

the polyester resin effluent.

Constant 32,2247

equal to 0.0001 at 95% confidence degree.

**Table 9.** ANOVA of multiple linear regression

**Table 8.** Regression parameters

**Table 6.** Results of replica 2 of the percentage reduction percentage obtained in experiments, initial TOC of 7920mg / l.

**Figure 6.** Main Effects in TOC percentage variation measurements in the effluent treatment of L9 planning

Statistical analysis at a level of 95%, showed the most significant factors for the removal of organic load. According to the distribution F whose critical value is 4.26 and a p-value less than 5%, the most important factors for the degradation of organic matter in the effluent were phenolic H2O2, pH, UV. The most significant factor was the ultraviolet lamp power with F of 60.65201 and a p-value less than 0.001%, and then the remaining factors are the pH (F = 30.11586; p-value = 0.10 %) and H2O2 (F = 4.67497; p-value = 4.053%). The values obtained by analysis of variance confirmed the significance shown in the graph of main effects.

The analysis of variance (ANOVA) with F> 2 demonstrated that the factor TiO2 is significant for TOC removal. According to Phadke (1989), an F value statistically greater than 2 is considered as a significant effect (factor). The statistical significance factor in TOC reduction in the effluent treatment was confirmed by ANOVA, as shown in Table7.



Multiple linear regressions provide another statistical approach to evaluate variables in a quantitative approach. Significant parameters to the regression analysis are shown in Table 8, where pH, UV and H2O2 are relevant for the degradation process of the organic load of the polyester resin effluent.


**Table 8.** Regression parameters

74 Multivariate Analysis in Management, Engineering and the Sciences

TiO2 Factor B

H2O2 Factor C

1 1 1 1 1 31,269 2 1 2 2 2 34,498 3 1 3 3 3 36,443 4 2 1 2 3 35,720 5 2 2 3 1 31,648 6 2 3 1 2 30,019 7 3 1 3 2 30,739 8 3 2 1 3 33,011 9 3 3 2 1 27,481 **Table 6.** Results of replica 2 of the percentage reduction percentage obtained in experiments, initial

**Figure 6.** Main Effects in TOC percentage variation measurements in the effluent treatment of L9

Statistical analysis at a level of 95%, showed the most significant factors for the removal of organic load. According to the distribution F whose critical value is 4.26 and a p-value less than 5%, the most important factors for the degradation of organic matter in the effluent were phenolic H2O2, pH, UV. The most significant factor was the ultraviolet lamp power

UV Factor D

Replica 2: reduction of total organic carbon (%)

pH Factor A

Experiment

TOC of 7920mg / l.

planning

Multiple linear regression showed a coefficient of determination (R2) of 0.817404, which demonstrates the efficiency of the degradation of effluent using the polyester resin of the experimental design. An ANOVA (Table 9) was performed in order to validate the multiple linear regression equation. The significance of equation shown is for a level of significance equal to 0.0001 at 95% confidence degree.


**Table 9.** ANOVA of multiple linear regression

The most influential factors in the process show the percentage removal of Total Organic Carbon in Figure 7. An increasing degradation of the organic load is observed on the surface. This is achieved by independent variables: pH and potency of the ultraviolet lamp. The percentage of the increased removal of organic load occurs when there is an increase of the power of the lamp and a decrease of the pH. The greatest percentage reduction of the organic load is equal to 39.489%, whose parameters used in this experimental condition = H2O2 were 182 g, pH = 3, TiO2 = 0.250 g / L and the lamp power of 21 W. The response variable was significant for the degradation of organic matter in the effluent.

Multivariate Analysis in Advanced Oxidation Process 77

the weight ratio of hydrogen peroxide at 183g, pH = 3, TiO 2 = 0.250 g/L and the lamp intensity = 21 W. We conclude that the process of heterogeneous photocatalysis is optimally

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Ana Paula Barbosa Rodrigues de Freitas, Carla Cristina Almeida Loures, Fatima Salman, Hilton Túlio Lima dos Santos and Messias Borges Silva

**Author details** 

Leandro Valim de Freitas

*Petróleo Brasileiro SA (PETROBRAS), Brazil* 

*São Paulo State University (UNESP), Brazil* 

*University of Texas at San Antonio (UTSA), USA* 

Publisher And Editorial Services Ltd, 1995.

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Publisher of Unicamp;1995.

Wiley and Sons; 1998.

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*University of São Paulo (USP), Brazil* 

Gisella Lamas Samanamud

**12. References** 

**Figure 7.** Graph of the two most influential factors in the process

#### **11. Conclusions**

Taguchi planning was applied to the degradation of effluent organic load. The experimental design showed that further reduction of TOC (%) is related to an increase in pH and ultraviolet intensity. The results obtained were significant for the removal of TOC (%) from polyester resin effluent treated with advanced oxidation processes, and heterogeneous photocatalysis.

In our Taguchi orthogonal array the removal-percentage achieved was COT = 39.489%, which corresponds to experimental condition number three. This condition is inclusive of the weight ratio of hydrogen peroxide at 183g, pH = 3, TiO 2 = 0.250 g/L and the lamp intensity = 21 W. We conclude that the process of heterogeneous photocatalysis is optimally suitable for treatment of the effluent studied in this work.
