M. Kobya, E. Demirbas, M.S. Oncel, Y.Yıldırım, E. Şık, A.Y. Goren and A. Ak yol
ICOEST’2014 - SIDE Side, Turkey, May 14-17, 2014
Journal of Selçuk University Natural and Applied Science Online ISSN: 2147-3781 www.josunas.org
Modeling and Optimization of Arsenite Removal from Groundwater Using Al Ball Anodes by Electrocoagulation Process M. Kobya1, E. Demirbas 2, M.S. Oncel 3, Y.Yıldırım 4, E. Şık5, A.Y. Goren 6 and A. Akyol7 1,3,6,7
Department of Environmental Engineering, Gebze Institute of Technology, Gebze,TURKEY (E-mail:
[email protected],
[email protected],
[email protected],
[email protected]) 2,5 Department of Chemistry, Gebze Institute of Technology, Gebze, TURKEY (E-mail:
[email protected],
[email protected]) 4 Department of Environmental Engineering, Bulent Ecevit University, TURKEY. (E-mail:
[email protected]) Abstract Electrocoagulation (EC) was applied for the present investigation to remove high concentration of As(III) (100-1000 µg/L) from groundwater. The effects of seven operating parameters such as initial pH, current, operating time, size of Al ball anode, initial As(III) concentration, height of Al in the reactor and air flow rate as well as their interactions on arsenite removal efficiency and operating cost were evaluated with a three level factorial design viz, Box-Behnken statistical experiment design method. Sixty-two experiments were carried out for construction of a quadratic model. The results indicated that current, operating time and concentration were significantly affected for As(III) removal efficiencies in the EC process. The model predicted for maximum removal efficiency of arsenite and minimum operating cost at the optimum operating conditions (5.89 of pH, 0.17 A, 21.79 min, ball size of 7.75 mm, column height of 8 cm and airflow of 4 L/min) was 99.94% and 0.642 $/m 3 for initial As(III) concentration of 1000 µg/L. This study showed that the model was adequate for meeting the permissible limit value of F < 0.0001 for all the responses indicated that the model equation adequately described the response surfaces of arsenite removal. Table 1. A full factorial design for seven independent variables and responses for the removal. Run No
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
pH (-)
i (A)
7.0 7.0 5.5 7.0 5.5 8.5 8.5 7.0 7.0 8.5 7.0 7.0 7.0 7.0 5.5 7.0 5.5 5.5 7.0 7.0 7.0 8.5 7.0 5.5 7.0 7.0
0.3 0.5 0.5 0.3 0.3 0.5 0.1 0.1 0.3 0.1 0.3 0.5 0.3 0.3 0.3 0.5 0.1 0.3 0.3 0.1 0.1 0.3 0.1 0.1 0.3 0.3
Independent Variables tEC dp Co (min) (mm) (mg/L) 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 22 15 15 8 22 8 15 15 15 22 15
5.0 7.5 10.0 10.0 7.5 10.0 7.5 7.5 5.0 5.0 10.0 7.5 5.0 7.5 7.5 7.5 10.0 7.5 5.0 7.5 7.5 7.5 7.5 5.0 10.0 7.5
1000 1000 550 1000 550 550 550 550 550 550 550 1000 1000 550 550 550 550 550 550 550 550 550 100 550 550 550
h (cm)
Qair (L/min)
2 5 5 8 2 5 2 8 5 5 5 5 8 5 8 8 5 2 5 8 2 8 5 5 5 5
6 10 6 6 10 6 2 6 10 6 2 2 6 6 10 6 6 2 2 6 6 2 2 6 10 6
Re (%) Al) 97.5 99.2 92.4 99.4 97.7 99.9 86.3 93.8 97.3 85.8 98.3 99.4 99.0 98.9 90.7 99.9 98.9 99.8 97.5 96.1 94.3 99.4 91.1 92.2 99.9 99.0
Responses OC qe ($/m3) (mgAs/mg 0.8675 1.7414 1.9143 0.8553 1.2669 1.8884 0.7762 0.5591 0.9463 0.3503 0.8573 2.3339 1.9778 1.1984 0.9712 2.7540 0.3415 1.2115 0.6373 0.2890 0.1806 0.8762 0.3255 0.2774 1.2941 0.8168
31.0 18.9 9.7 31.6 17.1 10.5 45.3 49.2 17.0 45.0 17.2 19.0 31.4 17.3 15.8 7.1 51.8 17.4 31.9 34.4 92.7 17.4 8.7 48.3 11.9 17.3
806
M. Kobya, E. Demirbas, M.S. Oncel, Y.Yıldırım, E. Şık, A.Y. Goren and A. Ak yol
27 28 29 30 31 32 33 34 35 36 37 38 39
7.0 7.0 7.0 7.0 8.5 7.0 5.5 7.0 7.0 8.5 5.5 7.0 8.5
0.5 0.3 0.5 0.5 0.3 0.3 0.5 0.3 0.1 0.1 0.3 0.5 0.3
22 15 8 8 15 15 15 22 22 15 15 15 22
7.5 7.5 7.5 7.5 7.5 10.0 5.0 5.0 7.5 10.0 7.5 7.5 7.5
550 550 550 550 550 1000 550 550 550 550 550 100 100
2 5 2 8 2 2 5 5 2 5 8 5 5
6 6 6 6 10 6 6 10 6 6 2 2 6
40 41 42 43 44 45 46
8.5 7.0 7.0 8.5 8.5 7.0 7.0
0.5 0.3 0.3 0.3 0.3 0.3 0.3
15 15 8 8 8 15 15
5.0 10.0 10.0 7.5 7.5 10.0 7.5
550 100 550 100 1000 100 550
5 2 5 5 5 8 5
6 6 10 6 6 6 6
47 48
8.5 7.0
0.3 0.3
15 15
7.5 5.0
550 100
8 8
10 6
49 50 51 52 53
8.5 7.0 7.0 5.5 7.0
0.3 0.3 0.1 0.3 0.5
22 15 15 22 15
7.5 7.5 7.5 7.5 7.5
1000 550 100 1000 100
5 5 5 5 5
6 6 10 6 10
54 55 56 57 58 59 60 61 62
7.0 7.0 7.0 7.0 7.0 7.0 5.5 5.5 5.5
0.1 0.3 0.3 0.3 0.3 0.1 0.3 0.3 0.3
15 22 15 8 15 15 8 22 8
7.5 5.0 5.0 10.0 7.5 7.5 7.5 7.5 7.5
1000 550 100 550 550 1000 1000 100 100
5 5 2 5 5 5 5 5 5
2 2 6 2 6 10 6 6 6
98.3 99.2 96.8 98.7 98.3 99.0 99.5 98.2 93.2 96.0 99.9 99.9 100. 0 99.7 96.7 98.7 95.3 96.5 98.5 100. 0 99.9 100. 0 99.2 99.9 91.7 99.0 100. 0 95.8 99.4 90.3 96.3 98.7 96.6 98.3 99.8 99.2
3.9448 0.8074 1.1239 1.2568 1.1108 0.8447 2.2253 1.8006 0.3745 0.2915 0.9469 2.3652 1.8786 2.5131 1.4447 0.6129 0.7513 0.6562 0.9436 1.1313 1.8970 1.2118 2.0365 1.2894 0.1500 1.0480 1.4750 0.1360 0.7670 0.4890 0.3650 0.5910 0.1220 0.3230 1.0260 0.3470
7.0 17.3 19.0 19.4 17.2 31.5 10.4 11.7 33.3 50.3 17.5 1.9 2.2 10.5 3.1 32.3 5.7 57.5 3.1 17.5 17.5 3.2 21.5 17.5 8.7 21.4 1.9 91.3 11.8 2.9 31.6 17.2 92.0 58.5 2.2 5.9
F-values from the ANOVA were 9.02, 11.73, 8.13, 22.47 and 25.23 for removal efficiency of arsenite, energy consumption, electrode consumption, operating cost and capacity of arsenite removal for aluminium ball anodes, respectively. Values of Prob>F were less than 0.0001 showed that the model terms were significant. The quality of the fit polynomial model expressed by the coefficient of R2 (0.916) and Adj-R2 (0.804) predicted from the quadratic regression models for all variables and responses indicating a good agreement with experimental data. The high R2 value, close to 1, is desirable and the predicted R2 must be in reasonable agreement with the Adj-R2 for a significant model. The coefficient of variance (CV) is the ratio of the standard error of estimate to the mean value of observed response and considered to be reproducible when it is not greater than 10%. In this study, CVs for y1 and y4 were 3.59 and 5.76. Adequate precision (AP) compares the range of the predicted values at the design points to the average prediction error. A ratio of AP > 4 is desirable. For the current study, AP values for the EC process were 12.43, 44.91, 11.65, 20.90 and 20.28 for the responses (y1-y5) which indicated an adequate signal. 807
M. Kobya, E. Demirbas, M.S. Oncel, Y.Yıldırım, E. Şık, A.Y. Goren and A. Ak yol
Table 2. ANOVA results for the response parameters. Responses Cf ( μg/L )
R2 0.9667
Adj R2 0.9219
S.D. 15.17
CV 30.86
PRESS 35654
F-value 21.56
Prob>F
