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Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa20
Two-stage electrochemical treatment of bio-digested distillery spent wash using stainless steel and aluminum electrodes a
a
b
Pinki Sharma , Himanshu Joshi & Vimal C. Srivastava a
Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee, India
b
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Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, India Published online: 02 Apr 2015.
To cite this article: Pinki Sharma, Himanshu Joshi & Vimal C. Srivastava (2015) Two-stage electrochemical treatment of biodigested distillery spent wash using stainless steel and aluminum electrodes, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 50:6, 617-630 To link to this article: http://dx.doi.org/10.1080/10934529.2015.994968
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Journal of Environmental Science and Health, Part A (2015) 50, 617–630 Copyright © Taylor & Francis Group, LLC ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2015.994968
Two-stage electrochemical treatment of bio-digested distillery spent wash using stainless steel and aluminum electrodes PINKI SHARMA1, HIMANSHU JOSHI1 and VIMAL C. SRIVASTAVA2 1
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2
Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee, India Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, India
The objective of this study was to determine the effectiveness of two-stage electro-coagulation (EC) process using multi-parameter optimization for treating bio-digested distillery spent wash by stainless steel (SS) and aluminum (Al) electrodes. Operating parameters have been optimized and treatment efficiency of SS and Al electrodes have been compared by central composite design of response surface analysis in terms of COD, color and total organic carbon (TOC) removal. Individual and interactive effects of four independent parameters namely initial pH (pHo: 2–10 and 4–10 for SS and Al electrodes, respectively), current density (j: 30.86– 154.32 A m¡2), inter-electrode distance (g: 0.5–2.5 cm) and electrolysis time (t: 30–150 min) on the COD, color and TOC removal efficiency were evaluated for both the electrodes. SS electrode was found to be more effective for the removal of COD, color and TOC with removal efficiencies of 70%, 93% and 72%, respectively, as compared to Al electrode, which showed respective removal efficiencies of 59%, 80% and 55%. A two-stage EC process was also conducted to study the predominance of different types of electrodes, and to increase the efficiency of EC process. Results shows that SS followed by Al electrode (with total COD, color and TOC removal efficiency of 81%, 94% and 78%, respectively) was found to be more effective than Al followed by SS electrode combination (with total COD, color and TOC removal efficiency of 78%, 89% and 76%, respectively). Present study shows that EC process can be used as an additional step to bio-methanation process so as to meet effluent discharge standards in distilleries. Keywords: Aluminum electrode, bio-digested distillery spentwash, electro-coagulation, stainless steel electrode, response surface methodology.
Introduction Distilleries are one of the most polluting industries listed by a number of environment monitoring agencies of the world and the central pollution control board (CPCB), India.[1] India is the Asia’s second largest ethanol producer with about 2300 million litres annual production in 2006– 07.[2] About 8–15 litre of wastewater i.e. spent wash gets generated for every litre of alcohol produced in molasses based distilleries. This wastewater has extremely high chemical oxygen demand (COD) (80000–100000 mg L¡1) and biochemical oxygen demand (BOD) (40000– 50000 mg L¡1), low pH, strong odor and dark brown color.[3] Bio-methanationis currently being used as secondary treatment in most of the distilleries so as to reduce the pollution load and recover energy in the form of
Address correspondence to Pinki Sharma, Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee 247667, India; E-mail: [email protected] Received August 16, 2014. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lesa.
methane.[4] However, bio-methanation alone does not meets the discharge standards, irrespective of aeration.[5] Electro-coagulation (EC) is one of the most promising technologies for the high strength industrial wastewater treatment. In this technique, wastewater is treated by applying current to different metal electrodes, which generate coagulants upon metal dissolution into the solution. Along with the ions, gas bubbles (in the form of hydrogen gas) also get generated at cathode, which stick to the pollutants and help in their removal through flotation, i.e., electro-flotation.[6] EC process has been utilized for the various types of wastewater treatment by different researchers,[7–11] widely used for removing the color from industrial wastewaters[12–14] and for the removal of COD and color from paper mill effluents,[15,16] laundry wastewater,[17] refinery waste water[18] and restaurant wastewater.[19] EC technology has also been used for the treatment of potable water. Emamjomeh and Sivakumar[20,21] showed the effectiveness of EC process for de-fluoridation of potable waterand suggested that it could also be utilized for the de-fluoridation of industrial wastewater. A complete review on removal of pollutants by electro-coagulation and electrocoagulation/flotation processes was given by Emamjomeh
618
(RuO2-Ti) as anode, SS as cathode Graphite
Raw spent wash
Ruthenium oxide coated titanium mesh acting as anode and SS as cathode Al
Fe
SS
Diluted distillery spent wash
Biodigester effluent
Biodigester effluent
Biodigestereffluent
Raw spent wash
Graphite +titanium particles Fe
Raw spent wash
Actual effluent from alcohol plant
Electrode Used
Spent-wash Used
j: 44.65–223.25 A m¡2; pHo: 2-8; g: 1–3 cm; t: 30– 150 min; Co: 15, 600 mg L¡1. j: 44.65–223.25 A m¡2; pHo: 2-8; g: 1–3 cm and t: 30– 150 min; Co: 15, 600 mg L¡1. j: 39.06–195.31A m¡2; pHo: 3.5-9.5; g: 1–2 cm and t: 30–150 min; Co: 9310 mg L¡1. CCD
CCD
Paretoanalysis
Factorial design
BB design
One at a time
One at a time
One at a time
j: 1.5 ¡5.5 A dm¡2. j: 1–6 Adm¡2; pHo: 2–13.5; Co: 1200015000mg L¡1; type of additive:NaCl, NaBr, NaF i: 1–10 A; pHo; 1-5; type of additive: H2O2 and NaCl. j: 12.5–37.5 Am¡2; dilution: (10–30%); t: 120–240 min j: 7.142 to 57.142 A m¡2; pHo: 4–10; dilution: (5– 30%); t: 60–300 min
Optimization Procedure
Parameters Studied
j: 146.75 A m¡2; pHo6.75; g: 1 cm t: 130 min
j: 44.65A m¡2; pHo: 8; g: 2 cm; t: 120 min
j: 120 A m¡2; pHo: 6.0; g: 1 cm; and t:150 min.
i: 9 A; pHo: 1; type of additive: 1.0 M NaCl j: 31 Am¡2 dilution: 17.5% and t: 240 min j: 14.285A m¡2 dilution; pHo: 5.5; 10% and t: 180 min
—
—
Optimized Parameters
Table 1. Comparison of various studies on electrochemical treatment of distillery spent wash.
61.6
50.5
52.23
37
—
89.62
85.2
92%
COD (%)
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98.4
95.2
81
93.5
—
92.24
100
100
Color (%)
Performance
[28]
—
[6]
[32]
[31]
[30]
[29]
[27]
[26]
Reference
—
—
TOC (%)
619
Al and Fe
Ozonation + Fe and Al
SS
Al
SS and Al(Twostage process)
Raw spent wash
Raw spent wash
Biomethanatedspent wash
Biomethanatedspent wash
Biomethanatedspent wash
j: 10–30 A m¡2; pHo: 3-9; and t: 30– 180 min; Co: 42240–46440 mg L¡1. j: 6.25– 18.75 A m¡2, pHo: 3-9; agitation speed: 200– 600 rpm; t: 20– 120 min; and g: 24 cm; Co:120000 mg L¡1. j: 1–5 A m¡2; pHo: 2– 10; g: 1-3 cm; Co: 1250-5000 mg L¡1. j: 30.86–154.32 A m¡2; pHo: 2-10; g: 0.5-2.5 cm; t: 30– 150 min; Co: 10, 500–12000 mg/l j: 30.86–154.32 A m¡2; pHo: 2-10 and 4-10; g: 0.5-2.5 cm; t: 30–150 min; Co: 10500–12000 mg/l j: 30.86–154.32 A m¡2; pHo: 2–10 and 4-10; g: 0.5– 2.5 cm; t: 30– 150 min; Co: 10500-12000 mg/l CCD
CCD
CCD
One at a time
One at a time
One at a time
For SS: j: 154.32 A m¡2; pHo: 7.8; g: 2.2 cm; t: 135 minFor Al: j: 154.32 A m¡2; pHo: 6.6; g: 0.5 cm; t: 120 min
Al: j: 154.32 A m¡2; pHo: 6.6; g: 0.5 cm; t: 120 min
j: 3 Adm¡2; pH: 6 ; g: 1 cm; Co: 2500 mg L¡1. SS: j: 154.32 A m¡2; pHo: 7.8; g: 2.2 cm; t: 135 min
j: 18.7 A m¡2;pHo: 3; agitation speed: 500 rpm; t: 120 min; g: 3 cm
j: 30 A m¡2; pHo 3; cm t: 120 min
80.07
94.28
80.86
92.73
69.63
58.82
100
—
—
83.0
81.3
72.3
77.85
55.03
72.30
Present study
Present study
Present study
[35]
[34]
[33]
Notes: j: current density; i: current intensity; g: electrode gap; Co: initial COD concentration; CCD: central composite design; BB: box-behnken design; RSM: response surface methodology; SS: stainless steel; Al: Aluminium.
Al
Anaerobically treated distillery wastewater
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Sharma et al.
Table 2. Process variables and their levels for EC treatment using SS and Al electrodes. Factors Variable Unit
X
Electrode
Initial pH, pH0
X1 X1 X2 X3 X4
SS Al Both Both Both
Current density, j (A m¡2) Inter-electrode distance, g (cm) Time of electrolysis, t (min)
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Level
and Sivakumar.[22] Results have demonstrated that pollution parameters can be effectively removed via EC treatment provided operating parameters and experiment conditions are carefully optimized.[22] EC process optimization with different operating parameters has been done by many researchers by using parametric and multiple response optimization for the treatment of textile printing wastewater[23,24] and acrylic dye bearing textile
¡2
¡1
2 4 30.86 0.5 30
4 5.5 61.72 1 60
0
1
2
6 7 92.60 1.5 90
8 8.5 123.45 2 120
10 10 154.32 2.5 150
wastewater.[25] EC has also been used for treatment of distillery spent wash (Table 1).[26–35] Manisankar et al.[26,27] investigated effect of pH and current density on the treatment of distillery effluent by EC process using graphite anode electrode in the presence of supporting electrolytes (sodium chloride, sodium fluoride and sodium bromide) which resulted in 85.2% COD removal.
Table 3. Experimental data and fits for SS electrode. % COD Removal Run
pH
j (A m¡2)
g (cm)
t (min)
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 27 28 29 30
4 8 4 8 4 8 4 8 4 8 4 8 4 8 4 8 2 10 6 6 6 6 6 6 6 6 6 6 6 6
60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 90.6 90.6 30.86 154.23 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6
1 1 1 1 2 2 2 2 1 1 1 1 2 2 2 2 1.5 1.5 1.5 1.5 0.5 2.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
60 60 60 60 60 60 60 60 120 120 120 120 120 120 120 120 90 90 90 90 90 90 30 150 90 90 90 90 90 90
Actual
Predicted
34.50 42.09 50.50 48.45 54.78 47.81 56.17 53.28 36.49 36.43 38.17 32.96 57.80 58.62 56.21 54.26 61.50 54.65 68.53 71.01 43.62 52.09 76.32 67.55 45.98 52.45 61.17 58.97 73.41 66.35 75.94 71.98 39.23 35.26 37.78 47.29 55.09 51.97 62.09 70.75 58.38 60.11 54.30 58.11 36.56 39.16 66.90 69.84 45.89 48.90 48.63 48.90 50.23 48.90 47.50 48.90 49.35 48.90 51.80 48.90 SD D 4.48
% Color Removal Actual
Predicted
58.60 63.02 55.93 53.88 84.48 79.24 77.02 70.38 47.80 47.82 59.17 61.48 76.85 66.74 76.29 80.69 83.80 74.44 45.31 55.44 97.37 95.14 81.32 76.42 58.24 64.83 68.00 68.63 91.00 88.23 97.00 92.31 26.14 33.04 30.00 27.97 76.51 67.29 92.51 106.42 79.35 84.85 86.04 85.41 65.60 69.61 91.58 92.44 95.77 89.76 86.70 89.76 87.80 89.76 94.30 89.76 85.35 89.76 88.45 89.76 SD D 14.24
% TOC Removal Actual
Predicted
32.76 41.87 48.67 47.60 59.12 54.02 58.22 55.39 22.86 26.98 30.00 30.05 50.11 52.42 51.74 51.14 58.46 56.76 62.08 62.63 61.42 64.47 72.17 65.99 42.55 48.72 49.36 51.94 71.21 69.73 74.39 68.59 44.23 36.39 34.13 41.18 59.40 49.61 69.40 78.10 59.49 61.97 52.31 49.04 39.15 36.55 67.29 69.10 53.08 57.78 59.80 57.78 60.11 57.78 54.10 57.78 60.11 57.78 59.15 57.78 SD D 5.02
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Two-stage electrochemical treatment of bio-digested distillery spent wash Table 4. Experimental data and fits for Al electrode.
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% COD Removal Run
pH
j (A m¡2)
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 27 28 29 30
5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 4 10 7 7 7 7 7 7 7 7 7 7 7 7
61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 92.6 92.6 30.86 154.32 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6
g (cm) 1 1 1 1 2 2 2 2 1 1 1 1 2 2 2 2 1.5 1.5 1.5 1.5 0.5 2.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
t (min) 60 60 60 60 60 60 60 60 120 120 120 120 120 120 120 120 90 90 90 90 90 90 30 150 90 90 90 90 90 90
Actual
Predicted
52.16 51.21 41.75 41.47 58.61 55.50 45.25 50.20 52.60 49.59 40.90 45.25 43.29 44.21 49.41 44.30 46.47 53.51 47.34 43.78 65.70 60.54 52.13 55.24 61.80 56.05 48.50 51.71 51.20 53.41 55.19 53.50 51.19 54.74 47.95 45.11 48.60 47.72 52.21 53.80 56.37 54.99 49.54 51.63 42.30 42.62 54.64 54.13 48.30 48.38 42.80 48.38 48.50 48.38 49.46 48.38 47.10 48.38 53.20 48.38 SD D 1.28
Piya-areetham et al.[28] carried out the EC study using graphite particles and titanium sponge as the voluminous anodes and Ti/RuO2 as cathode placed above anode particles and 89.62% COD and 92.24% color removal efficiency was reported. Prasad et al.[29] reported 95% color removal from distillery spent wash by EC process using Fe anode. Prasad and Srivastava.[30] employed ruthenium oxide coated titanium mesh as anode and stainless steel (SS) as cathode for distillery spent wash treatment. COD and color removal were found to be37% and 81%, respectively, at optimal conditions. Krishna et al.[33] reported 72.3% COD removal efficiency at optimum condition using aluminium (Al) electrodes and also suggested the further treatment of effluent before discharging. Khandegar and Saroha[34] studied EC treatment process by Al and Fe electrodes in various combinations and observed maximum 81.3% COD removal by Al-Al electrodes. Asaithambi et al.[35] investigated the synergistic effect of ozone assisted EC treatment on distillery effluent. Results concluded that combined technique was more
% Color Removal Actual
Predicted
72.72 72.78 54.70 53.78 84.98 84.81 66.66 60.25 59.26 51.78 53.06 50.92 72.69 77.06 73.91 70.65 81.09 84.82 68.51 58.80 91.57 88.37 48.84 56.80 75.36 76.43 67.90 68.55 91.84 93.24 85.21 79.81 84.45 82.13 42.51 49.69 54.71 59.65 83.00 82.93 72.47 74.37 73.42 76.38 53.51 59.05 80.93 80.25 74.20 73.21 74.60 73.21 73.70 73.21 72.24 73.21 70.90 73.21 73.60 73.21 SD D 2.04
% TOC Removal Actual
Predicted
37.89 40.87 30.16 29.96 50.75 47.88 42.47 47.43 44.20 45.77 34.38 36.53 43.09 42.56 47.88 43.79 45.02 49.42 36.13 35.33 60.43 56.94 54.58 53.32 63.67 57.38 41.79 44.97 54.20 54.70 57.07 52.75 57.65 59.00 46.47 46.15 40.89 36.88 46.62 51.66 49.19 46.82 47.75 51.15 32.83 30.33 44.31 47.84 46.70 45.51 44.60 45.51 45.90 45.51 45.29 45.51 44.80 45.51 45.78 45.51 SD D 2.63
efficient than either technique alone. Yavuz et al.[36] studied the effect of H2O2 on electro chemical treatment of distillery spent wash and showed 92.6% removal of COD by electro-Fenton study. Also, EC treatment of bio-digested effluent from the distillery were reported using Fe, SS and Al electrodes.[31,32] Ponselvan et al.[31] reported maximum COD removal efficiency of 52.2% at optimized condition using Al electrodes. Kumar et al.[32] used Fe electrode and studied the effect of pH, current density, inter-electrode distance and time on COD and color degradation. Maximum COD and color removal of 50.5% and 95.2%, respectively, was reported at optimized conditions. Thakur et al.[6] reported COD and color reduction of 61.6% and 98.4%, respectively, using SS electrodes. These previous studies reported COD and color removal in single stage using EC process. However, a comparative study using SS and Al electrodes and effect of two-stage EC treatment have not been reported for the treatment of distillery spent-wash. In earlier studies, multi-objective optimization of parameters was not reported. Total organic
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Sharma et al.
Table 5. Analysis of variance for %COD, color and TOC removal with SS electrode.
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COD
Color
Source
Sum of Squares
D F
Mean Square
Mean Linear 2FI Quadratic Cubic Residual Total
84781.7 2152.6 549.4 603.9 533.9 175.7 887970.2
1 4 6 4 9 6 30
84781.69 538.2 91.6 150.9 59.3 29.3 2959.9
F Sum of Value Squares 7.22 1.32 3.19 2.03
167893.1 3162.1 676.3 6086.1 869.8 113.8 178801.2
carbon (TOC) parameter is an important parameter that indicates mineralization of organic fraction of the wastewater. This parameter has not been considered in previous studies. In the present study, the effectiveness of two-stage EC process using multi-parameter optimization for treating bio-digested distillery spent wash by SS and Al electrodes was evaluated. Three responses COD, color and TOC have been selected for optimizing the operating parameters namely initial pH (pHo), current density (j), inter-electrode distance (g) and electrolysis time (t). Response surface methodology (RSM) based central composite design (CCD) has been used for designing the experiments for the treatment of biologically treated spent wash using SS and Al electrodes. Further two-stage treatment has been performed using combination of SS and Al electrodes with and without pH adjustment between the two-stages.
Materials and methods
D F
Mean Square
1 4 6 4 9 6 30
167893.1 790.5 112.7 1521.5 96.6 18.9 5960.0
TOC F Value 2.55 0.303 23.20 5.095
Sum of Squares
D F
Mean Square
87142.3 3084.9 269.6 757.8 551.3 82.8 918880.8
1 4 6 4 9 6 30
87142.29 771.23 44.9 189.5 61.3 13.8 3062.9
F Value 11.6 0.61 4.48 4.44
are: pH: 8.0–8.3, COD: 10000–12000 mg L¡1, BOD: 3500–4000 mg L¡1, Total suspended solids (TSS): 14.5– 14.8 g L¡1, Total dissolved solids (TDS): 8.7-9.0 g L¡1 and the color was dark brown. Experimental setup The experimental setup used for EC study was similar to previous studies.[6] The 1.5 L main reactor was cubical in shape having dimensions (110 mm £ 110 mm £ 140 mm) and was made of Perspex glass. A digital direct current (DC) power of 0–18 V, 0–5 A was used to supply regulated current to the EC cell. Four mono-polar, parallel connected electrodes made of either Al or SS and of a rectangular-shaped plate with dimensions of 90 mm £ 105 mm were used in the EC experiments. The area of the electrodes exposed to the wastewater was 90 mm £ 90 mm. The gap between anodes and cathodes was varied in the range of 0.5 to 2.5 cm. To maintain the uniformity throughout the reactor, magnetic stirrer was used for providing proper stirring.
Effluent source and characterization Effluent used in present the study was collected from a nearby distillery. Samples were collected after secondary treatment. The characterization of the effluent for different parameters was done as per standard method of analysis. The effluent showed basic nature and having high COD/ BOD ratio. The main characteristics of the effluent
Experimental procedure CCD (discussed later) was used to decide the operating conditions of different EC run. At the beginning of each experimental run, the reactor was thoroughly washed and rinsed with de-ionized water followed by rinsing with the
Table 6. Analysis of variance for %COD, color and TOC removal with Al electrode. COD
Color
Source
Sum of Squares
D F
Mean Square
Mean Linear 2FI Quadratic Cubic Residual Total
75446.6 410.4 170.4 49.6 259.2 64.6 76400.7
1 4 6 4 9 6 30
75446.6 102.6 28.4 12.4 28.8 10.8 2546.7
F Value 4.72 1.45 0.57 2.68
TOC
Sum of Squares
D F
Mean Square
151590.9 3070.8 815.9 126.04 437.8 43.4 156084.9
1 4 6 4 9 6 30
151590.9 767.7 136.0 31.5 48.7 7.23 5202.8
F Value 4.26 0.98 6.73 13.48
Sum of Squares
D F
Mean Square
63709.2 1063.5 236.3 207.9 244.7 5.7 65467.4
1 4 6 4 9 6 30
63709.2 265.9 39.4 51.9 27.2 0.95 2182.3
F Value 9.57 1.63 3.11 28.60
623
Two-stage electrochemical treatment of bio-digested distillery spent wash Table 7. Coefficients, standard deviation, t and P for COD, color and TOC removal by SS electrode.
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COD Factor
Coeff icient
Intercept A-pH B- j C- g D- t A2 B2 C2 D2 AB AC AD BC BD CD
48.82 3.01 4.08 ¡0.58 7.71 ¡1.91 2.88 2.55 1.40 ¡0.21 ¡2.46 2.50 3.94 ¡1.98 0.86
Color
Standard Deviation
Prob > F
2.81 0.0019 1.41 0.049 1.37 0.009 1.41 0.686 1.41 < 0.0001 1.31 0.167 1.24 0.034 1.31 0.071 1.31 0.303 1.64 0.898 1.72 0.174 1.72 0.168 1.64 0.030 1.64 0.247 1.72 0.623 R-Squared: 0.823
Standard Deviation
Prob > F
Coeff icient
Standard Deviation
Prob > F
3.30 1.66 1.61 1.66 1.66 1.55 1.46 1.55 1.55 1.94 2.02 2.02 1.94 1.94 2.02 R-Squared: 0.909
< 0.0001 0.455 < 0.0001 0.939 0.004 < 0.0001 0.575 0.465 0.178 0.973 0.013 0.242 0.743 0.588 0.501
57.64 1.22 6.70 ¡3.30 8.16 ¡4.75 1.33 ¡0.57 ¡1.24 ¡1.04 ¡0.66 0.04 3.18 ¡1.06 1.72
2.65 1.33 1.29 1.33 1.33 1.24 1.17 1.24 1.24 1.55 1.63 1.63 1.55 1.55 1.63 R-Squared: 0.866
0.0003 0.374 0.0001 0.026 < 0.0001 0.002 0.272 0.654 0.334 0.513 0.689 0.983 0.059 0.505 0.308
Coefficient 89.57 ¡1.27 9.66 0.13 5.69 ¡14.81 ¡0.83 ¡1.16 ¡2.18 0.07 5.70 ¡2.47 0.65 1.07 1.40
TOC
sample solution. A sample volume of 1.2 L was used for each experimental run. The pH of the solutions was initially measured andthen adjusted as per the designed runs by adding 0.1 N NaOH or 0.1 N H2SO4 solutions.[6] After that the electrode distance was set and current density was maintained constant throughout the run by adjusting the current supplied. Color and TOC of the effluent samples before and after the EC were measured by double beam UV visible spectrophotometer (HACH, DR 5000, Loveland, CO, USA) and TOC analyser (TOC-V-CSN 39208967, Shimadzu, Japan), respectively. COD was
measured initially and after specified period of timeusing digestion unit (DRB 200, HACH) and UV visible spectrophotometer (HACH, DR 5000). COD removal was calculated by using the following relationship: % COD removal ðYÞ D 100.CODo ¡ CODt / /CODo (1) where, CODo is the initial COD (mg L¡1) and CODt is the COD after specified time (mg L¡1).
Table 8. Coefficients, standard deviation, t and P for COD, color and TOC removal by Al electrode. COD Factor
Coeff icient
Intercept 48.25 A-pH ¡2.50 B- j 1.38 C- g ¡0.64 D- t 2.82 A2 0.39 B2 0.56 C2 1.23 AB 1.08 AC 1.35 BC ¡2.35 BD 0.67 CD 1.04
Color
Standard Deviation
Prob > F
1.51 0.90 0.88 0.90 0.90 0.83 0.78 0.83 1.07 1.10 1.07 1.07 1.10
0.029 0.013 0.136 0.488 0.006 0.647 0.482 0.155 0.327 0.236 0.042 0.541 0.357
R-Squared: 0.656
Factor Intercept A-pH B- j C- g D- t A2 B2 C2 D2 AB AC AD BC BD CD
TOC
Coeff Standard icient Deviation
Prob > F
72.71 2.31 ¡7.99 1.16 5.73 1.14 0.22 1.16 5.48 1.16 ¡1.82 1.08 ¡0.45 1.02 0.54 1.08 ¡0.89 1.08 ¡1.35 1.38 4.54 1.42 ¡1.76 1.42 3.22 1.38 ¡2.06 1.38 3.15 1.42 R-Squared: 0.892
< 0.0001 < 0.0001 0.0001 0.849 0.0003 0.112 0.664 0.623 0.424 0.343 0.006 0.234 0.034 0.155 0.042
Coeff icient 45.20 ¡3.43 3.64 1.30 4.37 1.77 ¡0.29 0.87 ¡1.61 2.54 0.42 ¡0.79 ¡2.48 0.13 0.77 R-Squared: 0.857
Standard Deviation 1.67 0.84 0.82 0.84 0.84 0.78 0.74 0.78 0.78 0.99 1.02 1.02 0.99 0.99 1.02
Prob > F 0.0005 0.001 0.0005 0.143 0.0001 0.039 0.696 0.283 0.057 0.022 0.687 0.449 0.025 0.899 0.464
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Sharma et al.
Experimental design
TOC removal D C 57:64 C 1:22 £ A C 6:70
In the present study, CCD with four factors and five levels has been used for the experimental design. Four variable parameters namely pHo, j, g and t have been taken as input parameters and percentage removal of COD, color and TOC has been taken as responses of the system. pHo was varied in the range of 2–10 for SS electrode and in the range of 4–10 for Al electrode. Range of other parameters, namely j (30.86–154.32 Am¡2), g (0.5–2.5 cm) and t (30– 150 min) were same for both the electrodes. For statistical calculations, the levels for the four main variables Xt[X1 (pHo), X2 (j), X3 (g), X4 (t)] were coded as xi according to the following relationship:[31]
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xi D .Xi ¡ Xo /= dX
(2)
where, Xo is value of the Xi at the center point and dX presents the step change. The different variables and their levels for SS and Al electrodes are given in Table 2.
£ B ¡ 3:30 £ C C 8:16 £ D ¡ 4:75 £ A2 C 1:33 £ B2 ¡ 0:57 £ C2 ¡ 1:24 £ D2 ¡ 1:04 £ A £ B ¡ 0:66 £ A £ C C 0:036 £ A £ D C 3:18 £ B £ C ¡ 1:06 £ B £ D C 1:71 £ C £ D (5) The final equations in terms of coded factors for COD, color and TOC removal by Al electrode are given as: COD removal D C 48:25 ¡ 2:50 £ A C 1:38 £ B ¡ 0:64 £ C C 2:82 £ D C 0:39 £ A2 C 0:56 £ B2 C 1:23 £ C2 C 1:08 £ A £ B C 1:35 £ A £ C ¡ 2:35 £ B £ C C 0:67 £ B £ D C 1:04 £ C £ D
Results and discussions
(6)
Statistical analysis and modeling Current density, pH, electrode distance and time are important factors which affect the performance of EC process. To study the combined effects of these factors on SS and Al electrodes performance, experiment with different combinations were conducted by using CCD design. The actual design matrix along with actual and predicted percent removal of COD, color and TOC by SS and Al electrodes is given in Tables 3 and 4, respectively. Out of linear, interactive, quadratic and cubic models, quadratic model was found to be best fitted for the experimental data to obtain the regression equations. The final equations in terms of coded factors for COD, color and TOC removal by SS electrode are given as:
Color removal D C 72:71 ¡ 7:99 £ A C 5:73 £ B C 0:22 £ C C 5:48 £ D ¡ 1:82 £ A2 ¡ 0:45 £ B2 C 0:54 £ C2 ¡ 0:89 £ D2 ¡ 1:35 £ A £ B C 4:54 £ A £ C ¡ 1:75 £ A £ D C 3:22 £ B £ C ¡ 2:06 £ B £ D C 3:15 £ C £ D (7) TOC removal D C 45:20 ¡ 3:43 £ A C 3:64 £ B C 1:30 £ C C 4:37 £ D C 1:77 £ A2 ¡ 0:29 £ B2 C 0:87 £ C2 ¡ 1:61 £ D2 C 2:54 £ A £ B C 0
COD Removal D C 48:82 C 3:01 £ A C 4:08
£ A £ C ¡ 0:79 £ A £ D ¡ 2:48 £ B £ C C 0:13
£ B ¡ 0:58 £ C C 7:71 £ D 1:91 £ A2 C 2:88
£ B £ D C 0:77 £ C £ D
£ B2 C 2:55 £ C2 C 1:40 £ D2 ¡ 0:21 £ A £ B
(8)
¡ 2:46 £ A £ C C 2:50 £ A £ D C 3:94 £ B £ C ¡ 1:98 £ B £ D C 0:86 £ C £ D (3) Color Removal D C 89:57 ¡ 1:27 £ A C 9:66 £ B C 0:13 £ C C 5:69 £ D ¡ 14:81 £ A2 ¡ 0:83 £ B2 ¡ 1:16 £ C ¡ 2:18D2 C 0:067 £ A £ B C 5:70 £ A £ C ¡ 2:47 £ A £ D C 0:65 £ B £ C C 1:07 £ B £ D C 1:40 £ C £ D (4)
The value of the regression coefficient and P value for the analysis by SS and Al electrodes are given in Tables 5 and 6, respectively. The analysis of variance results for COD, color and TOC removal show F values of 3.19, 23.20 and 4.48, respectively, for SS electrode; and F values of 2.71, 8.93 and 6.45, respectively, for Al electrode. If the value of F is larger and the value of P is smaller, then the terms of coefficient are more significant.[37] These values indicate that the regression equations are able to explain the variation in responses properly. Values of P, i.e., P < 0.05 indicate that the factor or interaction of factors play a significant role. If the probability
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Two-stage electrochemical treatment of bio-digested distillery spent wash P (< 0.0001) is less than 0.05 or close to zero, then it indicates that the model terms are significant at 95% of probability level and factors play significant role which shows that the model is statistically significant.[6,38,39] Analysis of variance (ANOVA) results by SS and Al electrode are shown in Tables 5 and 6, respectively. The P value of lack of fit for COD, color and TOC is 0.0034, < 0.0467, 0.0362, respectively, for an SS electrode; and 0.1806, 0.0012, 0.0004, respectively, for an Al electrode, which are significantly low, indicating that the model fits closely with the experimental results.[29] The R2 values for COD, color and TOC removal are 0.82, 0.91 and 0.86, respectively by SS electrode and 0.66, 0.89 and 0.86, respectively by Al electrode. The P values as shown in Tables 7 and 8 can be used to find the pair of parameters among various parameters which have mostsignificant interaction.[29] In case of SS electrode, among different operating parameters the value of p for parameter ‘t’ is
Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa20
Two-stage electrochemical treatment of bio-digested distillery spent wash using stainless steel and aluminum electrodes a
a
b
Pinki Sharma , Himanshu Joshi & Vimal C. Srivastava a
Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee, India
b
Click for updates
Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, India Published online: 02 Apr 2015.
To cite this article: Pinki Sharma, Himanshu Joshi & Vimal C. Srivastava (2015) Two-stage electrochemical treatment of biodigested distillery spent wash using stainless steel and aluminum electrodes, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 50:6, 617-630 To link to this article: http://dx.doi.org/10.1080/10934529.2015.994968
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Journal of Environmental Science and Health, Part A (2015) 50, 617–630 Copyright © Taylor & Francis Group, LLC ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2015.994968
Two-stage electrochemical treatment of bio-digested distillery spent wash using stainless steel and aluminum electrodes PINKI SHARMA1, HIMANSHU JOSHI1 and VIMAL C. SRIVASTAVA2 1
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2
Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee, India Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, India
The objective of this study was to determine the effectiveness of two-stage electro-coagulation (EC) process using multi-parameter optimization for treating bio-digested distillery spent wash by stainless steel (SS) and aluminum (Al) electrodes. Operating parameters have been optimized and treatment efficiency of SS and Al electrodes have been compared by central composite design of response surface analysis in terms of COD, color and total organic carbon (TOC) removal. Individual and interactive effects of four independent parameters namely initial pH (pHo: 2–10 and 4–10 for SS and Al electrodes, respectively), current density (j: 30.86– 154.32 A m¡2), inter-electrode distance (g: 0.5–2.5 cm) and electrolysis time (t: 30–150 min) on the COD, color and TOC removal efficiency were evaluated for both the electrodes. SS electrode was found to be more effective for the removal of COD, color and TOC with removal efficiencies of 70%, 93% and 72%, respectively, as compared to Al electrode, which showed respective removal efficiencies of 59%, 80% and 55%. A two-stage EC process was also conducted to study the predominance of different types of electrodes, and to increase the efficiency of EC process. Results shows that SS followed by Al electrode (with total COD, color and TOC removal efficiency of 81%, 94% and 78%, respectively) was found to be more effective than Al followed by SS electrode combination (with total COD, color and TOC removal efficiency of 78%, 89% and 76%, respectively). Present study shows that EC process can be used as an additional step to bio-methanation process so as to meet effluent discharge standards in distilleries. Keywords: Aluminum electrode, bio-digested distillery spentwash, electro-coagulation, stainless steel electrode, response surface methodology.
Introduction Distilleries are one of the most polluting industries listed by a number of environment monitoring agencies of the world and the central pollution control board (CPCB), India.[1] India is the Asia’s second largest ethanol producer with about 2300 million litres annual production in 2006– 07.[2] About 8–15 litre of wastewater i.e. spent wash gets generated for every litre of alcohol produced in molasses based distilleries. This wastewater has extremely high chemical oxygen demand (COD) (80000–100000 mg L¡1) and biochemical oxygen demand (BOD) (40000– 50000 mg L¡1), low pH, strong odor and dark brown color.[3] Bio-methanationis currently being used as secondary treatment in most of the distilleries so as to reduce the pollution load and recover energy in the form of
Address correspondence to Pinki Sharma, Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee 247667, India; E-mail: [email protected] Received August 16, 2014. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lesa.
methane.[4] However, bio-methanation alone does not meets the discharge standards, irrespective of aeration.[5] Electro-coagulation (EC) is one of the most promising technologies for the high strength industrial wastewater treatment. In this technique, wastewater is treated by applying current to different metal electrodes, which generate coagulants upon metal dissolution into the solution. Along with the ions, gas bubbles (in the form of hydrogen gas) also get generated at cathode, which stick to the pollutants and help in their removal through flotation, i.e., electro-flotation.[6] EC process has been utilized for the various types of wastewater treatment by different researchers,[7–11] widely used for removing the color from industrial wastewaters[12–14] and for the removal of COD and color from paper mill effluents,[15,16] laundry wastewater,[17] refinery waste water[18] and restaurant wastewater.[19] EC technology has also been used for the treatment of potable water. Emamjomeh and Sivakumar[20,21] showed the effectiveness of EC process for de-fluoridation of potable waterand suggested that it could also be utilized for the de-fluoridation of industrial wastewater. A complete review on removal of pollutants by electro-coagulation and electrocoagulation/flotation processes was given by Emamjomeh
618
(RuO2-Ti) as anode, SS as cathode Graphite
Raw spent wash
Ruthenium oxide coated titanium mesh acting as anode and SS as cathode Al
Fe
SS
Diluted distillery spent wash
Biodigester effluent
Biodigester effluent
Biodigestereffluent
Raw spent wash
Graphite +titanium particles Fe
Raw spent wash
Actual effluent from alcohol plant
Electrode Used
Spent-wash Used
j: 44.65–223.25 A m¡2; pHo: 2-8; g: 1–3 cm; t: 30– 150 min; Co: 15, 600 mg L¡1. j: 44.65–223.25 A m¡2; pHo: 2-8; g: 1–3 cm and t: 30– 150 min; Co: 15, 600 mg L¡1. j: 39.06–195.31A m¡2; pHo: 3.5-9.5; g: 1–2 cm and t: 30–150 min; Co: 9310 mg L¡1. CCD
CCD
Paretoanalysis
Factorial design
BB design
One at a time
One at a time
One at a time
j: 1.5 ¡5.5 A dm¡2. j: 1–6 Adm¡2; pHo: 2–13.5; Co: 1200015000mg L¡1; type of additive:NaCl, NaBr, NaF i: 1–10 A; pHo; 1-5; type of additive: H2O2 and NaCl. j: 12.5–37.5 Am¡2; dilution: (10–30%); t: 120–240 min j: 7.142 to 57.142 A m¡2; pHo: 4–10; dilution: (5– 30%); t: 60–300 min
Optimization Procedure
Parameters Studied
j: 146.75 A m¡2; pHo6.75; g: 1 cm t: 130 min
j: 44.65A m¡2; pHo: 8; g: 2 cm; t: 120 min
j: 120 A m¡2; pHo: 6.0; g: 1 cm; and t:150 min.
i: 9 A; pHo: 1; type of additive: 1.0 M NaCl j: 31 Am¡2 dilution: 17.5% and t: 240 min j: 14.285A m¡2 dilution; pHo: 5.5; 10% and t: 180 min
—
—
Optimized Parameters
Table 1. Comparison of various studies on electrochemical treatment of distillery spent wash.
61.6
50.5
52.23
37
—
89.62
85.2
92%
COD (%)
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98.4
95.2
81
93.5
—
92.24
100
100
Color (%)
Performance
[28]
—
[6]
[32]
[31]
[30]
[29]
[27]
[26]
Reference
—
—
TOC (%)
619
Al and Fe
Ozonation + Fe and Al
SS
Al
SS and Al(Twostage process)
Raw spent wash
Raw spent wash
Biomethanatedspent wash
Biomethanatedspent wash
Biomethanatedspent wash
j: 10–30 A m¡2; pHo: 3-9; and t: 30– 180 min; Co: 42240–46440 mg L¡1. j: 6.25– 18.75 A m¡2, pHo: 3-9; agitation speed: 200– 600 rpm; t: 20– 120 min; and g: 24 cm; Co:120000 mg L¡1. j: 1–5 A m¡2; pHo: 2– 10; g: 1-3 cm; Co: 1250-5000 mg L¡1. j: 30.86–154.32 A m¡2; pHo: 2-10; g: 0.5-2.5 cm; t: 30– 150 min; Co: 10, 500–12000 mg/l j: 30.86–154.32 A m¡2; pHo: 2-10 and 4-10; g: 0.5-2.5 cm; t: 30–150 min; Co: 10500–12000 mg/l j: 30.86–154.32 A m¡2; pHo: 2–10 and 4-10; g: 0.5– 2.5 cm; t: 30– 150 min; Co: 10500-12000 mg/l CCD
CCD
CCD
One at a time
One at a time
One at a time
For SS: j: 154.32 A m¡2; pHo: 7.8; g: 2.2 cm; t: 135 minFor Al: j: 154.32 A m¡2; pHo: 6.6; g: 0.5 cm; t: 120 min
Al: j: 154.32 A m¡2; pHo: 6.6; g: 0.5 cm; t: 120 min
j: 3 Adm¡2; pH: 6 ; g: 1 cm; Co: 2500 mg L¡1. SS: j: 154.32 A m¡2; pHo: 7.8; g: 2.2 cm; t: 135 min
j: 18.7 A m¡2;pHo: 3; agitation speed: 500 rpm; t: 120 min; g: 3 cm
j: 30 A m¡2; pHo 3; cm t: 120 min
80.07
94.28
80.86
92.73
69.63
58.82
100
—
—
83.0
81.3
72.3
77.85
55.03
72.30
Present study
Present study
Present study
[35]
[34]
[33]
Notes: j: current density; i: current intensity; g: electrode gap; Co: initial COD concentration; CCD: central composite design; BB: box-behnken design; RSM: response surface methodology; SS: stainless steel; Al: Aluminium.
Al
Anaerobically treated distillery wastewater
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Sharma et al.
Table 2. Process variables and their levels for EC treatment using SS and Al electrodes. Factors Variable Unit
X
Electrode
Initial pH, pH0
X1 X1 X2 X3 X4
SS Al Both Both Both
Current density, j (A m¡2) Inter-electrode distance, g (cm) Time of electrolysis, t (min)
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Level
and Sivakumar.[22] Results have demonstrated that pollution parameters can be effectively removed via EC treatment provided operating parameters and experiment conditions are carefully optimized.[22] EC process optimization with different operating parameters has been done by many researchers by using parametric and multiple response optimization for the treatment of textile printing wastewater[23,24] and acrylic dye bearing textile
¡2
¡1
2 4 30.86 0.5 30
4 5.5 61.72 1 60
0
1
2
6 7 92.60 1.5 90
8 8.5 123.45 2 120
10 10 154.32 2.5 150
wastewater.[25] EC has also been used for treatment of distillery spent wash (Table 1).[26–35] Manisankar et al.[26,27] investigated effect of pH and current density on the treatment of distillery effluent by EC process using graphite anode electrode in the presence of supporting electrolytes (sodium chloride, sodium fluoride and sodium bromide) which resulted in 85.2% COD removal.
Table 3. Experimental data and fits for SS electrode. % COD Removal Run
pH
j (A m¡2)
g (cm)
t (min)
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 27 28 29 30
4 8 4 8 4 8 4 8 4 8 4 8 4 8 4 8 2 10 6 6 6 6 6 6 6 6 6 6 6 6
60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 60.72 60.72 123.45 123.45 90.6 90.6 30.86 154.23 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6 90.6
1 1 1 1 2 2 2 2 1 1 1 1 2 2 2 2 1.5 1.5 1.5 1.5 0.5 2.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
60 60 60 60 60 60 60 60 120 120 120 120 120 120 120 120 90 90 90 90 90 90 30 150 90 90 90 90 90 90
Actual
Predicted
34.50 42.09 50.50 48.45 54.78 47.81 56.17 53.28 36.49 36.43 38.17 32.96 57.80 58.62 56.21 54.26 61.50 54.65 68.53 71.01 43.62 52.09 76.32 67.55 45.98 52.45 61.17 58.97 73.41 66.35 75.94 71.98 39.23 35.26 37.78 47.29 55.09 51.97 62.09 70.75 58.38 60.11 54.30 58.11 36.56 39.16 66.90 69.84 45.89 48.90 48.63 48.90 50.23 48.90 47.50 48.90 49.35 48.90 51.80 48.90 SD D 4.48
% Color Removal Actual
Predicted
58.60 63.02 55.93 53.88 84.48 79.24 77.02 70.38 47.80 47.82 59.17 61.48 76.85 66.74 76.29 80.69 83.80 74.44 45.31 55.44 97.37 95.14 81.32 76.42 58.24 64.83 68.00 68.63 91.00 88.23 97.00 92.31 26.14 33.04 30.00 27.97 76.51 67.29 92.51 106.42 79.35 84.85 86.04 85.41 65.60 69.61 91.58 92.44 95.77 89.76 86.70 89.76 87.80 89.76 94.30 89.76 85.35 89.76 88.45 89.76 SD D 14.24
% TOC Removal Actual
Predicted
32.76 41.87 48.67 47.60 59.12 54.02 58.22 55.39 22.86 26.98 30.00 30.05 50.11 52.42 51.74 51.14 58.46 56.76 62.08 62.63 61.42 64.47 72.17 65.99 42.55 48.72 49.36 51.94 71.21 69.73 74.39 68.59 44.23 36.39 34.13 41.18 59.40 49.61 69.40 78.10 59.49 61.97 52.31 49.04 39.15 36.55 67.29 69.10 53.08 57.78 59.80 57.78 60.11 57.78 54.10 57.78 60.11 57.78 59.15 57.78 SD D 5.02
621
Two-stage electrochemical treatment of bio-digested distillery spent wash Table 4. Experimental data and fits for Al electrode.
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% COD Removal Run
pH
j (A m¡2)
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 27 28 29 30
5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 5.5 8.5 4 10 7 7 7 7 7 7 7 7 7 7 7 7
61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 61.72 61.72 123.45 123.45 92.6 92.6 30.86 154.32 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6 92.6
g (cm) 1 1 1 1 2 2 2 2 1 1 1 1 2 2 2 2 1.5 1.5 1.5 1.5 0.5 2.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
t (min) 60 60 60 60 60 60 60 60 120 120 120 120 120 120 120 120 90 90 90 90 90 90 30 150 90 90 90 90 90 90
Actual
Predicted
52.16 51.21 41.75 41.47 58.61 55.50 45.25 50.20 52.60 49.59 40.90 45.25 43.29 44.21 49.41 44.30 46.47 53.51 47.34 43.78 65.70 60.54 52.13 55.24 61.80 56.05 48.50 51.71 51.20 53.41 55.19 53.50 51.19 54.74 47.95 45.11 48.60 47.72 52.21 53.80 56.37 54.99 49.54 51.63 42.30 42.62 54.64 54.13 48.30 48.38 42.80 48.38 48.50 48.38 49.46 48.38 47.10 48.38 53.20 48.38 SD D 1.28
Piya-areetham et al.[28] carried out the EC study using graphite particles and titanium sponge as the voluminous anodes and Ti/RuO2 as cathode placed above anode particles and 89.62% COD and 92.24% color removal efficiency was reported. Prasad et al.[29] reported 95% color removal from distillery spent wash by EC process using Fe anode. Prasad and Srivastava.[30] employed ruthenium oxide coated titanium mesh as anode and stainless steel (SS) as cathode for distillery spent wash treatment. COD and color removal were found to be37% and 81%, respectively, at optimal conditions. Krishna et al.[33] reported 72.3% COD removal efficiency at optimum condition using aluminium (Al) electrodes and also suggested the further treatment of effluent before discharging. Khandegar and Saroha[34] studied EC treatment process by Al and Fe electrodes in various combinations and observed maximum 81.3% COD removal by Al-Al electrodes. Asaithambi et al.[35] investigated the synergistic effect of ozone assisted EC treatment on distillery effluent. Results concluded that combined technique was more
% Color Removal Actual
Predicted
72.72 72.78 54.70 53.78 84.98 84.81 66.66 60.25 59.26 51.78 53.06 50.92 72.69 77.06 73.91 70.65 81.09 84.82 68.51 58.80 91.57 88.37 48.84 56.80 75.36 76.43 67.90 68.55 91.84 93.24 85.21 79.81 84.45 82.13 42.51 49.69 54.71 59.65 83.00 82.93 72.47 74.37 73.42 76.38 53.51 59.05 80.93 80.25 74.20 73.21 74.60 73.21 73.70 73.21 72.24 73.21 70.90 73.21 73.60 73.21 SD D 2.04
% TOC Removal Actual
Predicted
37.89 40.87 30.16 29.96 50.75 47.88 42.47 47.43 44.20 45.77 34.38 36.53 43.09 42.56 47.88 43.79 45.02 49.42 36.13 35.33 60.43 56.94 54.58 53.32 63.67 57.38 41.79 44.97 54.20 54.70 57.07 52.75 57.65 59.00 46.47 46.15 40.89 36.88 46.62 51.66 49.19 46.82 47.75 51.15 32.83 30.33 44.31 47.84 46.70 45.51 44.60 45.51 45.90 45.51 45.29 45.51 44.80 45.51 45.78 45.51 SD D 2.63
efficient than either technique alone. Yavuz et al.[36] studied the effect of H2O2 on electro chemical treatment of distillery spent wash and showed 92.6% removal of COD by electro-Fenton study. Also, EC treatment of bio-digested effluent from the distillery were reported using Fe, SS and Al electrodes.[31,32] Ponselvan et al.[31] reported maximum COD removal efficiency of 52.2% at optimized condition using Al electrodes. Kumar et al.[32] used Fe electrode and studied the effect of pH, current density, inter-electrode distance and time on COD and color degradation. Maximum COD and color removal of 50.5% and 95.2%, respectively, was reported at optimized conditions. Thakur et al.[6] reported COD and color reduction of 61.6% and 98.4%, respectively, using SS electrodes. These previous studies reported COD and color removal in single stage using EC process. However, a comparative study using SS and Al electrodes and effect of two-stage EC treatment have not been reported for the treatment of distillery spent-wash. In earlier studies, multi-objective optimization of parameters was not reported. Total organic
622
Sharma et al.
Table 5. Analysis of variance for %COD, color and TOC removal with SS electrode.
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COD
Color
Source
Sum of Squares
D F
Mean Square
Mean Linear 2FI Quadratic Cubic Residual Total
84781.7 2152.6 549.4 603.9 533.9 175.7 887970.2
1 4 6 4 9 6 30
84781.69 538.2 91.6 150.9 59.3 29.3 2959.9
F Sum of Value Squares 7.22 1.32 3.19 2.03
167893.1 3162.1 676.3 6086.1 869.8 113.8 178801.2
carbon (TOC) parameter is an important parameter that indicates mineralization of organic fraction of the wastewater. This parameter has not been considered in previous studies. In the present study, the effectiveness of two-stage EC process using multi-parameter optimization for treating bio-digested distillery spent wash by SS and Al electrodes was evaluated. Three responses COD, color and TOC have been selected for optimizing the operating parameters namely initial pH (pHo), current density (j), inter-electrode distance (g) and electrolysis time (t). Response surface methodology (RSM) based central composite design (CCD) has been used for designing the experiments for the treatment of biologically treated spent wash using SS and Al electrodes. Further two-stage treatment has been performed using combination of SS and Al electrodes with and without pH adjustment between the two-stages.
Materials and methods
D F
Mean Square
1 4 6 4 9 6 30
167893.1 790.5 112.7 1521.5 96.6 18.9 5960.0
TOC F Value 2.55 0.303 23.20 5.095
Sum of Squares
D F
Mean Square
87142.3 3084.9 269.6 757.8 551.3 82.8 918880.8
1 4 6 4 9 6 30
87142.29 771.23 44.9 189.5 61.3 13.8 3062.9
F Value 11.6 0.61 4.48 4.44
are: pH: 8.0–8.3, COD: 10000–12000 mg L¡1, BOD: 3500–4000 mg L¡1, Total suspended solids (TSS): 14.5– 14.8 g L¡1, Total dissolved solids (TDS): 8.7-9.0 g L¡1 and the color was dark brown. Experimental setup The experimental setup used for EC study was similar to previous studies.[6] The 1.5 L main reactor was cubical in shape having dimensions (110 mm £ 110 mm £ 140 mm) and was made of Perspex glass. A digital direct current (DC) power of 0–18 V, 0–5 A was used to supply regulated current to the EC cell. Four mono-polar, parallel connected electrodes made of either Al or SS and of a rectangular-shaped plate with dimensions of 90 mm £ 105 mm were used in the EC experiments. The area of the electrodes exposed to the wastewater was 90 mm £ 90 mm. The gap between anodes and cathodes was varied in the range of 0.5 to 2.5 cm. To maintain the uniformity throughout the reactor, magnetic stirrer was used for providing proper stirring.
Effluent source and characterization Effluent used in present the study was collected from a nearby distillery. Samples were collected after secondary treatment. The characterization of the effluent for different parameters was done as per standard method of analysis. The effluent showed basic nature and having high COD/ BOD ratio. The main characteristics of the effluent
Experimental procedure CCD (discussed later) was used to decide the operating conditions of different EC run. At the beginning of each experimental run, the reactor was thoroughly washed and rinsed with de-ionized water followed by rinsing with the
Table 6. Analysis of variance for %COD, color and TOC removal with Al electrode. COD
Color
Source
Sum of Squares
D F
Mean Square
Mean Linear 2FI Quadratic Cubic Residual Total
75446.6 410.4 170.4 49.6 259.2 64.6 76400.7
1 4 6 4 9 6 30
75446.6 102.6 28.4 12.4 28.8 10.8 2546.7
F Value 4.72 1.45 0.57 2.68
TOC
Sum of Squares
D F
Mean Square
151590.9 3070.8 815.9 126.04 437.8 43.4 156084.9
1 4 6 4 9 6 30
151590.9 767.7 136.0 31.5 48.7 7.23 5202.8
F Value 4.26 0.98 6.73 13.48
Sum of Squares
D F
Mean Square
63709.2 1063.5 236.3 207.9 244.7 5.7 65467.4
1 4 6 4 9 6 30
63709.2 265.9 39.4 51.9 27.2 0.95 2182.3
F Value 9.57 1.63 3.11 28.60
623
Two-stage electrochemical treatment of bio-digested distillery spent wash Table 7. Coefficients, standard deviation, t and P for COD, color and TOC removal by SS electrode.
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COD Factor
Coeff icient
Intercept A-pH B- j C- g D- t A2 B2 C2 D2 AB AC AD BC BD CD
48.82 3.01 4.08 ¡0.58 7.71 ¡1.91 2.88 2.55 1.40 ¡0.21 ¡2.46 2.50 3.94 ¡1.98 0.86
Color
Standard Deviation
Prob > F
2.81 0.0019 1.41 0.049 1.37 0.009 1.41 0.686 1.41 < 0.0001 1.31 0.167 1.24 0.034 1.31 0.071 1.31 0.303 1.64 0.898 1.72 0.174 1.72 0.168 1.64 0.030 1.64 0.247 1.72 0.623 R-Squared: 0.823
Standard Deviation
Prob > F
Coeff icient
Standard Deviation
Prob > F
3.30 1.66 1.61 1.66 1.66 1.55 1.46 1.55 1.55 1.94 2.02 2.02 1.94 1.94 2.02 R-Squared: 0.909
< 0.0001 0.455 < 0.0001 0.939 0.004 < 0.0001 0.575 0.465 0.178 0.973 0.013 0.242 0.743 0.588 0.501
57.64 1.22 6.70 ¡3.30 8.16 ¡4.75 1.33 ¡0.57 ¡1.24 ¡1.04 ¡0.66 0.04 3.18 ¡1.06 1.72
2.65 1.33 1.29 1.33 1.33 1.24 1.17 1.24 1.24 1.55 1.63 1.63 1.55 1.55 1.63 R-Squared: 0.866
0.0003 0.374 0.0001 0.026 < 0.0001 0.002 0.272 0.654 0.334 0.513 0.689 0.983 0.059 0.505 0.308
Coefficient 89.57 ¡1.27 9.66 0.13 5.69 ¡14.81 ¡0.83 ¡1.16 ¡2.18 0.07 5.70 ¡2.47 0.65 1.07 1.40
TOC
sample solution. A sample volume of 1.2 L was used for each experimental run. The pH of the solutions was initially measured andthen adjusted as per the designed runs by adding 0.1 N NaOH or 0.1 N H2SO4 solutions.[6] After that the electrode distance was set and current density was maintained constant throughout the run by adjusting the current supplied. Color and TOC of the effluent samples before and after the EC were measured by double beam UV visible spectrophotometer (HACH, DR 5000, Loveland, CO, USA) and TOC analyser (TOC-V-CSN 39208967, Shimadzu, Japan), respectively. COD was
measured initially and after specified period of timeusing digestion unit (DRB 200, HACH) and UV visible spectrophotometer (HACH, DR 5000). COD removal was calculated by using the following relationship: % COD removal ðYÞ D 100.CODo ¡ CODt / /CODo (1) where, CODo is the initial COD (mg L¡1) and CODt is the COD after specified time (mg L¡1).
Table 8. Coefficients, standard deviation, t and P for COD, color and TOC removal by Al electrode. COD Factor
Coeff icient
Intercept 48.25 A-pH ¡2.50 B- j 1.38 C- g ¡0.64 D- t 2.82 A2 0.39 B2 0.56 C2 1.23 AB 1.08 AC 1.35 BC ¡2.35 BD 0.67 CD 1.04
Color
Standard Deviation
Prob > F
1.51 0.90 0.88 0.90 0.90 0.83 0.78 0.83 1.07 1.10 1.07 1.07 1.10
0.029 0.013 0.136 0.488 0.006 0.647 0.482 0.155 0.327 0.236 0.042 0.541 0.357
R-Squared: 0.656
Factor Intercept A-pH B- j C- g D- t A2 B2 C2 D2 AB AC AD BC BD CD
TOC
Coeff Standard icient Deviation
Prob > F
72.71 2.31 ¡7.99 1.16 5.73 1.14 0.22 1.16 5.48 1.16 ¡1.82 1.08 ¡0.45 1.02 0.54 1.08 ¡0.89 1.08 ¡1.35 1.38 4.54 1.42 ¡1.76 1.42 3.22 1.38 ¡2.06 1.38 3.15 1.42 R-Squared: 0.892
< 0.0001 < 0.0001 0.0001 0.849 0.0003 0.112 0.664 0.623 0.424 0.343 0.006 0.234 0.034 0.155 0.042
Coeff icient 45.20 ¡3.43 3.64 1.30 4.37 1.77 ¡0.29 0.87 ¡1.61 2.54 0.42 ¡0.79 ¡2.48 0.13 0.77 R-Squared: 0.857
Standard Deviation 1.67 0.84 0.82 0.84 0.84 0.78 0.74 0.78 0.78 0.99 1.02 1.02 0.99 0.99 1.02
Prob > F 0.0005 0.001 0.0005 0.143 0.0001 0.039 0.696 0.283 0.057 0.022 0.687 0.449 0.025 0.899 0.464
624
Sharma et al.
Experimental design
TOC removal D C 57:64 C 1:22 £ A C 6:70
In the present study, CCD with four factors and five levels has been used for the experimental design. Four variable parameters namely pHo, j, g and t have been taken as input parameters and percentage removal of COD, color and TOC has been taken as responses of the system. pHo was varied in the range of 2–10 for SS electrode and in the range of 4–10 for Al electrode. Range of other parameters, namely j (30.86–154.32 Am¡2), g (0.5–2.5 cm) and t (30– 150 min) were same for both the electrodes. For statistical calculations, the levels for the four main variables Xt[X1 (pHo), X2 (j), X3 (g), X4 (t)] were coded as xi according to the following relationship:[31]
Downloaded by [New York University] at 07:43 25 May 2015
xi D .Xi ¡ Xo /= dX
(2)
where, Xo is value of the Xi at the center point and dX presents the step change. The different variables and their levels for SS and Al electrodes are given in Table 2.
£ B ¡ 3:30 £ C C 8:16 £ D ¡ 4:75 £ A2 C 1:33 £ B2 ¡ 0:57 £ C2 ¡ 1:24 £ D2 ¡ 1:04 £ A £ B ¡ 0:66 £ A £ C C 0:036 £ A £ D C 3:18 £ B £ C ¡ 1:06 £ B £ D C 1:71 £ C £ D (5) The final equations in terms of coded factors for COD, color and TOC removal by Al electrode are given as: COD removal D C 48:25 ¡ 2:50 £ A C 1:38 £ B ¡ 0:64 £ C C 2:82 £ D C 0:39 £ A2 C 0:56 £ B2 C 1:23 £ C2 C 1:08 £ A £ B C 1:35 £ A £ C ¡ 2:35 £ B £ C C 0:67 £ B £ D C 1:04 £ C £ D
Results and discussions
(6)
Statistical analysis and modeling Current density, pH, electrode distance and time are important factors which affect the performance of EC process. To study the combined effects of these factors on SS and Al electrodes performance, experiment with different combinations were conducted by using CCD design. The actual design matrix along with actual and predicted percent removal of COD, color and TOC by SS and Al electrodes is given in Tables 3 and 4, respectively. Out of linear, interactive, quadratic and cubic models, quadratic model was found to be best fitted for the experimental data to obtain the regression equations. The final equations in terms of coded factors for COD, color and TOC removal by SS electrode are given as:
Color removal D C 72:71 ¡ 7:99 £ A C 5:73 £ B C 0:22 £ C C 5:48 £ D ¡ 1:82 £ A2 ¡ 0:45 £ B2 C 0:54 £ C2 ¡ 0:89 £ D2 ¡ 1:35 £ A £ B C 4:54 £ A £ C ¡ 1:75 £ A £ D C 3:22 £ B £ C ¡ 2:06 £ B £ D C 3:15 £ C £ D (7) TOC removal D C 45:20 ¡ 3:43 £ A C 3:64 £ B C 1:30 £ C C 4:37 £ D C 1:77 £ A2 ¡ 0:29 £ B2 C 0:87 £ C2 ¡ 1:61 £ D2 C 2:54 £ A £ B C 0
COD Removal D C 48:82 C 3:01 £ A C 4:08
£ A £ C ¡ 0:79 £ A £ D ¡ 2:48 £ B £ C C 0:13
£ B ¡ 0:58 £ C C 7:71 £ D 1:91 £ A2 C 2:88
£ B £ D C 0:77 £ C £ D
£ B2 C 2:55 £ C2 C 1:40 £ D2 ¡ 0:21 £ A £ B
(8)
¡ 2:46 £ A £ C C 2:50 £ A £ D C 3:94 £ B £ C ¡ 1:98 £ B £ D C 0:86 £ C £ D (3) Color Removal D C 89:57 ¡ 1:27 £ A C 9:66 £ B C 0:13 £ C C 5:69 £ D ¡ 14:81 £ A2 ¡ 0:83 £ B2 ¡ 1:16 £ C ¡ 2:18D2 C 0:067 £ A £ B C 5:70 £ A £ C ¡ 2:47 £ A £ D C 0:65 £ B £ C C 1:07 £ B £ D C 1:40 £ C £ D (4)
The value of the regression coefficient and P value for the analysis by SS and Al electrodes are given in Tables 5 and 6, respectively. The analysis of variance results for COD, color and TOC removal show F values of 3.19, 23.20 and 4.48, respectively, for SS electrode; and F values of 2.71, 8.93 and 6.45, respectively, for Al electrode. If the value of F is larger and the value of P is smaller, then the terms of coefficient are more significant.[37] These values indicate that the regression equations are able to explain the variation in responses properly. Values of P, i.e., P < 0.05 indicate that the factor or interaction of factors play a significant role. If the probability
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Two-stage electrochemical treatment of bio-digested distillery spent wash P (< 0.0001) is less than 0.05 or close to zero, then it indicates that the model terms are significant at 95% of probability level and factors play significant role which shows that the model is statistically significant.[6,38,39] Analysis of variance (ANOVA) results by SS and Al electrode are shown in Tables 5 and 6, respectively. The P value of lack of fit for COD, color and TOC is 0.0034, < 0.0467, 0.0362, respectively, for an SS electrode; and 0.1806, 0.0012, 0.0004, respectively, for an Al electrode, which are significantly low, indicating that the model fits closely with the experimental results.[29] The R2 values for COD, color and TOC removal are 0.82, 0.91 and 0.86, respectively by SS electrode and 0.66, 0.89 and 0.86, respectively by Al electrode. The P values as shown in Tables 7 and 8 can be used to find the pair of parameters among various parameters which have mostsignificant interaction.[29] In case of SS electrode, among different operating parameters the value of p for parameter ‘t’ is
