Treatment of multicomponent aqueous solution of purified terephthalic acid wastewater by electrocoagulation process: Optimization of process and analysis of sludge

Journal of the Taiwan Institute of Chemical Engineers 60 (2016) 383–393

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Treatment of multicomponent aqueous solution of purified terephthalic acid wastewater by electrocoagulation process: Optimization of process and analysis of sludge Krishan Kishor Garg∗, Basheshwer Prasad Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India

a r t i c l e

i n f o

Article history: Received 24 May 2015 Revised 22 October 2015 Accepted 25 October 2015 Available online 17 November 2015 Keywords: Terephthalic acid Benzoic acid Para-toluic acid Electrocoagulation Optimization Sludge analysis

a b s t r a c t The present research work is based on degradation of major pollutants of purified terephthalic acid (PTA) wastewater by electrocoagulation (EC) process. Terephthalic acid (TPA), benzoic acid (BA) and para-toluic acid (p-TA) are the major pollutants of PTA wastewater. A central composite design (CCD) has been developed for maximum removal of TPA, BA, p-TA, COD and minimum consumption of energy. Effects of various process parameters viz. pH: (5–13), current density: (49.5–255.5 A/m2 ), supporting electrolyte concentration, NaCl: (0.25–2.25 g/L) and electrolysis time: (15–95 min) are studied on removal efficiencies of responses. Aluminium (Al) and iron (Fe) were selected as electrode materials. Maximum percentage removal of TPA: 56.21, 54.10; BA: 59.52, 53.84; p-TA: 45.71, 39.91, and COD: 49.91, 42.95 are achieved at optimum operating conditions by Al and Fe electrodes respectively. Operating cost of the process was calculated based on energy consumption, electrode consumption, sludge disposable, and transportation costs and found $13.64 and $14.46 per kg of COD removed by Al and Fe electrodes respectively. Sludge residues obtained after EC treatment at optimum operating conditions are analyzed by settling, sludge volume index (SVI), XRD, SEM/EDX, point of zero charge (PZC), FTIR and DGA/TGA. © 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1. Introduction Purified terephthalic acid (PTA) wastewater mainly consists of terephthalic acid (TPA), benzoic acid (BA) and para-toluic acid (p-TA). These compounds contribute about 75% of the COD of PTA wastewater. High reproductive toxicity is exhibited by PTA wastewater on male mice and public health [1–2]. Aromatic compounds in PTA wastewater are responsible for damage in kidneys, bladder, testis, and liver [3–6]. Pollutants of PTA wastewater also diminish the density of viable spermatogenic cells, relative testis weights and responsible for histopathological abnormalities. It is also cause of acute toxicity, molecular toxicity, chronic toxicity, and subacute toxicity [2,7]. PTA wastewater is extremely toxic at concentrations higher than 1000 mg/L [8–10]. Toxic nature of PTA wastewater pollutants has been investigated by histopathological observation, hematological analysis and epidemiological investigation [4–5,11]. According to Zhang et al. [12] at lower concentration (15 mg/L at 10 °C), toxicity of TPA becomes very less (Non Toxic) but at higher concentration it is very harmful for human being and microorganisms

∗

Corresponding author. Tel.: +91 8979528557. E-mail address: [email protected], [email protected] (K.K. Garg).

[7]. According to World Health Organization (WHO) maximum tolerable intake capacity of BA for a human should not be more than 5 mg/kg of body weight per day. Due to toxic nature of BA, some countries have stopped the usage of BA as a food additive even in trace amount [13–14]. Para-toluic acid is also a major pollutant of PTA wastewater and characterized in the class of highly hazardous pollutants due to its toxic nature. It can be a cause of decrease in epididymal oligozoospermia. Due to toxic nature of TPA, BA and p-TA, USEPA added these pollutants in the list of priority pollutants [15–17]. Precipitating nature of TPA, BA and p-TA is similar to arsenic and depends on pH of the solution. The most common methods of removing arsenic from aqueous process streams are by precipitation as calcium arsenate, As(III) sulfide, or ferric arsenate [18–20]. The sulfide As2 S3 has its lowest solubility below pH = 4, but that solubility is significantly higher than has been generally accepted. Calcium arsenates can be precipitated from As(V) solutions, by addition of lime at high pH (> 8) [20–21]. As(V) can also be precipitated from process solutions below pH = 2 with Fe(III) to form ferric arsenate, FeAsO4 .2H2 O. TPA, BA, and p-TA containing wastewater shows similar behavior at natural pH (̴ 5.6). These compounds are present in PTA wastewater in the ionized state with these pKa (TPA: 3.51; BA: 4.2; p-TA: 4.36) constants. These acids are precipitated in the solution at low pH (<5). Solubility of these compounds increases in the solution with increasing OH– ions in the solution [22–24].

http://dx.doi.org/10.1016/j.jtice.2015.10.038 1876-1070/© 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

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K.K. Garg, B. Prasad / Journal of the Taiwan Institute of Chemical Engineers 60 (2016) 383–393 Table 1 Electrocoagulation reactor specifications and electrodes characteristics. Electrode characteristics Material (anode and cathode) Shape Size of electrode Affected area of electrode No. of electrode Effective area Electrode arrangement

Reactor specifications Al, Fe Rectangular 11 cm × 6 cm × 0.1 cm 7 cm × 6 cm × 0.1 cm 6 259.80 cm2 Parallel connection

In India, no discharge limit has been prescribed for these compounds by pollution regulating agencies like Central Pollution Control Board (CPCB) or Ministry of Environment and Forest (MOEF). MOEF has given maximum permissible discharge limit of COD < 250 mg/L for petrochemical wastewater [25]. Hence, it is utmost important to determine the efficient methods for treatment of PTA wastewater to meet requirement of discharge limit. In recent years, many researchers have worked on the treatment of PTA wastewater by various methods like anaerobic and aerobic biological treatment [26–34], electrochemical [35], adsorption [36–39], coagulation–flocculation [25,33,40], advanced oxidation processes (AOP)–UV assisted ozonation (UV/O3 ), photo Fenton oxidation (UV/H2 O2 /Fe2 SO4 ), ozone assisted photochemical oxidation (UV/O3 /H2 O2 ), photo catalytic degradation, ozone assisted photo-Fenton oxidation (UV/O3 /H2 O2 /FeSO4 ), supercritical water oxidation, radiation treatment (using γ -rays) [41–42], oxidation process [43–44], crystallization [45] and thermochemical precipitation [46]. Electrocoagulation (EC) is an important process used for treatment of various industries wastewater. In this process, coagulant ions are generated in-situ by electro-oxidation of anode. In recent years, EC process has been successfully applied for removal of dimethyl phthalate, indium, COD, and turbidity from chemical mechanical polishing (CMP) wastewater, polyvinyl alcohol, and salicylic acid from various industries wastewater [47–53]. Response surface methodology (RSM) is an important tool in Design Expert Software, which is mainly used for optimization of the various processes. In recent years, RSM has been successfully employed for treatment of various industries wastewater like chicken processing, rice mill, pulp and paper, chromium, petroleum refinery, shrimp cooking, tannery, cheese whey, textile, tetra-hydro-furan, electro-less plating industry etc. [54–64]. However, being such an important tool of optimization, it has never been used previously for this type of studies. Accordingly in present study, EC process has been employed for treatment of multicomponent aqueous solution of purified terephthalic wastewater using Al and Fe electrodes. RSM in Design Expert Software (8.0.7.1, 2010, Stat-Ease Inc. Minneapolis) was used for optimization of operating parameters (pH, current density, electrolysis time, and NaCl concentration) for maximum removal of TPA, BA, p-TA and COD simultaneously with minimum energy consumption. Sludge samples obtained after EC treatment at optimum operating conditions are also analyzed briefly. Operating cost of the process is also estimated based on energy consumption, electrode consumption, and sludge disposal and transportation costs.

Reactor type Shape and material Dimensions Volume (m3 ) Stirring mechanism Electrode gap (cm) Magnetic stirrer speed (RPM)

Batch Plexiglass (rectangular) 13 cm × 12 cm × 0.5 cm 0.0016 Magnetic bar 1 cm (constant) 500–700 RPM (constant)

dia. Sodium hydroxide (NaOH), sulfuric acid (H2 SO4 ), isopropyl alcohol (C3 H8 O), methanol (CH3 OH), acetic acid (CH3 COOH), silver sulfate (AgSO4) and mercury (II) sulfate (HgSO4 ) were purchased from Ranbaxy Chemical Limited, New Delhi, India. Stock solutions of TPA (1000 mg/L), p-TA (1000 mg/L) and BA (1000 mg/L) were prepared at laboratory scale. Tap water purified by Millipore Milli-Q system was used. All wastewater samples and reagents were always preserved at 4 °C to reduce unwanted microorganism growth and biodegradation. Working concentrations of TPA (400 mg/L), BA (400 mg/L) and p-TA (500 mg/L) are chosen according to previous studies [25,28,46,65–67]. Initial COD of wastewater was estimated as 2055 mg/L. 3. Experimental procedure and analysis of samples The experimental conditions for batch electrocoagulation study for treatment of synthetic multicomponent (TPA + BA + p-TA) wastewater are given in Table 1. Fig. 1 shows the schematic diagram of experimental setup. The ranges of operating parameters as determined by conducting initial test runs are given in Table 2. Direct current (DC) power supply with provision of varying voltage (0–24 V) and current (0–10 A) was used to power electrodes connected in parallel mode. All experiments were conducted at room temperature (25 ± 2 °C). Current density (CD) of the electrolytic solution was adjusted by using voltage regulator and variable rheostat (5–9). pH of electrolytic solution was adjusted by (1 N, 2 N and 5 N) solutions of NaOH and H2 SO4 during the whole experimentation. The collected samples were analyzed by using HPLC System with detector wavelength set to 240 nm [68–70]. HPLC was operated in isocratic mode with a C-18 column at ambient temperature. A solution of 91% Millipore water, 2% acetic acid, 7% isopropyl alcohol was used as a mobile phase [25,43] with 1.2 mL/min flow rate. Eqs. 1 and 2 were used for the calculation of percentage removal of TPA, BA, p-TA, or COD and energy consumption (kWh/kgCODremoved ) respectively.

% Removal of TPA, BA, p − TA and COD =

Ci –C f × 100 Ci

(1)

where Ci and Cf are the initial and final concentrations of TPA, BA, p-TA or COD.



Energy consumption =

kWh kgCODremoved

VIt × 100

(% Removal of COD)CCODi × VR



× 1000

(2)

2. Materials and methods

where V is voltage, I is current, t is operating time in hours, VR is the volume of the wastewater treated in L and CCODi is the initial COD of wastewater, mg/L [71].

2.1. Chemicals and wastewater sample preparation

4. Results and discussion

All the chemicals used in this study were of analytical reagent (AR) grade. Terephthalic acid (C8 H6 O4 ), benzoic acid (C7 H6 O2) and potassium dichromate (K2 Cr2 O7 ) were supplied by Himedia Laboratories Pvt. Ltd. Mumbai, India. Para-toluic acid (C8 H8 O2 ) and sodium chloride (NaCl) were supplied by Loba chemical Pvt. Ltd. Mumbai In-

4.1. Effect of pH, CD, time, and NaCl concentration on % removal of TPA, BA, p-TA and COD by Al and Fe electrodes All experimental runs were conducted according to sets predicted by central composite design (CCD) as given in Table 3. The removal

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Power Source

A

V

+ Al or Fe Anode in Parallel Connection

Al or Fe Cathode in Parallel Connection

Rheostat

Aqueous solution of (TPA+BA+p-TA)

Electrocoagulation Cell

Magnetic Bar Stirrer

Magnetic stirrer

TEMPERATURE

SPEED

Fig. 1. Schematic diagram of experimental set up. Table 2 Experimental regions of operating parameters for central composite design. Central composite design characteristics Levels

–2(–α ) –1 0 +1 +2(α )

Parameter (Range) X1 pH (5–13)

X2 CD (A/m2 ) (49.5→255)

X3 NaCl concentration (g/L) (0.25→2.25)

X4 Time (min) (15→95)

5.00 7 9 11 13

49.50 101.00 152.50 204.00 255.50

0.25 0.75 1.25 1.75 2.25

15 35 55 75 95

efficiency of TPA decreases with increasing value of pH of the solution using Al and Fe electrodes respectively as shown in Fig 2(a and e). It is due to the dissolution of Al and Fe electrodes in metal (M) ions which are subsequently hydrolyzed to form monomeric and polymeric species and solid precipitates: MOH2+ , M(OH)2 + , M2 (OH)2 4+ , M(OH)4 5+ , M(OH)3 0 (s) and M(OH)4− . The removal of TPA from the solution at different pH follows two different mechanisms, viz., charge neutralization, and adsorption. At low pH, the anionic TPA molecules present in the solution coordinate with metal cations to form insoluble charge-neutral products. The neutralized organics are

able to form bigger flocs by van der Waal forces of attraction. These bigger flocs then settle down. However, as the pH of the solution increases to alkaline range, the OH− ions compete with TPA for metal adsorption sites and the precipitation of metal hydroxides occurs by co-precipitation. Under highly alkaline conditions, the coagulating species become less positively charged diminishing their attraction to the anionic TPA molecules. Therefore, the growth rate of aggregates or solid precipitates is small at high pH, resulting in reduced removal of TPA [72–73]. Maximum removal of TPA—56.21% and 54.10% is achieved at optimal operating conditions for Al and Fe electrodes

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Fig. 2. Effect of pH, C.D., time and NaCl concentration on % removal of TPA, BA, p-TA and COD for both Al and Fe electrodes.

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Table 3a (Part-1): Actual and CCD predicted Removal efficiencies of TPA, BA, p-TA, COD and Energy consumption with Al and Fe electrodes. Run no. Independent variables X1 (pH)

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

7 11 7 11 7 11 7 11 9 9 7 13 7 11 7 11 7 11 9 9 5 11 9 9 9 9 9 9 9 9

X2 (CD) (A/m2 )

101 101 204 204 101 101 204 204 152.5 152.5 101 101 204 204 101 49.5 204 204 152.5 152.5 152.5 152.5 101 204 152.5 255.5 152.5 101 101 204

% Removal of TPA:(Y1 ) X3 (NaCl) (g/L)

0.75 0.75 1.75 2.25 1.75 1.75 1.75 1.75 1.25 1.75 0.75 0.75 0.75 0.25 1.75 1.75 1.75 1.75 0.75 1.25 1.25 1.25 1.25 1.25 0.75 1.25 1.25 1.25 1.25 0.75

X4 (t) (min.) Al

75 35 35 75 35 75 75 35 55 55 35 75 75 15 95 35 35 75 55 75 55 55 55 55 35 55 35 75 35 55

% Removal of BA:(Y2 ) Fe

Al

Fe

Actual (Exp.)

CCD Predicted

Actual (Exp.)

CCD Predicted

Actual (Exp.)

RSM Predicted

Actual (Exp.)

CCD Predicted

24.36 15.33 54.27 33.38 25.36 32.26 64.27 35 45 43.27 28.25 22.26 53 15 44.87 16.11 45.26 40.22 40.66 52.27 98.5 40.98 33.26 49 26.3 30.66 37.73 36.37 24 36.27

26.78 16.85 48.34 31.49 26.84 35.51 64.41 34.07 43.96 46.25 28.39 22.59 55.22 12.32 48.21 13.63 53.00 40.96 38.67 44.90 95.20 45.75 33.44 46.62 32.16 33.00 38.40 29.17 23.62 36.69

23.26 13.66 51.88 32.6 23.25 29.2 61.55 33.2 44.6 42.8 29.13 19.86 51.9 13.85 41.66 14.22 39.33 34.7 37.33 50 96.3 34.87 33.8 44.5 26.7 28.77 36 33.3 23.3 33.66

27.22 16.75 43.87 30.01 25.50 33.71 61.91 31.10 42.09 43.83 28.75 18.53 53.33 11.13 44.64 11.89 44.90 36.94 36.43 41.43 92.68 42.37 31.51 43.61 30.41 30.07 36.24 29.05 22.44 34.82

22.76 21.87 31.28 33 22.18 38.37 52 30.22 64 61.37 15 21.22 43.2 17.87 34.36 22.11 34.9 32.87 54.21 64.27 19 45.27 41.55 55.55 47.65 50 43.35 42.25 33.25 47

23.36 29.05 34.56 29.41 22.94 42.30 51.05 29.40 62.40 61.57 13.95 19.25 45.20 18.13 33.65 19.65 37.96 41.08 55.78 58.35 18.32 48.13 46.30 55.13 39.35 45.21 42.50 44.81 32.35 52.77

17.9 17.45 29.5 26.7 18.8 31.33 47.6 25.55 58.66 55.88 13.8 18.75 36.65 16.8 28.85 20.46 28.31 25.6 49.9 57.43 17.4 38.77 36.73 49.34 41.88 42.56 36.9 36.2 30.22 40.68

19.09 26.61 30.38 23.16 20.57 36.09 45.73 24.16 57.55 52.01 11.95 18.16 36.06 16.50 28.39 19.43 32.02 31.01 50.72 55.30 16.67 41.19 40.18 48.34 34.43 38.55 36.83 38.22 27.86 42.43

respectively. The removal efficiency of BA, p-TA and COD increases by increasing pH value of the solution. Removal efficiency of these compounds decreases beyond optimum pH (Al: 8.18 Fe; 8.00) values (Fig. 2b–d; f–h). This trend appears due to the formation of Al(OH)4 and Fe(OH)4 flocs. These flocs remain in highly soluble form or show poor binding nature with pollutant ions. The removal efficiency of TPA, BA, p-TA and COD also increases with increasing value of CD, time and NaCl concentration. The removal efficiency of pollutants depends upon the concentration of ions produced by the electrodes during the electrolysis process. CD of electrolytic solution shows metal dissolution rate and size of bubble formation. It also affects the rate of formation of flocs [74–75]. Generation of metal ions increases in the solution with increasing value of CD. Thereafter, small size of flocs aggregate together and form bigger sized flocs. The rate of formation of flocs decreases in the solution with decreasing concentration of metal ions, thereafter, removal efficiency of TPA, BA, p-TA and COD decreases (Fig. 2a–h). Optimum percentage removal of TPA: 56.21, 54.10; BA: 59.52, 53.84; p-TA: 45.71, 39.91 and COD: 49.91, 42.95 are found at optimum operating conditions by Al and Fe electrodes respectively (Table 4). Removal efficiency of pollutant ions increases with increasing value of electrolysis time and after optimum value of time: 63.47 min (Al) and 65.55 min (Fe) removal efficiency of TPA, BA, p-TA and COD decreases. This is due to poor availability of metal hydroxide ions in the electrolytic solution. Concentration of supporting electrolyte (NaCl) supports to increase the density of ions (anions and cations) in the solution. Ionic strength of the electrolytic solution increases with increasing concentration of NaCl resulting in removal efficiency of TPA, BA, p-TA and COD to increase. (Fig. 2i–p). Electrode passivation is a serious problem in the application of electrocoagulation. To eliminate the

passivation layer and enhance the dissolution rate of Al or Fe electrodes is thus crucial. The removal efficiency of TPA, BA, p-TA and COD decreases beyond NaCl concentration-1.69 g/L (Al), 1.74 g/L (Fe). This demonstrated that an excess amount of Cl– in the solution is detrimental to the coagulation of the pollutants. The likely explanation may be that Cl– ions in the solution containing Al(OH)3 form some transitory compounds, such as Al(OH)2 Cl, Al(OH)Cl2 , and AlCl3 . The transitory compounds then finally dissolve in the solution with excess Cl− , as a form of AlCl4 − [76], thus, the amount of Al(OH)3 coagulants decreases, resulting in the decrease of the removal efficiency. In addition to the coagulation process, an indirect electrochemical oxidation occurs if the solution contains Cl− . The Cl− will be discharged at the anode to generate Cl2 , which will be immediately dissolved in the solution, chemically converted to ClO− . The ClO− can oxidize the pollutants effectively. Therefore, the removal efficiency of pollutants will increase [77–79]. Al and Fe electrodes show similar behavior with addition of Cl− ions in the solution. Following physiochemical reactions occur during the process by addition of Cl− in the solution using Al electrodes [77–79].

Al(OH)3 + Cl− = Al(OH)2 Cl + OH−

(3)

Al(OH)2 Cl + Cl− = Al(OH)Cl2 + OH−

(4)

Al(OH)Cl2 + Cl− = AlCl3 + OH−

(5)

AlCl3 + Cl− = AlCl4

−

(6)

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Table 3b (Part -2): Actual and CCD predicted removal efficiencies of TPA, BA, p-TA, COD and Energy consumption with Al and Fe electrodes. % Removal of p-TA: (Y3 ) Al Run no. Actual (Exp.) 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

17 16.33 22.36 35 15.27 32.63 34.36 34 47 48.17 13.88 19 36.4 20.2 28.66 18.44 20.8 36 44.4 50.36 16.22 44.8 32.26 41.88 35.08 35 35.9 30.38 22.3 39

% COD removal: (Y4 ) Fe

Al

Energy consumption (kWh/kg CODremoved ): (Y5 ) Fe

Al

Fe

CCD Predicted

Actual (Exp.)

CCD Predicted

Actual (Exp.)

CCD Predicted

Actual (Exp.)

CCD Predicted

Actual (Exp.)

CCD Predicted

Actual (Exp.)

CCD Predicted

18.45 18.69 20.86 32.77 16.12 35.75 34.00 33.57 44.45 45.46 11.22 16.01 37.13 21.01 26.82 16.77 22.48 41.75 44.79 47.17 16.77 43.52 34.12 43.05 32.88 31.78 34.23 32.83 23.92 41.71

14.3 13.77 18.55 28.9 14.26 28.7 31.5 28.47 41.9 40.34 12.13 15.77 29.44 19.5 25.4 17.33 18.2 29.8 39 43.5 14.66 39.7 28.56 36.8 30.88 29.85 32.7 25.8 20.2 33

14.68 18.91 17.88 26.78 14.75 31.09 29.80 28.27 38.82 39.72 9.96 13.00 30.85 19.86 24.29 15.46 22.02 33.26 38.71 40.67 15.44 38.09 30.31 37.40 27.33 27.19 30.30 22.55 21.64 35.89

21.9 15.3 29.2 33.1 16.8 31.2 43 31.2 52.3 50.7 16.2 19.3 39.2 19.3 33.3 18 27.1 34.8 46 53 25.6 41 35.5 46 40 42 38.9 36.2 26.2 42.3

22.92 19.68 28.22 32.70 17.54 31.74 42.15 30.71 46.75 47.29 14.75 17.23 41.25 19.55 32.26 15.12 32.45 35.77 46.61 51.21 25.01 43.43 38.26 47.48 38.07 38.81 36.92 37.62 26.74 45.36

18.6 14.6 25.9 29.7 15.2 27.2 39.7 26.4 45.8 43.2 14 17.3 34.9 17 29.6 16.3 23.8 29.7 38.8 49 22.1 34.4 28.2 37.4 34 33 33.4 31.5 22.8 34.8

19.51 20.29 25.21 27.12 16.63 31.38 38.72 25.89 44.59 40.95 12.86 14.01 37.32 16.79 29.57 13.48 28.33 34.77 39.72 48.54 21.04 34.49 30.40 39.45 32.20 30.08 31.96 31.52 23.18 37.28

57.2 36.8 81.5 159.1 33.9 39.7 121.8 76.7 36.2 37.7 34.4 65.6 133.6 53.5 47 12.7 87.9 150.5 40.9 49.4 74 45.5 25.1 83 28.9 121.9 46.2 34.2 21 90.7

53.3 30.5 83.3 163.4 33.1 35.3 124.6 80.8 37.4 43.0 39.7 71.0 130.1 51.8 48.8 15.6 78.8 145.1 41.7 52.8 74.1 49.7 25.1 81.0 32.3 129.4 38.9 31.6 24.4 84.2

95.7 55.3 91.5 177.3 53.5 65.9 134.0 90.7 54.4 57.3 57.2 102.9 151.7 61.0 75.4 17.6 100.0 177.3 63.5 69.9 112.8 72.5 46.1 102.6 45.7 150.7 45.9 56.9 35.4 110.8

94.4 51.4 93.1 182.4 52.2 59.9 140.9 96.3 58.9 59.9 65.4 110.1 147.1 61.0 75.3 22.0 88.0 170.4 64.1 73.2 112.5 72.8 38.9 100.9 53.2 156.2 46.7 57.5 34.6 105.7

Fig. 3. Effect of pH, C.D., time and NaCl concentration on E. consumption for both Al and Fe electrodes.

4.2. Effect of pH, CD, time, and NaCl concentration on energy consumption for Al and Fe electrodes

5. Response surface methodology (RSM) study 5.1. Optimization

Consumption of electrical energy strongly depends upon the current density and time. Energy consumption is an inverse function of removal efficiency of COD. In present study energy consumption (kWh/kg COD removed) varies from (12.7 to 159.1) for Al and (17.63 to 177.29) for Fe electrodes. Energy consumption decreases with increasing value of pH, CD, time and NaCl concentration for Al and Fe electrodes (Fig. 3a–d). Values of energy consumption increase after optimum values of operating variables. Minimum consumption of energy: 80.15 (Al), 110.85 (Fe) was found at optimum operating conditions.

Process was optimized for maximum removal of TPA, BA, p-TA, COD, and minimum consumption of energy according to the central composite design (Table 3). All optimum operating conditions along with their test run values are given in Table 4. All optimum operating conditions were reconfirmed by conducting test runs. The test results indicate that optimum operating conditions given by the CCD are closer to test run values, which shows good adequacy of the model.

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Table 4 Optimum-operating conditions predicted by CCD and at experimental test runs using Al and Fe electrodes. pH

Al Fe

8.18 8.0

CD (A/m2 )

172.97 180.04

NaCl Conc. (g/L)

1.69 1.74

Time (min) % Removal of TPA (mg/L) % Removal of BA

63.47 65.55

% Removal of p-TA

% Removal of COD (mg/L) Energy Kwh/kg COD removed

CCD Suggested

Test Run

CCD Suggested

Test Run

Rsm Suggested

Test Run

CCD Suggested

Test Run

CCD Suggested

Test Run

56.21 54.10

54.3 51.5

59.52 53.84

56.6 52.3

45.71 39.91

43.5 37.2

49.91 42.95

44.6 40.1

80.15 110.85

90.9 125.3

5.2. Model equations for responses based on ANOVA results for Al and Fe electrodes Regression model equations in terms of independent variables have been expressed by a second order polynomial for both Al and Fe electrodes for different responses Y1 , Y2 , Y3 as given below: General equation

Yi = b0 + b1 × pH + b2 × j + b3 × C + b4 × t + b11 × pH2 + b22 × j2 + b33 × C 2 + b44 × t 2 + b12 × pH × j + b13 × pH × C + b34 × C × t

(7)

TPA : Y1 − Al = 47.74 − 8.72 × pH + 6.68 × j + 7.01 × C + 1.34 ×t + 7.78 × pH2 − 6.75 × j2 − 4.96 × C 2 −6.93 × t − 3.71 × pH × j + 1.94 × pH × j × t + 4.72 × C × t

(8)

TPA : Y1 − Fe = 44.45 − 9.23 × pH + 6.10 × j + 6.15 × C + 1.09 ×t + 7.55 × pH2 − 6.52 × j2 − 4.56 × C 2 − 6.72 ×t 2 − 3.80 × pH × j + 2.40 × pH × C

+ 1.56 × C × t

(14)

COD : Y4 − Fe = 41.35 + 0.84 × pH + 3.96 × j + 2.28 × C + 3.88 ×t − 4.33 × pH2 − 4.32 × j2 − 1.70 × C 2 − 4.23 ×pH × t − 1.58 × j × C + 0.36 × j × t +1.24 × C × t

(15)

Energy consumption : Y5 − Al = 37.76 − 1.13 × pH + 31.03

× pH × t + 5.61 × j × C + 10.84 × j × t − 3.87 × C × t

×t + 4.88 × C × t

(9)

BA : Y2 − Al = 57.82 + 1.23 × pH + 4.31 × j + 2.78 × C + 5.26 × t − 8.74 × pH2 − 4.52 × j2 − 2.24 × C 2 − 8.02 × t 2 − 3.08 × pH × j − 2.98 × pH × C − 2.27 × pH × t − 2.28 × j × C − 1.09 × j × t (10)

BA : Y2 − Fe = 51.92 + 0.69 × pH + 3.50 × j + 2.61 × C + 4.24 × t − 7.85 × pH2 − 4.21 × j2 − 1.86 × C 2 − 8.40 × t 2 − 2.92 × pH × j − 3.32 × pH × C − 2.46 × pH × t − 2.23 × j × C − 1.04 × j × t (11)

p − TA : Y3 − Al = 45.71 + 4.26 × pH + 4.44 × j + 2.74 × C + 3.85 × t − 4.68 × pH2 − 4.95 × j2 − 1.56 × C 2 − 5.98 × t 2 − 0.19 × pH × j − 0.24 × pH × C − 2.52 × pH × t − 2.66 × j × C (12)

p − TA : Y3 − Fe = 40.02 + 3.56 × pH + 3.53 × j + 265 × C + 2.93 × t − 4.00 × pH2 − 4.30 × j2 − 1.63 × C 2 − 5.42 × t 2 − 0.20 × pH × j − 0.54 × pH × C − 2.37 × pH × t − 2.52 × j × C (13)

(16)

Energy consumption : Y5 − Fe = 58.17 + 5.00 × pH + 75.95 × j −17.45 × C + 50.38 × t + 32.71 × pH2 + 22.00 × j2 + 16.74 ×C 2 + 20.13 × t 2 + 26.23 × pH × j + 20.91 × pH × C + 26.00 ×pH × t + 6.76 × j × C + 14.61 × j × t − 19.51 × C × t

−4.24 × pH × t − 2.00 × j × C − 1.21 × j

− 0.62 × j × t + 1.36 × C × t

× pH × t − 1.98 × j × C − 1.23 × j × t

× C 2 + 7.19 × t 2 + 5.34 × pH × j + 2.73 × pH × C + 5.35

×C − 4.34 × pH × t − 2.20 × j × C − 1.41

− 0.71 × j × t + 0.99 × C × t

× t 2 − 1.31 × pH × j − 0.95 × pH × C − 2.41

× j − 4.68 × C + 22.28 × t + 12.11 × pH2 + 8.09 × j2 + 5.70

2

+ 2.12 × C × t

× t − 5.06 × pH2 − 4.23 × j2 − 1.80 × C 2 − 6.28

×t 2 − 1.78 × pH × j − 0.78 × pH × C − 2.06

+ b14 × pH × t + b23 × j × C + b24 × j × t

+ 1.92 × C × t

COD : Y4 − Al = 48.29 + 1.10 × pH + 4.56 × j + 2.57 × C + 4.30

(17)

6. Analysis of sludge generated by Al and Fe electrodes 6.1. Settling characteristics and sludge volume index (SVI), XRD spectra, and SEM/EDX analyses 6.1.1. Settling Settling tests of the sludge obtained at optimum operating conditions using Al and Fe electrodes were conducted in graduated glass cylinder (h = 12 cm, d = 7.28 cm) having 500 mL working capacity. The position of the sludge supernatant interface as a function of time is given in Fig 4a. At time t = 0, the level of sludge was 12 cm and at time (t = 1 min) the level of Al and Fe electrodes generated sludge was 10.5 cm and 9.0 cm respectively. At time (t = 30 min) level of Al and Fe electrodes generated was 2.0 cm and 1.4 cm respectively. The settling level was virtually constant at 1.9 cm (Al electrodes) and 1.1 cm (Fe electrodes) after 90 min. Results show that settling level of Fe electrodes generated sludge was faster than the Al electrodes. It is due to the higher density of iron hydroxide flocs in comparison to the aluminum hydroxide flocs. 6.1.2. Sludge volume index (SVI) In present study treating 1 L of wastewater at optimum operating conditions by Al and Fe electrodes generated 5.837 g and 3.947 g metallic sludge (dried at 105 °C) respectively. SVI of Al electrodes (42.21 mL/g) generated sludge was higher in comparison of Fe electrodes (28.55 mL/g). 6.1.3. XRD XRD spectra of Al and Fe electrodes generated sludge are shown in Fig. 4(b). XRD spectra of Al electrodes generated sludge shows

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Fig. 4. Settling characteristics, (b) XRD spectra and (c, d → Al; e, f → Fe) SEM/EDX images of sludge obtained by Al and Fe electrodes.

very broad and shallow diffraction peaks. Bragg reflection having very broad and lower intensity peaks indicates that analyzed phase possesses an order of short range, i.e. poorly crystalline and most likely amorphous phase for aluminum hydroxide/oxy-hydroxide [80]. XRD spectra of Fe electrodes generated sludge does not show any peak or sharp peak which means Fe generated sludge shows poor amorphous nature. 6.1.4. SEM/EDX SEM and EDX images of Al and Fe electrodes generated sludge are shown in Fig. 4(c and d) and Fig. 4(e and f) respectively. The spectra show that Fe electrodes generated sludge is much porous as compared to Al electrodes. Thus, particle size of Fe generated sludge remains much more downcast than Al electrodes. Elemental composition (in weight percent) of Al and Fe generated sludge based on EDX spectra are given in Table 5. EDX analysis of sludge shows higher weight percentage of Al and Fe in comparison to carbon, sodium, oxygen and chlorine, etc. 6.2. Point of zero charge (PZC), FTIR and DTA/TGA analysis of sludge generated by Al and Fe electrodes 6.2.1. PZC Point of zero charge is pH value associated with specific requirement on surface charge and used for characterizing the adsorption properties of the sludge material [82]. PZC is the function of pH where a solid submerged in an electrolyte exhibits zero net charge (ZNC) at the surface of a solid. Salt addition method given by American Society for Testing of Materials (ASTM) D-3838-05 was used in this study [81]. In this method sludge sample react with H+ or OH− ions of the solution during the agitation time. The difference between the initial and final pH values (pH0 –pHf = ࢞pH) was plotted against the initial pH (pH0 ). The cross over point on the resulting curve at ࢞pH = 0 gives the value of pHPZC . Fig. 5a shows the PZC for sludge obtained after EC treatment by Al and Fe electrodes. Adsorption of anions favored at pH < PZC (surface positively charges), while adsorption of cations favored at pH > PZC (surface negatively charged). The specific

adsorption of cations shifts pHPZC toward higher values. Fig. 5a shows 9.0 and 8.4 PZC values of sludge for Al and Fe electrodes respectively. 6.2.2. FTIR FTIR spectra of sludge generated by Al and Fe electrodes are given in Fig. 5a. A functional group in sludge samples generally shows electrolyte interaction between flocs and cations, which plays an important role for the removal of colloids during EC experiment. The wavelength of carbonyl group exists between regions of 1070 and 1820 cm−1 . Peaks in the region of 1600–400 cm−1 depict aromatic C=C stretching [65]. Peaks in the region of (1600–400 cm−1 ) are quite sharp for Al and Fe electrode generated sludge. Wavelengths (1386.53 cm−1 , 1638.85 cm−1 ) of Al electrodes generated sludge and (1400 cm−1 , 1600 cm−1 ) for Fe electrodes generated sludge lie in the range of carbonyl group, so this pattern confirms the presence of carbonyl groups in sludge samples. A wavelength (3427.50 cm−1 ) of Al electrodes generated sludge and low intensity peaks 3419.34 cm−1 , 3599.13 cm−1 , 3732.40 cm−1 of Fe electrodes generated sludge confirms presence of hydroxyl group or characteristics of hydrogen atoms in sludge samples. Wavelengths in the range of 800–400 cm−1 show characteristics of infrared bands of organic halogen compounds [83]. 6.2.3. DTA/TGA DTA/TGA analysis of Al and Fe generated sludge was performed in a dynamic air atmosphere from ambient temperature to 1000 °C at a heating rate of 10 K/min using calcined Al2 O3 as the reference material and are shown in Fig. 5 (b). TGA graph of Al or Fe electrode generated sludge shows three oxidation stages. In all stages oxidation rates of Fe electrodes generated sludge are lower in comparison to Al electrodes generated sludge as shown in Fig. 4c and d. Al and Fe electrodes generated sludge samples reduced their weights about 5.04%, 5.31% respectively below temperature 100 °C. It is due to evaporation of the pore water or solution that was not removed during drying at ambient temperature. Rate of weight loss for Al and Fe electrodes generated sludge was in the range of 0.190–0.49 mg/min. Sludge samples lose their weight with temperature due to the formation of CO

K.K. Garg, B. Prasad / Journal of the Taiwan Institute of Chemical Engineers 60 (2016) 383–393

391

Table 5 Elemental composition (weight percentage) of sludge by EDAX using Al and Fe electrodes. Element Weight %

Al (sludge) Fe (sludge)

CK

OK

Na K

Al K

Cl K

Fe K

Zn L

Total

16.88 12.68

42.52 35.06

10.59 7.09

28.84 —-

1.17 0.58

—42.4

—2.19

100 100

0.8

Al electrodes generated sludge Fe electrodes generated sludge

Al electrodes generated sludge Fe electrodes generated sludge

6

0.4

5

0.2

4

Absorbance

pHi-pHf

0.6

0.0 -0.2

472.44

3427.50 3732.40

3

-0.4

2

-0.6

1

-0.8

3972.80

3419.34 3599.13

1638.85 1029.87 806.99 1386.53 516.68

0

-1.0 2

4

6

8

8.4 9.0

10

0

12

500

1000

1500

2000

2500

3000

3500

Wave numbers (cm )

5(a)

5(b) 60.0

281Cel 0.49 mg/min

140.00

54Cel 190 ug/min

0.20 115.00

0.50

40.00

40.0 130.00

20.00

4000

-1

pH

20.0

509 mJ/mg 120.00

0.00

322Cel 23.36 uV

0.00

110.00 27.7 mJ/mg

-0.20 -81.3 mJ/mg

-0.50

0.0

-1.50

28Cel 99.94 %

100.00

-0.40

-0.60

-40.0

DTG mg/min

100.00

-20.0

TG %

282Cel -8.46 uV 200Cel 92.68 %

DTA uV

31Cel 99.95 %

DTG mg/min

-1.00 -20.00

105.00

60Cel -0.50 uV

110.00 TG %

DTA uV

0.00

-0.80 -40.00

100Cel 94.95 %

90.00 -2.00 300Cel 73.35 %

-60.00

-80.00

1017Cel 62.75 %

400Cel 68.87 % 500Cel 66.29 % 600Cel 700Cel 800Cel 900Cel 64.78 % 64.06 % 63.53 % 63.13 %

80.00

-80.0

200

300

400

500 600 Temp Cel

700

800

900

100Cel 94.69 %

95.00

200Cel 92.86 %

-1.00 300Cel 90.69 %

-2.50 70.00

-100.0 -3.00

60.00 100

-60.0

400Cel 500Cel 600Cel 1017Cel 90.00 88.99 % 88.44 % 88.20 % 700Cel 800Cel 85.65 % 87.84 % 87.45 % 900Cel 86.26 %

-1.20

-1.40 85.00

-120.0 100

1000

200

300

400

5 (c)

500 600 Temp Cel

700

800

900

1000

5 (d)

Fig. 5. (a) Point of zero charge (b) FTIR spectra and DTA/TGA (c →Al; d →Fe) graphs for Al and Fe electrodes generated sludge. Table 6 Operating cost of the process at optimum operating conditions given by CCD and at experimental test runs. Type of electrode Al Fe

CCD based Test run based CCD based Test run based

Energy consumed kWh/kgCODremoved

Electrode Cons. kg/kg COD removed

Operating cost ($) 1 $ = 60 Rs

80.15 90.90 110.85 125.30

3.6 3.8 6.2 6.0

13.64 14.92 14.46 15.50

and CO2 during the reaction [71]. Reaction shows exothermic nature because of carbon chain fragmentation and endothermic nature, because of decomposition with early oxidation of different fragments or condensation of some functional groups that are removed in the EC process.

conditions. Operating cost of the process was calculated for CCD and experimentally confirmed optimum conditions and calculated by following equation and given in Table 6.

OC = Energy consumption(kWh/kg COD removed) × EEC +Electrode consumption(kg/kg CODremoved )

7. Operating cost (OC) Operating cost of the process was calculated based on the energy consumption, electrode consumption, sludge disposal and transportation costs in case of Al and Fe electrodes at optimum operating

×EMC + Sludge disposal and transportation cost

(18)

Where, EEC is electrical energy cost: Rs. 5/kWh, EMC is electrode material cost: Rs. 50/kg for Fe electrode and Rs. 115/kg for Al electrode; sludge disposal and transportation cost [84]: $60/ton.

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From Table 6 it may be inferred that treatment of synthetic PTA wastewater with Al electrodes is marginally cheaper than Fe electrodes. Operating costs of the process, based on the CCD and experimental test run results show < ± 5% variation. 8. Conclusion CCD developed for this study show good correlation between actual and model predicted values of responses. Maximum percentage removal of TPA: 56.21, 54.10; BA: 59.52, 53.84; p-TA: 45.71, 39.91; COD: 49.91, 42.95 and energy consumption (kWh/kgCODremoved ): 80.15, 110.85 are achieved at optimum operating conditions: pH: 8.18, 8.00, CD (A/m2 ): 172.97, 180.04; time (min): 63.47, 65.55 and NaCl dosages (g/L): 1.69, 1.74 using Al and Fe electrodes respectively. Al electrodes give higher removal efficiencies in comparison to Fe electrodes. The sludge generated by Fe electrodes exhibit better settling properties in comparison of the Al generated sludge. XRD analysis of Al and Fe electrodes generated sludge show porous and crystalline nature respectively. SEM images of Al and Fe anodes show larger number of pits and cracks. EDX analysis of sludge show higher weight percentage of Al and Fe with respect to C, O, Na, Cl, etc. Al and Fe electrodes generated sludge show PZC at pH 9.0 and 8.4 respectively. Presence of carbonyl group, aromatic C=C stretching, hydroxyl group and hydrogen atom in Al and Fe electrodes generated sludge show effective removal of TPA, BA and p-TA. Thermal analysis of Al electrodes generated sludge shows higher ultimate weight loss in comparison of Fe electrodes generated sludge in air atmosphere. Operating costs of the process $13.64 and $14.46 (per kg of CODremoved ) are found for Al and Fe electrodes respectively. Based on the removal efficiency and operational cost, Al electrodes are better in comparison of Fe electrodes. References [1] Zhang Z, Ma L, Zhang X, Li W, Zhang Y, Wu B, et al. Genomic expression profiles in liver of mice exposed to purified terephthalic acid manufacturing wastewater. J Hazard Mater. 2010;181(1):1121–6. [2] Zhang X, Sun S, Zhang Y, Wu B, Zhang Z, Liu B, et al. Toxicity of purified terephthalic acid manufacturing wastewater on reproductive system of male mice muscles. J Hazard Mater. 2010;176(1):300–5. [3] Meyer RB, Fischbein A, Rosenman K, Lerman Y, Dennis ED, Marcus MR. Increased urinary enzyme excretion in workers exposed to nephrotoxic chemicals. Am J Med. 1984;76:989–98. [4] Cui LB, Shi Y, Dai GD, Pan HX, Chen JF, Song L, et al. Modification of n-methyln-nitrosourea initiated bladder carcinogenesis in wistar rats by terephthalic acid. Toxicol Appl Pharmcol. 2006;210:24–31. [5] Cui LB, Dai GD, Xu LC, Wang SL, Song L, Zhao RZ, et al. Effect of oral administration of terephthalic acid on testicular functions of rats. Toxicology 2004;201:59–66. [6] Lamb JC, Chapin RE, Teague J, Lawton AD, Reel JR. Reproductive effects of four phthalic acid esters in the mouse. Toxicol Appl Pharmcol. 1987;88:255–69. [7] Matsumoto M, Hirata KM, Ema M. Potential adverse effects of phthalic acid esters on human health: A review of recent studies on reproduction. Regular Toxicol Pharmacol. 2008;50:37–49. [8] Lee MW, Joung JY, Lee DS, Park JM, Woo SH. Application of a moving windowadaptive neural network to the modeling of a full-scale anaerobic filter process. Ind Eng Chem Res. 2005;44:3973–82. [9] Razo E, Macarie H, Morier F. Application of biological treatment systems for chemical and petrochemical wastewaters. UK: IWA Publishing, London; 2006. ISBN 1843391147. p. 267–97. [10] Zhang XX, Wan YQ, Cheng SP, Sun SL, Zhu CJ, Li WX, et al. Purified terephthalic acid wastewater biodegradation and toxicity. J Environ Sci. 2005;17:876–80. [11] Li DQ, Lin YJ, David GE, Xue D. Solid-liquid equilibrium for benzoic acid + ptoluic acid + chloroform, benzoic acid + p - toluic acid + acetic acid, and terephthalic acid + iso-phthalic acid + N, N-dimethyl-formamide. J Chem Eng Data 2005;50(1):119–21. [12] Zhang XX, Cheng SP, Wan YQ, Sun SL, Zhu CJ, Zhao DY, et al. Degradability of five aromatic compounds in a pilot wastewater treatment system. Int Biodeterior Biodegrad. 2006;58(2):94–8. [13] Wibbertmann A, Kielhorn JG, Koennecker I, Mangelsdorf C, Melber C. International chemical assessment document 26 benzoic acid and sodium benzoate. Geneva: World Health Organization; 2000. [14] Xin X, Wei S, Yao Z, Feng R, Du B, Yan L, et al. Adsorption of benzoic acid from aqueous solution by three kinds of modified bentonites. J Colloid Interface Sci. 2011;359(2):499–504. [15] Wu CH. Photodegradation of toluic acid isomers by UV/TiO2 ,. React Kinet Catal Lett. 2007;90(2):301–8.

[16] Shirota M, Seki T, Tago K, Katoh H, Marumo H, Furuya M, et al. Screening of toxicological properties of 4-methylbenzoic acid by oral administration to rats. J Toxicol Sci. 2008;33:431–45. [17] US EPA, Code of Federal Regulations, 40 CFR, 1992; Part 136. [18] Nishimura T, Tozawa K, Robins RG. The calcium-arsenic-water system. In: Proceedings MMIJ /Aus. IMM joint symposium, Sendai, Japan; 1983 Paper JD-2-1: 105-120. [19] Nishimura T, Tozawa K. The reaction for the removal of As(III) and As(V) from aqueous solutions by adding calcium hydroxide. J Min Metals Inst Japan 1984;100:1085–91. [20] Nishimura T, Robins RG. A re-evaluation of the solubility and stability regions of calcium arsenites and calcium arsenates in aqueous solution at 25 °C. Min Process Extract Metals Rev. 1998;18:283–308. [21] Young CA, Robins RG. The solubility of As2 S3 in relation to the precipitation of arsenic from process solutions. In: Young CA, editor. Minor metals 2000. Littleton CO: SME; 2000. p. 381–91. [22] Robins RG. The stability and solubility of ferric arsenate: an update. In: Gaskell DR, editor. EPD Congress ’90. Warrendale PA.: TMS; 1990. p. 93–104. [23] Thamer BJ, Voigt AF. The spectrophotometric determination of overlapping constants of dibasic acids. The acid constants of isophthalic, terephthalic and chloranilic acids. J Phys Chem A 1952;56(2):225–32. [24] Verma S, Prasad B, Mishra IM. Treatment of petrochemical wastewater by acid precipitation and carbon adsorption. J Hazard Toxic Radioact Waste 2013;18((3):04014013. [25] Verma S, Prasad B, Mishra IM. Pretreatment of petrochemical wastewater by coagulation and flocculation and the sludge characteristics. J Hazard Mater. 2010;178:1055–64. [26] Feng Y, Lu B, Jiang Y, Chen Y, Shen S. Performance evaluation of anaerobic fluidized bed reactors using brick beads and porous ceramics as support materials for treating terephthalic acid wastewater. Desalin Water Treat. 2015;53(7):1814– 21. [27] Joung JY, Lee HW, Choi H, Lee MW, Park JM. Influences of organic loading disturbances on the performance of anaerobic filter process to treat purified terephthalic acid wastewater. Bioresour Technol. 2009;100(8):2457–61. [28] Kim JY, Woo SH, Lee MW, Park JM. Sequential treatment of PTA wastewater in a two-stage UASB process: focusing on p-toluate degradation and microbial distribution. Water Res. 2012;46((8):2805–14. [29] Li X, Ma K, Meng L, Zhang J, Wang K. Performance and microbial community profiles in an anaerobic reactor treating with simulated PTA wastewater: from mesophilic to thermophilic temperature. Water Res. 2014;61:57–66. [30] Piterina AV, Bartlett J, Tony PJ. Phylogenetic analysis of the bacterial community in a full scale auto-thermal thermophilic aerobic digester (ATAD) treating mixed domestic wastewater sludge for land spread. Water Res. 2012;46(8):2488–504. [31] Pophali GR, Khan R, Dhodapkar RS, Nandy T, Devotta S. Anaerobic–aerobic treatment of purified terephthalic acid (PTA) effluent; a techno-economic alternative to two-stage aerobic process. J Environ Manage. 2007;85:1024–33. [32] Zhu G, Wu P, Wei Q, Lin J, Gao Y, Liu H. Bio-hydrogen production from purified terephthalic acid (PTA) processing wastewater by anaerobic fermentation using mixed microbial communities. Int J Hydrogen Energy 2010;35(15):8350–6. [33] Karthik M, Dafale N, Pathe P, Nandy T. Biodegradability enhancement of purified terephthalic acid wastewater by coagulation–flocculation process as pretreatment. J Hazard Mater. 2008;154(1):721–30. [34] Wang Z, Teng L, Zhang J, Huang X, Zhang J. Study on optimal biodegradation of terephthalic acid by an isolated Pseudomonas sp. Afr J Biotechnol. 2013;10((16):3143–8. [35] Garg KK, Prasad B, Srivastava VC. Comparative study of industrial and laboratory prepared purified terephthalic acid (PTA) wastewater with electro-coagulation process. Sep Purif Technol. 2014;128:80–8. [36] Anbia M, Salehi S. Synthesis of polyelectrolyte-modified ordered nonporous carbon for removal of aromatic organic acids from purified terephthalic acid wastewater. Chem Eng Res Des. 2012;90((7):):975–83. [37] Chen J. Preparation of highly efficient PTA degradation bacteria and biological treatment of PTA wastewater. Environ Sci Technol. 2006;10:75–6. [38] Chen CY, Chen CC, Chung YC. Removal of phthalate esters by R- cyclodextrin linked chitosan bead. Bioresour Technol. 2007;98:2578–83. [39] Verma S, Basheshwar P, Mishra IM. Adsorption kinetics and thermodynamics of COD removal of acid pre-treated petrochemical wastewater by using granular activated carbon. Sep Sci Technol. 2014;49(7):):1067–75. [40] Wen YZ, Tong SP, Zheng KF, Wang LL, Lv JZ, Lin J. Removal of terephthalic acid in alkalized wastewater by ferric chloride. J Hazard Mater. 2006;B. 138:169–72. [41] Deng Y, Zhang K, Chen H, Krzyaniak TWM, Wellons A, Bolla D, et al. Iron-catalyzed photochemical transformation of benzoic acid in atmospheric liquids: product identification and reaction mechanisms. Atm Environ. 2006;40:3665–76. [42] Yuefeng C, Hui W, Mingjuan H, Guofeng G. Photocatalytic degradation of organic pollutants in purified terephthalic acid wastewater with activated carbon supported titanium dioxide. In: International Conference on Energy and Environment Technology. ICEET’09.; 2009. p. 658–61. [43] Park TJ, Lima JS, Lee YW, Kim SH. Catalytic supercritical water oxidation of wastewater from terephthalic acid manufacturing process. J Supercrit Fluids 2003;26:201–13. [44] Thiruvenkatachari R, Tae OK, Jung CJ, Subramanian B, Manickam M, Shik M. Application of several advanced oxidation processes for the destruction of terephthalic acid. J Hazard Mater. 2007;142(1):308–14. [45] Wu S, Cheng Z, Wang S, Shan X. Recovery of terephthalic acid from alkali reduction wastewater by cooling crystallization. Chem Eng Technol. 2011;34:1614–18.

K.K. Garg, B. Prasad / Journal of the Taiwan Institute of Chemical Engineers 60 (2016) 383–393 [46] Verma S, Prasad B, Mishra IM. Thermochemical treatment (Thermolysis) of petrochemical wastewater: COD removal mechanism and floc formation. Ind Eng Chem Res. 2011;50(9):5352–9. [47] Huang KY, Chou WL, Wang CT, Shu CM. Electrochemical destruction of polyvinyl alcohol mediated by electrogenerated Ce (IV) in aqueous solution. Desalin Water Treat. 2014:1–8. [48] Huang KY, Chou WL, Wang CT, Chang YC, Shu CM. Electrochemically assisted coagulation for the adsorptive removal of dimethyl phthalate from aqueous solutions using iron hydroxides. J Taiwan Inst Chem Eng. 2015;50:236–41. [49] Chou WL, Wang CT, Huang KY. Effect of operating parameters on indium (III) ion removal by iron electrocoagulation and evaluation of specific energy consumption. J Hazard Mater. 2009;167(1):467–74. [50] Chou WL, Wang CT, Chang SY. Study of COD and turbidity removal from real oxide-CMP wastewater by iron electrocoagulation and the evaluation of specific energy consumption. J Hazard Mater. 2009;168(2):1200–7. [51] Chou WL, Wang CT, Huang KY. Investigation of process parameters for the removal of polyvinyl alcohol from aqueous solution by iron electrocoagulation. Desalination 2010;251(1):12–19. [52] Chou WL, Wang CT, Huang KY, Liu TC. Electrochemical removal of salicylic acid from aqueous solutions using aluminum electrodes. Desalination 2011;271(1):55–61. [53] Chou WL, Wang CT, Liu TC, Chou LC. Effect of process parameters on removal of salicylic acid from aqueous solutions via electrocoagulation. Environ Eng Sci. 2011;28(5):365–72. [54] Achour S, Eltaief K, Lamia A, Ahmed NH, Amina B. Response surface methodology for textile wastewater decolourization and biodegradation by a novel mixed bacterial consortium developed via mixture design. Desalin Water Treat. 2014;52(7):1539–49. [55] Ahmad NA, Mohd AAH, Zainura ZN, Abdullahi ME, Jibrin MD. Optimization of nickel removal from electroless plating industry wastewater using response surface methodology. J Teknol. 2014;67(4). [56] Amado IR, José AV, Miguel AM, González MP. Recovery of astaxanthin from shrimp cooking wastewater: Optimization of astaxanthin extraction by response surface methodology and kinetic studies. Food Bioprocess Technol. 2015;8(2):371–81. [57] Anupam K, Jaya S, Sayan P, Gopinath H. Optimizing the cross-flow nanofiltration process for chromium (VI) removal from simulated wastewater through response surface methodology. Environ Progress Sustainable Energy 2015;34(5):1332–40. [58] Cao X, Huiqing L, Wei W, Lijuan Z. Treatment of tetrahydrofuran wastewater by Fenton process: the response surface methodology as the optimization tool. IWA J. 2014. [59] Thirugnanasambandham K, Sivakumar V, Prakash MJ, Kandasamy S. Treatment of rice mill wastewater using continuous electrocoagulation technique: optimization and modelling. J Korean Chem Soc. 2013;57.6:761–8. [60] Pakravan P, Aazam A, Hojatollah M, Abbas HA, Amir MM, Mojtaba S. Process modeling and evaluation of petroleum refinery wastewater treatment through response surface methodology and artificial neural network in a photocatalytic reactor using poly ethyleneimine (PEI)/titania (TiO2 ) multilayer film on quartz tube. Appl Petrochem Res. 2014;5(1):47–59. [61] Thirugnanasambandham K, Sivakumar V, Maran JP. Efficiency of electrocoagulation method to treat chicken processing industry wastewater modeling and optimization. J Taiwan Inst Chem Eng. 2014;45(5):2427–35. [62] Thirugnanasambandham K, Sivakumar V, Maran JP. Evaluation of an electrocoagulation process for the treatment of bagasse-based pulp and paper industry wastewater. Environ Progress Sustainable Energy 2015;34(2):411–19. [63] Tezcan UU, Kandemir A, Erginel N, Ocal SE. Continuous electrocoagulation of cheese whey wastewater: an application of response surface methodology. J Environ Manage. 2014;146:245–50.

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[64] Varank G, Erkan H, Yazýcý S, Demir A, Engin G. Electrocoagulation of tannery wastewater using monopolar electrodes: process optimization by response surface methodology. Int J Environ Res. 2014;8(1):165–80. [65] Anand MV, Srivastava VC, Singh S, Bhatnagar R, Mall ID. Electrochemical treatment of alkali decrement wastewater containing terephthalic acid using iron electrodes. J Taiwan Inst Chem Eng. 2014;45:908–13. [66] Chidambararaj CB, Ramkumar N, Siraj AHJ, Chidambaram SP. Bio-degradation of acetic, benzoic, isophthalic, toluic and terephthalic acids using a mixed culture: effluents of PTA production. Trans IChemE. 1997;75B:245–56. [67] Marashi SKF, Kariminia HR, Savizi ISP. Bimodal electricity generation and aromatic compounds removal from purified terephthalic acid plant wastewater in a microbial fuel cell. Biotechnol Lett. 2013;35(2):197–203. [68] Pillai KC, Kwon TO, Moon IS. Degradation of wastewater from terephthalic acid manufacturing process by ozonation catalyzed with Fe2+ , H2 O2 and UV light: direct versus indirect ozonation reactions. Appl Catal B: Environ. 2009;91(1– 2):319–28. [69] Shafaei A, Nikazar M, Arami M. Photocatalytic degradation of terephthalic acid using titania and zinc oxide photocatalysts: comparative study. Desalination 2010;252(1):8–16. [70] Thiruvenkatachari R, Tae OK, Shik M. Degradation of phthalic acids and benzoic acid from terephthalic acid wastewater by advanced oxidation processes. J Environ Sci Health Part A 2006;41(8):1685–97. [71] Garg KK, Prasad B. Removal of para-toluic acid (p-TA) from purified terephthalic acid (PTA) waste water by electrocoagulation process. J Environ Chem Eng. 2015;3(3):1731–9. [72] Dentel SK, Gossett JM. Mechanisms of coagulation with aluminum salts. J. Am Water Works Assoc. 1988;80:187–98. [73] Stephenson RJ, Duff SJB. Coagulation and precipitation of a mechanical pulping effluent. I. Removal of carbon, colour and turbidity.. Water Res. 1996;30(4):781– 92. [74] Daneshvar N, Oladegaragoze A, Djafarzadeh N. Decolorization of basic dye solutions by electrocoagulation: an investigation of the effect of operational parameters. J Hazard Mater. 2006;129:116–22. [75] Modirshahla N, Behnajady MA, Kooshaiian S. Investigation of the effect of different electrode connections on the removal efficiency of tartrazine from aqueous solutions by electrocoagulation. Dyes Pigm. 2007;74:249–57. [76] Lee WJ, Pyun SI. Effects of hydroxide ion addition on anodic dissolution of pure aluminum in chloride ion containing solution. Electrochim Acta 1999;44(3):4041–9. [77] Pyun SI, Moon SM, Ahn SH, Kim SS. Effects of Cl− , NO3 − and SO4 2− ions on anodic dissolution of pure aluminum in alkaline solution. Corros Sci. 1999;41(4):653–67. [78] Nguyen TH, Foley RT. On the mechanism of pitting of aluminum. J. Electrochem. Soc. 1979;126(11):1855–60. [79] Lee SM, Pyun SI. Effect of hydrogen on the impedance of passivating oxide films formed on aluminum in sodium nitrate solution. J Appl Electrochem. 1992;22(2):151–5. [80] Garg KK, Prasad B. Electrochemical treatment of benzoic acid (BA) from aqueous solution and optimization of parameters by response surface methodology (RSM). J Taiwan Inst Chem Eng. 2015;56:122–30. [81] ASTM, Annual book of ASTM standard, standard test for pH of activated carbon, ASTM D 3838-05, Philadelphia PA, United State of America 2011. [82] Song G, Cao C, Chen SH. A study on transition of iron from active into passive state. Corros Sci. 2005;47(2):323–39. [83] Stuart BH. Infrared spectroscopy: fundamentals and applications. John Wiley; 2004. p. 72–93. [84] Arslan AI, Kobya M, Akyol A, Bayramoglu M. Electro coagulation of azo dye production wastewater with iron electrodes: process evaluation by multi-response central composite design. Color Technol. 2009;125:234–41.