Treatment of Textile Dyeing Wastewater Using Ozone ...

IJEP 36 (7) : 529-540 (2016)

(Received on March 21, 2016)

Treatment of Textile Dyeing Wastewater Using Ozone Based Advanced Oxidation Processes in a Pilot-Scale Reactor B. Shriram and S. Kanmani Anna University, Centre for Environmental Studies, Chennai - 600 025 The treatment of textile dyeing wastewater is difficult by conventional methods and would damage the environment if discharged without treatment. The present work investigated the ozone based advanced oxidation treatment of the dyeing wastewater. The dyeing wastewater samples of different colours were collected from a yarn dyeing unit in Perundurai. The colour absorbance of the wastewaters ranged between 23.4 and 84.2/m at 436 nm, 14.2 and 92.2/m at 520 nm and 3.3 and 73.0/m at 620 nm. The COD of the raw wastewater was varying from 600 to 1060 mg/L. The treatment studies were conducted in a 200 L reactor fed with ozone at the rate of 10 g/hr to asses its efficiency in reducing the colour and COD. Complete decolourisation and 28–32 % COD reduction was achieved in UV/O3/H2O2 process with ozone consumption of 50 mg/L and H2O2 dose of 500 mg/L after 60 min of treatment. The degradation was found to be higher in UV/H2O2 than that of simple ozonation. The ozone based advanced oxidation processes followed pseudo first order kinetics and the UV/O 3/H2O2 treatment was fastest in degradation. When the ozonation and peroxide treatment were carried out in sequence, about 95 % decolourisation and 50% COD reduction was observed. KEYWORD Ozone, Advanced oxidation, H 2O 2, Dyeing wastewater, Colour, COD. INTRODUCTION Textile dyeing industry is one of the major industries consuming large amount of water for its various operations. The textile units use a number of dyes, chemicals and other materials to impart desired quality to the fabrics. The textile effluents are intensely coloured and known to present extreme variations of pH, temperature, high COD and dissolved solids (Sevinmli and Kinachi, 2002). Strong colour of the textile wastewater is the most serious problem of the textile waste effluent. The recalcitrant nature of synthetic dyes makes the conventional biological treatment processes ineffective and adsorption and coagulation practices result in secondary pollution (Fang Han et al., 2009). Ozone based advanced oxidation processes (AOPs) have been studied extensively for

decolourisation and degradation of textile dyes. The high oxidation potential allows ozone to degrade most organic compounds (Chu and Ma, 2000). Ozone and hydroxyl radical (HO°) species generated in aqueous solution are able to open aromatic rings. The hydroxyl radical is a powerful and nonselective oxidant that can react through the possible mechanisms, like hydrogen abstraction and electron transfer (or) radical addition (Metcalf and Eddy, 2004). The advantage is that ozone can be applied directly in its gaseous state and thereof doesn’t increase the volume of wastewater and sludge (Sheng and Chi, 1993). Removal of colour and recalcitrant organic content of the textile effluent can be achieved with high efficiency. In the lab scale level colour removal of 90% and COD reduction of 80 % could be achieved by ozone based advanced oxidation treatment (Javier Benitez et al., 2008). In addition the ozonation treatment also increases the biodegradability of the

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wastewater (Wu et al., 2008). The photo aided ozonation (UV/O3) yields more intermediates thus leading to more mineralization of the organic content (Chu and Rao, 2010). But most of the lab scale studies were conducted with simulated dyeing wastewater. The real textile dyeing wastewater differs significantly from that of the simulated wastewaters as it contains mixture of dyes in addition to the salts. The present study focused on the pilotscale advanced oxidation treatment of real textile dyeing wastewater. The dyeing wastewaters are usually alkaline with pH > 10. The studies conducted shows that ozonation is effective at basic pH than acidic pH (Cleder et al., 2010). Shu and Huang (1995) reported little enhancement in degradation by UV enhanced ozonation. Hydrogen peroxide (H 2O2) is also a source of hydroxyl radical which is produced through hemolytic cleavage in the presence of UV-C radiation (Khan et al., 2010). The objective of the present study is to determine the feasibility of ozone based advanced oxidation in treatment of textile dyeing wastewater using a pilot-scale reactor.

Analysis

MATERIAL AND METHOD

The wastewater samples are the composite dye bath obtained directly from the machinery source in the study unit and used in all experiments as required. The various treatment processes adopted for the study are, namely ozonation, UV/O3, UV/O3/H2O2 and UV/O3-UV/ H2O 2 in sequence. The working volume of reactor and contact time were maintained at 200 L and 60 min, respectively. For the optimization studies H2O2 dosage was varied from 100 to 1000 mg/L. The reactor was operated in batch mode and the content of the reactor was recirculated using a centrifugal pump for better mixing. Treated samples were taken for analysis of colour, COD and BOD. Analytical samples treated with MnO 2 were centrifuged and their supernatant was taken for COD analysis. All experiments were carried out at ambient temperature (35 °C) and actual pH of wastewater samples. The percentage of colour and COD removal () was calculated using equation 1 :

Material The real textile dyeing industrial wastewater samples (IWW1-IWW5) were obtained as required from the study unit which is a textile dyeing industry located in Erode district of Tamil Nadu. The pilot-scale experimental setup consisted of ozone generator (Faraday Ozone L20 G) that was fed with liquid oxygen, an immersion type reactor of capacity 200 L, UV-C lamp (120 W, 254 nm) and a centrifugal pump (0.5 HP). The reactor was made of high density polymer material with 54 cm diameter and 90 cm height and the UV lamp was immersed at the center of the reactor using quartz tube. The liquid oxygen for ozone generation and the industrial grade hydrogen peroxide (H 2O 2 , 50% w/w) were kindly provided by the industry, which they use in their processes. The production capacity of ozone generator was 10 g/hr which was measured using an ozone analyzer (model AZ UV 200-8). 530

The dyeing wastewater samples, namely IWW1-IWW5 were characterized for pH, chemical oxygen demand (COD), total dissolved solids (TDS), Total suspended solids (TSS), alkalinity, chloride and sulphate based on standard methods (APHA, 1998). For the biodegradability assessment, 3 day biochemical oxygen demand (BOD 3 ) was analyzed as per standard analytical procedure (IS 3025, 2007). The concentration of H 2O 2 was confirmed through titration using potassium permanganate solution. The colour measurements were made at room temperature with the help of CL-310 Chemiline digital spectrophotometer having a path length of 1 cm. The absorbance measurement was done at 3 different wavelengths (436, 525 and 620 nm) based on German method (Sundrarajan et al., 2007). The interference of residual H2O2 in treated samples during COD analysis was eliminated by using manganese dioxide (MnO 2 ) powder (Zangeneh et al., 2014). Experiment

 = ((C 0 - C1)/C1) x 100

...(1)

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Table 1. Characteristics of textile dyeing wastewater samples, in mg/L Parameter

IWW 1

IWW 2

IWW 3

IWW 4

IWW 5

Colour

Red

Mustard yellow

Burgandy red

Navy blue

Charcoal

Colour 436 nm absorbance, 525 nm m-1 620 nm pH BOD3 COD BOD3/COD TDS TSS Total alkalinity as CaCO3 Chloride Sulphate

84 .2 92 .2 28 .0 10 .4 72 60 0 0.12 31 10 39 13 10 47 2 21 10

72 .8 14 .2 3 .3 10 .5 60 75 0 0.08 42 32 35 14 08 75 5 20 65

69 .8 61 .1 12 .0 10 .4 95 10 60 0.09 72 10 32 13 80 65 3 22 50

23 .4 51 .8 73 .0 10 .2 11 4 10 40 0.11 62 85 33 12 20 41 2 24 50

67 .0 37 .2 31 .7 10 .7 90 90 0 0.10 36 74 38 12 62 56 0 23 46

where, C0 is initial absorbance or initial COD of the sample (mg/L) and C 1 is final absorbance or final COD of the sample after treatment (mg/L). The decolourization and aromatic content removal kinetics of most dyes can be safely treated using a pseudo-first order rate law, based on the steady state approximation (Nunez et al., 2007). Kinetic pathway of colour degradation is expressed by equation 2 : -dC/dt=kC

...(2)

Where k is the reaction apparent rate constant (min-1 ) and t, the exposure time (min). This equation after integration with initial condition C=C 0 for t=0, leads to equation 3 : ln C=ln C0 - k app x t

...(3)

The electrical energy per order (EEO) calculations was done using the following equation 4 (Khan et al., 2010):

EEO 

P x t x 1000 V x 60 x log (C 0 / C)

...(4)

Where, P is the power input of ozonator, UV lamp, pump in Kw, t is reaction time in min,

V is volume of wastewater in liter, C0 is initial COD in mg/L, C is final COD after treatment in mg/L RESULT AND DISCUSSION The initial characteristics of IWWs are presented in table 1. The colour absorbance of the wastewaters ranged between 23.4 and 84.2/m at 436 nm, 14.2 and 92.2/m at 520 nm and 3.3 and 73.0/m at 620 nm. The chemical oxygen demand of wastewater was varying from 600 to 1060 mg/L while their BOD3 value was ranging from 60 to 114 mg/L and their biodegradability, that is BOD 3/COD was between 0.08 and 0.12. The total dissolved solids of the samples were high ranging from 3674 to 7210 mg/L due to the addition of large quantity of salt in dyeing process. The addition of Glauber’s salt in dyeing, contributed to sulphate whose concentration was ranging from 2250 to 2450 mg/L while the usage of soda ash contributed to the total alkalinity which was between 1220 and 1408 mg/L. The chloride concentration was relatively low with values ranging from 412 to 755 mg/L. All the samples possessed pH values greater than 10 confirming their alkaline nature.

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(a)

(b)

(c)

(d)

Figure 1. Decolourisation and degradation by ozonation : (a) Colour removal at 436 nm, (b) colour removal at 525 nm, (c) colour removal at 620 nm and (d) COD removal Effect of ozone Ozone being a powerful oxidizing agent has an important role to play in the oxidation of textile dyeing wastewater. The results of ozonation experiments are illustrated in figure 1. Decolourisation at 436, 525 and 620 nm were 86, 97 and 90 % in IWW1, 94, 78 and 43 % in IWW2, 96, 97 and 87 % in IWW3, 84, 97 and 99 % in IWW4 and 97, 92 and 93 % in IWW5, respectively for an ozone dosage of 10 g/hr after 60 min of treatment. The actual ozone consumption during the period was 50 mg/L and no significant change in pH of wastewater samples noticed after treatment. The indirect ozonation is favoured in alkaline pH (>8.5) and hence high decolourisation efficiency obtained in all the dyeing wastewater samples tested (Aplin and 532

White, 2000). The decolourisation improved initially with time as the mass transfer coefficient increases with mixing and overall dye decomposition thereof increases ( Wu and Chung, 2006). After 60 min of ozonation the increase in decolourisation efficiency was not significant which can be attributed to the saturation of ozone concentration in liquid phase (Bai et al., 2011). The COD reduction of 15 % in IWW1, 12 % in IWW2, 13 % in IWW3, 17 % in IWW4 and 15 % in IWW5 was noticed. Ensar and Bulent (2008) also obtained similar results revealing that ozonation is faster in decolourisation than degradation of dyestuffs. It is understood that application of ozone in oxidation of textile dyeing wastewater leads to faster destruction of chromophore group in dyestuff in turn yielding high decolourisation efficiency

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Table 2. Decolourisation rate constant, k, min-1 Sample UV/H2O2

IWW1 IWW2 IWW3 IWW4 IWW5

O3

UV/O3

UV/O3/H2O2

43 6 nm

52 5 nm

62 0 nm

43 6 nm

52 5 nm

62 0 nm

43 6 nm

52 5 nm

62 0 nm

43 6 nm

52 5 nm

62 0 nm

0.008 0.008 0.008 0.004 0.008

0.011 0.007 0.008 0.008 0.006

0.010 0.004 0.005 0.008 0.006

0.033 0.050 0.057 0.033 0.059

0.060 0.027 0.059 0.059 0.043

0.036 0.010 0.037 0.077 0.046

0.041 0.056 0.059 0.051 0.061

0.066 0.034 0.061 0.064 0.050

0.042 0.014 0.048 0.081 0.054

0.056 0.072 0.072 0.072 0.078

0.075 0.052 0.074 0.073 0.061

0.061 0.038 0.061 0.083 0.071

Table 3. Degradation rate constant, k, min -1 Sample UV/H2O 2 O 3

UV/O 3

UV/O 3 / H2 O 2

IWW1 IWW2 IWW3 IWW4 IWW5

0 .0 0 4 3 0 .0 0 3 1 0 .0 0 3 2 0 .0 0 4 6 0 .0 0 3 8

0 .0 0 6 1 0 .0 0 5 8 0 .0 0 6 2 0 .0 0 6 5 0 .0 0 6 1

0 .0 0 3 3 0 .0 0 2 7 0 .0 0 2 9 0 .0 0 3 6 0 .0 0 3 4

0 .0 0 3 0 0 .0 0 2 3 0 .0 0 2 5 0 .0 0 3 2 0 .0 0 2 9

leaving behind the intermediate organics contributing for the chemical oxygen demand in the treated sample (Shu and Huang, 2006; Turhan et al., 2012). The decolourisation and degradation by ozonation was observed to be pseudo first order reaction and the rate constants are presented in tables 2 and 3 (R2> 0.96). The fastest rate constants at 436, 525 and 620 nm were 0.059, 0.060 and 0.077/ min determined for samples, namely IWW5, IWW1, IWW4, respectively while the fastest degradation constant of only 0.0032/min was obtained for IWW4 sample. The degradation of dyestuffs could be affected by the chemical structure of the dyes (Shu and Huang, 1995). Effect of UV/O3 The UV enhanced ozonation experiments were conducted with the same ozone flow of 10 g/hr. It can be inferred from the results depicted in figure 2 that decolourisation ef f icien cy increased in U V /O 3 process with observed decolourisation at 436, 525 and 620 nm as 92, 98 and 90 % in IWW1, 96, 86 and 55 % in IWW2, 97, 98 and 94 % in IWW3,

95, 98 and 99 % in IWW4 and 97, 95 and 96 % in IWW5, respectively after 60 min of treatment. The improvement in decolourisation of dyeing wastewater samples was accompanied by substantial increase in degradation of dyestuffs with chemical oxygen demand reduction of 21 % in IWW1, 18 % in IWW2 and IWW3, 23 % in IWW4 and 20 % in IWW5. Increase in the pseudo-first order rate constants can also be noted from the results presented in tables 2 and 3. It is interpreted that the presence of UV in ozonation process can enhance the degradation of intermediates which resist oxidation by ozone (Jie Sun et al., 2013). One of the reasons for the enhancement could be the increase in production of hydroxyl radical when ozone coupled with UV wherein one molecule of ozone would give rise to 2 molecules of hydroxyl radical (Mika et al., 2011). Further, Rajeshwar et al. (2008) in their review documented that ozone absorbs radiation at 260 nm strongly. Hence the integration of UV-C in an ozonation system significantly increases the degradation of organic pollutants in sample wastewater subjected to treatment. The enhancement in process efficiency by coupling UV irradiation with ozone has been reported by many researchers (Wu and Chang, 2006; Hsing et al., 2007; Bai et al., 2011). Effect of UV/O3/H2O2 The effect of UV/O 3/H2O2 in decolourisation and degradation of textile dyeing wastewater samples was assessed by varying the

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(a)

(b)

(c)

(d)

Figure 2. Decolourisation and degradation by UV/O3 : (a) Colour removal at 436 nm, (b) colour removal at 525 nm, (c) colour removal at 620 nm and (d) COD removal hydrogen peroxide dosage from 100 and 2000 mg/L at a constant ozone flow of 10 g/hr and at their actual pH. The results are represented by figure 3. Complete decolourisation was observed in all the samples with chemical oxygen demand reduction of 30, 28, 29, 32 and 31 % in IWW1, IWW2, IWW3, IWW4 and IWW5 samples, respectively for the H2O2 dose of 500 mg/L. It was observed that the process efficiency increased with hydrogen peroxide dose upto 500 mg/L. Further increase in H2O2 dose slightly decreased the degradation efficiency which can be attributed to the scavenging of hydroxyl radical as a result of which hydroperoxy radicals of less oxidizing power are formed ( Haji et al., 2010). From tables 2 and 3 it can be noted that the fastest pseudo-first order rate constants at 436, 525 and 620 nm were 0.078, 0.075 and 0.083/ min obtained for samples, namely IWW5, IWW1, IWW4, respectively while the fastest 534

degradation constant of 0.0065/min was obtained for IWW4 sample. It can also be noticed that the degradation rate of UV/O 3/ H2O2 was almost twice that of simple ozonation and UV/O3 processes. The enhancement in colour removal efficiency with addition of H2O2 to UV/O3 was also reported by Khan et al. (2010). In order to examine the effect of UV/H2O2 alone in treatment of textile dyeing wastewater experiments were conducted with constant H2O2 dose of 500 mg/L for 60 min at their actual alkaline pH. It can be noted from the results depicted in figure 4 that decolourisation and degradation less than 50 and 20 %, respectively only were obtained. Control experiments in the absence of UV and H2O2 separately were carried out. In both the cases the decolourisation efficiency dipped to less than 3 % even after 60 min of treatment. Several researchers reported that the photo

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100 90 80 70 60 50 40 30 20 10 0 100 250 500 1000 2000 100 250 500 1000 2000 100 250 500 1000 2000 100 250 500 1000 2000 mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L 436 nm

525 nm

620 nm

Decolorisation (%) IWW1

IWW2

COD Reduction (%) IWW3

IWW4

IWW5

Figure 3. Effect of H2O2 dose in UV/O3/H2O2

100 90 80 70 60 50 40 30 20 10 0 436 nm

525 nm

620 nm

Decolorisation (%) IWW1

IWW2

COD Reduction (%)

IWW3

IWW4

IWW5

Figure 4. Effect of UV/H2O2 oxidation with H2O2 is more efficient in acidic pH but in this study the alkaline pH of textile dyeing wastewater was observed to be favourable for the ozone enhanced UV/H2O2 process. This may be due to the increase in conjugate anion of H2O2 at alkaline pH which

increases hydroxyl radical generation (Morgana et al., 2014). Effect of H2O2 in sequence From the above results it can be noted that UV/ozonation contributes more for decolo-

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100 90

Decolourisation (%)

80 70 60 50 40 30 20 10 0 IWW1 IWW2 IWW3 IWW4 IWW5 IWW1 IWW2 IWW3 IWW4 IWW5 IWW1 IWW2 IWW3IWW4 IWW5 436 nm

525 nm UV/O3

620 nm UV/H2O2

Figure 5. Decolourisation by UV/O3 – UV/H2O2 in sequence 100 90 80

COD Reduction (%)

70 60 50 40 30 20 10 0 IWW1

IWW2

IWW3 UV/O3

IWW4

IWW5

UV/H2O2

Figure 6. COD reduction by UV/O 3-UV/H2O2 in sequence urisation while UV/H 2 O 2 for degradation. Since their combined effect did not yield satisfactory results, a sequence process by UV/O3 with UV/H2O2 was studied. The ozone dosage of 10 g/hr was given for 70-90 % colour removal in 30 min and then H2O2 was 536

added. The H2O 2 dosage for this sequence process was 0.5 g/L. No change in the solution pH was made. The overall treatment period was 60 min and the results are illustrated in figures 5 and 6. It could be noted that the decolourisation of about 95 % and chemical oxygen demand reduction greater than 40 % were obtained with the chemical oxygen demand removal efficiency reaching a maximum of 51 % in sample, namely IWW4 which can be attributed to the increased mineralization of the dyestuff in the sample wastewater. The dye molecules in the wastewater also absorbs UV in turn obstructing the hydroxyl radical generation in UV/H2O2 process and hence the UV/O 3 was given prior to UV/H 2 O 2 for significant decolourisation first (Shu and Chang, 2006). Effect of inorganic ions The textile dyeing wastewaters are characterized by the presence of strong colour and high concentration of inorganic salts that are used in dyeing processes. The wastewater samples, namely IWW1-IWW5 were also

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Decolorisation (%)

100 90 80 70 60 50 40 30 20 10 0 436 nm

525 nm

620 nm

436 nm

IWW1

525 nm

620 nm

436 nm

IWW2

UV/H2O2

O3

525 nm

620 nm

436 nm

IWW3

UV/O3

525 nm

620 nm

436 nm

IWW4

UV/O3/H2O2

525 nm

620 nm

IWW5

UV/O3 - UV/H2O2

Figure 7. Effect of AOPs in decolourisation of IWWs 0.35

90 80

0.3

70

0.25

60

BOD 3 /COD

COD Reduction (%)

100

50 40 30 20

0.2 0.15 0.1

10 0

0.05

IWW1

IWW2

IWW3

IWW4

IWW5 0

UV/H2O2

O3

UV/O3

UV/O3/H2O2

UV/O3 - UV/H2O2

IWW1 Initial

Figure 8. Effect of AOPs in degradation of IWWs containing high amount of inorganic ions as reflected by the high concentration of total dissolved solids and alkalinity in them. Figures 7 and 8 depict the effects of advanced oxidation processes (AOPs) on various samples tested. It can be noted that the degradation was low in all the processes tested with a maximum of only 51 % chemical oxygen demand reduction obtained in the sequence process which did not increase significantly with increase in exposure time

UV/H2O2

IWW2 O3

UV/O3

IWW3 UV/O3/H2O2

IWW4

IWW5

UV/O3- UV/H2O2 (in squence)

Figure 9. Effect of AOPs on biodegradability of wastewater albeit, the samples turning colourless after treatment. This indicates that only colour causing chromophore groups in the dyestuffs were destructed leading to formation of intermediates which could still be contributing to chemical oxygen demand (Turhan et al., 2012). It is also important to mention that sample, namely IWW4 showed relatively higher degradation eventhough it contained high amount of total dissolved solids. This may be due to the presence of higher

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Table 4. Electrical energy per order in IWWs Sample EEO, Kwh/m3

IWW1 IWW2 IWW3 IWW4 IWW5

UV/ O 3 H 2O 2

UV/ UV/H2 UV/O3 O3 O 2/O 3 UV/H2O2 (in sequence)

28 .5 35 .0 32 .4 28 .4 26 .9

36 .2 43 .0 42 .9 32 .7 38 .3

44 .1 56 .0 51 .3 38 .4 44 .0

23 .9 26 .0 24 .9 22 .1 23 .0

14 .3 16 .7 14 .8 11 .9 12 .7

concentration of sulphate ions which can enhance the oxidation through formation of persulphate radical (Muthukumar et al., 2004). Biodegradability The effect of advanced oxidation processes on biodegradability is depicted in figure 9. It was noticed that simple ozonation showed low performance while the sequence process showed high performance in biodegradability improvement. The textile dyeing wastewater samples, namely IWW4 showed the maximum improvement in biodegradability with BOD 3/ COD increasing from 0.11 to 0.32, in UV/O 3UV/H2O2 sequential treatment process. Electrical energy per order (EEO) The electrical energy per order calculation gives the actual energy requirement per order of pollutant removal which can be used as the scale-up factor and a measure of treatment efficiency (Khan et al., 2010). The advanced oxidation processes adopted in this study were also compared based on their energy requirement measured in terms of electrical energy per order and the results are presented in table 4. It is observed that the electrical energy per order was high for ozonation and low for UV/O 3 -UV/H 2 O 2 in sequence. The low electrical energy per order for UV/H2O2 is lower than UV/O3 process due to less number of electricity consuming entities otherwise, the UV/H2O2 alone was not efficient in textile wastewater treatment. The treatment of sample, namely IWW4 required 538

less energy in terms of electrical energy per order. CONCLUSION The treatment of textile dyeing wastewater using the selected advanced oxidation processes at pilot-scale was found to be feasible. The ozonation and UV/O3 processes removed 90 % of colour 12-23 % of chemical oxygen demand after 60 min treatment while the UV/O 3/H 2O 2 process yielded complete colour removal with 28-31% chemical oxygen demand reduction. The UV/H 2O 2 oxidation process carried in sequence with UV/O 3 produced the maximum chemical oxygen demand reduction of 51 % while the ozonation removed 70-90 % colour initially. The ozonation and other coupled advanced oxidation processes followed pseudo-first order kinetics and the presence of inorganic salts observed to be inhibiting the process efficiency. Biodegradability of the wastewater samples found to increase after advanced oxidation processes treatment and the maximum improvement was obtained for UV/O 3-UV/ H2O2 process carried out in sequence which was also produced low electrical energy per order values. Hence adopting the sequential UV/O 3-UV/H 2O 2 process could be a better pretreatment method since the exhausted dye bath contributes to major amount of organics in textile dyeing wastewater. The treated water could be combined with the streams coming from the processes prior to dyeing in the production unit and taken for biological treatment so as to remove the residual organics that are biodegradable. This process also avoids the chemical sludge that would result if conventional physico-chemical treatment methods are adopted for colour removal. REFERENCE APHA. 1998. Standard methods for the examination of water and wastewater (20th edn). American Public Health Association, Washington, D.C. Aplin, R. and T.D. White. 2000. Comparison of three advanced oxidation processes for degradation of textile dyes. Water Sci.

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INDIAN J. ENVIRONMENTAL PROTECTION, VOL. 36, NO. 7, JULY 2016 © 2016 - Kalpana Corporation