**4.2 Optimization of operational parameters**

Optimization of operational parameters in electrocoagulation process such as (applied current, pH, reaction time, NaCl (electrolyte) concentration) were investigated. Optimization of the above mentioned operational parameters is necessary to improve the performance of EC process and the economic viability. Since the influence of these parameters depend on the type of waste water and its concentration, optimal value of the operational parameters were identified for the textile dyeing waste water synthesized using disperse dye powder. The CRE at varied current supplied for the process, pH, reaction time, and the concentration of the electrolyte used is discussed here with. Two sets of EC with TiO2/Zn-TiO2/Zn (electrode 'A') and Zn-Zn (electrode 'B') were conducted for optimization and the results were compared.

#### **4.3 Effect of pH**

The pH is one of the most important parameters in the performances of EC process in order to achieve a compromise between best coagulation and best

**197**

**Figure 5.**

*XRD Pattern for Zn and TiO2/Zn.*

when soluble Ti(OH)4

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis…*

flotation. The optimum range may however vary as a function of electrode material and dye structure. And the fact is that pH determinates the metallic ions speciation, the chemical state of other species in the solution, and solubility. Hence the optimum pH is necessary to minimize environmental remediation costs and make the process more efficient. To investigate this effect in this work, a series of experiments were performed using synthetic disperse dye solution. Experiments were carried out at various values of pH (4.5, 5.5, 6.6, 7.5, 8.5 and 9.5) under which the applied current was kept at 0.05A for electrode 'A' and 0.15A for electrode 'B'. The pH was adjusted to a desirable value using NaOH, or H2SO4 and varied in the range 4.5 to 9.5. The treated sample is collected and filtered and the % of CRE estimated.

It can be noticed that decolorization was most effective in a pH range between 4.5 to 8.5 for coated and 4.5 for zinc electrodes and removal of CRE% reached values between 91.7 to 98.1 for the coated and 80.4 for Zn electrodes. This refers to the area where Ti(OH)2+ and Ti2(OH)2+ would have been formed, and Ti(OH)3 as insoluble species prevailed. On the other hand, above pH 8.5, % of CRE fell

of 4.5, dye process was completed within 5 minutes with high efficiency. And also at pH 4.5, the dye separated well from solution and the sludge floated with good

anions become predominant at high pH. At an initial pH

The obtained results are shown in **Figure 6(a)**.

−

*DOI: http://dx.doi.org/10.5772/intechopen.95325*

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis… DOI: http://dx.doi.org/10.5772/intechopen.95325*

**Figure 5.** *XRD Pattern for Zn and TiO2/Zn.*

*Dyes and Pigments - Novel Applications and Waste Treatment*

The X-ray diffractograms of TiO2/Zn and zinc are shown in **Figure 5**. The diffraction peaks of TiO2 phase, and the substrate zinc are present in the investigated

The particle size of TiO2 is related to the diffraction peak broadening, so X-ray diffraction spectra of coated TiO2 nanoparticles were taken and particle size and phase composition were determined. The lattice parameter observed a = b = 3.780, c = 9.513. The average particle size calculated by using Scherer Eq. indicated high

The particle size of nanomaterial is related to the diffraction peak broadening, so X-ray diffraction spectra of synthesized TiO2 nanoparticles were taken and peak size and composition were determined. Sharp peaks obtained corresponding to the planes (104), (018), (110), (024), (024) and (300) confirmed the nanocrystalline anatase structure. It shows the primitive hexagonal structure of nanoparticles of TiO2. TiO2 deposition is consistent with 2 theta values (30,32,35,47,56,63,68) and Zn deposition with 2 theta values (36,43,54,70,78) from the XRD results. The data was compared with JCPDS card no:71-1059 for TiO2 and 65-3358 for Zn. In the XRD

Optimization of operational parameters in electrocoagulation process such as (applied current, pH, reaction time, NaCl (electrolyte) concentration) were investigated. Optimization of the above mentioned operational parameters is necessary to improve the performance of EC process and the economic viability. Since the influence of these parameters depend on the type of waste water and its concentration, optimal value of the operational parameters were identified for the textile dyeing waste water synthesized using disperse dye powder. The CRE at varied current supplied for the process, pH, reaction time, and the concentration of the electrolyte used is discussed here with. Two sets of EC with TiO2/Zn-TiO2/Zn (electrode 'A') and Zn-Zn (electrode 'B') were conducted for optimization and the results were compared.

The pH is one of the most important parameters in the performances of EC process in order to achieve a compromise between best coagulation and best

**196**

**4.3 Effect of pH**

electrode.

**Figure 4.**

surface area [28].

pattern, no other impurity peak was observed.

*(a, b) SEM, EDS image of Zinc, (c, d) TiO2/Zn.*

**4.2 Optimization of operational parameters**

flotation. The optimum range may however vary as a function of electrode material and dye structure. And the fact is that pH determinates the metallic ions speciation, the chemical state of other species in the solution, and solubility. Hence the optimum pH is necessary to minimize environmental remediation costs and make the process more efficient. To investigate this effect in this work, a series of experiments were performed using synthetic disperse dye solution. Experiments were carried out at various values of pH (4.5, 5.5, 6.6, 7.5, 8.5 and 9.5) under which the applied current was kept at 0.05A for electrode 'A' and 0.15A for electrode 'B'. The pH was adjusted to a desirable value using NaOH, or H2SO4 and varied in the range 4.5 to 9.5. The treated sample is collected and filtered and the % of CRE estimated. The obtained results are shown in **Figure 6(a)**.

It can be noticed that decolorization was most effective in a pH range between 4.5 to 8.5 for coated and 4.5 for zinc electrodes and removal of CRE% reached values between 91.7 to 98.1 for the coated and 80.4 for Zn electrodes. This refers to the area where Ti(OH)2+ and Ti2(OH)2+ would have been formed, and Ti(OH)3 as insoluble species prevailed. On the other hand, above pH 8.5, % of CRE fell when soluble Ti(OH)4 − anions become predominant at high pH. At an initial pH of 4.5, dye process was completed within 5 minutes with high efficiency. And also at pH 4.5, the dye separated well from solution and the sludge floated with good

#### **Figure 6.**

*Effect of varying (a) pH on CRE (%), (b) concentration of NaCl on CRE (%), (c) applied current on CRE (%), (d) Time on CRE (%).*

percent of CRE removal in the case of electrode 'A', and the separation was clear and high % of CRE removal as the pH was increased from 4.5 to 7.5 may be due to the formation of more monomeric and polymeric insoluble Ti species.

The percentage of CRE was 80.49 in the case of zinc electrodes at pH 4.5, as the pH increased from 4.5 to 9.5 there was a gradual and sudden decrease in percent of CRE, this could be attributable to the development of more soluble Zn(OH)2 than insoluble zinc ion and prevented coagulation.

#### **4.4 Effect of electrolyte**

NaCl is typically used by electrocoagulation treatment to improve the solution conductivity, so that current consumption could be reduced. In addition, increasing water conductivity using NaCl has other advantages; for example, chloride anions can significantly reduce the adverse effects of other anions, such as bicarbonate and sulphate ions. Conversely, an excessive amount of NaCl induces an overconsumption of the TiO2/Zn electrodes due to 'corrosion pitting'; zinc dissolution may become irregular. This is the reason why NaCl addition should be limited and optimized. It also allows the passivity of the electrodes to be decreased by removing the surface passivation of the oxide film produced because of its catalytic action on the electrode surface. The adverse effects of other anions (due to their oxidation) and the availability of metal hydroxide in the solution could greatly reduce chloride ions. This parameter could, therefore have a substantial effect on the efficiency of pollutant removal. The ability to remove pollutants under certain conditions depends on the amount of coagulant produced that is related to the media's conductivity. In order to improve the conductivity of the waste water to be treated, NaCl is applied in this process and the increase in salt concentration increases the concentration of ions in the solution, thus reducing the electrical resistance of the solution, thus reducing the resistance between electrodes. Greater the electrical conductivity means higher electrical conductivity of the solution, and for creating a fixed current conductivity, a higher voltage is needed. Therefore, for creating a fixed current

**199**

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis…*

other hand, producing acidic species such as HCl and ClO−

conductivity, less NaCl is needed compared with other electrolytes like Na2SO4, or Na2SO3, Moreover NaCl has a higher ionization speed and mobility due to the lower radiuses of Na and Cl as a result, and more current passes through wastewater and by increasing passing current, the speed of anode dissolution increases. On the

of revival conditions. Therefore, using NaCl as electrolyte has advantage for lower price. Also, textile and dying industries use plenty of NaCl and wastewaters of these industries comprise ions of NaCl, because it is cheap and the solution containing this salt has high conductivity thus it need low voltage for electro-coagulation and

To study the effect of wastewater conductivity on dye removal, various experiments were performed using NaCl as the electrolyte in the range of 0.1–0.35 g/L and the CRE removal efficiencies observed during EC process are given in **Figure 6(b)**. It is believed that the main pollutant removal mechanism observed during electro-coagulation is adsorption and entrapment onto the amorphous titanium and Zn(OH)2 precipitate formed due to the anodic reaction at maximum rate at pH 8.5 and 4.5 for 'A' and 'B' electrodes and the anodization of Ti, Zn are given in

As is evident in **Figure 6(b)** increasing the electrolyte concentration from 0.1 to 0.35 g/L the high % of CRE reducing rates (98.2 for electrode 'A' and for 'B' 98.1), Due to the improved conductivity of the aqueous medium and the addition of NaCl up to 0.35 g/L, the improvement in the removal efficiency of CRE can be related to a shift in ionic strength resulting in a moderate but substantial decrease in treatment efficiencies in terms of CRE removal in the electrode 'A.' But there was a sudden decrease in the CRE in the case of Zn electrodes as the electrolyte concentration increased from 0.1 g/L (from 98 percent sudden decrease in percentage of CRE) a further increase in electrolyte concentration did not improve, these findings can be clarified by the fact that when the NaCl concentration increased, the electrolyte conductivity correspondingly increased. This was possibly because the chloride ions could destroy the passivation layer and increase the metal's anodic dissolution rate, either by integrating chloride ion into the oxide film or by involving the same in the electrochemical reaction. A further increase in NaCl concentration in both electrodes showed negative degradation and salt film formation on the electrode surface, which would obstruct the interaction between the electrode and the waste water. The chance of successful interaction between the organic contaminants and

It is clear that the applied current is strongly influenced in EC. Increased current results in increased anodic dissolution of metal ions, resulting in the formation of high quantities of precipitate for pollutant removal. In batch electro-coagulation, operating current density is important as it is the only operational parameter which can be directly regulated. The quantity of oxidised metal ions increased when the current increased, and the quantity of metal hydroxide compounds for pollutant precipitation and adsorption also increased. In addition, as the applied current grows, the rate of development of hydrogen bubbles increases and their sizes

Ti s Ti aq 3e ( ) ( ) → + <sup>3</sup>+ − (2)

Zn Zn aq 2e ( ) → + <sup>2</sup>+ − (3)

enhances the desirability

*DOI: http://dx.doi.org/10.5772/intechopen.95325*

so it is economical in industrial scale.

the hydroxyl radicals was therefore reduced.

**4.5 Effect of applied current**

Eqs (2)and (3)

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis… DOI: http://dx.doi.org/10.5772/intechopen.95325*

conductivity, less NaCl is needed compared with other electrolytes like Na2SO4, or Na2SO3, Moreover NaCl has a higher ionization speed and mobility due to the lower radiuses of Na and Cl as a result, and more current passes through wastewater and by increasing passing current, the speed of anode dissolution increases. On the other hand, producing acidic species such as HCl and ClO− enhances the desirability of revival conditions. Therefore, using NaCl as electrolyte has advantage for lower price. Also, textile and dying industries use plenty of NaCl and wastewaters of these industries comprise ions of NaCl, because it is cheap and the solution containing this salt has high conductivity thus it need low voltage for electro-coagulation and so it is economical in industrial scale.

To study the effect of wastewater conductivity on dye removal, various experiments were performed using NaCl as the electrolyte in the range of 0.1–0.35 g/L and the CRE removal efficiencies observed during EC process are given in **Figure 6(b)**.

It is believed that the main pollutant removal mechanism observed during electro-coagulation is adsorption and entrapment onto the amorphous titanium and Zn(OH)2 precipitate formed due to the anodic reaction at maximum rate at pH 8.5 and 4.5 for 'A' and 'B' electrodes and the anodization of Ti, Zn are given in Eqs (2)and (3)

$$\text{Ti}(\text{s}) \rightarrow \text{Ti}^{3+}\left(\text{aq}\right) + \text{3e}^-\tag{2}$$

$$\text{Zn} \rightarrow \text{Zn}^{2+} \text{ (aq)} + 2\text{e}^- \tag{3}$$

As is evident in **Figure 6(b)** increasing the electrolyte concentration from 0.1 to 0.35 g/L the high % of CRE reducing rates (98.2 for electrode 'A' and for 'B' 98.1), Due to the improved conductivity of the aqueous medium and the addition of NaCl up to 0.35 g/L, the improvement in the removal efficiency of CRE can be related to a shift in ionic strength resulting in a moderate but substantial decrease in treatment efficiencies in terms of CRE removal in the electrode 'A.' But there was a sudden decrease in the CRE in the case of Zn electrodes as the electrolyte concentration increased from 0.1 g/L (from 98 percent sudden decrease in percentage of CRE) a further increase in electrolyte concentration did not improve, these findings can be clarified by the fact that when the NaCl concentration increased, the electrolyte conductivity correspondingly increased. This was possibly because the chloride ions could destroy the passivation layer and increase the metal's anodic dissolution rate, either by integrating chloride ion into the oxide film or by involving the same in the electrochemical reaction. A further increase in NaCl concentration in both electrodes showed negative degradation and salt film formation on the electrode surface, which would obstruct the interaction between the electrode and the waste water. The chance of successful interaction between the organic contaminants and the hydroxyl radicals was therefore reduced.

#### **4.5 Effect of applied current**

It is clear that the applied current is strongly influenced in EC. Increased current results in increased anodic dissolution of metal ions, resulting in the formation of high quantities of precipitate for pollutant removal. In batch electro-coagulation, operating current density is important as it is the only operational parameter which can be directly regulated. The quantity of oxidised metal ions increased when the current increased, and the quantity of metal hydroxide compounds for pollutant precipitation and adsorption also increased. In addition, as the applied current grows, the rate of development of hydrogen bubbles increases and their sizes

*Dyes and Pigments - Novel Applications and Waste Treatment*

percent of CRE removal in the case of electrode 'A', and the separation was clear and high % of CRE removal as the pH was increased from 4.5 to 7.5 may be due to the

*Effect of varying (a) pH on CRE (%), (b) concentration of NaCl on CRE (%), (c) applied current on CRE* 

The percentage of CRE was 80.49 in the case of zinc electrodes at pH 4.5, as the pH increased from 4.5 to 9.5 there was a gradual and sudden decrease in percent of CRE, this could be attributable to the development of more soluble Zn(OH)2 than

NaCl is typically used by electrocoagulation treatment to improve the solution conductivity, so that current consumption could be reduced. In addition, increasing water conductivity using NaCl has other advantages; for example, chloride anions can significantly reduce the adverse effects of other anions, such as bicarbonate and sulphate ions. Conversely, an excessive amount of NaCl induces an overconsumption of the TiO2/Zn electrodes due to 'corrosion pitting'; zinc dissolution may become irregular. This is the reason why NaCl addition should be limited and optimized. It also allows the passivity of the electrodes to be decreased by removing the surface passivation of the oxide film produced because of its catalytic action on the electrode surface. The adverse effects of other anions (due to their oxidation) and the availability of metal hydroxide in the solution could greatly reduce chloride ions. This parameter could, therefore have a substantial effect on the efficiency of pollutant removal. The ability to remove pollutants under certain conditions depends on the amount of coagulant produced that is related to the media's conductivity. In order to improve the conductivity of the waste water to be treated, NaCl is applied in this process and the increase in salt concentration increases the concentration of ions in the solution, thus reducing the electrical resistance of the solution, thus reducing the resistance between electrodes. Greater the electrical conductivity means higher electrical conductivity of the solution, and for creating a fixed current conductivity, a higher voltage is needed. Therefore, for creating a fixed current

formation of more monomeric and polymeric insoluble Ti species.

insoluble zinc ion and prevented coagulation.

**4.4 Effect of electrolyte**

*(%), (d) Time on CRE (%).*

**Figure 6.**

**198**

decrease. For successful dye removal, all these effects are significant. Other side reactions in the vicinity of the anode, such as the direct oxidation of one of the components of the contaminant or the formation of oxygen that restricts the efficacy of electro-coagulation, can be caused by high-current activity. In comparison, a high current causes the passivity of the cathode to decrease, resulting in high energy consumption. The best conditions correspond to a low applied current and substantial electrolysis time especially in terms of energy consumption and electrode consumption. It is essentially critical to avoid operating at too high current to address the excessive generation of Ti, Zn poly hydroxides in wastewater. The efficiency of the reduction of contaminants depends on the production of Ti (IV or III) and Zn (II) by the anode, so that a high period of electrolysis will lead to a higher production of titanium hydroxide or zinc hydroxide, which is responsible for the coagulation process. To optimise the applied current in the EC method, experiments were performed under other optimised parameters at different applied current from 0.05 to 0.30A and the results are given in **Figure 6(c)**.

As the applied current increased from 0.05 to 0.30A, the anodisation accompanied by floc formation with the Tin+ ions increased, the CRE percentage was 99.5 at 0.15A and consequently the removal efficiency decreased marginally in the case of electrode 'A' and in Zn-Zn electrodes as the applied current increased, the CRE removal increased gradually, the maximum CRE was 86 percent at 0.15A. The increase using the electrode 'A' was due to the dissolution of both Ti3+ and Zn2+, whereby at lower applied current highest CRE removal was obtained, moreover it could be observed that increasing the applied current above the optimum value decreases the CRE is due to undesirable side reaction such as electrolysis of water and oxygen evolution from OH free radicals. However energy consumption leads to be higher for increased applied current and indicates that increase in current density led to less efficient sprocess.

### **4.6 Effect of time**

The percentage color removal efficiency depends directly on the concentration of ions produced by the electrodes. This can be achieved by parameter like EC time. Because the formation of metal ions and concentration of the metal hydroxides play an important role on pollutant removal, this depends on operation time. To study its effect, the EC time was varied for different time intervals i.e., 5, 10, 15, 20, 25, 30 min and the other optimized parameters were kept constant. The results obtained are illustrated in **Figure 6(d)**. The H2 and O2 release and flocs formation increased over time and the foam became thicker.

A plot is drawn between time verses % CRE for two different electrodes as shown in graph, it was clearly known that as the time increases the percentage of CRE increased in the case of electrode 'A' at 15 mins was 97.2 and then there was slight reduction in CRE. Whereas in the case of electrodes 'B' there was a gradual increase of CRE from 50 to 92% and high % of CRE was achieved at 30 minutes which will be with more of energy as well electrode consumption compared to the electrodes 'A'.

In the EC process, the anode produces metal ions during electrochemical reaction. Metal ions are destabilization agent. If the charge loading were low, the metal ion released from the anode would not be sufficient to destabilize all the colloidal and suspended particles, so dye removal was not efficient in the case of zinc electrodes at applied current 5A. When EC time changed from 5 to 30 minutes the energy consumption increased from 0.0004966 to 0.00174 kWh/m3 in the case of electrode 'A' and 0.000843 to 0.005227 kWh/m3 forZn electrodes. From these results it is shown that % CRE removal is high with less energy consumption in the case TiO2/Zn than zinc electrodes. Treatment time is related with energy

**201**

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis…*

consumption and wastewater treatment performance. It is well known that the removal efficiency did not improve much after 25 min electrolysis, but the prolonged time would increase the electrochemical treatment cost. The results indicate that the optimum electrolysis time for best removal efficiencies is 10 min for TiO2/

The SEM images that display the sludge's morphology characteristics are shown

The results obtained in this study shows that the color can be eliminated with high percentages using the newly prepared TiO2/Zn electrodes from TiCl3 by spray

current increased the removal of organic matter also increased. In all the experimental parameters, dye removal efficiencies (CRE%) was observed in short period of operational time in using TiO2/Zn. The increase in applied current is also considered to mean an increase in energy usage. Thus, due to local discharge limits, energy and electrode usage, local energy unit prices and some other limiting factors, an

The effect of applied current on CRE% can clearly be understood. As the applied

Furthermore this research showed that the initial pH of the waste water at which high CRE% was obtained as the optimized pH 8.5 in the case of TiO2/Zn but 4.5 for Zn electrode. Overall, high color removal efficiency of disperse dye was obtained

The EC process has the potential to treat the textile dyeing wastewater and thus to reduce the contamination of the environment by the dye molecules as the real time textile dyeing waste water can be treated with this newly developed TiO2/Zn.

pyrolysis method compared with using Zn in EC process.

acceptable current density has to be considered.

using newly modified TiO2/Zn.

Further work can be done as given.

in **Figure 7**. It can be visualised that the flaky structure of the particulates produced from electrocoagulation is confirmed by the adsorbed dye molecules (grey or black portion) on the surface and the presence of a peak at 4.8 keV in the EDS spectra confirms the titanium ion floc. It is assumed from SEM, EDS sludge study, that the first titanium flocs which were involved in electrocoagulation, once after the depletion of the same, then the dye molecules have been removed by zinc flocs.

*DOI: http://dx.doi.org/10.5772/intechopen.95325*

Zn and 30 min for Zn electrodes.

*a) SEM, b) EDS of Sludge after electrocoagulation.*

**4.7 Sludge charaterization**

**Figure 7.**

**5. Conclusion**

*Treatment of Textile Dyeing Waste Water Using TiO2/Zn Electrode by Spray Pyrolysis… DOI: http://dx.doi.org/10.5772/intechopen.95325*

**Figure 7.** *a) SEM, b) EDS of Sludge after electrocoagulation.*

consumption and wastewater treatment performance. It is well known that the removal efficiency did not improve much after 25 min electrolysis, but the prolonged time would increase the electrochemical treatment cost. The results indicate that the optimum electrolysis time for best removal efficiencies is 10 min for TiO2/ Zn and 30 min for Zn electrodes.

#### **4.7 Sludge charaterization**

*Dyes and Pigments - Novel Applications and Waste Treatment*

to 0.30A and the results are given in **Figure 6(c)**.

density led to less efficient sprocess.

increased over time and the foam became thicker.

**4.6 Effect of time**

decrease. For successful dye removal, all these effects are significant. Other side reactions in the vicinity of the anode, such as the direct oxidation of one of the components of the contaminant or the formation of oxygen that restricts the efficacy of electro-coagulation, can be caused by high-current activity. In comparison, a high current causes the passivity of the cathode to decrease, resulting in high energy consumption. The best conditions correspond to a low applied current and substantial electrolysis time especially in terms of energy consumption and electrode consumption. It is essentially critical to avoid operating at too high current to address the excessive generation of Ti, Zn poly hydroxides in wastewater. The efficiency of the reduction of contaminants depends on the production of Ti (IV or III) and Zn (II) by the anode, so that a high period of electrolysis will lead to a higher production of titanium hydroxide or zinc hydroxide, which is responsible for the coagulation process. To optimise the applied current in the EC method, experiments were performed under other optimised parameters at different applied current from 0.05

As the applied current increased from 0.05 to 0.30A, the anodisation accompanied by floc formation with the Tin+ ions increased, the CRE percentage was 99.5 at 0.15A and consequently the removal efficiency decreased marginally in the case of electrode 'A' and in Zn-Zn electrodes as the applied current increased, the CRE removal increased gradually, the maximum CRE was 86 percent at 0.15A. The increase using the electrode 'A' was due to the dissolution of both Ti3+ and Zn2+, whereby at lower applied current highest CRE removal was obtained, moreover it could be observed that increasing the applied current above the optimum value decreases the CRE is due to undesirable side reaction such as electrolysis of water and oxygen evolution from OH free radicals. However energy consumption leads to be higher for increased applied current and indicates that increase in current

The percentage color removal efficiency depends directly on the concentration of ions produced by the electrodes. This can be achieved by parameter like EC time. Because the formation of metal ions and concentration of the metal hydroxides play an important role on pollutant removal, this depends on operation time. To study its effect, the EC time was varied for different time intervals i.e., 5, 10, 15, 20, 25, 30 min and the other optimized parameters were kept constant. The results obtained are illustrated in **Figure 6(d)**. The H2 and O2 release and flocs formation

A plot is drawn between time verses % CRE for two different electrodes as shown

in the

forZn electrodes. From

in graph, it was clearly known that as the time increases the percentage of CRE increased in the case of electrode 'A' at 15 mins was 97.2 and then there was slight reduction in CRE. Whereas in the case of electrodes 'B' there was a gradual increase of CRE from 50 to 92% and high % of CRE was achieved at 30 minutes which will be with more of energy as well electrode consumption compared to the electrodes 'A'. In the EC process, the anode produces metal ions during electrochemical reaction. Metal ions are destabilization agent. If the charge loading were low, the metal ion released from the anode would not be sufficient to destabilize all the colloidal and suspended particles, so dye removal was not efficient in the case of zinc electrodes at applied current 5A. When EC time changed from 5 to 30 minutes

the energy consumption increased from 0.0004966 to 0.00174 kWh/m3

these results it is shown that % CRE removal is high with less energy consumption in the case TiO2/Zn than zinc electrodes. Treatment time is related with energy

case of electrode 'A' and 0.000843 to 0.005227 kWh/m3

**200**

The SEM images that display the sludge's morphology characteristics are shown in **Figure 7**. It can be visualised that the flaky structure of the particulates produced from electrocoagulation is confirmed by the adsorbed dye molecules (grey or black portion) on the surface and the presence of a peak at 4.8 keV in the EDS spectra confirms the titanium ion floc. It is assumed from SEM, EDS sludge study, that the first titanium flocs which were involved in electrocoagulation, once after the depletion of the same, then the dye molecules have been removed by zinc flocs.

#### **5. Conclusion**

The results obtained in this study shows that the color can be eliminated with high percentages using the newly prepared TiO2/Zn electrodes from TiCl3 by spray pyrolysis method compared with using Zn in EC process.

The effect of applied current on CRE% can clearly be understood. As the applied current increased the removal of organic matter also increased. In all the experimental parameters, dye removal efficiencies (CRE%) was observed in short period of operational time in using TiO2/Zn. The increase in applied current is also considered to mean an increase in energy usage. Thus, due to local discharge limits, energy and electrode usage, local energy unit prices and some other limiting factors, an acceptable current density has to be considered.

Furthermore this research showed that the initial pH of the waste water at which high CRE% was obtained as the optimized pH 8.5 in the case of TiO2/Zn but 4.5 for Zn electrode. Overall, high color removal efficiency of disperse dye was obtained using newly modified TiO2/Zn.

The EC process has the potential to treat the textile dyeing wastewater and thus to reduce the contamination of the environment by the dye molecules as the real time textile dyeing waste water can be treated with this newly developed TiO2/Zn. Further work can be done as given.

	- Attempt can be made in the preparation of TiO2/M (M for metal) with different metals as electrode materials,
	- different precursor
	- preparation parameters like flow rate, number of coating etc. can be adopted in spary pyrolysis.
	- In EC process the other operational parameters like varying the distance between the electrodes, height of electrodes immersed in the waste water etc. can be optimized.
	- Investigation other than CRE%, like COD, BOD etc. can be calculated.
	- Applied current,
	- dye concentration,
	- electrolyte concentration
	- and pH,
