Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater

Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater

Accepted Manuscript Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate indust...

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Accepted Manuscript Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater Brahmi Khaled, Bouguerra Wided, Hamrouni Béchir, Aloui Limam, Loungou Mouna, Zied Tlili PII: DOI: Reference:

S1878-5352(14)00362-1 http://dx.doi.org/10.1016/j.arabjc.2014.12.012 ARABJC 1523

To appear in:

Arabian Journal of Chemistry

Received Date: Accepted Date:

2 October 2014 27 December 2014

Please cite this article as: B. Khaled, B. Wided, H. Béchir, A. Limam, L. Mouna, Z. Tlili, Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater, Arabian Journal of Chemistry (2015), doi: http://dx.doi.org/10.1016/j.arabjc.2014.12.012

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Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater BRAHMI Khaled a, BOUGUERRA Wided a, HAMROUNI Béchir a, ALOUI Limam b, LOUNGOU Mouna c, Zied Tlili d a U. R Traitement et Dessalement des Eaux, Département de Chimie, Faculté des Sciences de Tunis, 2092 Manar II, TUNISIE, Tel./ Fax: +2167187128. b U. R Matériaux, Environnement et Energie, Département de Chimie, Faculté des Sciences de Gafsa, Campus Universitaire Sidi Ahmed Zarroug -2112 Gafsa, TUNISIE, Tel +216 76 211 026. c Groupe Chimique Tunisien, Usine de M’Dhilla Gafsa, Km. 14 Route M’Dhilla- 2100 Gafsa, Tel +216 76211515. d Higher Institute of Business Administration of Gafsa, Campus Universitaire Sidi Ahmed Zarroug -2112 Gafsa, TUNISIE, Tel +216 24951825. Tel./ Fax: +21671871282; Corresponding author E-mail:[email protected]

ABSTRACT This study investigates the effect of reactor design parameters on cadmium removal from industrial wastewater discharged by the Tunisian Chemical Group (TCG) to improve as much as possible efficiency and cost of electrocoagulation (EC) process. Based on an examination of the design parameters one by one, the best cadmium removal was achieved for an inter-electrode distance (die) of 0.5 cm, monopolar connection mode, stirring speed of 300 rev min-1, surface-area-to-volume ratio (S/V) of 13.6 m-1, and an initial temperature of 50 C°. These operating conditions allowed to achieve efficient removal in a relatively short operating time with the lowest energy consumption and cost possible. The present study proved that the parameters that have an effect on the operating cost are the electrode configuration, inter-electrode distance and S/V ratio. The energy consumption, the pH evolution, and the treatment cost were studied. The investigation of the effect of all the selected optimum EC design parameters together on the removal of cadmium from the TCG wastewater proved that the treatment was highly efficient; 100 % of cadmium removal was reached in 5 min, with a very low power consumption (1.6 kWh m-3) and very low cost (0.116 TND m-3). Moreover, EC was found to be capable of removing cadmium as well as other pollutants at the same time from the case-study industrial wastewater. The investigation carried out in this work explores and proposes a very cost-effective treatment method to remove heavy metals from industrial wastewater if compared to results reported about cost of this treatment process through other widely used technologies such as coagulation (4.36 Tunisian National Dinar (TND) m-3) and precipitation (9,96 TND m-3) employed in previous studies. Keywords: Wastewater treatment; Electrocoagulation; treatment cost; Investigation of reactor design parameters; Cadmium removal; Energy consumption. 1

1. Introduction The removal of heavy metals from industrial waste has become one of the most essential applications in wastewater treatment in terms of protection of health as well as the environment. These heavy metals are known to be among the most common pollutants found in industrial wastewaters and pose serious health hazard, and are environmentally-unfriendly because they are not biodegradable and tend to accumulate in living organisms (Saha and Sanyal, 2010). Cadmium is a toxic non-essential heavy metal in the environment; it is teratogenic and carcinogenic (Young, 2005). Cadmium toxicity causes renal damage (Suwazono et al. , 2000), pulmonary insufficiency and negative effects on bones, liver and blood (IRAC, 2006). Cadmium poisoning, therefore, creates far greater likelihood of weaker and weaker constitution of such parts of the body obviously performing vital bodily functions. The drinking water guideline value is 0.005 mg L-1 (Health Canada, 2012). The increased water use and wastewater discharge, particularly industrial wastewater, have added impurities to water which requires cleaning processes (Vasudevan and Lakshmi, 2011). It is important to note that the overall treatment cost of metal-contaminated water varies, depending on the process employed and the local conditions. In general, the technical applicability, simplicity and cost-effectiveness are the key factors in selecting the most suitable treatment of inorganic effluent. Physical methods like ion exchange, reverse osmosis and electrodialysis have proven to be either too expensive or inefficient to remove cadmium from water (Vasudevan and Lakshmi, 2011). During the past few years, EC has been proposed as an effective method to treat many types of effluents such as wastewater charged with heavy metals (Kumar et al. , 2004), natural water charged with Fluor (Emamjomeh and Sivakumar, 2006), surface water (Lai and Lin, 2006), suspended solids, oil and fat in restaurant wastewater (Chen et al. , 2000), black liquor from paper industry (Zaieda and Bellakhala, 2009), and cigarette factory wastewater (Bejankiwar, 2002). All these investigations showed that EC could achieve a significant reduction of major pollutants and has become of growing interest for the industrial scale. EC is a simple and efficient process where the production of the coagulating agent is managed in situ by means of electro-oxidation of a sacrificial anode. In this case, there is no need for adding chemical coagulants or flocculants to perform the treatment (Elham et al. , 2011). In the EC process, the destabilization mechanism of the contaminants, particles suspension, and breaking of emulsions can be summarized as three successive steps: (1) compression of the diffuse double layer around the charged species by the interactions of ions 2

generated by oxidation of the sacrificial anode, (2) charge neutralization of the ionic species present in wastewater by counter ions produced by the electrochemical dissolution of the sacrificial anode. These counter ions reduce the electrostatic inter-particle repulsion to the extent that the van der Waals attraction predominates, thus causing coagulation. A zero net charge results in the process, and (3) flocs formation; the flocs formed as a result of coagulation creates a sludge blanket that entraps and bridges colloidal particles that are still remaining in the aqueous medium (Thirugnanasambandham et al. , 2013). The EC has been used for treatment of various types of wastewater and effluents containing algae, phosphate, sulfide, sulfate, sulfite, fluoride and heavy metals ions such as; Fe2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+ (Emamjomeh and Sivakumar, 2009; Merzouket al. , 2009; Lekhlif et al. , 2014; Rajesh et al. , 2014; Umran et al. , 2015). The proposed mechanism of chemical reactions occurring in the EC process is shown by the following main reactions at the aluminum electrodes (Ilhan et al. , 2007) : Anode: Cathode:

Al(s) ↔ Al3+ (aq) + 3 e-

3 H2O (aq) + 3 e- ↔

3/2 H2 (g) + 3 OH - (aq)

Eq. (1) Eq. (2)

The hydroxyl ions produced at the cathode increase the pH in the electrolyte and we have a reaction in the aqueous solution between Al3+ and OH- ions to form aluminum hydroxide: In bulk:

Al3+ (aq) + 3OH- (aq) ↔ Al (OH)3 (s)

Eq. (3)

In the presence of sufficiently high potential, secondary reactions such as direct oxidation of organic compounds and of H2O or Cl- are also likely to occur at the anode present in wastewater. These reactions are shown by the following main reaction: In bulk:

2 Cl - (aq) ↔ Cl2 (g) + 2 e-

Eq. (4)

In bulk:

2 H2O (aq) ↔ O2 (g) + 4 H+ (g) + 4e-

Eq. (5)

The chlorine produced is a strong oxidant that can oxidize the same organic compounds and promote electrode reactions. The generated Al3+ ions would immediately undergo further spontaneous reactions to produce corresponding hydroxides and/or poly-hydroxides in a wide pH range. These hydroxides/ poly-hydroxides/poly-hydroxy metallic compounds such as Al6(OH)153+, Al7(OH)174+, Al8(OH)204+, Al13O4(OH)247+, Al13(OH)345+, which transform finally 3

into Al(OH)3 according to complex precipitation kinetics, have a strong affinity with dispersed/dissolved ions as well as the counter ions to cause coagulation/adsorption. The advantages of EC include high removal efficiency, a compact treatment facility, relatively low cost, and the possibility of complete automation (Vasudevan and Lakshmi, 2011). The effect of EC reactor design parameters on the treatment of wastewater has received a great deal of attention in the existing literature on the utilization of EC technology (Chopra et al. , 2011; Rajesh et al. , 2014; Umran et al. , 2015), yet it seems that previous studies have not set out to apply all design parameters at the same time to achieve high rate of removal efficiency much more cost-effectively. The present study was designed to investigate the effect of reactor design parameters on cadmium removal from industrial wastewater one by one then apply their optimal yields on the treatment of the case-study wastewater in order to improve as much as possible the efficiency of EC process and significantly reduce its cost as well. Different parameters such as the surface-area-to-volume ratio, the inter-electrode distance, the state of the aluminum plates, the stirring speed, the electrodes configuration mode and the initial temperature of water were studied in detail. EC-based process was applied on the treatments of wastewater discharged from phosphate and acid manufacturing TCG in M’Dhilla, Gafsa, Tunisia, which is highly acid (pH = 2.02) and contains large amounts of heavy metals. This industry consumes 400 m3 day-1, yet the treatment of this particular hazardous wastewater containing large quantity of cadmium has never been studied in previous research. This investigation sets out to achieve high-rate cadmium removal from TCG industrial wastewater cost-effectively. Additionally, the treatment process carried out in this study enables the reusability of the case-study wastewater and thus could allow a significant reduction in water consumption, and promises to be very useful for further applications of the EC process on the treatment of wastewater containing heavy metal ions. 2. Materials and methods 2.1. Reagents and analytical procedures All the chemicals used were of analytical grade. Total Cadmium concentration was determined by using flame atomic absorption spectroscopy (FAAS) method. The conductivity was measured during the experiments using the conductivity meter Jenway 4510 (Ω Metrohm). A calibrated Digital pH-meter Cyber Scan 510 (WDW, Germany) was used to measure the pH and the temperature of the solution. 4

2.2. Validation of the analytical method The flame atomic absorption spectroscopy (FAAS) method was used to determine cadmium concentration. This method was the most feasible one because it could be adequately adapted to higher concentration of the cadmium measurement. The flame atomic absorption spectroscopy Analytik Jenna Nova 400 was used. In order to perform the experiments and assure the reliability and validity of the atomic absorption method whereby residual cadmium (II) concentration could be determined, several tests had been done to calculate the linearity, specificity, fidelity (reproducibility and repeatability) as well as limits of both instrumental method detection and quantification. The result of the experimental validation of the atomic absorption analytical method is shown in table.1. The method for Cd(II) determination by AASF is efficient, with a detection limit of 0.0187 and a quantification limit of 0.0624 in a range of linearity of 0.02 to 2 mg L-1. 2.3. Cell construction The experimental setup is shown in Fig. 1. The EC cell was made up of 1L cylindrical Plexiglas beaker, with a wooden cover supporting the set of parallel aluminum sheets used as sacrificial electrodes. The electrodes used in this work were formed by two parallel rectangular aluminum plates (250 mm * 80 mm * 2 mm). The total immersed area of each electrode was active (85mm * 80mm * 2mm) S = 68 cm2, the other section of the electrodes was wrapped and inactivated with a durable water-resistant sellotape in order to fix the immersed area and avoid the anode loss. The anode-cathode spacing was varied from 5 to 20 mm. A small hole was drilled in the cover to serve as a sampling port. The experimental runs were performed at a magnetic stirring speed varied from 0 to 600 rev min-1. 2.4. Treatment procedure The treatments were carried out using aluminum as electrodes. Before each treatment, and in order to avoid a passivation film, the electrodes (anode and cathode) were rubbed with sandpaper then cleaned with NaOH (2 M) and HCl (2 M) aqueous solutions. The solutions were prepared using CdSO4, 10 H2O. If required, the pH of the electrolyte was adjusted with HCl (0. 1 M) and NaOH (0. 1 M) solutions before each EC test started. The current intensity was maintained at the range from 0 to 3 A using a regulated direct current power supply (DC) AFX 2930 SB DC and the voltage cell between the electrodes was continuously recorded. As has been already noted, the wastewater under investigation was collected from a Tunisian sulfuric 5

acid and superphosphate manufacturing industry. Sample filtration, collection and preservation were carried out immediately in the industry laboratory of quality control of TCG. For each sample, cadmium concentration was measured three times to determine the average concentration as a result with respect to reproducibility and repeatability. The investigation of the EC reactor design parameter using aluminum electrodes was carried out for an initial concentration of 100 ppm keeping constant the volume of the solution (1L), the current density (j) at 3.68 mA cm ², the initial pH at 7, the conductivity ( ) at 5.86 mS cm-1. Only the studied parameter was varied, in order to clearly show its effects on the removal efficiency and the treatment cost, keeping constant the other parameters (the initial temperature (θi) at 16.5 C°, the stirring speed at 300 rev min-1, and the inter-electrode distance (d) at 2 cm). The pH, the temperature, the difference in potential between the two electrodes and the final cadmium concentration were measured for each sample. Also, the energy, electrodes consumption and the treatment cost were calculated for each sample as a function of time. The characterization and the treatment of the effluent were performed at the Water Treatment and Desalination Research Unit of Tunis, Tunisia. The method of cadmium removal through EC used in this study proved to be cost-effective. 2. 5. Treatment cost The EC process required an operating cost which encompassed material (electrodes and electrical energy) as well as other essential expenses consisting of sludge dewatering and disposal. The low operating cost could be calculated as follows: Operating cost = a C energy + b C electrode + D

Eq. (6)

Where: (a) the energy cost: 0.2 (TND)/KWh; (b) the aluminum cost: 2. 8 Tunisian National Dinar (TND) kg-1; C

energy

(kW h m-3) and C

electrode

(kg Al m-3) are consumption

quantities for the Cd (II) removal; D is cost of the chemicals used (D= cost of salt + cost acid = 0.1 TND m-3). Cost of electrical energy (kW h m-3) is calculated as:

Cénergie (kWh / m 3 ) =

UC × I × t V

Eq. (7)

Where U is the voltage cell (V), I is the current (A), t is the time of electrolysis (h) and V is the volume (m3) of Cd (II) solution. Cost of electrode (kg Al m-3) is calculated by the following equation according to Faraday’s Law: 6

Célectrodes (kg / m3 ) =

I ×t × M n × F ×V

Eq. (8)

Where I is current (A), t is time of electrolysis (s), M is molecular mass of aluminum (26.98 g mol-1), z is number of electron transferred (z = 3), F is Faraday’s constant (96487 C mol-1) and V is volume (m3). 3- Results and discussion 3.1. Choice of electrode configuration The EC efficiency is strongly related to the dissolution of the electrodes and the production of a large amount of aluminum metal ions (Mollah et al. , 2001; Modirshahla et al. , 2008), which is reinforced by an increase in the number of plates to get a larger active surface. However, it is important to note that the number of plates should be increased in a way that enables us to avoid the generation of a significant ohmic, and this depends on the type of electrode configuration and the number of the electrodes used. Generally, we have two types of electrode configuration (Fig. 2) where the number of the electrodes is varying between 4 and 8: The first configuration is a monopolar electrode configuration, i.e. each electrode is connected to either the anode or the cathode, and the second one is bipolar and thus involves connecting only the first electrode to the anode and the last electrode to the cathode (Mamerie et al. , 1998; Meunier et al. , 2004; Beauchesne et al. , 2005). In order to investigate the influence of electric configuration and to choose one of the two configurations, two tests were carried out using 4 aluminum electrodes. The first test was done with a bipolar configuration, and the second one with a monopolar configuration. Table 2 shows that the electrode consumptions calculated through Eq. (8) above were the same at each time interval, which could be explained by the fact that we had the same active anode surface and the same current density in the same conditions, changing only the electrode configuration. Electrode configuration, therefore, had no effect on the aluminum electrode consumption. The obtained results presented in Fig. 3. support the hypothesis that increasing the number of electrodes results in an increase in the removal efficiency. It was found that using four electrodes made the treatment process much faster; 30 min to reach 90 % of cadmium reduction, while 45 min were required if two electrodes were used for the same performance. It is also clear from Fig. 3 and Table 2, that in the case of bipolar configuration cadmium elimination was more efficient but required much energy and high cost if compared to 7

monopolar configuration. For the bipolar configuration, the removal efficiency reached 92% and cost 0.55 TDN in 60 min of electrolysis time. However, for monopolar configuration, the removal efficiency reached 87% and cost 0. 160 TND m-3 in 60 min. Thus, the choice of monopolar configuration allowed high rate of removal efficiency negligibly lower than that with bipolar configuration, and significant reduction in treatment cost. This result could be explained by the fact that in bipolar connection there is a higher surface area resulting in more anodic oxidation compared to that of monopolar connection. On the other hand, the increase of the distance between the electrodes connected to DC current supply created an ohmic drop relative to the anode and cathode voltages. This could be further explained through the following equation: R ohm

=

d (S × k )

Eq. (9)

In the case of bipolar configuration, the increase in the inter-electrode distance resulted in greater resistance to mass transfer and slower kinetics of charge transfer, which involved much energy consumption as well as high cost (N. Meunier et al. , 2004; Khaoula et al. , 2013). Therefore, based on the aforementioned results, the monopolar configuration had to be chosen because of the high-rate removal efficiency it would yield with very low energy consumption and cost. 3.2. Effect of the variation of the surface-area-to-volume ratio 3.2.1. Determination of the optimum S/V ratio The surface-area-to-volume ratio S/V is an extremely important reactor design parameter in EC. This ratio, whose unit of measurement is known as m-1, is the ratio of the active surface area of the volume of the treated solution. According to the literature, the increase in the ratio S/V results in the reduction of the current density consumption (Belhouta et al. , 2010). Hence, it is made necessary to take into account this parameter and determine its effect on the performance of the EC process. The effects of the variation of S/V on the cadmium removal efficiency were studied by covering and deactivating either a part or all of the face of each electrode using durable water-resistant sellotape. Fig. 4. shows a schematic view of the electrodes covers. EC tests were performed for the S/V ratio values: 3.4, 6.8, 10.2 and 13.6 m-1. As for the width, it was the result of a compromise; it had to be large enough as required by the active 8

surface but it was limited by the width of the reactor to ensure homogeneity and constant stirring of the solution. The variation of pH, difference in potential and energy consumption versus time for the different values of the ratio S/V are summarized in table 3. Fig. 5. shows the variation of the removal of cadmium over time for different values of the ratio S/V. For the different values of ratio S/V studied, a percentage of cadmium removal of 99% was achieved after 60 min, but there was a huge difference in terms of cost. As shown in table 3, the larger was the S/V ratio, the much better were the removal efficiency and cost. An increase in S/V ratio promoted the electrical transport, ensured better chemical dissolution of aluminum and increased the resistance of the electrochemical cell. This resulted in an increasing removal efficiency of cadmium by virtue of better chemical dissolution. The best cadmium removal percentage as well as treatment cost was achieved for the S/V value of 13.6 m-1. Within 30 min of electrolysis time, increasing the S/V value from 3.4 to 13.6 m-1 allowed an increase in cadmium removal efficiency from 90.95% to 99.76% and a significant reduction in both treatment cost from 1.130 to 0.280 TND m-3 and energy consumption from 10.2 to 1.75 KWh m-3 proved by the decrease in the temperature of the solution from 21.1 to 18.4 °C. Thus, we had to choose the largest S/V ratio possible. Accordingly, 13.6 m-1 was chosen as an optimum value for the tests to significantly minimize the cost as well as electrolysis time and achieve maximum removal. 3.2.2. Verification of Faraday's law as a function of S/V value In order to verify Fraday’s law for the different S/V value studied and for an electrolysis time of 30 min, the amount of aluminum oxide was theoretically calculated using Faraday's law as follows: é 

.. .

Eq. (10)

Aluminum concentration was measured before and after each test to determine the mass loss during each EC test. It should be noted that the experimental value is 80% of the faraday efficiency. The experimental mass was determined by the following equation:        

Eq. (11)

The Faradic efficiency was calculated using the following equation:

9

  

೐ೣ೛೐ೝ೐೘೐೙೟ೌ೗ ೟೓೐೚ೝ೐೟೔೎ೌ೗

 100

Eq. (12)

The experimental results are summarized in Table 4. The effect of current density on the experimental evolution of the mass losses at the anode and cathode as well as those which were theoretically expected according to Faraday's law is illustrated in Fig. 6. Fig. 6 confirms that the theoretical mass was linearly proportional to the current density. Meanwhile, the experimental mass varied in proportion to the applied current density, but it was slightly higher than the theoretical mass. This resulted in a Faraday's efficiency above 100 %. The evaluation of the Faradic yield of aluminum for various current densities is shown in Fig. 7. The average Faradic efficiency obtained was 115.08 %. This result could be explained by an anodic oxidation of the aluminum which simultaneously led to the formation of Al3+ and Al+ (Picard et al. , 2000). Similar to the results reported in previous studies, in the case of aluminum configuration, 20% of the total electrode mass dissolved was due to chemical dissolution and the remaining 80% by electrochemical dissolution (Anantha et al. , 2013). This difference in valence directly affected the calculation of the theoretical mass dissolved. This consumption may be also due to the chemical hydrolysis of the cathode according to the following equation: 2 6   2   2 



3  Eq. (13)

In addition, this phenomenon could be explained by the phenomenon of corrosion and oxidation of the surface of the electrodes. The mechanism of corrosion of the electrodes suggested involvement of chloride ions. This mechanism can result in greater production of aluminum hydroxide and hydrogen bubbles compared to the amount that is expected to produce the main reaction at the anode (Secula et al. , 2012). 3.4. Effect of inter-electrode distance To study the effect of the inter-electrode distance on the cadmium removal efficiency, several EC tests were carried out for different inter-electrode distances of 0.5, 1 and 2 cm. The variation of pH, difference in potential, temperature, and treatment cost and energy consumption versus time for the different values of the S/V ratio are summarized in table 5. When the inter-electrode distance increased, the ohmic loss in relation to the anode and cathode over voltages and the resistance to mass transfer became larger; the kinetics of both charge transfer and the aluminum oxidation was slowed down. Consequently, there was a 10

smaller amount of Al3+ cations at the anode leading to slower formation of coagulants in the middle (Ghosh et al., 2008). The rate of particle aggregation and adsorption of cadmium became lower, which explained the decrease in cadmium removal efficiency. This resulted in lower removal efficiency at a larger inter-electrode distance. Fig.8. and Table 5 clearly show that the removal percentages of Cd (II) decreased with the increase of inter-electrode distance. The best cadmium removal percentage as well as treatment cost was achieved for the inter-electrode distance value of 0.5 cm. Within 30 min of electrolysis time, decreasing the inter-electrode distance from 2 to 0.5 cm resulted in an increase in cadmium removal efficiency from 82.33% to 91.63% and a reduction in both treatment cost (from 0.270 to 0.210 TND m-3) and energy consumption (from 0.87 to 0.55 KWh m-3) which was clear from the decrease in the temperature of the solution from 19.5 to 17.8 °C. This result proved that, unlike the case of electrode configuration and S/V ratio, the effect of the inter-electrode distance on energy consumption and treatment cost was insignificant. On the other hand, as the time progressed, it was clear that the formation of a gelatinous aluminum hydroxide film on the anode developed a resistance that increased whenever the inter-electrode distance increased. Hence, it was beneficial to choose an optimum short inter-electrode distance of 0.5 cm to minimize energy consumption and increase the cadmium removal efficiency. 3.5. Effect of the initial water temperature Temperature is one of the most important factors that can influence the cadmium removal by EC (Chen, 2004; Koren and Syversen, 1995). To determine the optimum initial temperature for the removal of cadmium through the EC process using two aluminum electrodes, various EC tests were conducted for the different initial temperatures of 18, 30, 50 and 70 C°. The results obtained during testing the EC for different values of

initial

temperature are reported in Table 5. Fig. 9. illustrates the importance of the initial temperature in the removal efficiency of cadmium from wastewater. It was found that with the increase in temperature and reduction of electrolysis time the removal efficiency was significantly improved, but no difference was made in terms of cost and energy consumption. In fact, due to the increase of the temperature, the mass transfer increased and the kinetics of particle collision improved. Furthermore, dissolution of the anode was improved and the amount of the hydroxide that was formed and necessary for the adsorption of cadmium was greater at elevated temperature than when at low 11

temperature. In addition, a higher temperature allowed a production of larger hydrogen bubbles, which increased the speed of flotation and reduced the adhesion of suspended particles (Koren and Syversen, 1995). This is why the EC process needed to start with a high temperature rather than heating the reaction. This allowed the removal efficiency to be improved. We found that the yield was significantly improved with increasing the initial temperature of the solution, which resulted in a reduction in the electrolysis time. As clearly shown in Fig. 9, the maximum elimination of 98.28% was obtained for a temperature of θi = 50 C° and an electrolysis time of 30 min. Thus, the temperature of 50 °C was chosen as an optimum initial EC temperature on the basis that it allowed the achievement of high removal efficiency in a short treatment time especially because it did not made any change in the cost. 3.6. Effect of stirring speed The effect of stirring speed was investigated in order to determine the influence of this parameter on the cadmium removal efficiency by EC. To study the effect of the stirring speed, EC was performed at different stirring speeds of 0, 300, 450 and 600 rev min-1. Results are presented in table 6. As shown in Fig. 10. the elimination of cadmium was much faster for a moderate agitation speed. Adsorption is a phenomenon intrinsically very fast and essentially limited by the mass transfer internally and externally. The cadmium elimination was low without agitation; and the percentage of removal did not exceed 68 % for an electrolysis time of 30 min and 80 % for an electrolysis time of 60 min. For a moderate agitation of 300 rev min-1, the elimination was much faster than 0 rev min-1 and even further increased when the agitation was up to 450 rev min-1 reaching a removal percentage of 95 %, 99.5 % after 30 and 60 min, respectively. This proved that the adsorption of Cd (II) ions by the coagulant aluminum hydroxide AlOH3 occurred very effectively for stirring speeds of 300 and 450 rev min-1. However, there was a slight decrease in removal efficiency when the agitation reached 600 rev min-1. This could be explained by the fact that excessive agitation resulted in the breaking of the flocs. Moreover, the higher was the agitation, the more energy the agitator consumed and thus required higher cost. Therefore, although moderate agitation speed of 300 rev min-1 had a significantly positive effect on the removal efficiency, it made no difference at the level of energy consumption and cost. This is why 300 rev min-1 was chosen as the optimum agitation speed.

12

3.7. Investigation of the effect of all the optimum reactor design parameters on the removal of cadmium from TCG industrial wastewater In order to examine the effect of EC reactor design found in the present study on the removal of cadmium from the TCG industrial wastewater under treatment, EC tests were applied on this effluent after adjusting the pH at 7. The sample industrial wastewater collected from the TCG contained a cadmium concentration of 2.83 mg L-1, a conductivity of 1.176 mS cm-1 and an acid pH of 2.02. The physico-chemical characteristics of the case-study industrial wastewater before and after the treatment are shown in Table 7. The pH, the temperature, the energy consumption and the difference in potential between the two electrodes were measured for each sample. The obtained results are summarized in Table 8. As shown in Fig. 11, the testing of cadmium removal through the application of all the selected optimum design parameters together was highly effective; it exceeded 100 % with a very low power consumption of 1.6 kWh m-3 and very low cost of 0.116 TND m-3 in only 5 min. Therefore, the time span chosen as an optimum parameter was 5 min. In this work, a quantitative comparison was made between the obtained results of EC using optimum reactor design parameters and results of precipitation and coagulation. The findings in this study indicated that precipitation required 3.700 TND m-3, whereas coagulation, using AlCl3 as coagulant, required 2.430 TND m-3 to remove the same quantity of cadmium from the case-study wastewater. Thus, it is important to note that EC process using the selected optimum design parameter proved to be highly efficient and, meanwhile, cost-effective; it enabled a significant reduction in operating cost. The contribution of this study in terms of both efficiency and cost can be further confirmed if we compare the cost of treatment process in previous study (Oncel et al., 2013) where the operating costs at the optimum operating conditions were determined to be 1.98 € € m3 (equivalent to 4.36 TND m-3) for EC and 4.53 €€ m-3 (equivalent to 9,96 TND m-3) for chemical precipitation. 3.8. Evolution of pH As has been pointed out in several previous studies (Bayramoglu et al. , 2007; Daneshvar et al. , 2006), the use of soluble anodes causes a change in the pH of the solution during EC. For each EC parameter studied, the pH of the treated solutions was measured as a function of time. As shown in tables. 2, 3, 5, and 6, the pH increased with increasing operating time. The final pH depended on the type of electrodes configuration. For the same initial pH of 7, there was a large 13

variation in the final pH. As shown in table 2, after 60 min of electrolysis time, with bipolar configuration the pH increased up to 10.90, whereas with the monopolar configuration the pH increased up to 9.03. This result can be explained by the fact that the evolution of the final solution pH depended on the buffer capacity (Eq.14) due to the production and consumption of OH- ions during the EC (Eq.15), and thus avoided a sudden change in pH (Chen, 2004). Al(OH)3 + OHH 2O + 1 e -





Al(OH)4-

1/2 H2 (g) +

OH-

Eq. (14) Eq. (15)

5. Conclusion The main objective of this study was to investigate the effect of reactor design parameters on cadmium removal from industrial wastewater to improve as much as possible efficiency and significantly reduce cost of EC process as well. Based on an examination of the design parameters one by one, the selected parameters were: an inter-electrode distance of 0.5 cm, a monopolar connection mode, a surface-area-to-volume ratio (S/V) of 13.6 m-1, a moderate agitation speed of 300 rev min-1, and an initial temperature of 50 °C. These operating conditions were selected because they could simultaneously achieve efficient removal in a relatively short operating time with the lowest energy consumption and cost possible. The obtained results showed that the parameters under examination influenced removal efficiency. However, the stirring speed and initial temperature do not have effect on energy consumption and cost, while the S/V ratio, electrode configuration, inter-electrode distance make significant change in terms of energy consumption as well as cost. The investigation of the effect of all the selected EC design parameters together on the removal of cadmium from the wastewater discharged by TCG proved that the treatment was highly effective; 100 % cadmium removal was achieved in only 5 min, a very low power consumption of 1.6 kWh m-3 and very low cost of 0.116 TND m-3. Furthermore, EC was found to be able to remove cadmium as well as other pollutants at the same time from the industrial wastewater under treatment. The investigation carried out in this work explores and proposes a very cost-effective treatment method to remove heavy metals from industrial wastewater if compared to results reported about cost of this treatment process through other technologies used such as coagulation (4.36 TND m-3) and precipitation (9,96 TND m-3) employed in previous studies. This treatment method is workable for researchers seeking to achieve high-rate cadmium removal efficiency under similar economic and operational conditions. 14

Acknowledgments These research and innovation study have been carried out within the framework of a MOBIDOC thesis funded by the European Union under the program PASRI. We greatly appreciate the support of the TCG. References Anantha, T. S., Singh, S. T., 2013. Ramesh, An experimental study of CI Reactive Blue 25 removal from aqueous solution by electrocoagulation using Aluminum sacrificial electrode: Kinetics and influence of parameters on electrocoagulation performance, Desalination and water science 1-9. Bayramoglu, M., Eyvaz, M., Kobya, M., 2007. Treatment of the textile wastewater by electrocoagulation: economical evaluation. Chem. Eng. J. 128, 155–161. Beauchesne, I., Meunier, N., Drogui, P., haulser, R., Mercier, G., Blais, J.F., 2005. Electrolytic recovery of lead in used lime leachate from municipal waste incinerator. J. Hazard. Mater. 120, 201-211. Bektas, N., Akbulut, H., Inan, H., Dimoglo, A., 2004. Removal of phosphate from aqueos solution by electrocoagulation. J. Hazard. Mater. 106, 101–105. Belhouta, D., Ghernaouta, D., Djezzar-Douakhb, S., Kellila, A., 2010. Electrocoagulation of a raw water of Ghrib Dam (Algeria) in batch using aluminium and iron electrodes. Desalination and Water Treatment. 1–9. Bejankiwar, R.S., 2002. Electrochemical treatment of cigarette industry wastewater: feasibility study. Water Res. 36, 4386-4390. Chen, G., 2004. Electrochemical technologies in wastewater treatment. Sep. Purif. Technol. 38, 11-41. Chen, X., Chen, G., Yue, P. L., 2000. Separation of pollutants from restaurant waste water by Electrocoagulation. Sep. Purif. Technol. 19, 65-76. Chopra, A. K., Sharma, A. K., Vinod K., 2011. Overview of Electrolytic treatment: An alternative technology for purification of wastewater. Applied Science Research. 3, 191-206. 15

Daneshvar. N., Oladegaragoze. A., Djafarzadeh, N., 2006. Decolorization of basic dye solutions by electrocoagulation: An investigation of the effect of operational parameters. J. Hazard. Mater. B129, 116–122. Elham, K., Somayeh, Y., Mohammad, R. K., 2011. An investigation on the new operational parameter effective in Cr (VI) removal efficiency: A study on electrocoagulation by alternating pulse current. J. Hazard. Mat. 190, 119–124.

Emamjomeh, M.M., Sivakumar, M., 2006. An empirical model for defluoridation by batch monopolar electrocoagulation/flotation (ECF) process. J. Hazard. Mater. 131, 118-125. Emamjomeh, M.M., Sivakumar, M., 2009. Fluoride removal by a continuous flow electrocoagulation reactor. J. Environ. Manag. 90, 1204–1212.

Ghosh, D., Solanki, H., Purkait, M.K., 2008. Removal of Fe (II) from tap water by electrocoagulation technique. J. Hazard. Mater. 155, 135–143.

Health Canada(2012). Guidelines for Canadian Drinking Water Quality—Summary. Table Water, Air and Climate Change Bureau, Healthy Environments and Consumer Safety Branch, Health Canada. p. 9-11.

Ilhan, F., Apaydin, O., kurt, U., Arslankaya, E., Gonullu, M.T., 2007. Treatment of leachate by electrocoagulation and electrooxidation processes, Third International Conference on Environmental Science and Technology (ICEST), August. 6–9, hoston-texas , USA.

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Kumar, P.R., Chaudhari, S., khilar, K.C., Mahajan, S.P., 2004. Removal of arsenic from water by electrocoagulation. Chemosphere 55, 1245-1252. Lai, C.I., Lin, K.S., 2006. Sludge conditioning characteristics of copper mechanical polishing wastewaters treated by electrocoagulation. J. Hazard. Mater. 136, 183-187. Lekhlif, B., Oudrhiri, L., Zidane, F., Drogui, P., Blais J.F., 2014. Study of the electrocoagulation of electroplating industry wastewaters charged by nickel (II) and chromium (VI). J. Mater. Environ. Sci. 5, 111-120 Mamerie, N., Yeddou, A. R., Lounici, H., Belhocine, D., Grib, H., Bariou, B., 1998. Defluoridation of north Africa by electrocoagulation process using bipolar aluminium electrodes. Water. Res. 32, 1604-1612.

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Meunier, N., Drogui, P., Gourvenec, C., Mercier, G., Hausler, R., Blais, J.F, 2004. Removal of metals in leachate from sewage sludge using electrochemical technology. Environ Technol. 25, 235-245. Meunier, N., Drogui, P., Gourvenec, C., Mercier, G., Hausler, R., Blais, J.F., 2004. Removal of metals in leachate from sewage sludge using electrochemical technology. Environ Technol. 25, 235-245. Modirshahla, N., Behnajadya, M. A., Mohammadi, S. A., 2008. Investigation of the effect of different electrodes and their connections on the removal efficiency of 4 – nitrophenol from aqueous solutions by electrocoagulation. J. Hazard. Mater. 154, 778 – 786. Mollah, M.Y.A., Morkovsky, P., Gomes, J.A.G., 2004. Fundamentals, present and future perspectives of electrocoagulation. J. Hazard. Mater. 114, 199–210. Mollah, M.Y.A., Schennach, R., Parga, J.R., Cocke, D.L., 2001. Electrocoagulation (EC) science and applications. J. Hazard. Mater. 84, 29–41.

17

Murugananthan, M., Bhaskar Raju, G., Prabhakar, S., 2004. Removal of sulfide, sulfate and sulfite ions by electrocoagulation. J. Hazard. Mater. 109, 37–44.

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Saha, P., Sanyal, S. K., 2010. Assessment of the removal of cadmium present in wastewater using soil–admixture membrane. Desalination 259, 131–139. Schroede, H.A., 1965. Cadmium as a factor in hypertension. J. Chronic. Dis. 18, 647–656. Secula, M.S., Cretescu, I., Petrescu, S., 2012. Electrocoagulation treatment of sulfide wastewater in a batch reactor: Effect of electrode material on electrical operating costs, Environ Eng Manag J. 11, 1485-1491. Suwazono, Y., Kobayashi, E., Okubo, Y., Nogawa, K., Kido, T., Nakagawa, H., 2000. Renal effects of cadmium exposure in cadmium nonpolluted areas in Japan. Environ Res. 1, 44-55. Thirugnanasambandham, K., Sivakumar, V., Prakash Maran, J., 2013. Optimization of electrocoagulation process to treat biologically pretreated bagasse effluent. J. Serb. Chem. Soc. doi: 10.2298/JSC130408074T. Umran, T. U., Sadettin E. O., 2015. Removal of Heavy Metals (Cd, Cu, Ni) by Electrocoagulation. Inter. J. Envir. Sci. Develop. Vol. 6, No. 6.

18

Vasudevan, S., Lakshmi, J., 2011. Effects of alternating and direct current in electrocoagulation process on the removal of cadmium from water– A novel approach. Sep. Purif. Technol. 80, 643–651. Young, R. (2005). Toxicity Profiles. Toxicity summary for cadmium. Risk Assessment Information System, RAIS, University of Tennessee. Zaieda, M., Bellakhala, N., 2009. Electrocoagulation treatment of black liquor from paper industry. J. Hazard. Mater. 163, 995–1000.

19

Fiig.11. Lab boraatorry scaale celll asssem mblly.

20 0

Fig. 2. Monopolar and bipolar electrode connection.

21

Fig. 3. Variation of residual cadmium concentration as a function of electrocoagulation time (die= 2 cm, S/V= 13.6 m-1, θi= 16.5 C° and stirring speed 300 rev min-1).

22

Fig. 4. Schematic view of different electrodes covers in the EC process. (d= 2cm, θi= 16.5 C° and stirring speed 300 rev min-1).

23

Fig. 5. Variation of cadmium removal efficiency as a function of time for different values of the S/V ratio (d= 2cm, θi= 16.5 C° and stirring speed 300 rev min-1).

24

0.0045 0.004 0.0035 0.003 masse 0.0025 disoute (g) 0.002

m thé

0.0015

m exp

0.001 0.0005 0

3.4

6.8

10.2 S/V

13.6

m-1

Fig. 6. Effect of S/V ratio on the anode consumption (d= 2cm, θi= 16.5 C° and stirring speed 300 rev min-1).

25

Rendement faradique (%)

140 120 100 80 60 40 20 0 0

2

4

6

8

10

12

14

16

S/V m-1

Fig. 7. Evolution of the faradic efficiency of aluminum as a function of S/V ratio (d= 2cm, θi= 16.5 C° and stirring speed 300 rev min-1).

26

Fig. 8. Effects of inter-electrode distance as a function of time on the Cd(II) removal (S/V= 13.6 m-1, θi=16.5 C° and stirring speed 300 rev min-1).

27

Fig. 9. Effects of initial temperature as a function of time on the Cd (II) removal (die= 2 cm, S/V= 13.6 m-1 and stirring speed 300 rev min-1).

28

Fig. 10. Variation of cadmium concentration as a function of electrocoagulation time for different agitation speeds (die= 2 cm, θi=16.5 C° and S/V= 13.6 m-1).

29

3

resudual cadmium removed

2.5 with application of EC design parameters

2

without application of EC design parameters

1.5 1 0.5 0 0

10

20

30

40

50

60

time (min)

Fig. 11. Evolution of the residual cadmium removal with and without application of reaction design parameters Vs time.

30

Table.1. Results of the validation of the cadmium analysis by AASF. Test

Linearity

Specificity

Cochran

Fidelity CVr =

Experiment value

Fl = 2724

Fnl = 2.712

Tobs =

T’obs =

1.60

0.179

0.278; Cxobs = 0.498

0.170; 0.216;

CVR = 0.844

0.118 C Cochran, Critic value

VCl = 8.1

VCnl = 4.94

t (8; 0,995) = 3.355

α=5%

=

0.629 No

Conclusion

C Cochran, α=1% = 0.721

CVr < 5%

Point

The

curvature

Slope equal to 1 Origin

group is

Point group

method

and the

and the method is

considere

is considered

is Linear

linearity is

specific

d no

no suspect

approved

aberrant

31

CVR< 5%

The Repeatable

method is

Faithful

Reprodctib le

Table. 2. Variation of pH, Temperature, difference between the potential, treatment cost, electrodes consumption and energy consumption versus time for the different electric configuration mode. Electrodes W Treatment cost tEC (min) θ (°c) pH U (V) (KWh m-3) Consumption (Kg) (TND m-3) 0

16.5

7.00

9.7

0.00

0.00

0.00

5

17

8.10

9.1

0.05

0.38

2.85 10-5

10

18

11.73

9

0.10

0.75

5.71 10-5

15

18

11.40

9

0.15

1.13

8.57 10-5

30

19

10.95

8.8

0.29

2.20

1.71 10-4

45

20

10.80

8.7

0.43

3.26

2.57 10-4

60

21

10.90

8.3

0.55

4.15

3.43 10-4

0

16.5

7.00

3.6

0

0.00

0.00

5

16.5

8.32

2.6

0.01

0.11

2.85 10-5

10

17

8.14

2.5

0.03

0.21

5.71 10-5

15

18

8.08

2.5

0.04

0.31

8.57 10-5

30

19

8.23

2.4

0.08

0.60

1.71 10-4

45

19

8.66

2.4

0.12

0.90

2.57 10-4

60

20

9.03

2.4

0.16

1.20

3.43 10-4

Bipolar Configuration

Monopolar Configuration

32

Table. 3. Variation of pH, difference between the potential, Temperature, treatment cost and energy consumption versus time for the different values of the S/V ratio. S/V (m-1)

3.4

6.8

10.2

13.6

t(EC) (min)

θ (°c)

U (V)

pH

0

16.5

20.7

15

18.7

30

Treatment cost

W (KWh m )

(TND m-3)

7.00

0.00

0.1

20.4

8.14

2.55

0.61

21.1

20.5

8.87

5.13

1.13

45

23.1

20.4

9.03

7.65

1.63

60

24.6

20.4

9.18

10.20

2.14

0

16.5

12.7

7.00

0.00

0.1

15

18.1

12.5

8.35

1.51

0.40

30

20.7

12.5

8.98

3.13

0.72

45

22.3

12.5

9.21

4.69

1.04

60

23.7

12.5

9.47

6.25

1.35

0

16.5

10.7

7.00

0.00

0.1

15

17.8

10.4

8.66

1.38

0.38

30

19.3

10.4

9.18

2.85

0.67

45

20.6

10.4

9.48

4.28

0.95

60

21.5

10.4

9.62

5.85

1.27

0

16.5

3.9

7.00

0.00

0.1

15

17.8

3.5

8.59

0.44

0.19

30

18.4

3.5

9.19

0.88

0.28

45

18.8

3.5

9.54

1.31

0.36

60

19.5

3.5

9.82

1.75

0.45

33

-3

Table. 4. Effect of S/V value on the anode consumption and Faraday's efficiency. S/V (m-1)

3.4

6.8

10.2

13.6

m theoretical(Kg)

0,00089

0,00176

0,002601

0,00329

m experimental(Kg)

0,00099

0,00199

0,002985

0,00398

R% Faradic

104.29

109.71

115.98

126.81

34

Table. 5. Variation of pH, difference between the potential, Temperature, treatment cost and energy consumption versus time for the different values of inters-electrode distance. die

0.5

1.0

2.0

t(EC) (min)

θ (°c)

U (V)

pH

W (KWh m-3)

0

16.5

2.3

7.00

0.00

15

17.2

2.1

8.58

0.26

30

17.8

2.2

9.20

0.55

45

18.6

2.2

9.39

0.82

60

19.0

2.2

9.48

1.10

0

16.5

3.0

7.00

0.00

15

17.6

2.5

8.35

0.31

30

18.7

2.5

8.78

0.62

45

19.5

2.5

8.95

0.94

60

20.6

2.5

9.13

1.25

0

16.4

3.9

7.00

0.00

15

18.6

3.5

7.82

0.44

30

19.5

3.5

8.14

0.87

45

20.7

3.5

8.16

1.31

60

21.2

3.5

8.32

1.75

35

Treatment cost (TND m-3) 0.1 0.152 0.21 0.264 0.32 0.1 0.162 0.224 0.288 0.35 0.1 0.188 0.274 0.362 0.45

Table. 6. Variation of pH, Temperature, difference between the potential, Treatment cost and energy consumption versus time for different initial temperatures. θi (°c)

18

30

50

Treatment cost (TND m-3)

t(EC) (min)

θ (c°)

U (V)

pH

0

18

2.3

7.00

0.1

0.00

15

18.2

2.1

8.93

0.1052

0.26

30

18.8

2.2

9.18

0.111

0.55

45

19.6

2.2

9.36

0.1164

0.82

60

20.0

2.2

9.41

0.122

1.10

0

30

3.0

7.00

0.1

0.00

15

30.6

2.5

8.45

0.1062

0.31

30

31.8

2.5

8.70

0.1124

0.62

45

32.9

2.5

8.45

0.1186

0.93

60

34.3

2.3

8.80

0.123

1.15

0

50

3.4

7.00

0.1

0.00

15

48.3

3.3

7.56

0.1082

0.41

30

46.7

3.3

8.08

0.1164

0.82

45

45.4

3.3

8.28

0.1246

1.23

60

42.8

3.3

8.96

0.133

1.65

0

70

3.9

7.00

0.1

0.00

15

66.1

3.5

8.49

0.1086

0.43

30

63.2

3.5

8.70

0.1174

0.87

45

59.9

3.5

8.98

0.1262

1.31

70

36

W (KWh m-3)

60

57.2

3.5

0.135

9.49

1.75

Table. 7. Variation of pH, Temperature, difference between the potential, Treatment cost and energy consumption versus time for different agitation speeds. stirring speed (rev min-1)

0

300

450

600

t(EC) (min)

θ (c°)

U (V)

pH

W (KWh m-3)

treatment cost (DT m-3)

0

16.5

3.9

7.00

0.00

0.000

5

17.4

3.6

8.70

0.16

0.020

10

17.9

3.6

8.85

0.32

0.040

15

18.4

3.5

8.93

0.49

0.058

30

19.4

3.5

9.18

0.95

0.117

45

20.7

3.5

9.36

1.43

0.175

60

21.6

3.9

9.41

1.85

0.234

0

16.5

3.9

7.00

0.00

0.000

5

17.5

3.6

8.30

0.15

0.020

10

17.9

3.6

8.26

0.30

0.040

15

18.4

3.5

8.45

0.44

0.058

30

19.3

3.5

8.70

0.88

0.117

45

20.4

3.5

8.80

1.31

0.175

60

21.5

3.5

8.71

1.75

0.234

0

16.5

3.9

7.00

0.00

0.000

5

17.5

3.6

8.96

0.15

0.020

10

17.9

3.6

7.31

0.30

0.040

15

18.4

3.5

7.56

0.45

0.058

30

19

3.5

8.08

0.90

0.117

45

20

3.5

8.28

1.35

0.175

60

21

3.9

8.52

1.80

0.234

0

16.5

3.9

7.00

0.00

0.000

5

17.6

3.6

8.12

0.16

0.020

10

17.8

3.6

8.21

0.31

0.040

15

18.5

3.5

8.11

0.48

0.058

30

19.5

3.5

8.49

0.95

0.117

45

20.6

3.5

8.70

1.43

0.175

37

60

21.5

3.9

8.98

1.90

0.234

Table. 8. Characteristics of the industrial wastewater before and after electrocoagulation treatment. Conductivit pH

y -1

(mS cm ) Before treatmen t After treatmen t

θ (°C)

P2O5%

MS %

[Cd2+] %

2+

[Ca ] %

[Mg2+]

[k+]

[Na+]

%

%

%

2.02

1.176

15.0

0.49

0.025

0.02800

0.17

0.05

0.02 4

0.57

10.94

1.158

18. 5

0.13

0.034

0.00029

0.07

0

0

0.13

38

Table. 9. Recording of the pH, the temperature, the energy consumption, the difference in potential between the two electrodes as a function of time for the treatment of the industrial wastewater. Treatment cost (TND m-3)

Time (min)

U (V)

pH

θ (c°)

W (KWh m-3)

0

2.3

7.00

15.0

0.000

0.100

5

2.0

7.26

15.9

0.083

0.116

10

2.0

7.60

16.2

0.166

0.133

15

2.0

7.83

16.3

0.250

0.150

20

2.0

7.99

16.6

0.333

0.166

30

2.0

9.15

17.1

0.500

0.200

45

2.0

10.28

17.9

0.750

0.250

60

1.9

10.94

18.5

0.950

0.290

39

Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater BRAHMI Khaled a, BOUGUERRA Wided a, HAMROUNI Béchir a, ALOUI Limam b, LOUNGOU Mouna c, Zied Tlili d a U. R Traitement et Dessalement des Eaux, Département de Chimie, Faculté des Sciences de Tunis, 2092 Manar II, TUNISIE, Tel./ Fax: +2167187128. b U. R Matériaux, Environnement et Energie, Département de Chimie, Faculté des Sciences de Gafsa, Campus Universitaire Sidi Ahmed Zarroug -2112 Gafsa, TUNISIE, Tel +216 76 211 026. c Groupe Chimique Tunisien, Usine de M’Dhilla Gafsa, Km. 14 Route M’Dhilla- 2100 Gafsa, Tel +216 76211515. d Higher Institute of Business Administration of Gafsa, Campus Universitaire Sidi Ahmed Zarroug -2112 Gafsa, TUNISIE, Tel +216 24951825. Tel./ Fax: +21671871282; Corresponding author E-mail:[email protected]

40