Abstract

Leachate is the most difficult wastewater to be treated due to its complex content and high pollution release. For this reason, since it is not possible to be treated with a single process, a pre-treatment is needed. In the present study, a batch electrocoagulation reactor containing aluminum and iron electrodes was used to reduce chemical oxygen demand (COD) from landfill leachate (Tunceli, Turkey). Optimization of COD elimination was carried out with response surface methodology to describe the interaction effect of four main process independent parameters (current density, inter-electrode distance, pH and time of electrolysis). The optimum current density, inter-electrode distance, pH and time of electrolysis for maximum COD removal (43%) were found to be 19.42 mA/m2, 0.96 cm, 7.23 and 67.64 min, respectively. The results shown that the electrocoagulation process can be used as a pre-treatment step for leachate.

INTRODUCTION

Landfill is the most used definitive waste disposal method in the world for domestic solid waste. However, one of the environmental problems related to the disposal of municipal wastes in storage sites is the occurrence of leachate. This type of wastewater is characterized by a high power complex mixture consisting of dissolved hazardous organic compounds, ammonia, heavy metals and inorganic salts, which must be removed due to toxicity and therefore environmental effects. In addition, the fact that leachates vary widely in quantity and quality throughout the year makes it difficult to identify an effective method of treatment (Silva et al. 2017).

The character and concentration of pollutants are mainly affected by the landfill age. Typically, older leachate (more than 10 years) has stabilized, and is characterized by a relatively low chemical oxygen demand (COD), mild basic (pH > 7.5) and low biodegradability (BOD5/COD < 0.1). This indicates that physical-chemical treatments are suitable for the stabilized leachate treatment (Dolar et al. 2016; El-Gohary & Kamel 2016).

Electrocoagulation in recent years is one of the processes used in water and wastewater treatment (Safari et al. 2016). Electrocoagulation is the technique of destabilizing suspended, emulsified, or dissolved contaminants in an aqueous environment by providing an electrical current to the medium (Emamjomeh & Sivakumar 2009). Aluminum and iron are the most commonly used electrocoagulation electrode materials because they are effective, easily available and cheap (Fernandes et al. 2015). Coagulant ions are formed in solution by anodic electro-oxidation in this process (Garg & Prasad 2016). When compared to conventional flocculation and coagulation, electrocoagulation has several advantages such as ease of operation, resistance to variable reaction conditions and wastewater species, simple equipment requirement, less retention time, rapid sedimentation of formed flocculants, less sludge production, less space requirement and cost of capital (Olmez-Hanci et al. 2012). Electrocoagulation method has been applied successfully for the treatment of various wastewaters such as cheese whey wastewater (Un et al. 2014), pharmaceutical wastewater (Singh et al. 2016), wastewater with heavy metals (Bhatti et al. 2009), refectory oily wastewater (Xu & Zhu 2004), potato chip manufacturing wastewater (Kobya et al. 2006), tannery wastewater (Elabbas et al. 2016), textile wastewater (Zodi et al. 2010) and nitrate wastewater (Ghanbari et al. 2014).

Guvenc et al. (2017) used the electrocoagulation process for COD and turbidity removal from metal working industry wastewater, and optimized the process by developing a mathematical model using the central composite design (CCD) method, which is one of the response surface methodologies. It was found that removal efficiencies obtained from aluminum electrodes were 76.72% for COD and 99.97% for turbidity, while the removal efficiencies obtained from iron electrodes were 76.55% for COD and 99.9% for turbidity under the optimum conditions. Chavalparit & Ongwandee (2009) used electrocoagulation to treat biodiesel wastewater and investigated the effects of initial pH, applied voltage, and reaction time on the process for the removal of COD using response surface methodology (RSM) to create the optimum operating conditions. The experimental results showed that electrocoagulation effectively reduced COD by 55.43% at the optimum conditions of pH 6.06, applied voltage 18.2 V, and reaction time 23.5 min. Bhagawan et al. (2014) investigated the performance of electrocoagulation for the treatability of mixed metals chromium, copper, lead, nickel, and zinc from metal plating industrial wastewater. Results showed that the maximum removal percentage of metals like chromium, nickel, zinc, copper, and lead was found to be 96.2, 96.4, 99.9, 98, and 99.5%, respectively, at a reaction time of 30 min. Similarly, Vlachou et al. (2013) studied the performance of a laboratory-scale electrocoagulation system for the removal of chromium and nickel from model wastewater, and the process efficiency was evaluated systematically using iron and aluminum electrodes with an effective surface area of 13.8 cm2 and a distance of 4 cm. The best removal efficiency, when metals existed separately in treated solutions, was accomplished with the use of iron electrodes for chromium (50%) and aluminum electrodes for nickel (90%).

In addition, some researchers used this process to treat leachate (Ilhan et al. 2008; Bouhezila et al. 2011; Ricordel & Djelal 2014).

Approximately 65.3% of the total solid waste produced in Turkey is stored in unsanitary solid waste disposal sites. An unsanitary municipal waste disposal site in Tunceli has been used for about 11 years. Approximately 25 tonnes of solid waste produced in Tunceli are dropped off in an uncontrolled way to this site on a daily basis. The leachate that originates from this solid waste site is collected in the dry stream bed at the lower part of the landfill, which has a natural inclination, by mixing with the other surface waters (from seasonal rainfall and groundwater) without any treatment, and flows directly into the Pulumur River (Demirbilek et al. 2013).

In this study, the electrocoagulation process was used for the treatment of leachate occurring in the unsanitary landfill site of Tunceli province. Most of the studies reported so far are based on a time-dependent change of a factor over the process, while in the present study RSM was used to assess the main effects of the parameters, their simultaneous interaction and quadrature, and provide optimum conditions for the electrocoagulation process. The effects of diverse operating factors such as current density, pH, inter-electrode distance and reaction time were investigated in order to obtain the best removal efficiency.

MATERIAL AND METHOD

Characterization of leachate

The leachate samples used in the present study were taken from a point in Tunceli province unsanitary municipal solid waste storage site just before the discharge of the water to the Pulumur River. The pH and conductivity parameters (Thermo Orion 420A) were measured with a pH meter. The experimental procedure was applied according to Standard Methods (APHA/AWWA/WEF 2005). The procedures used are as follows: COD-closed reflux method, total Kjeldahl nitrogen (TKN)-total Kjeldahl method, phosphate (PO4-P)-vanadomolybdophosphoric acid method, ammonia nitrogen (NH3-N)-titrimetric method, color-RES method, total suspended solids (TSS) drying at 103–105 °C, total volatile solids (TVS) burning at 550 °C. The removal efficiency of the parameters examined was calculated with Equation (1):  
formula
(1)
where C0 and C are the starting and final values of the measured parameter.

Experimental setup

Experiments were performed in a laboratory-scale batch electrocoagulation reactor made of plexiglass material of size 180 mm × 170 mm × 110 mm (length, width, height, respectively) by using 0.4 L sample of leachate (Figure 1). The electrocoagulation process is a treatment method based on the transfer of ions by means of the applied current. During this process, a stable solution medium will be effective to facilitate the electron flow (Ilhan et al. 2008). If the coagulant substance is not dispersed efficiently, the content of the reactor cannot be homogeneous; subsequently, regional differences can occur. The speed of the mixing provides homogenization of system variables such as temperature and pH. In addition, high mixing speeds can break up the flocs formed in the reactor and create small flocs that cannot be removed from the water (Bayar et al. 2011).

Figure 1

Electrocoagulation setup.

Figure 1

Electrocoagulation setup.

Due to this, a magnetic stirrer was used to mix the reaction medium at the bottom of the reactor (150 rpm). The reactor has a water jacket in order to keep the temperature of the wastewater constant (25 °C). The reactor contains a 30 mm × 100 mm iron (Fe) electrode and aluminum (Al) electrode connected in monopolar parallel as anode and cathode, respectively. The current density was set by using a digital DC power source (AATech 3303D, 0–30 V/0–3A). After each test run, the electrodes used were immersed in HCl solution and rinsed with deionized water. 0.1 M HCl and 0.1 M NaOH solutions were used to adjust the pH of the wastewater. After the electrocoagulation reaction was completed, the wastewater was left to naturally precipitate for 45 minutes for the removal of metal hydroxides and flocs formed during the process, and the analyses were carried out with the supernatant.

Mechanism of electrocoagulation

According to Figure 1, the simplest form of the electrocoagulation reactor is made up of an electrolytic cell with one anode and one cathode. During electrocoagulation, the anode material will electrochemically corrode due to the oxidation, while the cathode will be subjected to passivation. The sacrificial anode produces the coagulating agent, while electrolytic gases are generated at the cathode. The mechanism involved for the iron anode and the aluminum cathode is given in the below Equations (2)–(4).

Anode (Iron):  
formula
(2)
Cathode (Aluminum):  
formula
(3)
Overall reaction:  
formula
(4)

To get a good performance, an Fe/Al electrode combination was used as the anode/cathode pair in the experiments.

Furthermore, different authors reported similar studies. For example, Hansen et al. (2007) studied the efficiency of combined electrodes such as aluminum anode and iron cathode (Al/Fe) and iron anode and aluminum cathode (Fe/Al) for the removal of arsenic from water using the electrocoagulation process. Kobya et al. (2014) performed the efficiencies of eight electrode combinations (Al-Al-Al-Al; Fe-Fe-Fe-Fe; Fe-Al-Al-Fe; Al-Fe-Fe-Al; Fe-Al-Fe-Al; Al-Fe-Al-Fe; Fe-Al-Al-Al; Al-Fe-Fe-Fe) for the decontamination of arsenic-contaminated water.

Experimental design with RSM

CCD Design Expert 7.0 software (trial version) was used to investigate the effect of key operating parameters in the electrocoagulation process of leachate by optimizing experimental conditions in the RSM category. The main purpose of the CCD method is to optimize the response surface and quantify the relationship between the response surfaces obtained with the controllable input parameters (Yoosefian et al. 2017). In the present study, the CCD consists of 2n axial points, 2n factorial points and also center points whose numbers are known, where n equals four which is the number of numerical factors including current density (x1), pH (x2), inter-electrode distance (x3) and time of electrocoagulation (x4). The center points are used to evaluate the experimental error and the reproducibility of data. The ranges and levels of process variables are given in Table 1.

Table 1

Electrocoagulation process factors and their levels

Factor Variables Unit Range of actual and coded variables
 
α −1 +1 +α 
x1 Current density mA/m2 10 15 20 25 30 
x2 pH – 10 
x3 Inter-electrode distance cm 0.2 0.52 0.85 1.18 1.5 
x4 Time of electrocoagulation min 15 33.75 52.5 71.25 90 
Factor Variables Unit Range of actual and coded variables
 
α −1 +1 +α 
x1 Current density mA/m2 10 15 20 25 30 
x2 pH – 10 
x3 Inter-electrode distance cm 0.2 0.52 0.85 1.18 1.5 
x4 Time of electrocoagulation min 15 33.75 52.5 71.25 90 
The RSM provides that it is possible to indicate independent process variables quantitatively:  
formula
(5)
where y is the response (efficiency of COD removal), f is the response function, ɛ is the experimental error, and x1, x2, x3, … , xn are independent variables. A surface known as the response surface can be ensured by plotting the expected response of y. In this study, a higher order polynomial is used as in the quadratic model shown in Equation (6). Analysis of variance (ANOVA) was utilized to find the relationship between process parameters and responses. Model terms and p-value (probability) were assessed with 95% confidence level (Gengec et al. 2012). The Design Expert desirability function was used to determine the optimum values of the independent variables for maximum COD removal.  
formula
(6)

RESULTS AND DISCUSSION

Regression model and statistical analysis

The relationship between COD removal (y) and four independent factors (current density (x1), pH (x2), inter-electrode distance (x3) and reaction time (x4)) was studied with 30 runs defined by CCD. The coded values of the independent factors, the experimental design and the experimental results obtained using this design are demonstrated in Table 2. Experimental results were fitted to a quadratic model to obtain the regression equation. The quadratic polynomial model found in terms of the coded factors is as follows:  
formula
(7)
Table 2

Design matrix for the central composite designs

Run x1: Current density (mA/m2x2: pH x3: Inter-electrode distance (cm) x4: Time of electrocoagulation (min) COD removal (%) 
25 
−2 41 
−1 −1 38 
−1 −1 22 
−1 −1 −1 33 
−1 −1 36 
43 
−1 −1 38 
42 
10 −1 20 
11 −1 39 
12 −1 −1 30 
13 −2 19 
14 −1 −1 37 
15 42 
16 35 
17 26 
18 −1 37 
19 28 
20 −1 −1 −1 12 
21 −1 −1 −1 25 
22 −1 −1 −1 −1 22 
23 −2 20 
24 42 
25 −2 30 
26 −1 −1 −1 18 
27 42 
28 −1 36 
29 42 
30 42 
Run x1: Current density (mA/m2x2: pH x3: Inter-electrode distance (cm) x4: Time of electrocoagulation (min) COD removal (%) 
25 
−2 41 
−1 −1 38 
−1 −1 22 
−1 −1 −1 33 
−1 −1 36 
43 
−1 −1 38 
42 
10 −1 20 
11 −1 39 
12 −1 −1 30 
13 −2 19 
14 −1 −1 37 
15 42 
16 35 
17 26 
18 −1 37 
19 28 
20 −1 −1 −1 12 
21 −1 −1 −1 25 
22 −1 −1 −1 −1 22 
23 −2 20 
24 42 
25 −2 30 
26 −1 −1 −1 18 
27 42 
28 −1 36 
29 42 
30 42 

Table 3 shows the results of variance analysis for Equation (7). It was found that the p-value of this model is 0.0031 and it is important at 95% confidence level. The correlation coefficient value (R2 = 0.81) in the current study is greater than 0.80. The correlation coefficient should be 80% for a good fit of the model (Abu Amr et al. 2014). In Equation (7), the magnitude of the coefficient shows the intensity of the specific variable on the response and is a negative value for the antagonistic influence when a positive value indicates a synergistic influence (Amini et al. 2008). As seen in Equation (7), the x1, x2, x3, x4 coefficients are all positive, and define that the efficiency of COD removal and the electrocoagulation process increases as these four factor levels increase. Values of p-value less than 0.05 show that the terms are significant. In this case x4, x1x3, , , , are significant model terms.

Table 3

ANOVA for COD removal

Source Sum of squares DF Mean square F-value p-value 
Model 1961.62 14 140.12 4.53 0.0031 
x1 45.38 45.38 1.47 0.2447 
x2 0.042 0.042 1.346E-003 0.9712 
x3 3.38 3.38 0.11 0.7458 
x4 442.04 442.04 14.28 0.0018 
x1x2 264.06 264.06 8.53 0.0105 
x1x3 280.56 280.56 9.07 0.0088 
x1x4 3.06 3.06 0.099 0.7574 
x2x3 18.06 18.06 0.58 0.4568 
x2x4 0.062 0.062 2.019E-003 0.9647 
x3x4 45.56 45.56 1.47 0.2438 
 621.57 621.57 20.08 0.0004 
 156.07 156.07 5.04 0.0402 
 172.86 172.86 5.59 0.0320 
 209.00 209.00 6.75 0.0202 
Source Sum of squares DF Mean square F-value p-value 
Model 1961.62 14 140.12 4.53 0.0031 
x1 45.38 45.38 1.47 0.2447 
x2 0.042 0.042 1.346E-003 0.9712 
x3 3.38 3.38 0.11 0.7458 
x4 442.04 442.04 14.28 0.0018 
x1x2 264.06 264.06 8.53 0.0105 
x1x3 280.56 280.56 9.07 0.0088 
x1x4 3.06 3.06 0.099 0.7574 
x2x3 18.06 18.06 0.58 0.4568 
x2x4 0.062 0.062 2.019E-003 0.9647 
x3x4 45.56 45.56 1.47 0.2438 
 621.57 621.57 20.08 0.0004 
 156.07 156.07 5.04 0.0402 
 172.86 172.86 5.59 0.0320 
 209.00 209.00 6.75 0.0202 

Effect of variables on COD removal

The effect of process variables on COD removal by electrocoagulation treatment in leachate was shown by the three-dimensional response surface plots and the two-dimensional contour plots as a function of two factors by making the other factors be constant (Figures 25).

The combined effect of initial pH and electrocoagulation time on COD removal is shown in Figure 2. The initial pH has an influence on electrocoagulation, as the type of ferrous hydroxide species formed in the aqueous environment and the particle surface load depend on the pH. At low and high pH, soluble iron hydroxide species are formed according to the Pourbaix diagram of iron (Un et al. 2014). In the literature, at pH 5.5–8.5, the majority of electrogened Fe3+ forms Fe(OH)3 flocs that can destroy speed contaminating molecules by complexation or electrostatic attraction, coagulation follows this. Conversely, Fe3+ that can solute in pH < 3.0 is the predominant species and while Fe(OH)3 flocs are produced in very weak form, a portion of Fe(OH)3 is dissolved as Fe(OH)4 at pH > 9.0 and the lower amount of contaminants can be removed (Fernandes et al. 2015). At a suitable pH, metal ions can be removed broadly from the metal hydroxides and coagulated species that destabilize and aggregate the suspended particles or that adsorb and precipitate the dissolved contaminants (Veli et al. 2016). As demonstrated in Figure 2, the pH parameter has a quadratic influence and effective COD removal occurs between the ranges of pH 6.5–8.5. Similar results were reported in different studies for leachate treatment with the electrocoagulation process (Ilhan et al. 2008; Veli et al. 2008; Labanowski et al. 2010).

Figure 2

Response surface plot and corresponding contour plot representing the effects of initial pH and time of electrocoagulation on COD removal at fixed current density of 20 mA/m2 and inter-electrode distance of 0.85 cm.

Figure 2

Response surface plot and corresponding contour plot representing the effects of initial pH and time of electrocoagulation on COD removal at fixed current density of 20 mA/m2 and inter-electrode distance of 0.85 cm.

As is known, the current density and the electrocoagulation time determine the coagulant rate and, in addition, they define the bubble production rate, size and floc growth which can affect the treatment efficacy of the electrocoagulation process (Gengec et al. 2012). Figure 3 shows the 3D response surface plot for the COD removal of the interaction between the current density and the electrocoagulation time. It was found that the percentage of COD removal from the results increases together with the increasing of applied current to 25 mA/m2. According to Faraday's Law, the amount of anode and cathode material dissolved in the solution is proportional directly to the current density. At higher current densities, the high dissolution of the electrode material (Faraday's Law) results in the formation of more iron oxide-hydroxide, thereby improving the removal efficiency. However, increasing of the current density to 30 mA/m2 reduced the efficiency of COD removal. A similar observation was obtained by Hanafi et al. (2010) and Holt et al. (2002). The faster production and supply of metal ions at higher current densities can reveal secondary reactions and can reverse the charge of overdose colloids and leads to a decrease in coagulation efficiency and electrode life by redistributing them (Olmez-Hanci et al. 2012; Hakizimana et al. 2017). Besides, faster removal of the metal hydroxide from the solution by means of flotation causes a decline in the possibility of collision between the contaminant and the coagulant (Katal & Pahlavanzadeh 2011). In addition, the increase in the current density increases the operational voltage and causes an aggravation of oxygen evolution. The oxygen generated on the electrode results in a reduction in the removal efficiency of organic molecules by inhibiting the mass transfer to the electrode surface (Thirugnanasambandham et al. 2014a, 2014b). For this reason, it is suggested that the current density is limited so as to prevent excessive oxygen evolution and remove other side effects such as heat generation (Katal & Pahlavanzadeh 2011).

Figure 3

Response surface plot and corresponding contour plot representing the effects of current density and time of electrocoagulation on COD removal at fixed inter-electrode distance of 0.85 cm and pH of 6.

Figure 3

Response surface plot and corresponding contour plot representing the effects of current density and time of electrocoagulation on COD removal at fixed inter-electrode distance of 0.85 cm and pH of 6.

The electric field can be controlled by changing the applied current in a parallel-plate monopolar electrocoagulation reactor, because the distance between the electrodes changes the electric current variances. The interaction effect of pH and inter-electrode distance on the process is shown in Figure 4. As can be seen from this, the removal efficiency increased when the inter-electrode distance increased to about 1.18 cm, and then decreased because the electron transfer rate was slower. The results obtained were consistent with other reported studies that showed by reduction of inter-electrode distance, the resistance was reduced due to the shorter travel route and consequently the efficiency of the process increased (Khandegar & Saroha 2013; Yoosefian et al. 2017). As the distance between the electrodes decreases, more electrochemically generated gas bubbles cause turbulence hydrodynamics to occur and thus lead to a high reaction rate with high mass transfer between the coagulant materials and contaminants. In addition, the inter-electrode gap determines the duration of the treatment required to achieve the desired electrocoagulation efficiency for a batch reactor (Hakizimana et al. 2017).

Figure 4

Response surface plot and corresponding contour plot representing the effects of pH and inter-electrode distance on COD removal at fixed time of electrocoagulation of 52.50 min and current density of 20 mA/m2.

Figure 4

Response surface plot and corresponding contour plot representing the effects of pH and inter-electrode distance on COD removal at fixed time of electrocoagulation of 52.50 min and current density of 20 mA/m2.

Time of electrolysis is another effective factor for COD removal in the electrocoagulation technique. In Figure 5, when the interaction effect between the inter-electrode distance and the time of electrocoagulation is examined, it is observed that the increment in electrocoagulation time increases the efficiency of COD removal (see also Figures 2 and 3). The electrocoagulation process involves two stages, destabilization and aggregation. While the second stage is relatively longer, the first stage is usually shorter (Kobya et al. 2006). Coagulation occurs with the starting of anodic dissolution in the electrocoagulation process. The concentration of ions produced by the electrodes in the removal of the contaminant parameters from the solution is directly important. If the duration of electrolysis increases, the concentration of ions and their hydroxide flocs (iron hydroxide) increase. Namely, the formation of flocs in appropriate and sufficient quantities is time dependent in the electrocoagulation process (Thirugnanasambandham et al. 2014b).

Figure 5

Response surface plot representing the effects of inter-electrode distance and time of electrocoagulation on COD removal at fixed current density of 20 mA/m2 and pH of 6.

Figure 5

Response surface plot representing the effects of inter-electrode distance and time of electrocoagulation on COD removal at fixed current density of 20 mA/m2 and pH of 6.

Figure 6

Optimum values of operation parameters for maximum COD removal.

Figure 6

Optimum values of operation parameters for maximum COD removal.

The desirability (1.000) function of Design Expert was used to determine optimum process parameters required for maximum COD removal. Optimum conditions for maximum COD removal of 43% according to CCD results were selected as current density 19.42 mA/m2, pH 7.23, inter-electrode distance 0.96 cm and time of electrocoagulation 67.64 minutes (Figure 6).

Confirmatory tests were carried out in triplicate under the specified conditions for the control of optimum conditions. Experimental results showed that COD removal efficiency was about 44%. There was a high concordance between the test results and the predicted optimum results. In addition, pH, conductivity, TSS, TVS, PO4-P, NH3-N, TKN, and color values found in the treated leachate at the experiments which were performed under optimum conditions are shown in Table 4. The characteristics of the leachate are also presented in Table 4.

Table 4

Characteristics of the leachate and the wastewater after treatment with electrocoagulation under optimum condition.

Parameters Raw leachate After treatment with electrocoagulation process 
COD, mg/L 840 472 
pH 7.48 8.15 
Conductivity, mS/cm 348 315 
TSS, mg/L 5,774 5,687 
TVS, mg/L 997 900 
PO4-P, mg/L 38.60 27.70 
NH3-N, mg/L 56.52 48.20 
TKN, mg/L 140 56 
Color436, 1/m 255 122.25 
Color525, 1/m 106.50 39.25 
Color620, 1/m 44.75 17.75 
Parameters Raw leachate After treatment with electrocoagulation process 
COD, mg/L 840 472 
pH 7.48 8.15 
Conductivity, mS/cm 348 315 
TSS, mg/L 5,774 5,687 
TVS, mg/L 997 900 
PO4-P, mg/L 38.60 27.70 
NH3-N, mg/L 56.52 48.20 
TKN, mg/L 140 56 
Color436, 1/m 255 122.25 
Color525, 1/m 106.50 39.25 
Color620, 1/m 44.75 17.75 

Leachate is difficult to treat to satisfy the discharge standards due to its variable composition and the high proportion of refractory materials. The factors such as current density, pH of the leachate, inter-electrodes distances, and electrolysis time are important in the electrocoagulation process. In this study, the percentages of TSS and TVS removal were found to be fairly low (Table 4). This situation can be explained by the fact that both the inter-electrodes distance and the time are short. Besides, these ranges can cause the minimum solubility of iron hydroxide (Fernandes et al. 2015).

The COD concentration of the leachate varies with the age of the landfill. The comparison of the COD removal efficient values obtained in this study and previously reported studies using leachate by the electrocoagulation process are given in Table 5.

Table 5

The comparisons of different research results for the COD removal from leachates by electrocoagulation

Leachate source COD concentration of leachate, mg/L Electrode material COD removal, % References 
İstanbul, Turkey 12,800 Fe/Al 56 Ilhan et al. (2008)  
Izmit, Turkey 4,022 Fe/Al 88 Veli et al. (2008)  
Limoges, France 380 Al 45 Labanowski et al. (2010)  
Xuzhou, China 2,566 Fe/Al 21 Li et al. (2011)  
Oued Smar, Algeria 28,200–34,200 Fe/Al 70 Bouhezila et al. (2011)  
Tunceli, Turkey 840 Fe/Al 43 This study 
Leachate source COD concentration of leachate, mg/L Electrode material COD removal, % References 
İstanbul, Turkey 12,800 Fe/Al 56 Ilhan et al. (2008)  
Izmit, Turkey 4,022 Fe/Al 88 Veli et al. (2008)  
Limoges, France 380 Al 45 Labanowski et al. (2010)  
Xuzhou, China 2,566 Fe/Al 21 Li et al. (2011)  
Oued Smar, Algeria 28,200–34,200 Fe/Al 70 Bouhezila et al. (2011)  
Tunceli, Turkey 840 Fe/Al 43 This study 

CONCLUSIONS

Electrocoagulation was investigated as a preliminary treatment process for COD removal from landfill leachate and the designed operating parameters were analyzed with the CCD for RSM. According to the mathematical model results (Equation (4)), time of electrolysis has a linear influence on COD removal, while current density, pH and inter-electrode distance have a quadratic influence on the removal efficiency of COD. The maximum COD removal has been 43% when the current density is 19.42 mA/m2, the pH is 7.23, the inter-electrode distance is 0.96 cm, and the time of electrocoagulation is 67.64 min. For this reason, the electrocoagulation process is suitable for primary treatment of landfill leachate. A further treatment process is still required for complete treatment.

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