Current Electrocoagulation Research Articles

Defluoridation by positive single-pulse current electrocoagulation from photovoltaic wastewater: Energy consumption assessment and mechanism analysis

The presence of fluoride ions (F−) in photovoltaic (PV) wastewater significantly affects the integrity of the ecological environment. In contrast to direct current electrocoagulation (DC-EC), positive single-pulse electrocoagulation (PSPC-EC) shows a significant reduction in both the formation of passivation films on electrodes and the consumption of electrical energy. Under the experimental conditions of an Al–Al–Al–Al electrode combination, an electrode spacing of 1.0 cm, a NaCl concentration of 0.05 mol L−1, an initial pH of 5.6, an initial F− concentration of 5 mg L−1, a current density of 5 A m−2, a pulse frequency of 500 Hz, and a 40 % duty cycle, the achieved equilibrium F− removal efficiencies were 84.0 % for DC-EC and 88.0 % for PSPC-EC, respectively, accompanied by power consumption of 0.0198 kWh·mg−1 and 0.0073 kWh·mg−1. The flocs produced in the PSPC-EC process were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy and it is revealed that the F− removal mechanisms in the PSPC-EC process include co-precipitation, hydrogen bond complexation, and ion exchange. When the actual PV wastewater was finally subjected to treatment under the optimal PSPC-EC conditions, the F− concentration in the wastewater was reduced from 4.6 mg L−1 to 1.4 mg L−1. This paper provides both a theoretical framework and a technological basis for the application of PSPC-EC in the advanced treatment of PV wastewater.

Hybrid Industrial Wastewater Treatment Using a Sono‐Alternating Current‐Electrocoagulation Technique with Power Usage Estimation

AbstractDistillery industrial wastewater (DIW) was tested for color and COD removal percentages using an electrochemical and advanced oxidation processes (AOPs). Specifically, the study compared direct/alternating–current–electrocoagulation (DC‐EC/AC‐EC), sono (US), and direct/alternating current–electrocoagulation coupled with sono (US) (DC‐EC/US and AC‐EC/US) processes. Also evaluated were the effects of these procedures on the power needed to treat DIW. Experimental results showed that compared to single processes such as DC‐EC, AC‐EC, US, hybrid DC‐EC/US, and the hybrid AC‐EC/US process achieved a total color elimination efficiency of 100 % and a COD elimination efficiency of 100 % while using a lower power consumption of 4.76 kWhrm−3. The effects of important operational factors such treatment duration, cycle of pulse duty, sonication power, current density, chemical oxygen demand, electrode spacing, electrode pairing, pH, concentration of electrolyte on the % removal of COD and power usage of DIW were investigated using hybrid AC‐EC/US process. When using a Fe/Fe electrode combination, the effectiveness of COD removal was shown to be enhanced by increasing the treatment duration, current, US power, and decreasing the COD concentration, electrode spacing. The study also provided the results of an investigation into the synergistic index between AC‐EC and US process and operational cost. Based on its ability to efficiently and effectively remove contaminants from wastewater and industrial effluent, the AC‐EC/US approach stands out among the other methods.

Development of an electrocoagulation method using alternating pulse current to treat wastewater generated by tanneries

ABSTRACT Direct current electrocoagulation has various drawbacks, including electrode passivation, heat creation from energy consumption, and high sludge formation. The restrictions limit its usage in tannery wastewater treatment. Therefore, alternating pulse current EC (APC-EC) was developed to solve these obstacles. The study was empirically examined, considering high-frequency (3,000–11,000 Hz), stirring speed (400–1,200 rpm), and reaction time (15–30 min). This research examined how factors affect chemical oxygen demand (COD) removal efficiency, turbidity from trivalent chromium (Cr+3), and energy consumption for perforated aluminum electrodes. The central composite design in the surface response design approach has improved various operational parameters in the APC-EC process for tannery wastewater treatment. The employment of mathematical and statistical methods resulted in optimal removal of COD, Cr+3, and turbidity while reducing energy usage. Using mathematical and statistical methods, we achieved maximum COD, Cr+3 ion, and turbidity reduction while reducing energy use. The investigation found that COD (70.3%), Cr+3 (89.56%), and turbidity (96%) were the most rapidly removed components at 11,000 Hz, 576 rpm, and 30 min. Surface response data explain high-frequency APC-EC dynamics.

Removal of major nutrients by sono-direct and sono-alternate current electrocoagulation process from domestic wastewater

Background: Electrocoagulation is becoming a promising eco-friendly wastewater treatment technique. It is a low-cost wastewater treatment method suitably applied for various wastewater effluent characteristics. Nevertheless, there are different kinds of electrocoagulation; comparison among them in terms of nutrient removal is investigated in the present research. This study analyzed nitrate (NO3 - ) and phosphate (PO4 3-) removal potential of the sono-alternative and direct-current electrocoagulation process. Methods: Batch reactor and sono-direct current (SDC)/sono-alternative current (SAC) electrocoagulation cell were employed to investigate NO3 - and PO4 3- removal efficiency from domestic effluents. The data gathered from laboratory experiments were analyzed using response surface methodology (RSM). ANOVA was used to examine the interaction effects of diverse parameters in terms of NO3 _ and PO4 3- removal from domestic wastewater effluents. Results: At extreme experimental conditions, the percentage of NO3 - and PO4 3- removal attained with sono-direct current electrocoagulation (SDCE) and sono-alternative current electrocoagulation (SACE) were 96.5%, 96.2% and 96.8%, 96.5, respectively. The SACE was more successful in eliminating NO3 - and PO4 3- than the SDCE process. The appearance of resistant oxide coating on the cathode and the appearance of corrosion on the anode due to oxidation processes in the case of SDCE were identified as principal factors highly affecting NO3 - and PO4 3- removal efficiency. Conclusion: With optimum process efficiency, experimental findings show that the SACE process is more capable of NO3 - and PO4 3- removal than the SDCE process.

Removal of Reactive Black 5 from simulated textile effluents by an electrocoagulation process: optimization by response surface methodology

Abstract The textile industry creates one-fifth of the world's industrial water pollution, thus, the electrocoagulation (EC) process was proposed and investigated as an alternative eco-friendly treatment for water reuse. This study aimed to assess the removal efficiency of the Reactive Black 5 (RB5) from synthetic textile effluent by EC. Key operating parameters on EC process efficiency were optimized using response surface methodology (RSM). The main independent variables studied were the current density, EC time, concentration, and pH while the RB5 dye removal was studied as the dependent variable. The range of the studied parameters affecting the EC process ranged from 10 to 60 mA/cm2, 5 to 30 min, 4 to 10 pH and 10 to 40 ppm for current density, EC time, pH, and RB5 concentration, respectively. The optimal operating parameters turned out to be 5.5 pH, 47.5 mA/cm2, 23.75 min, 17.5 ppm, and the predicted RB5 dye removal was 96.33%. The experimental dye removal with optimum operating conditions was in good agreement with the predicted removal efficiency. Therefore, the experiment results revealed the high potential of the EC process to effectively treat textile industry effluents and the RB5 dye removal was successfully optimized using Response Surface Methodology (RSM).

Evaluation of the toxicity of textile effluent treated by electrocoagulation

Abstract Textile effluents are complex, making it difficult to choose an effective treatment. The textile effluent toxicity in Lactuca sativa after pulsed current (PC) electrocoagulation (EC) was evaluated in this study. The EC was performed using 304 stainless steel electrodes in batch mode. Parameters monitored included pH, temperature, color, and turbidity. Additionally, the process residue was subjected to energy-dispersive X-ray fluorescence (XFR) to determine the elements present. The process achieved proportional color and turbidity removal ranging from 97 to 99% and from 74 to 85%, respectively. Chemical oxygen demand (COD) and total nitrogen removal were 81 and 49%, respectively, in a 50 min time-lapse. The process generated approximately 1.7 kg of solid residue/m3 treated effluent. The XFR results revealed the presence, mainly, of Fe, Cr, and Ni ions in the residue, as well as chlorine. The germination index (GI) and relative growth values showed that EC reduced effluent toxicity slightly, indicating the need for complementary treatment.

Industrial indigo dyeing wastewater purification: Effective COD removal with peroxi-AC electrocoagulation system

Direct current (DC) electrocoagulation has obvious decolorization effect on indigo dyeing wastewater produced in actual production, while the removal rate of chemical oxygen demand (COD) was less than 40%, accompanied by serious electrode corrosion and high energy consumption. In order to enhance the COD removal rate, reduce the electrode loss and power consumption, a peroxi-alternating current (AC) electrocoagulation (EC) system was constructed. With COD as the main evaluation index, the effects of power type, electrode combination and process parameters on COD removal rate and decolorization rate were focused on and explored, as well as revealing the degradation mechanism of COD. The results showed that AC electrocoagulation enhanced the floc adsorption capacity by improving the floc structure, and the COD removal rate after treatment was 51.19%. The coupled system of peroxi-AC electrocoagulation further removed sulfite and residual dyes in the wastewater, and the COD removal and decolorization rate of the treated wastewater reached 78.09% and 98.47%, respectively. In addition, the specific energy consumption analysis of COD removal showed that the coupled system was far less energetic than the DC electrocoagulation process, with only 30% of its energy consumption. The uniform corrosion of the electrode under the action of AC weakened the passivation, which reduced the electrode loss and power consumption by 22.73% and 43.75%, respectively. Results from the present work indicated that the peroxi-AC EC system could be an effective method for reducing the concentration of COD in indigo dyeing wastewater.

Removal of chloramphenicol by direct current and pulse current electrocoagulation: implications for energy consumption and sludge reduction

The discharge of antibiotics in wastewater endangers human health. Electrocoagulation (EC) technology can effectively treat chloramphenicol (CAP) in wastewater, but its practical application is limited by issues such as plate passivation, high energy consumption, and a large sludge volume. This study compared the CAP removal performances of positive single pulse current electrocoagulation (PSPC-EC), alternating pulse current electrocoagulation (APC-EC), and conventional direct current electrocoagulation (DC-EC). Under optimal operating conditions, all three methods achieved similar CAP removal rates of >98%, although DC-EC was significantly faster. However, PSPC-EC and APC-EC reduced the sludge quality by 34.95% and 87.48%, respectively, compared with DC-EC and the energy consumption by 57.74% and 39.62%, respectively. PSPC-EC produced a slightly larger floc size than the other methods, which weakened the adsorption capacity. Energy-dispersive spectrometry demonstrated that APC-EC produced flocs with a higher carbon content, which indicates greater adsorption capacity. Fourier transform infrared spectroscopy showed that the flocs produced by the three methods had absorption peaks with similar intensities at the same characteristic wavelengths. The results confirmed that pulse current EC may be a better choice than DC-EC for CAP removal and can effectively reduce operating costs and sludge production in actual wastewater treatment.

Performance analysis of pulsed direct current electrocoagulation for chemical oxygen demand removal from wastewater: energy savings and cost minimization

Performance analysis of pulsed direct current electrocoagulation for chemical oxygen demand removal from wastewater: energy savings and cost minimization

(Digital Presentation) Application of Polarity Reversal and Performance Analysis of Continuous Electrocoagulation

An important challenge for continuous treatment by electrocoagulation (EC) is the passivation and fouling of electrodes which increases during the longer operation (Ingelsson et al., 2020). The application of polarity reversal (PR) and treatment performance of EC was investigated using continuous flow reactor for simultaneous removal of silica and hardness (calcium and magnesium) from produced water. Polarity reversal times (PRT) from 30 s to 10 min were studied at a fixed charge loading of 2000 C L- 1 (i.e., the amount of charge passed per unit volume of produced water treated) using Fe and Al electrodes. Periodic PR was found to reduce the fouling and de-passivate the electrodes by changing the surface chemistry at the electrode-electrolyte interface (Ingelsson et al., 2020; Yasri et al., 2022). During 90 minutes of continuous treatment the chronopotentiometric data indicated that a PRT of 10 min was more effective in reducing the cell voltage for both Fe and Al electrodes [Fig. 1 (a & b)]. With a longer PRT of 10 min, there is more time for the acid boundary layer to form on the anode, which mitigates metal precipitation at the anode. In contrast the higher cell voltage that persists in direct current EC (DC-EC) could be due to the precipitation of Ca and Mg minerals in the alkaline solution on the cathode surface, leading to cathode passivation (Chow et al., 2021). After the first polarity reversal, both electrodes have been anodic, removing passivation layers from the surface and reducing the cell voltage. On reversing the polarity, the cathode becomes the anode, and the acidic pH on the formed at the electrode interface will facilitate the dissolution of Ca and Mg precipitates on the electrode surface, reducing the cell voltage significantly. For Fe-EC, the contaminant removal performance increased with PRT, and the highest removal was observed with DC-EC (Fig. 1c). The increasing removal performance with PRT for Fe-EC is consistent with the increase in faradaic efficiency observed of 55%, 68%, 85%, and 99.8% with 30 sec, 2 min and 10 min PRT, and DC respectively. The lower faradaic efficiencies for Fe-EC with short PRTs are likely due to redox reactions of iron species at the electrode surface (Chow et al. 2021).The contaminant removal at a charge loading of 2000 C L–1 using DC-EC with Al electrodes was similar to that for PR-EC with PRTs of 2 to 10 min (Fig. 1d). Slightly lower Si and hardness removal was observed for Al-EC at the shortest PRT of 30 s. For Al-EC, the faradaic efficiency was also observed to increase with PRT, with values of 150%, 220% and 287% obtained at 30 sec, 2 min and 10 min PRT respectively. The super-faradaic (>100%) efficiencies can be explained by dissolution of the Al from the cathode under the local alkaline conditions that develop on the electrode surface. With a short PRT, there is less time for the alkaline pH to develop at the surface and hence the faradaic efficiency was reduced.

A comparative study of electrocoagulation treatment with iron, aluminum and zinc electrodes for selenium removal from flour production wastewater

Electrocoagulation (EC) using iron (Fe), zinc (Zn) and aluminum (Al) electrodes was comparatively applied in the treatment of selenium (Se) in flour production (FP) wastewater. It was indicated that EC treatment with Fe anode obtained highest removal efficiency (79.1%) for Se in the 90 min treatment in the comparative study, which could be attributed to the superior adsorption capacity of in-situ generated iron flocs. Removal of Se resulted from electrodeposition and adsorption to in-situ generated flocs in EC treatment, and the operational conditions significantly influenced the Se removal performance in this work. The results showed the acidic condition and higher current density favored EC treatment on Se removal, EC removed up to 97.8% of Se at pH 4 under 15 mA cm−2, whereas it obtained 83.5% and 50.4% of removal efficiency at pH 7 and 10, respectively. There was competitive adsorption in the process of selenium removal, as the in-situ generated flocs effectively removed 35.6% of humic acid-like (HA-like) substance in FP wastewater after 90 min treatment. The FTIR results showed that HA-like substance mainly contained the protein water hydrogen bond, carboxylate COO antisymmetric stretching and other functional groups. Through the analysis of existence of Se in flocs and wastewater, it can be found that approximately 2.8%–3.92% of Se was removed by electrodeposition process. This study illustrated the Se removal mechanism and provided constructive suggestion for food manufacturing to the metal removal and utilization of advanced treatment.

Comparison of sono-direct and sono-alternate current electro-coagulation processes for removal of color and turbidity from domestic wastewater

Background: Nowadays there is a problem related to wastewater handling which is released from different activities. Electrocoagulation has been a dominant treatment method for wastewater treatment. There are different forms of electrocoagulation methods for wastewater treatment. Nevertheless, there was no comparison made for the removal efficiency of the sono-alternate current (SAC), alternate current (AC), sono-direct current (SDC), and direct current (DC) electrocoagulation process. Methods: The efficiency of electrocoagulation method was compared for removal of color and turbidity from Jimma University domestic wastewater. Batch reactor DC/AC electrocoagulation cell was used to determine the removal efficiency. During the comparison, the response surface methodology (RSM) was used to analyze and optimize the data taken from the laboratory. In addition, ANOVA was used to analyze the interaction effects of different parameters. Results: The removal of color and turbidity from domestic wastewater was about 97.53% and 95.28% respectively, using direct current electrocoagulation (DCE). For alternate current electrocoagulation (ACE), the removal of color and turbidity was 98.35% and 96.12%, respectively. The removal of color and turbidity for sono-DCE (SDCE) was obtained to be 98.55% and 98.27%, respectively and for sono-ACE (SACE), the removal of color and turbidity was 99.95% and 99.76%, respectively at the optimum experimental conditions of chemical oxygen demand (COD) 960 g/L, initial wastewater pH of 6.8, the current density of 0.4 A/dm2 , inter-terminal spacing of 1 cm, and the association of electrode of Al-Al. Conclusion: According to the findings of this study, it can be concluded that, the SAC electrocoagulation method is the best and promising technique compared with all other electrocoagulation methods.

Comparison Study on Sonodirect and Sonoalternate Current Electrocoagulation Process for Domestic Wastewater Treatment.

Nowadays, there is a problem related to wastewater handling which is released from different activities. The electrocoagulation method has been a dominant treatment method for wastewater treatment. There are different forms of electrocoagulation methods for wastewater treatment. Nevertheless, there was no comparison made for the removal efficiency of the sonoalternate current (SAC), alternate current (AC), sonodirect current (SDC), and direct current (DC) electrocoagulation process. The efficiency of electrocoagulation methods was compared for their removal of chemical oxygen demand (COD) from Jimma University domestic wastewater. Batch Reactor DC/AC electrocoagulation cell was used to determine the removal efficiency. During the comparison, the response surface methodology (RSM) was used to analyze and optimize the data taken from the laboratory. Besides, ANOVA was used to analyze the interaction effects of different parameters. The removal of COD from domestic wastewater was achieved with DCE, ACE, SDCE, and SACE which were 82.6%, 86.58%, 88.6%, and 92.5%, respectively, under optimal experimental conditions. From the finding, SACE was more successful at removing % COD than the DCE, ACE, and SDCE methods. For DCE and SDCE, the formation of an impermeable oxide layer at the cathode and the occurrence of corrosion at the anode due to oxidation made the COD removal process less efficient compared with SACE processes. From the experimental results it can be concluded that the SACE has the lowest power consumption and higher process efficiency than the other EC methods and can be a promising solution for removing pollutants from domestic wastewater.

Effect of iron ion configurations on Ni2+ removal in electrocoagulation

Electrocoagulation (EC) has been widely used to treat the heavy metal wastewater in industry. A novel process of sinusoidal alternating current electrocoagulation (SACC) is adopted to remove Ni2+ in wastewater in this study. The morphology of precipitates and the distribution of the main functional iron configurations were investigated. Ferron timed complex spectroscopy can identify the monomeric iron configurations [Fe(a)], oligomeric iron configurations [Fe(b)] and polymeric iron configurations [Fe(c)]. The optimal operating conditions of SACC process were determined through single-factor experiments. The maximum Ni2+ removal efficiency [Re(Ni2+)] was achieved under the conditions of pH0=7, current density (j) = 7 A/m2, electrolysis time (t) = 25 min, c0(Ni2+) = 100 mg/L. At pH=7, the proportion of Fe(b) and Fe(c) in the system was 50.4 at.% and 23.1 at.%, respectively. In the SACC process, Fe(b) and Fe(c) are the main iron configurations in solution, while Fe(c) are the vast majority of the iron configurations in the direct current electrocoagulation (DCC) process. Re(Ni2+) is 99.56% for SACC and 98.75% for DCC under the same optimum conditions, respectively. The precipitates produced by SACC have a high proportion of Fe(b) configurations with spherical α-FeOOH and γ-FeOOH structures which contain abundant hydroxyl groups. Moreover, it is demonstrated that Fe(b) has better adsorption capacity than Fe(c) through adsorption experiments of methyl orange (MO) dye. Fe(a) configurations in the homogeneous solution had no effect on the removal of nickel.

Investigation of electrode passivation during electrocoagulation treatment with aluminum electrodes for high silica content produced water.

One of the main challenges for the implementation of electrocoagulation (EC) in water treatment are fouling and passivation of the electrodes, especially for applications with high contaminant concentrations. For the first time, we investigated in this study the process of fouling mitigation by polarity reversal during the EC treatment of boiler blowdown water from oil-sands produced water, characterized by high silica concentrations (0.5-4 g L-1). This effluent is typically obtained from an evaporative desalination process in oil production industries. Potentiodynamic characterisation was used to study the impact of passivation on the anode dissolution. Although a charge loading of 4,800 C L-1 was found to remove about 98% of silica from a 1 L batch of 4 g L-1 Si solution, fouling reduced the performance significantly to about 40% in consecutive cycles of direct current EC (DC-EC) treatment. Periodic polarity reversal (PR) was found to reduce the amount of electrode fouling. Decreasing the polarity period from 60 to 10 s led to the formation of a soft powdery fouling layer that was easily removed from the electrodes. In contrast, with DC operation, a hard scale deposit was observed. The presence of organics in the field samples did not significantly affect the Si removal, and organics with high levels of oxygen and sulfate groups were preferentially removed. Detailed electrochemical and economic investigations suggest that the process operating at 85 °C achieves 95% silica removal (from an initial concentration of 481 mg L-1) with an electrical energy requirement of 0.52 kWh m-3, based on a charge loading of 1,200 C L-1, an inter-electrode gap of 1.8 cm and a current density of 16 mA cm-2.

Improving Degradation Efficiency of Organic Pollutants through a Self-Powered Alternating Current Electrocoagulation System.

Although electrocoagulation technology has been widely researched in wastewater treatment, high energy consumption and electrode passivation are still the main challenges for its widespread applications. Here, we propose a self-powered electrocoagulation system based on a triboelectric nanogenerator (TENG) with alternating current (AC) outputs to solve these two issues, and thus enhance the removal efficiency of organic pollutants. Compared with the direct current source, the AC power source can reduce the electrode passivation, produce more aluminum hydroxide compounds after consuming an equal amount of charges, and thus improve the degradation efficiency. Moreover, the removal efficiency can be further enhanced by decreasing the frequency AC, in which a 5.7-fold improvement was achieved at 0.2 Hz compared to DC at 1.8 Hz. Inspired by the low frequency of ocean wave water, we developed a self-powered AC-electrocoagulation system to directly drive the electrocoagulation reaction by harvesting water wave energy, which can effectively remove 94.8% of xylenol orange and 98.8% of water-oil emulsion, and thus completely address the problem of energy consumption. This study further promotes the application of self-powered electrochemical systems in treating environmental pollution.

Removal of tetracycline from livestock wastewater by positive single pulse current electrocoagulation: Mechanism, toxicity assessment and cost evaluation

The widespread use of veterinary antibiotics has led to the significant problem of contamination of livestock wastewater with significant amount of antibiotics. Electrocoagulation (EC) has become a prominent research topic because of the technique's ability to remove antibiotics from livestock wastewater. However, an urgent solution is needed to reduce the high operating costs associated with the process. Therefore, in this study, we developed a positive single pulse current (PSPC)-EC system to remove tetracycline (TC) from synthetic and actual livestock wastewater. Influential factors were investigated, and the optimal PSPC-EC operating parameters were identified as follows: duty ratio = 60%, pH = 4, electrode spacing = 1 cm, current intensity = 0.2 A, and conductivity = 2 mS cm−1. The mechanism of PSPC-EC was characterised using techniques including scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TC decomposition pathway was proposed based on the generation of its intermediate products. A toxicity estimation software tool (TEST) model was used to evaluate the toxicity of TC and its main degradation products, and most of its intermediates were found to be less toxic than TC. The contribution ratios of floc adsorption and electrochemical oxidation for removing TC were 74.17% and 21.48%, respectively. The highest TC removal rate reached 95% with an operating cost of 0.011 USD/m3. Finally, under the optimum conditions identified, actual livestock wastewater was treated by PSPC-EC. Compared with conventional EC and coagulation treatment techniques that consume electricity and produce pollution, the results indicate that the PSPC-EC technique with changing current operation mode is a more cost-effective and attractive option for removing TC from livestock wastewater.

Continuous Treatment of Oil-Sands Produced Water By Electrocoagulation

The treatment performance of electrocoagulation (EC) was investigated using continuous flow reactor for simultaneous removal of silica and hardness causing ions calcium and magnesium from produced water. The amount of charge passed per unit volume of produced water treated (i.e., the charge loading, C L- 1) was adjusted either by varying the electrode area or the current density, under a range of inlet flowrates (20―120 mL min-1) using Fe and Al electrodes. It was found that direct current (DC) EC operation with Fe electrodes was able to remove about 87% of the total silica, whereas with Al electrodes more than 95% silica removal was achieved. These removals were achieved with an influent silica concentration of 60 mg L- 1, a charge loading 2000 C L- 1, current density 8 mA cm- 2, pH of 7.75 and feed flow rate 60 mL min-1 (corresponding to a Reynolds number of 116). In addition, the calcium removal was observed to be around 85% with both Fe and Al electrodes. Al electrodes were found to be more effective for removal of magnesium achieving about 70% removal in comparison to 39% removal achieved with Fe electrodes at the same operating conditions.The average faradaic efficiency of DC-EC with Fe and Al electrodes was observed to be 99.9% and 149% respectively over the range of charge loading between (600―2000 C L- 1) and flow rate. The super faradaic efficiency of Al was due to the chemical dissolution of Al cathode which provides additional Al coagulant [1]. The specific energy consumption in DC-EC operation was found to be 1.79 and 1.76 kWh m- 3 for Fe and Al respectively at 2000 C L- 1, at a current density of 8 mA cm- 2 and a fixed Reynolds number of 116. During DC-EC operation, the cell voltage was found to increase in time, however this increase was reduced with the application of polarity reversal (PR-EC) [2]. It was found that a longer appropriate polarity reversal duration of 10 min provided sufficient time to remove the fouling / passivation layers from the electrode surface [1], [3]. Ca and Mg precipitates form a passivating layer in the alkaline pH on the cathode surface. This layer can be dissolved from the electrode surface by the acidic pH generated at the interface of the anode after polarity reversal [1]. This results in reduced cell voltage and hence energy consumption in comparison to DC-EC. PR-EC with 10 min reversal time reduced the energy consumption to 1.53 kWh m- 3 and 1.57 kWh m- 3 for Fe and Al electrodes respectively at the same operating conditions as for DC-EC discussed above. Under these conditions (charge loading = 2000 C L- 1, current density = 8 mA cm- 2), the silica removal was found to be only 65% with Fe electrodes, compared to above 95% with Al electrodes. Finally, the use of hybrid electrodes (Fe/Al) for DC-EC in which Fe was anode and Al as cathode produced a slightly higher cell voltage than non-hybrid Fe and Al, probably due to the more negative redox potential of the Al cathode. However, for PR-EC with a 10 min reversal time using a combination of electrodes (Fe/Al) had a similar cell voltage than for Fe or Al-EC. This hybrid electrode system had an energy consumption of about 1.53 kWh m- 3 while achieving 96% Si, 84% Ca and 73% Mg removal. The results indicate that EC can effectively remove silica and hardness causing ions from synthetic produced water while reducing the cell voltage with the application of PR. As shown in Fig. 1, a lower operating cost was estimated for Fe-EC due to the low cost of the metal consumption, since the cost of Al is around 2.8 times higher than the cost of Fe. The cost of metal consumption for the hybrid combination of Fe/Al electrodes was significantly lower than for Al-EC, while sustaining more than 95% Si removal.

Modeling and Optimization of COD Removal from Leachate by Electrocoagulation: Application of Central Composite Design

The present study aims to investigate the treatment of leachate by the electrocoagulation (EC) process using aluminum electrodes. A response surface methodology (RSM)-based central composite design (CCD) was carried out to design the experiments, develop a statistical model, assess the relationship between the four variables, and predict the responses, namely, the chemical oxygen demand (COD). The removal efficiency of COD, biological organic matter (BOD5), and turbidity were about 90%, 92.3%, and 99.6%, respectively, under optimum operational conditions, i.e., initial pH (5.3), current intensity (1.2 A), electrolysis time (75 min), and stirring speed (150 rpm). The operating cost of the current EC treatment was 0.6 €/m3. Moreover, the coefficient of determination (R2) revealed a satisfactory agreement between observed and expected results. Therefore, RSM is an appropriate approach to determine the key parameters for electrocoagulation process.

Enhanced removal of humic acid from aqueous solution by combined alternating current electrocoagulation and sulfate radical.

Application of alternating current in electrocoagulation and activation of persulfate (AEC-PS) for the effective removal of humic acid (HA) from aqueous solution was evaluated. In order to optimize the removal efficiency HA by the AEC-PS process, several influencing parameters such as pH, reaction time, PS dose, current density (CD), concentration of NaCl, initial concentration of HA, and coexisting cations and anions influence were investigated. From the batch experiments, the highest HA removal efficiency obtained was 99.4±0.5% at pH of 5, reaction time of 25min, CD of 4.5mA/cm2, PS dose of 200mg/L, and NaCl concentration of 0.75g/L for an initial HA concentration of 30mg/L. When CD increased from 1.25 to 4.5mA/cm2, the HA removal efficiency was improved from 88.8±4.4% to 96.1±1.5%. In addition, the type of coexisting cations and anions exerted a significant role, leading to a reduction in the removal efficiency of HA. To investigate the dominant free activated radical, radical scavengers such as tert-butyl alcohol and ethanol were employed. It was observed that both OH and SO4- radicals substantially contributed to the removal of HA, and the contribution of SO4- radical was higher than that of OH radical, suggesting that AEC-PS process could serve as a novel and effective treatment technique for the removal of organic matters from aqueous sources.