Article

Removal mechanism of heavy metal (Cu, Ni, Zn, and Cr) in the presence of cyanide during electrocoagulation using Fe and Al electrodes

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Abstract

Heavy metals have frequently been detected in metal plating wastewater. In this study, electrocoagulation method using iron (Fe) and aluminum (Al) electrodes was applied to simultaneously remove four heavy metals (Cu, Ni, Zn, Cr) in artificial metal plating wastewater. The Fe electrode showed greater removal efficiency for especially Cr than did the Al electrode due to the reduction of Cr⁶⁺ ion by Fe²⁺ ions produced from electrode. Alkaline pH favored electrocoagulation because of the abundance of hydroxide (OH⁻) ions; thus, metal hydroxides can be formed readily under alkaline pH. The metal removal increased with current density, as Fe²⁺ ion was generated more effectively at high current. However, the electrolyte concentration did not significantly affect metal removal efficiency. In electrocoagulation experiments using Fe electrodes, the mass of sludge formed was 0.68–2.50 kg/m³ and the amount of energy consumed was 0.37–2.78 kW h/m³, respectively, during the treatment of artificial metal plating wastewater containing four heavy metals in the absence of cyanide, which increased to 3.64–4.74 kg/m³ and 4.80–5.04 kW h/m³ for artificial wastewater in the presence of cyanide. The FTIR spectra of the sludge samples generated when using Fe and Al electrodes showed that all four metals exhibited OH stretching peaks, implying that main removal mechanism of metals during electrocoagulation is the precipitation with metal hydroxide. Iron sludge was composed mainly of Fe3O4 and FeO(OH), and Al sludge was mostly AlO(OH). When using Fe electrode in the presence of cyanide, cyanide was also adsorbed onto iron sludge via Fe-CN bonding.

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... Heavy metals are common contaminants found in many kinds of industrial wastewater, including that from mining and electroplating. Electroplating effluent often contains metals like zinc, copper, chromium, and nickel, which have been demonstrated to be very harmful in aquatic ecosystems [3][4][5][6]. Heavy metals are inherently highly toxic, even at very low concentrations [7]. Heavy metals are not degradable and can accumulate in human tissues, leading to the development of various chronic diseases [8]. ...
... The most popular and regarded as the most cost-effective of these methods is precipitation. But this procedure produces a lot of settling sludge, which needs to be processed further [3,5,9]. Although membrane separation methods like reverse osmosis are successful at reducing metal ions, their application is restricted because to drawbacks such membrane fouling and expensive material and operating expenses [5]. ...
... But this procedure produces a lot of settling sludge, which needs to be processed further [3,5,9]. Although membrane separation methods like reverse osmosis are successful at reducing metal ions, their application is restricted because to drawbacks such membrane fouling and expensive material and operating expenses [5]. Ion exchange methods provide fast and efficient removal of metals, but the pH of the wastewater can strongly influence this process. ...
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Wastewater from electroplating is often found to contain heavy metals. This study used the electrocoagulation (EC) method with iron (Fe) electrodes to remove two heavy elements (Cr and Zn) from actual electroplating effluent at the same time. The effect of EC time and wastewater pH on removal performance was investigated. It was determined that optimum Cr and Zn removal occurred at a pH of 9 and after 30 minutes. It was discovered that the clearance rates for Zn and Cr were 79% and 99%, respectively. The elimination of these heavy metal ions was compatible with a pseudo-first-order model, according to kinetic investigations. The removal of electroplating wastewater by the EC method occurs with low energy consumption, making the process economically viable and scalable. In the EC experiments using Fe electrodes, the electrode consumption was found to be 1.07 kg/m³, and the energy consumed was 25 kWh/m³.
... Other factors, such as variations in the current strength and detention time, have less influence on the nickel removal rate [29]. In first-order reaction kinetics, the main mechanism is physisorption [30], in which nickel cations are removed by adsorption on the surface of aluminum hydroxide flocs [31]. Kim et al. [30] also reported that a first-order kinetic reaction occurred during the removal of nickel from metal plating wastewater using iron and aluminum electrodes with a current density of 2-4 mA/cm 2 . ...
... In first-order reaction kinetics, the main mechanism is physisorption [30], in which nickel cations are removed by adsorption on the surface of aluminum hydroxide flocs [31]. Kim et al. [30] also reported that a first-order kinetic reaction occurred during the removal of nickel from metal plating wastewater using iron and aluminum electrodes with a current density of 2-4 mA/cm 2 . However, Moersidik et al. [32] reported that the reaction kinetics of nickel removal from electroplating wastewater using aluminum electrodes with a current density of 20 mA/cm 2 is second order. ...
... This indicates that EC can remove Cr more quickly than Fe. Kim et al. [30] described a second-order kinetic model that refers to the metal removal mechanism in EC through chemisorption. The results showed that the removal of chromium and iron from EC occurs through a chemisorption process. ...
Article
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High global demand for nickel metal has contributed significantly to the growth of the nickel mining industry in Indonesia. This growth has a positive multiplier effect on the economy, with the potential to affect aquatic life and humans owing to the high levels of chromium, nickel, and iron in mine water. Therefore, this study aims to develop an electrocoagulation (EC) reactor to remove nickel, chromium, and iron from mine water. This study used a continuous reactor and aluminum electrodes with variations in current density (3.378, 6.757, and 10.135 mA/cm²) and inflow (0.3, 0.5, and 1 L/min). The results showed that the operating scenario with a current strength of 6 A and an inflow of 0.3 L/min had a removal efficiency of 86.89 % nickel, 99.51 % chromium, and 80.61 % iron with a charge loading value of 11,194 F/ma³ and Reynolds number of 39. These results are expected to provide valuable information for the development of an effective EC technology, thereby demonstrating its potential for the removal of metals from nickel mine water.
... Everyone concern for water's value and its protection is paramount to avoid environmental pollution, making it human's responsibility to protect and conserve water for life [5,6]. Heavy metals, including copper, zinc, nickel, and chromium, are common pollutants in industrial wastewaters like metal plating and mining, posing high toxicity to aquatic environments [7,8]. Heavy metals are metallic elements in the periodic table, grouped 3-16 in periods 4 and higher, with atomic weights between 63.5 and 200.6 g mol -1 [9]. ...
... Cr (VI) can be removed from wastewater using a variety of treatment techniques, including chemical precipitation, co-precipitation, electrodeposition, membrane treatment, cementation, electrodialysis, biological reduction, electrocoagulation, ion-exchange, photocatalysis, adsorption, and biosorption. However, many technologies have limitations to various extents in practical applications due to the influence of high energy requirements, complex procedures, or the development of harmful by-products [7]. Among these, electrocoagulation (EC) is a green, cost-effective, low sludge generation and environmentally friendly method for treating wastewater, offering a simple and environmentally friendly solution without the need for additional chemicals [16]. ...
... EC performance is influenced by water electrolysis, redox reactions of contaminants at the electrode surface, electrostatic effects, and ion migration. However, the main EC steps include, generation of cationic metal ions at the anode and hydroxide ions (OH -) at the cathode solution interface, transport of metal ions and OH-to the bulk solution, generation of metal hydroxide coagulants, and aggregation (agglomeration) of coagulants along with the contaminants [7,13,[17][18][19]. The proposed mechanism of chemical reactions in the EC process is illustrated through the main reactions at the aluminum electrodes (1-5) [20][21][22][23][24]: ...
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The presence of chromium (Cr) in synthetic wastewater has become a serious environmental issue. Therefore, main aim of this work was to investigate Cr removal from synthetic wastewater via electrocoagulation (EC) with a natural coagulant using aluminum electrodes. The central composite design (CCD) of the response surface methodology (RSM) method was used to optimized the operating variables of solution pH (5–9), initial Cr concentration (225–475 mgL-1), reaction time (30–40 min), and applied current (0.35–0.55 A). The ANOVA results clearly show that the quadratic model (p < 0.0001) was sufficient to best predict the removal performance of Cr (R2 = 0.9994 for electrode distance of 0.5 cm and 0.9924 for 1 cm). The maximum removal (99.836 % for electrode distance of 0.5 cm, and 98.175 % for 1 cm) of Cr was achieved with optimized conditions of solution pH 7.053, initial Cr concentration 337.795 mgL−1, reaction time 37.148 min, and applied current of 0.505 A. This finding proved that the EC process assisted with natural coagulant, an efficient, cost-effective method for removing Cr from synthetic wastewater.
... Other factors, such as variations in the current strength and detention time, do not significantly influence the nickel removal rate (Ridantami, 2021). In first-order reaction kinetics, the main mechanism is physisorption (Kim et al., 2020), in which nickel cations are removed by adsorption on the surface of aluminum hydroxide flocs (Chen dkk., 2018). Kim et al. (2020) also reported that a first-order kinetic reaction occurred during the removal of nickel from metal plating wastewater using iron and aluminum electrodes with a current density of 2-4 mA/cm 2 . ...
... In first-order reaction kinetics, the main mechanism is physisorption (Kim et al., 2020), in which nickel cations are removed by adsorption on the surface of aluminum hydroxide flocs (Chen dkk., 2018). Kim et al. (2020) also reported that a first-order kinetic reaction occurred during the removal of nickel from metal plating wastewater using iron and aluminum electrodes with a current density of 2-4 mA/cm 2 . However, Moersidik dkk. ...
... This indicates that EC can remove Cr more quickly than Fe. Kim et al. (2020) described a second-order kinetic model that refers to the metal removal mechanism in EC through chemisorption. The results showed that the removal of chromium and iron from EC occurs through a chemisorption process. ...
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High global demand for nickel metal has contributed significantly to the growth of the nickel mining industry in Indonesia. This growth has a positive multiplier effect on the economy, with the potential to affect aquatic life and humans owing to the high levels of chromium, nickel, and iron in mine water. Therefore, this study aims to develop an electrocoagulation (EC) technology to remove nickel, chromium, and iron from mine water. This study used a continuous reactor and aluminum electrodes with variations in current strength (2, 4, and 6 A) and detention times (15, 30, and 45 min). The results showed that the operating scenario with a current strength of 6 A and an inflow of 0.3 L/minute had a removal efficiency of 86.89% nickel, 99.51% chromium, and 80.61% iron with a charge loading value of 11,194 F/ma 3 and Reynolds number of 39. These results are expected to provide valuable information for the development of an effective EC technology, thereby demonstrating its potential for the removal of metals from nickel mine water.
... Electrocoagulation (EC), which adopts an electrochemical mode, is a preferred alternative treatment because of its simplicity, versatility, low chemical requirements, low sludge production, ease of automation, energy efficiency, and cost-effectiveness [18][19][20][21]. This process has been widely studied and is considered effective for wastewater treatment in various industries, including textiles [22,23], oil [24], personal care [25], and plating [10,26]. Several parameters influence the performance of the electrocoagulation process, such as current density, electrode type and shape, electrode space, pH, conductivity, reaction time, and wastewater characteristics [18,27]. ...
... Several parameters influence the performance of the electrocoagulation process, such as current density, electrode type and shape, electrode space, pH, conductivity, reaction time, and wastewater characteristics [18,27]. A previous study [26] revealed that electrocoagulation could significantly reduce heavy metals (e.g., Cu, Ni, Zn, and Cr) concentration, with only approximately 0.37-2.78 kWh of energy consumed and 0.68-2.5 kg of sludge generated per m 3 of wastewater treated. ...
... The wastewater from the Cr rinse tank was pumped into the reduction tank at a flow rate of 3.5 m 3 /h. Cr(IV) reduction was performed at pH 2-3 using 5-10 % NaHSO 3 to reduce the toxicity of the chromium species and promote the generation of insoluble Cr(OH) 3 , which can easily be removed from wastewater [26,33]. In the neutralization tank, the effluent of the reduction process (Cr 3+ ) was mixed with wastewater from the spent solvent and nickel rinse tanks at flow rates of 10 m 3 /h and 1.25 m 3 /h, respectively. ...
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... Electrochemical methods can be classified as electrocoagulation, electroflotation, electrodeposition, and electrodialysis. Electrocoagulation is the use of electrolysis to aggregate suspended matter and colloidal particles into floc, which is useful for eliminating suspended matter and colloidal matter from wastewater while also reducing COD and chroma [27,28]. Electroflotation is the separation of charged particles using an electric field force. ...
... Depending on the resin structure, the resin has slow adsorption speed, high swelling rate, poor mechanical properties, and increased process costs [25] Electroche-mistry Electrocoagulation Simple operation, high efficiency, environmental protection, low cost Need to replace the consumed sacrificial electrode, cathode passivation, high electricity cost, increase the conductivity of treated water [27,28] Electricflotation High performance, easy to operate and automate, obtain sludge with good structural and mechanical properties, exclude reagent facilities, high current sterilization effect ...
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Heavy metal effluent generated during the electroplating process poses a considerable hazard to both the environment and human health. Traditional wastewater treatment technology has significant drawbacks, including lengthy process flows, low efficiency, high chemical consumption, high cost, resource loss, and a low percentage of water recycling. Crystallization technology has recently gained popularity among academics due to its high efficiency, low cost, minimal equipment requirements, and ease of use. This review had discussed the fundamental processes of crystallization, thermodynamic and kinetic concepts, and various crystallization technologies accessible. Then, the utilization of crystallization technology in copper, nickel, lead, iron, chromium, cobalt, and zinc is extensively discussed in terms of recycling heavy metals from electroplating effluent. The majority of researchers prefer fluidized bed crystallization technology, and it is noted that in the recovery process, it is preferable to recover compounds that can form stable, safe, and valuable compounds, such as lead carbonate formed during the treatment of lead plating wastewater. Finally, the review concluded by highlighting existing issues with crystallization technology and proposing potential future research and application directions to encourage the further development and enhancement of this technique in the field of electroplating wastewater treatment. Graphical Abstract
... Although commercial AC is one of the most popular adsorbents for removing heavy metals from wastewater, its usage is occasionally restricted because of its greater cost [3,28]. Ultimately, peat, coal, lignite, and wood are used to synthesis AC, which is costly, highly exhaustible, and seen as an annoyance [29]. ...
... This circumstance has led numerous researchers to investigate less expensive carbonaceous based materials for the production of activated carbon from biomass derived from cellulose, lignin, and hemicelluloses [30][31][32]. Indeed, agriculture waste disposal being widely accessible including walnut shell [33], wood sawdust [34], coconut shell [25], cotton cakes [28], lemon peel [35], pecan shell [11], corn cob [6], xhanthoceras sorbifolia [29], jatropha shell [36] and, rice husk [37], etc. have been examined. ...
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The presence of heavy metals in water is one of the major environmental issues. In this study, desert date seed shells were employed as precursors for the production of activated carbon by chemical activation process using phosphoric acid (DDSSA) and potassium hydroxide (DDSSS). The activated carbon derived desert date seed were characterized using XRD, FTIR, Raman spectroscopy, SEM analysis and point of zero charge. The most significant variables that affect the adsorption of iron ions, including pH, contact time, and initial concentration, have been investigated. The results of the research were successfully assessed by Langmuir model. Interestingly, the maximum adsorption ability of Fe2+ was found to be 132.25 mg/g onto DDSSA and 126.35 mg/g onto DDSSS, this was found to be higher in comparison to the similar activated carbon obtained by other researchers. The pseudo 2nd order model was also utilized to describe the adsorption and the data showed that adsorption kinetic of Fe2+ ions onto the DDSSA and DDSSS is dominated by chemisorption. Moreover, thermodynamic parameters suggested that DDSSA and DDSSS for Fe (II) adsorption phenomenon were endothermic and spontaneous. Taken together the high availability, facile production along with high performance of activated carbon from desert date seed shells make it an economically adsorbent for Fe (II) adsorption.
... The decrease in Cu removal at pH 10 (99.5%) is attributable to the anode's increased oxidation of hydroxide anion. The final pH indicates a slight decrease in basicity (pH > 8) due to the precipitation of insoluble hydroxide Cu(OH) 2 39 . Due to the formation of metal hydroxides during the ECF process, the environment's pH is optimal for removing copper. ...
... .Kim et al. (2020) observed that the formation of metal hydroxide is complex at acidic pH due to the formation The plots of first-and second-order reaction models with the Cu removal experimental data in batch ECF reactor (Experimental conditions: Temperature: 20 ºC; pH: 7; Reaction time: 0-30 min). ...
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The presence of copper in aqueous environments such as drinking water has led to several environmental effects, such as flavor and odor. The increase in Cu levels in ground and surface water has been mainly attributed to anthropogenic and natural sources. Consequently, this applied-analytical study aimed to investigate copper removal from urban drinking water through batch reactor electrocoagulation/flotation (ECF) with aluminum electrodes. The copper removal efficiency was evaluated under various operating conditions of current density (0.8–2.4 mA/cm²), initial concentration (1–100 mg/L), pH (3.5–10.5), and time (10–30 min). Cu was determined using the method outlined in the standard procedures (3500-Cu B at 4571 nm). The results indicated that increasing the current density from 0.8 to 2.4 mA/cm² and the reaction time from 10 to 30 min improved Cu⁺² removal efficiency (from 95 to 100%). In addition, the results demonstrated that Cu⁺² reduction is 100% with an initial concentration of 100 mg/L, a pH of 7.5, a reaction time of 30 min, and an anode current density of 2.4 mA/cm². The Taguchi method results for copper removal efficiency show that reaction time is the most significant variable. Furthermore, Cu removal kinetics models in an ECF reactor are second-order (R² > 0.92). The Cu removal in the ECF reactor is due to redox and adsorption. Moreover, the operational costs of Cu treatment with Al electrode pairs are estimated to range from 8857 and 9636 Rial/kg of Cu removed. Thus, it can be concluded that the ECF process is very efficient in removing Cu from aqueous environments under optimum conditions.
... EC is a wastewater treatment method that utilizes electric current to coagulate suspended particles in water. It combines principles of electrochemistry, coagulation and flotation, and it has been applied to remove contaminants from the wastewater produced from textile industry, mining sites, petrochemical production plants, and agroprocessing facilities among others to remove contaminants from wastewater produced from these plants (Babu et al. 2021;Idusuyi et al. 2022;Igwegbe et al. 2024;Kim et al. 2020;Merzouk et al. 2011). EC can be used to remove contaminants from dairy effluents before being discharged into environment. ...
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Dairy industry wastewater, laden with high levels of biological oxygen demand (BOD), chemical oxygen demand (COD), and various pollutants, poses significant environmental concerns. This study introduces the innovative use of recycled aluminium cans as electrodes for electrocoagulation, presenting an eco-friendly and cost-effective approach to wastewater treatment that aligns with circular economy principles. This study explores the efficacy of electrocoagulation (EC) in treating dairy wastewater, focusing on the influence of treatment duration, voltage, and pH levels on BOD, COD, and turbidity reduction. Utilizing recycled aluminium electrodes derived from beverage cans, a Taguchi design of experiments with a 3-factor, 3-level orthogonal array was employed. Results from nine experiments reveal that higher voltages and alkaline pH levels notably enhanced COD and BOD removal efficiencies. For instance, high removal rates of 91.67 % for COD and 95.36 % for BOD were achieved at 20 V and pH 9 over a 15-minute treatment duration were obtained from experiments. Furthermore, optimal overall EC performance parameters were obtained using Taguchi and Multi-response optimization using TOPSIS. Analysis of turbidity removal efficiencies demonstrates the significant impact of voltage and treatment duration. The study provides valuable insights into optimizing electrocoagulation processes for efficient treatment of dairy wastewater, offering a sustainable solution for environmental preservation and resource recovery.
... Metal ions in water are particularly worrisome due to their toxicity, bioaccumulation through the food chain, and potential to harm aquatic ecosystems and human health [4,5]. While various removal methods such as ion exchange, chemical precipitation, reverse osmosis, and adsorption have been explored, many have limitations, including high costs and inefficiency in low-concentration scenarios [6,7]. Among these, adsorption has emerged as a preferred method due to its cost-effectiveness, simplicity, and adaptability [8]. ...
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... Альтернативой химической коагуляции является электрокоагуляция, которая оказалась эффективным методом осаждения загрязнителей промышленных сточных вод [6,7,8,9,10]. ...
... In the treatment of water with electrocoagulation, its use is reported for the removal of heavy metals such as chromium, cadmium, and nickel, among others, as well as other inorganic contaminants [1], [11], such as fluorides, phosphates and nitrates [12], [13], [14]. It has also been applied for the treatment of turbid water [15], as well as the removal of organic contaminants such as surfactants like linear alkylbenzene sulfate [3], phenolic substances [16] or distillery effluents [17]. ...
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... However, when more reactive metals are used as anodes, electrocoagulation is then possible. This technique involves the use of a cation-generating anode, typically iron or aluminum 115 . Once released into the solution, these cations facilitate the precipitation of cyanide as insoluble coordination complexes (e.g., Prussian blue) (Fig. 5). ...
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The main chemical, ecotoxicological, and environmental fate characteristics of cyanide, along with its treatment methods for cyanide-contaminated wastewater, were thoroughly examined. A global biogeochemical cycle of cyanide is proposed, covering the key physicochemical processes occurring in aqueous, soil, and atmospheric environments. The principles, advantages, and disadvantages of various treatment methods—including chemical, physicochemical, electrochemical, photochemical, and biological approaches—are evaluated. Finally, the feasibility of reusing cyanide waste is explored.
... Several non-AI models have been used to optimize the operating parameters. One approach utilized a multi-objective state transition algorithm (MOSTA) to compare different current reversal periods in the removal of lead [31]. It was demonstrated that varying current reversal periods (OS-VCRP) outperformed both manual setting (MS) and regular current reversal periods (OS-RCRP). ...
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This article examines the utilization of scrap metals as electrodes in the electrocoagulation process. Recent literature within the past two years focuses on optimizing electrode configuration, identifying the most effective scrap metals for electrocoagulation, exploring sustainable energy sources to power the electrodes, and fine-tuning process parameters. Traditional statistical methods like response surface methodology, as well as AI-based techniques, have been employed to optimize these process parameters. These techniques have emerged as tools for process optimization, control precision, and enhancing efficiency and quality. Consequently, they have significantly improved the removal efficiency of contaminants in wastewater. Future work should evaluate the applicability of AI- based models in managing systems that involve complex parameters specific to scrap metal electrodes. By fully leveraging the potential of scrap metals in electrocoagulation and optimizing the overall process, effective removal of contaminants can be achieved, contributing to the creation of cleaner and safer water systems.
... Several non-AI models have been used to optimize the operating parameters. One approach utilized a multi-objective state transition algorithm (MOSTA) to compare different current reversal periods in the removal of lead [31]. It was demonstrated that varying current reversal periods (OS-VCRP) outperformed both manual setting (MS) and regular current reversal periods (OS-RCRP). ...
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This article examines the utilization of scrap metals as electrodes in the electrocoagulation process. Recent literature within the past two years focuses on optimizing electrode configuration, identifying the most effective scrap metals for electrocoagulation, exploring sustainable energy sources to power the electrodes, and fine-tuning process parameters. Traditional statistical methods like response surface methodology, as well as AI-based techniques, have been employed to optimize these process parameters. These techniques have emerged as tools for process optimization, control precision, and enhancing efficiency and quality. Consequently, they have significantly improved the removal efficiency of contaminants in wastewater. Future work should evaluate the applicability of AI- based models in managing systems that involve complex parameters specific to scrap metal electrodes. By fully leveraging the potential of scrap metals in electrocoagulation and optimizing the overall process, effective removal of contaminants can be achieved, contributing to the creation of cleaner and safer water systems.
... Consequently, it is necessary to increase the current densities to produce an equivalent quantity of Al 3+ ions at the aluminium anode, as opposed to the Fe 2+ and Fe 3+ ions formed at the iron anode. Iron anodes have a higher ability to produce metal hydroxides with the same current density, leading to improved metalremoval efficiency [32]. This significant effect can be seen in Hg, where the Fe electrode provides a higher removal efficiency than the Al electrode. ...
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This study uses electrocoagulation to investigate reducing heavy metal content in wastewater from discharging spent batteries. ICP-OES analysis shows that heavy metals exceed the environmental water standard. The electrocoagulation procedure was conducted within a reactor with a 500 mL volume and a rectifier with a 5 A current capacity. Three types of electrode material combinations were used: iron (Fe) and aluminium (Al) as well as Fe-Fe, Al-Al, and Fe-Al pairs with 1 cm in the distance by parallel monopolar cells. Alternating current was used with 30, 40, and 50 A/m2 current density. The best result shown in the Fe-Al electrode pair combination system at 40 A/m2 for 30 min contact time and removal efficiencies for Co, Cd, Ni, Zn, and As is 98.76, 90.73, 99.32, 97.93, and 97.78%, respectively, while for Hg it is 31.84%, even though only Cd is above the standard limit. The heavy metal bearing was confirmed using SEM-EDS in the floc and the precipitate residue. The dissolved electrode materials and electrical energy consumed are 0.32 g and 0.109 kWh/m3, respectively. This method can be a good alternative for treating wastewater compared to direct current electrocoagulation, where the electrode and energy will be less consumed.
... ECF is considered a successful technology in terms of removing metallic pollutants (Yasasve et al., 2022) and suspended solids, as well as oils and greases (Lu et al., 2021). Kim et al. (2020) found that metal removal by ECF occurs through co-precipitation, adsorption, and sedimentation mechanisms. Regarding the removal of oils and grease, Khalifa et al. (2020) deduced that the adsorption mechanism and the entrapment of oil emulsions in insoluble complexes are the main contributors to the removal of these contaminants. ...
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... The EC produces directly coagulating species in the medium to be treated through the electrochemical oxidation of submerged metal anodes, this advanced technology combines principles of flotation, coagulation, and electrochemistry (Moussa et al., 2017). In particular, the electrocoagulation technique has been used to treat quantities ranging from tens to hundreds of milligrams per liter of heavy metals such as Chromium (Cr), Nickel (Ni), Zinc (Zn), Copper (Cu), and others (Kim et al., 2020). ...
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... Previous studies used EC to assess the effect of physicochemical parameters on copper reduction in aqueous solutions (Kim et al., 2020;Vasudevan et al., 2012a). However, these studies were mainly concerned with the effect of a single factor, so they could not show the interactions of the parameters on copper reduction in aqueous systems. ...
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The current study presents an overview of heavy metals bioremediation from halo–alkaline conditions by using extremophilic microorganisms. Heavy metal remediation from the extreme environment with high pH and elevated salt concentration is a challenge as mesophilic microorganisms are unable to thrive under these polyextremophilic conditions. Thus, for effective bioremediation of extreme systems, specialized microbes (extremophiles) are projected as potential bioremediating agents, that not only thrive under such extreme conditions but are also capable of remediating heavy metals from these environments. The physiological versatility of extremophiles especially halophiles and alkaliphiles and their enzymes (extremozymes) could conveniently be harnessed to remediate and detoxify heavy metals from the high alkaline saline environment. Bibliometric analysis has shown that research in this direction has found pace in recent years and thus this review is a timely attempt to highlight the importance of halo-alkaliphiles for effective contaminant removal in extreme conditions. Also, this review systematically presents insights on adaptive measures utilized by extremophiles to cope with harsh environments and outlines the role of extremophilic microbes in industrial wastewater treatment and recovery of metals from waste with relevant examples. Further, the major challenges and way forward for the effective applicability of halo-alkaliphilic microbes in heavy metals bioremediation from extremophilic conditions are also highlighted.
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In this study, the effectiveness of integrating electrocoagulation (EC) and ultrafiltration (UF) membranes for palm oil mill effluent (POME) wastewater treatment was investigated. The impact of various parameters on contaminant removal efficiency, including electrode configuration (monopolar and bipolar), number of anodes, agitation rate, and current density, was studied. The findings demonstrated that using bipolar (BP) electrodes in the EC reactor improved coagulation efficiency. However, an increase in agitation rate led to a decrease in removal efficiency. The electrode configuration of 2A-2C–2B achieved high contaminant removal with a lower electrode consumption compared to the 4A-2C and 4A-2C–2B configurations. The removal efficiencies for total dissolved solids (TDS), total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD) were 59.1%, 99.9%, 96.8%, and 96%, respectively. The operating cost for the electrode configuration of 2A-2C–2B was estimated to be 2.71 USm3ataneffluentcapacityof50m3d1and20hd1ofoperatingtime,whiletheenergyrequirementwas6.20kWhm3.Anincreaseinoperatingtimefrom5to24hd1raisedthespecificoperatingcostfrom2.17to2.85US m−3 at an effluent capacity of 50 m3 d−1 and 20 h d−1 of operating time, while the energy requirement was 6.20 kWh m−3. An increase in operating time from 5 to 24 h d−1 raised the specific operating cost from 2.17 to 2.85 US m−3. This study provides valuable insights into optimizing EC and UF processes for POME wastewater treatment, which could have significant implications for sustainable industrial practices.
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The confectionery wastewater contains high amount of biodegradable organic matter with an acidic characterization that should be treated before the discharge to receiving water bodies. The post-treatment method should be combined with biological treatment in order to enhance the treatment performance. In this study, chemical coagulation (CC) and electrocoagulation (EC) processes were studied as post-treatment methods for anaerobically treated confectionery wastewater. The influences of operational conditions such as pH, coagulant dosage for CC process and pH, current density, treatment time, electrode connection type for EC process were investigated. The conditions were optimized based on treatment performance and operating cost. Scanning electron microscopy–energy-dispersive index (ESEM–EDX) analysis was performed for the sludge samples. The removals of 65% COD, 84% SS and 93% DFZ436 were obtained using ferric chloride in CC process. EC process with Fe electrode achieved better removals compared with CC providing 77% COD, 93% SS, 93% DFZ436, 84% sulphate and 60% chloride removals under the optimized conditions (pH 8, 90 A/m2, 75 min, MP–P). Although EC process provided a higher operating cost (5.9 /m3)comparedwithCCprocess(5.4/m3) compared with CC process (5.4 /m3), it was able to meet the discharge standards for confectionery industry effluent.
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This review focuses on combined biological treatment with electrocoagulation as a post-polishing process to enhance treated effluents quality. We analyzed the main findings found in the literature and discussed many parameters used to optimize the process. Some studies used biological-pretreated wastewater while others applied combined system consisted of biological step followed by electrocoagulation step. The effluent quality in this combined system has been improved since more pollutants have been removed, especially when using an aluminum electrode. The main problems associated with the electrocoagulation process are energy consumption and electrode passivation. We presented many concluding remarks and recommendations for further studies. ARTICLE HISTORY
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The combination of electrocoagulation with another process is a promising approach to enhance the removal efficiency of water pollutants. For instance, free radical-assisted electrocoagulation is a new combination showing higher performance. There are different combinations depending on the free radical source. This article reviews free radical-assisted electrocoagulation processes. We discuss electrocoagulation mechanisms; ozone-assisted electrocoagulation processes; advanced oxidation-assisted electrocoagulation processes; and ultrasound-assisted electrocoagulation. We present kinetic models used in free radical-assisted electrocoagulation, scale-up of free radical-assisted electrocoagulation and cost estimation. The major points are: most of the available studies have been done at laboratory scale with synthetic wastewater, and lack holistic and systematic approaches to consider the process complexity. The performance of the combined process is improved, and the removal efficiency is increased especially with ozone-assisted electrocoagulation, which gives a removal efficiency of more than 95%. The use of ultrasound energy with electrocoagulation is advantageous in reducing the problem of electrode passivation.
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A vast number of publications have investigated the application of electrocoagulation (EC) process heavy metal ions removal from wastewaters. Most of these studies were simple lab-scale using synthetic wastewater with the absence of holistic and systematic approach to consider the process complexity. This comprehensive review considers the fundamental aspects of EC processes such as mechanisms, kinetic models and isotherm models used by different researchers. Furthermore, the impact of the main design and process operational parameters on the removal efficiency is discussed and analyzed. Many concluding remarks and perspectives were stated to give insights for possible future investigations.
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Methods for treating industrial wastewater containing heavy metals often involve technologies for reduction of toxicity in order to meet technology-based treatment standards. This article was focused on the recently developed and newly applicable various treatment processes for the removal of heavy metals from industrial wastewater. Physico-chemical removal processes such as; adsorption on new adsorbents, ion exchange, membrane filtration, electrodialysis, reverse osmosis, ultrafiltration and photocatalysis were discussed. Their advantages and drawbacks in application were evaluated. In the processes of biological treatments microorganisms play a role of settling solids in the solution. Activated sludge, trickling filters, stabilization ponds are widely used for treating industrial wastewater. Bioadsorption is a new biological method and various low cost bioadsorbents (agricultural waste, forest waste, industrial waste, algae etc.) are used for maximum removal of heavy metals from wastewater. Bioadsorption techniques are eco friendly best solutions for removing heavy metals from wastewater rather than physic-chemical methods. But chemical methods are most suitable treatments for toxic inorganic compounds produced from various industries which cannot removed from any biological and physical techniques.
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Heavy metals pollution has become a more serious environmental problem in the last several decades as a result releasing toxic materials into the environment. Various techniques such as physical, chemical, biological, advanced oxidation and electrochemical processes were used for the treatment of domestic, industrial and agricultural effluents. The commonly used conventional biological treatments processes are not only time consuming but also need large operational area. Accordingly, it seems that these methods are not cost-effective for effluent containing toxic elements. Advanced oxidation techniques result in high treatment cost and are generally used to obtain high purity grade water. The chemical coagulation technique is slow and generates large amount of sludge. Electrocoagulation is an electrochemical technique with many applications. This process has recently attracted attention as a potential technique for treating industrial wastewater due to its versatility and environmental compatibility. This process has been applied for the treatment of many kinds of wastewater such as landfill leachate, restaurant, carwash, slaughterhouse, textile, laundry, tannery, petroleum refinery wastewater and for removal of bacteria, arsenic, fluoride, pesticides and heavy metals from aqueous environments. The objective of the present manuscript is to review the potential of electrocoagulation process for the treatment of domestic, industrial and agricultural effluents, especially removal of heavy metals from aqueous environments. About 100 published studies (1977-2016) are reviewed in this paper. It is evident from the literature survey articles that electrocoagulation are the most frequently studied for the treatment of heavy metal wastewater.
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Treatment of industrial wastewaters by electrocoagulation is very efficient to remove numerous types of pollutant (organic, mineral, colored, metal). However, few researches are devoted to the elimination of metals contained in the generated sludge. The objective of this paper was to study the possible simultaneous removal of aluminum (issued from the electrodes) and chromium (initially present in the effluent) contained in the sludge by electrochemical migration. Electrocoagulation treatment of textile industrial wastewater in which chromium has been added was carried out using aluminum electrodes. Turbidity, COD, and TOC could be efficiently removed with abatement yields, respectively, at 97, 93, and 90%. For chromium, only 62% of the initial amount was eliminated by applying the highest current with a long operating time. The generated sludge contained high amounts of Cr and Al (749 and 1,260 mg/kg of dry sludge), far above the maximum level allowed by legislation. The possibility of removing these pollutants from the resulting sludge using electrokinetic technique was investigated. Acetic acid at 1 or 3 M and citric acid at 3 and 6 M were used as catholyte solutions to enhance the removal of aluminum and chromium(III). Best results for aluminum removal were obtained using 3 M acetic acid: up to 82% of the initial Al was recovered in the cathode chamber, whereas citric acid was more effective in chromium removal: up to 79% was transported to the cathode chamber with 6 M citric acid. Specific energy consumption is also discussed.
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In this work, the performance of batch electrocoagulation (EC) using iron electrodes with monopolar configuration for simultaneous removal of copper (Cu), nickel (Ni), zinc (Zn) and manganese (Mn) from a model wastewater was investigated. The influences of current density (from 2 to 25 mA/cm2), initial metal concentration (from 50 to 250 mg/L) and initial pH (3, 5.68, 8.95) on removal efficiency were explored in a batch stirred cell to determine the best experimental conditions.The results indicated that EC was very efficient to remove heavy metals from the model wastewater having an initial concentration of 250 mg/L for each metal under the best experimental conditions. According to initial pH results, high pH values are more suitable for metal removal with EC treatment. At the current density of 25 mA/cm2 with a total energy consumption of ∼49 kWh/m3, more than 96% removal value was achieved for all studied metals except Mn which was 72.6%.
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Innovative processes for treating industrial wastewater containing heavy metals often involve technologies for reduction of toxicity in order to meet technology-based treatment standards. This article reviews the recent developments and technical applicability of various treatments for the removal of heavy metals from industrial wastewater. A particular focus is given to innovative physico-chemical removal processes such as; adsorption on new adsorbents, membrane filtration, electrodialysis, and photocatalysis. Their advantages and limitations in application are evaluated. The main operating conditions such as pH and treatment performance are presented. Published studies of 94 cited references (1999–2008) are reviewed.It is evident from survey that new adsorbents and membrane filtration are the most frequently studied and widely applied for the treatment of metal-contaminated wastewater. However, in the near future, the most promising methods to treat such complex systems will be the photocatalytic ones which consume cheap photons from the UV-near visible region. They induce both degradation of organic pollutants and recovery of metals in one-pot systems. On the other hand, from the conventional processes, lime precipitation has been found as one of the most effective means to treat inorganic effluent with a metal concentration of >1000mg/L. 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, plant simplicity and cost-effectiveness are the key factors in selecting the most suitable treatment for inorganic effluent
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Experiments were performed in batch mode of operation using iron electrodes to remove chromium from effluent by electro-coagulation, and the effect of various operating parameters was investigated. The maximum hexavalent chromium removal efficiency of 100% from a synthetic solution containing hexavalent chromium was obtained for an electrolysis time of 15 min at the optimum current density of 50 mA cm −2 , interelectrode distance 0.5 cm, and solution pH of 4. The real electroplating industry effluent was characterized using the standard diphenylcarbazide (DPC) method. A 100% chromium removal efficiency was obtained for both trivalent and hexavalent chro-mium, for an electrolysis time of 45 min at 4 pH. It was found that Cr(VI) is initially reduced to Cr(III) in the acidic medium. An increase in the pH of the effluent was also noticed in the acidic medium due to the generation of hydroxyl ions. Experiments were performed for the removal of chromium using ferric chloride as the coagulant, and it was found that electrocoagulation is more efficient and relatively faster compared to chemical coagulation. DOI: 10.1061/(ASCE)HZ.2153-5515.0000170. © 2013 American Society of Civil Engineers.
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The nickel(II) ions biosorption process by marine algae Sargassum filipendula in a fixed bed column was investigated for the following experimental conditions: temperature = 30 °C and pH 3.0. The experimental breakthrough curves were obtained for the following chosen flow rates 0.002, 0.004, 0.006, and 0.008 L/min. A mathematical model was developed to describe the nickel ion sorption in a fixed bed column. The model of three partial differential equations (PDE) has considered the hydrodynamics throughout the fixed bed column as well as the sorption process in the liquid and solid phases. The internal and external mass transfer limitations were considered, as well. The nickel ion sorption kinetics has been studied utilizing the Langmuir isotherm. The PDE of the system were discretized in the form of ordinary differential equations (ODE) and were solved for the given initial and boundary conditions using the finite volume method. A new correlation for external mass transfer coefficient was developed. Some of the model parameters were experimentally determined (ɛ, dp) where the others such as (KF, KS) were evaluated on the base of experimental data parameters. The identification procedure was based on the least square statistical method. The robustness and flexibility of the developed model was checked out using four sets of experimental data and the predictive power of the model was evaluated to be good enough for the all studied cases. The developed model can be useful tool for nickel ion removal process optimization and design of fixed bed columns using biomass of S. filipendula as a sorbent.
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The adsorption characteristics of zeolites synthesized from fly ash were combined in a composite with the magnetic properties of iron oxides to produce adsorbents which were magnetic materials. Such zeolite/iron oxide magnetic composites were prepared with weight ratios of 3:1, 2:1 and 1:1. The experimental data for the equilibrium adsorption isotherms of Zn ²⁺ ions onto the composites were modelled using the Freundlich and Langmuir equations. The presence of iron oxide had no significant effect on the adsorption capacities of the magnetic composites. The experimental data were also employed to determine the kinetic characteristics of the adsorption process. The adsorption of Zn ²⁺ ions was found to follow pseudo-second-order type kinetics. Although intra-particle diffusion occurred in the adsorption processes, it could not be accepted as the primary rate-determining step. The evaluated thermodynamic parameters indicated that the adsorption of Zn ²⁺ ions onto zeolite/iron composites was spontaneous and endothermic.
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The purpose of this study was to investigate the effects of the operating parameters. such as pH, initial concentration (C(i)), duration of treatment (t), current density (j). interelectrode distance (d) and conductivity (K) on the treatment of a synthetic wastewater in the batch electrocoagulation (EC)-electroflotation (EF) process. The optimal operating conditions were determined and applied to a textile wastewater. Initially a batch-type EC-EF reactor was operated at various current densities ranging from 11.55 to 91.5 mA/cm(2) and various electrode gaps (1, 2 and 3 cm). For solutions with 300 mg/L of silica gel, good turbidity removal (89.6%) was obtained without any coagulant when the current density was 11.55 mA/cm(2), and with initial pH at 7.6, conductivity at 2.1 mS/cm: the treatment time was hold for 10 min and the electrode gap was 1 cm. Application of the optimal operating parameters on a textile wastewater showed a high removal efficiency for the following variables: suspended solid (SS) 85.5%, turbidity 76.2%, biological oxygen demand (BOD(5)) 88.9%, chemical oxygen demand (COD) 79.7%, and color over 93%.
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In this study, we developed a UV-LED/H2O2/Cu2+ system to remove cyanide, which is typically present in metal electroplating wastewater. The results showed the synergistic effects of UV-LED, H2O2, and Cu2+ ions on cyanide removal in comparison with UV-LED photolysis, H2O2 oxidation, UV-LED/H2O2, and H2O2/Cu2+ systems. Cyanide was removed completely in 30 min in the UV-LED/H2O2/Cu2+ system, and its loss followed pseudo-first order kinetics. Statistically, both H2O2 and Cu2+ ions showed positive effects on cyanide removal, but Cu2+ ions exhibited a greater effect. The highest cyanide removal rate constant (k = 0.179 min-1) was achieved at pH 11, but the lowest was achieved at pH 12.5 (k = 0.064 min-1) due to the hydrolysis of H2O2 (pKa of H2O2 = 11.75). The presence of dissolved organic matter (DOM) inhibited cyanide removal, and the removal rate constant exhibited a negative linear correlation with DOM (R2 = 0.987). The removal rate of cyanide was enhanced by the addition of Zn2+ ions (from 0.179 to 0.457 min-1), while the co-existence of Ni2+ or Cr+6 ion with Cu2+ ion reduced cyanide removal. The formation of OH radicals in the UV-LED/H2O2/Cu2+ system was verified using an aminophenyl fluorescence (APF) probe. Cyanate ions and ammonia were detected as the byproducts of cyanide decomposition. Finally, an acute toxicity reduction of 64.6% was achieved in the system within 1 h, despite a high initial cyanide concentration (100 mg/L). In terms of removal efficiency and toxicity reduction, the UV-LED/H2O2/Cu2+ system may be an alternative method of cyanide removal from wastewaters.
Article
In this work, the research focused on the Zn2+ removal from the synthetic wastewater by electrocoagulation (EC) with aluminum electrodes. The effects of current density (2.1–12.5 mA/cm2), initial concentration (50–2000 mg/L), solution pH (2.9–7.4) and conductivity (0.15–14.11 mS/cm) on the removal efficiency and energy consumption were systematically investigated. It indicated that Zn2+ removal efficiency increased with the increasing of current density and residence time. With a relatively low energy consumption of 0.35 kWh/m3, all of Zn2+ (50 mg/L) was removed in 20 min EC treatment, 8.3 mA/cm2 for current density, and 5.3 for pH. With an energy consumption of 0.88 kWh/m3, all of Zn2+ (250 mg/L) were removed in 50 min. In addition, kinetic study was applied to analyze Zn2+ removal rate at different current densities and initial concentrations. Different mechanisms of Zn2+ removal were implied by comparing the results of low initial concentration (≤250 mg/L) and high one (≥500 mg/L). It was reasonable to conclude that, besides the precipitation effect of aluminum hydroxide flocculation, electrochemical reduction of Zn2+ at the cathode also contributed to Zn2+ removal, especially at a high initial concentration.
Article
The problem of water pollution is of a great concern. Adsorption is one of the most efficient techniques for removing noxious heavy metals from the solvent phase. This paper presents a detailed information and review on the adsorption of noxious heavy metal ions from wastewater effluents using various adsorbents - i.e., conventional (activated carbons, zeolites, clays, biosorbents, and industrial by-products) and nanostructured (fullerenes, carbon nanotubes, graphenes). In addition to this, the efficiency of developed materials for adsorption of the heavy metals is discussed in detail along with the comparison of their maximum adsorption capacity in tabular form. A special focus is made on the perspectives of further wider applications of nanostructured adsorbents (especially, carbon nanotubes and graphenes) in wastewater treatment.
Article
The electrocoagulation (EC) process is an electrochemical means of introducing coagulants and removing suspended solids, colloidal material, and metals, as well as other dissolved solids from water and wastewaters. EC process has been successfully employed in removing pollutants, pesticides, and radionuclides. This process also removes harmful microorganisms. More often during EC operation, direct current is applied and electrode plates are sacrificed (dissolved into solution). The electrodissolution causes an increased metal concentration in the solution that finally precipitates as oxides and hydroxides. Due to the process design and low cost material, the EC process is widely accepted over other physicochemical processes. In this frame, this paper presents a general review of efficient EC technologies developed to remove organic and inorganic matter from wastewaters for environmental protection. Fundamentals and main applications of EC as well as progress of emerging EC treatments are reported. The influence of iron or aluminum anode on depollution of synthetic or real effluents is explained. The advantages of EC mechanisms with Al and Fe electrodes are extensively discussed. There are presented the advanced EC processes with in situ generation of hydroxyl radical. The importance of the operating parameters for efficient application of the EC process as well as the combination of this electrochemical technology with electroanalysis techniques and other technologies are commented.
Article
Electrocoagulation was investigated for the removal of copper, silicon, manganese, aluminum, iron and zinc as well as sulfate from real mine water. Batch experiments with monopolar iron anode and stainless steel cathode as well as monopolar aluminum anode and stainless steel cathode were conducted separately to identify the best electrocoagulation conditions. The removal efficiency in mine water increased with increasing reaction time and increasing current density and the type of electrodes affected the metals and sulfate removal as could be shown by the adsorption isotherms. Copper and silicon were obeying a Langmuir isotherm with an iron anode, whereas they were following a Freundlich isotherm when an aluminum anode was applied. The aluminum electrode resulted in a higher Langmuir constant qmax for all metals, while the iron electrode showed a better efficiency for removing the metals. This might be a result of the higher kinetic rate of iron compared to aluminum. Sulfate removal was better with aluminum electrodes resulting in removal rates of up to 41%, removing up to 5700 mg/L sulfate from the initial sulfate concentrations, whereas iron could only remove 3833 mg/L of sulfate from the real mine water. Furthermore, sulfate removal by aluminum electrode was faster compared to iron electrode.
Article
Treatments of alkaline non-cyanide, alkaline cyanide and acidic zinc electroplating rinse wastewaters were investigated in an electrocoagulation (EC) reactor using Fe plate electrodes. This is the first study involved with removals of zinc and cyanide together from three different wastewaters in the literature. The effects of the operating parameters namely, initial pH (pHi), current density and operating time on the removal efficiencies were evaluated. The removal efficiencies and operating costs were determined as 99.8% for Zn and 0.74 €/m³ at a pH of 7, 80 A/m² and 60 min for alkaline non-cyanide, 99.9% for Zn, 99.9% for CN and 1.72 €/m³ at a pH of 9.5, 60 A/m² and 60 min for alkaline cyanide, and 99.9% for Zn and 2.26 €/m³ at a pH of 8, 80 A/m² and 60 min for acidic zinc electroplating wastewaters, respectively. Moreover, toxicity test was conducted to obtain information about the toxic effect of the raw and treated wastewaters. The toxicity results indicated that all the raw wastewaters contained hardly toxic effect (EC50 for acidic, alkaline cyanide and alkaline non-cyanide were 0.62, 5.25 and 3.38). On the other hand, the treated wastewater was non-toxic. This study revealed that the EC process with Fe electrode was very effective for removal of zinc and cyanide ions from different zinc electroplating rinse wastewaters.
Article
Electrocoagulation process (EC) has been the subject of several reviews in the last decade, and is still a very active area of research. Most published works deals with applications for treatment of drinking water and urban, industrial or agricultural wastewaters so as to enhance the simultaneous abatement of soluble and colloidal pollution. These also include contributions to theoretical understanding, electrode materials, operating conditions, reactor design and even techno-economic analysis. Even though, the numerous advantages reported in the literature, and the pros and cons of EC in comparison to alternative processes, its industrial application is not yet considered as an established wastewater technology because of the lack of systematic models for reactor scale-up. This paper presents a comprehensive review on its development and design. The most recent advances on EC reactor modeling are summarized with special emphasis on four major issues that still constitute the cornerstone of EC: the theoretical understanding of mechanisms governing pollution abatement, modeling approaches, CFD simulations, and techno-economic optimization. Finally, outlooks for future research and developments are suggested.
Article
Low-cost by-products from agricultural, household and industrial sectors have been recognized as a sustainable solution for wastewater treatment. They allow achieving the removal of pollutants from wastewater and at same time to contribute to the waste minimization, recovery and reuse. Despite numerous reviews have been published in the last few years, a direct comparison of data obtained using different sorbents is difficult nowadays because of inconsistencies in the data presentation. In this context, the aim of the study was to revise the current literature concerning the application of low-cost adsorbents for wastewater treatment highlighting, systematically, both adsorbents characteristics and adsorption capacities. For this scope, low-cost sorbents have been divided into the following five groups: (i) Agricultural and household wastes, (ii) industrial by-products, (iii) sludge, (iv) sea materials, (v) soil and ore materials and (vi) novel low-cost adsorbents. The affinity of sorbents in removing various pollutants, their applications on real wastewater, costs and considerations on their reuse after adsorption processes, has been discussed. Finally, in order to better highlights the affinity of sorbents for more pollutants (dyes, heavy metals, biorecalcitrant compounds, nitrogen and phosphate compounds), simple methodological tools such as “adsorbents-pollutants” matrices have been proposed and applied. In this manner, the adsorbent candidates for replacing commercial activated carbons have been identified.
Article
A batch electrocoagulation study was conducted using aluminium electrodes to check the treatability of synthetic bilge water. The studies were conducted to investigate the effect of various operational parameters on the treatment efficiency. At a pH of 7, applied voltage of 10 V, spacing of 1 cm and effective electrode area of 45 cm2, a maximum soluble COD (CODS) removal efficiency of 85% was obtained after an electrolysis time of 120 min. The second order rate constant was derived and a maximum rate constant of 3 × 10-6 L/mg-min was observed at optimum experimental conditions. CODS experimental measurements give an acceptable fit for both Langmuir model and Freundlich isotherm models. A comparative study between electrocoagulation and chemical coagulation was performed and chemical coagulation showed only 59.3% removal efficiency. The sludge formed after the electrocoagulation process was characterized for mineral composition and functional groups. XRD and FTIR results represent the formation of aluminium hydroxide during electro coagulation process and the presence of hydrocarbons and heavy metals in the sludge indicates the removal of these pollutants from bilge water by electrocoagulation process. Among different electrode combinations of aluminium and iron, Al-Al combination showed maximum removal efficiency. A case study on real bilge water was conducted and a maximum removal of 89.84% was obtained at optimum conditions using aluminium electrodes.
Article
This work explores the possibility of using electrocoagulation to remove phenolic compounds fromoil refinery waste effluent using an electrochemical reactor with a fixed bed anode made of randomly oriented Al raschig rings packed in a perforated plastic basket located above the horizontal cathode.The removal of phenolic compounds was investigated in terms of various parameters in batch mode namely: pH, operating time, current density, initial phenol concentration, addition of NaCl, temperature and the effect of phenol structure (effect of functional groups). The chemical oxygen demand (COD) was also measured. In order to throw some light on the economics of the process, energy consumption as well as Al consumption were calculated under different conditions. The study revealed that the optimum conditions for the removal of phenolic compounds were achieved at current density = 8.59 mA/cm2, pH = 7, NaCl concentration = 1 g/L and temperature of 25°C. Remarkable removal of 100% of phenol compound after 2 hrs can be achieved for 3 mg/L phenol concentration of real refinery wastewater. The new anode design of electrocoagulation cell permits high efficiencies with lower energy consumption in comparison with other cell design used in previous studies.
Article
Ion chromatography (IC) for the separation and determination of the cyanide ion and metal cyanide complexes is reviewed. The United States Environmental Protection Agency (USEPA) classifies cyanides as hazardous substances, hazardous waste constituents and priority toxic pollutants. IC is a reliable analytical technique that is not affected by the high salt concentration typical of process and environmental samples. The technique of IC is routinely used for the analysis of wastewater, soils and sediments, plating solutions and hydrometallurgical effluent for cyanides and other ions. IC provides knowledge of all cyanide species, free and complexed (to metal) and conveniently provides speciation information for different oxidation states, for example, iron II and III, and gold I and III cyanide complexes. This obviates the necessity for distillation to convert metal cyanide species to hydrogen cyanide for determination of total cyanide. Detection limit ranging down to 1μg/L CN− and 5üg/L Au(CN)2−, without preconcentration, have been reported.
Article
The solubilities of freshly precipitated and aged hydroxides of 21 metals have been calculated. The initial data set used for calculations comprised the stability constants and solubility products of hydroxides. The compositions and pHs of saturated solutions and the solubilities of hydroxides are dictated by the polarizing ability of charged metal atoms. The results of solubility calculations are in satisfactory agreement with experimental values.
Article
Of late, electrocoagulation has been widely used to treat a wide variety of wastewaters, including textile, dye, electroplating, chemical mechanical polishing wastewaters, etc. Excessive coagulant material may be avoided by electrocoagulation. The contaminants present in wastewaters are maintained in solution by electrical charges. When metal ions of opposite electric charge, provided by an electrocoagulation system, may become unstable and precipitate in a form that is usually very stable. The present work involves the treatment of nearby restaurant effluent in Surat, Gujarat, India. Two different electrodes, aluminum and iron, are used for electrocoagulation. The effect of applied voltage and time of electrolysis on various parameters - such as conductivity, COD, TDS, and turbidity are studied. The removal efficiency of COD is found to be between 50-72% and the optimum time is between 15-30 minutes. Electrocoagulation proved to be a process which could neutralize pH significantly. The major impact of change in electrode is considered and aluminum is found to be better than iron in many respects. The operating cost is estimated from the power cost and cost of electrode material.
Article
In this study, effects of both Fe and Al electrode connection modes (parallel and series) and electrode materials on arsenic removal efficiency from potable water by electrocoagulation (EC) process were investigated. Experiments were carried out to remove arsenic by the EC covering wide range in operating conditions such as pH (4–9), current density (1.75–7.5A/m2) and operating time (0–15min). The highest arsenic removal was obtained in the monopolar series (MP-S) electrode connection mode for both electrodes as pH 6.5 for Fe and pH 7 for Al electrodes to achieve a residual arsenic concentration of 10μg/L or less for potable water in the EC process. As the current density increased, arsenic removal efficiencies were increased with all types of electrode connection modes. However, the optimum arsenic removal at 2.5A/m2 was obtained with 2.5min of operating time for Fe (94.1%) and 4min of operating time (93.5%) for Al electrodes at MP-S mode. The electrode and energy consumption values at MP-S connection mode for Fe and Al electrodes were calculated as 0.00140kgFe/m3 and 0.0025kgAl/m3, and 0.0140kWh/m3 and 0.0254kWh/m3, respectively. Therefore, the lowest operating costs were 0.0047€/m3 and 0.0064€/m3 for Fe and Al electrodes. The optimum arsenic removal from potable water by the EC process showed that Fe electrodes gave the best results at MP-S connection mode as compared to the rest in terms of operating time and operating cost. The sludge was analyzed using scanning electron microscope (SEM) imaging. The SEM image suggested that amorphous Fe/Al oxyhydroxides were present in the sludge.
Article
The ability of electrocoagulation to remove Cr(III) from aqueous solutions is studied using aluminium anode and taking into account many factors such as pH, potential, time and temperature.In order to check these factors and their effects on the electrocoagulation of Cr(III), we have established a model of this technique following a methodological strategy using experiments design. The mathematical model is established, using a central composite design rotatable and uniform. The model describes the change of the measured responses of chromium removal efficiency, energy consumption and aluminium dissolved according to the pH, potential, time and temperature.The graphical representation of this model in the space of the variables enabled us to define the optimum conditions for these parameters. The optimum value of pH, potential, time and temperature are respectively 4.23, 9.14V, 10min, and 27.5°C. An efficiency of 91% of the removal chromium is observed with an energy consumption of 3.536kWh/m3.
Article
The nature of Cu 2+ adsorption by boehmite, gibbsite, and noncrystalline alumina was studied over a range of equilibrium pH (4.5-7.5) and Cu 2§ concentration (10 a-10 -8 M) by electron spin resonance (ESR). Available chemisorption sites at pH 4.5 were the most numerous for noncrystalline alumina (-1 mmole/100 g), less for boehmite, and least for gibbsite as indicated by the relative strength of the rigid-limit ESR signal attributed to Cu z+ adsorbed at discrete sites. The chemisorption process involved immobili- zation of Cu 2+ by displacement of one or more H20 ligands by hydroxyl or surface oxygen ions, with the formation of at least one Cu-O-AI bond. As the pH was raised from 4.5 to 6.0, essentially all of the solution Cu 2+ appeared to be adsorbed by the solids. However, the noncrystalline alumina and boehmite chemi- sorbed much of the total adsorbed Cu 2+ (10 mmole/100 g), whereas precipitation or nucleation of Cu(OH)~ in the gibbsite system was indicated. Precipitated Cu z+ was more readily redissolved by exposure to NH3 vapor than chemisorbed Cu 2+.
Article
The electrocoagulation process (ECP) was investigated for the removal of cyanide fromwastewater in batch and continuous operation under different conditions. The batch experiments indicated that an iron–aluminum electrode arrangement as anode–cathode attained the highest removal efficiency. The increase of the current densities of 2 to 15 mA/cm2 resulted in an increase of cyanide removal from43% to 91.8% after 20 min of reaction in the absence of aeration. Under similar conditions, aeration of the reactor enhanced removal efficiencies from 45% to 98%. Continuous operation of the ECP reactor with various hydraulic retention times (HRT) led to an increase of cyanide removal from57% at anHRT of 15 min to complete elimination at anHRT of 140 min. Thus,we conclude that electrocoagulation is a cost-effective promising process for efficient treatment of cyanide-laden wastewater.
Article
The electrocoagulation (EC) treatment of Acid Blue 113 (AB 113) was performed on the basis of chemical oxygen demand (COD) removal efficiency using an iron anode. The process variables, including current density (1–5 A/dm2), pH (5.5–7.5), and supporting electrolyte concentration (1–3 g/L) were investigated. Under the optimum operating conditions, more than 91% COD removal efficiency was found. The optimum conditions were obtained with 3 A/dm2 of current density, pH 6.5, and 2 g/L of supporting electrolyte concentration. COD removal rates obtained during the EC process can be described using a pseudo-kinetic model. The experimental kinetic data fit well with pseudo first-order kinetic model, with no significant change on the rate constant after 3 A/dm2 of current density. The absorption spectra and Fourier transform infra red analysis were also performed to characterize the mechanism and nature of dye cleavage.
Article
Removal of copper (Cu), chromium (Cr) and nickel (Ni) from metal plating wastewater by electrocoagulation with iron and aluminum electrodes with monopolar configurations was investigated. The influence of electrode material, current density, wastewater pH and conductivity on removal performance was explored. The results showed that metal removal increased with increasing current density, pH and conductivity. The efficiency of different electrode materials (iron, aluminum) was compared. The results indicated that electrocoagulation with an Fe–Al electrode pair was very efficient and was able to achieve 100% Cu, 100% Cr and 100% Ni removal at an electrocoagulation time of 20 min, a current density of 10 mA/cm2 and a pH of 3.0. Corresponding energy and electrode consumptions were determined as 10.07 kWh/m3 and 1.08 kg/m3, respectively.Graphical abstractResearch highlights► Electrocoagulation treatment achieves a fast and effective reduction of metals. ► The Fe-Fe and Fe-Al electrode combinations were more effective for metal removal. ► The highest current density (10 mAcm−2) produced the quickest treatment.