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Estimating Dosing Rates and Energy Consumption for Electrocoagulation Using Iron and Aluminum Electrodes
Abstract
The effect of current density on dosing rates and energy requirements for iron and aluminum electrodes in a bench-scale electrocoagulation (EC) reactor have been investigated. Dissolution rates of the iron and aluminum anodes were independent of bulk solution pH values. Iron dosing rates followed Faraday’s law, but aluminum dosing rates averaged 83% greater than those predicted by Faraday’s law. Chemical corrosion of both the anode and cathode contributed to the extra-faradaic aluminum dosing. A method was developed to determine the faradaic power consumption as a function of the current density. An equation describing power dissipation by ohmic and faradaic mechanisms was derived and used to estimate energy consumption per unit coagulant dose for EC reactors operating over a wide range of conditions. The derived equation can be used to compare the operational costs for EC with those using chemical additives, such as alum or ferric chloride.
... Meanwhile, pH dropped to 6.4 in both coagulation processes. The actual consumption of aluminum electrodes is higher than the theoretical value, due to electrochemical corrosion of both the anode and cathode that contributes to the extra-faradaic aluminum dosing [36]. Picard et al. demonstrated cathodic dissolution in the EC process due to chemical attack by hydroxyl ions generated during water reduction [37]. ...
... Picard et al. demonstrated cathodic dissolution in the EC process due to chemical attack by hydroxyl ions generated during water reduction [37]. The actual coagulant dose in Al-EC can be 1.2 to 2.2 times higher than the calculated faradaic aluminum amount [36,37]. ...
... The unit operating costs for EC can be estimated by adding the electrical costs and the costs for the sacrificial anodes. To achieve 70% turbidity recovery, the energy requirement was calculated to be 0.36 kWh/m 3 of water treated; this value is 2-10 times lower than other EC studies generating the same amount of aluminum dose during treatment of synthetic water and wastewater [35][36][37], because higher salinity of produced water reduced the electrical resistance of the solution during EC. Given an electrical cost of $0.10/kWh, the electrical power cost was estimated $0.036/m 3 . ...
Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53%–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing.
... Measured total iron concentrations were higher than the estimated values from Faraday's law (≈5-65 mg/L Fe for current densities of 0.67 to 10 mA/cm 2 ). On average, the actual total iron doses were 1.3 times greater than that of the estimated values, similar to findings by Gu et al. (2009) [38]. The difference was attributed to the dissolution of iron in water without an applied current [38,39]. ...
... Measured total iron concentrations were higher than the estimated values from Faraday's law (≈5-65 mg/L Fe for current densities of 0.67 to 10 mA/cm 2 ). On average, the actual total iron doses were 1.3 times greater than that of the estimated values, similar to findings by Gu et al. (2009) [38]. The difference was attributed to the dissolution of iron in water without an applied current [38,39]. ...
... On average, the actual total iron doses were 1.3 times greater than that of the estimated values, similar to findings by Gu et al. (2009) [38]. The difference was attributed to the dissolution of iron in water without an applied current [38,39]. ...
Insufficient funding and operator training, logistics of chemical transport, and variable source water quality can pose challenges for small drinking water treatment systems. Portable, robust electrochemical processes may offer a strategy to address these challenges. In this study, electrocoagulation (EC) and electrooxidation (EO) were investigated using two model surface waters and two model groundwaters to determine the efficacy of sequential EC-EO for mitigating Escherichia coli. EO alone (1.67 mA/cm2, 1 min) provided 0.03 to 3.9 logs mitigation in the four model waters. EC alone (10 mA/cm2, 5 min) achieved ≥1 log E. coli mitigation in all model waters. Sequential EC-EO did not achieve greater mitigation than EC alone. To enhance removal of natural organic matter, the initial pH was decreased. Lower initial pH (pH 5–6) improved E. coli mitigation during both stages of EC-EO. EC-EO also had slightly greater E. coli mitigation than EC alone at lower pH. However, EO alone provided more energy efficient E. coli mitigation than either EC or EC-EO.
... Generally, the value of ϕ is less than 1. However, when chemical and electrochemical oxidation happens on anode simultaneously, the value of ϕ exceeds 1 [106][107][108]. The released metal cation in the system undergoes several equilibrium reactions such as precipitation, acid/base, and redox reaction. ...
... Similar to Al dissolution, Fe dissolution on anode also follows Faraday's law where the value of ϕ is around 0.8-1.0 [106][107][108]. Despite this, the value is greater than one at lower pH [116]. ...
Increasing dependency on pharmaceutical compounds including antibiotics, analgesics, antidepressants, and other drugs has threatened the environment as well as human health. Their occurrence, transformation, and fate in the environment are causing significant concerns. Several existing treatment technologies are there with their pros and cons for the treatment of pharmaceutical wastewater (PWW). Still, electrocoagulation is considered as the modern and decisive technology for treatment. In the EC process, utilizing electricity (AC/DC) and electrodes, contaminants become coagulated with the metal hydroxide and are separated by co-precipitation. The main mechanism is charge neutralization and adsorption of contaminants on the generated flocs. The range of parameters affects the EC process and is directly related to the removal efficiency and its overall operational cost. This process only could be scaled up on the industrial level if process parameters become optimized and energy consumption is reduced. Unfortunately, the removal mechanism of particular pharmaceuticals and complex physiochemical phenomena involved in this process are not fully understood. For this reason, further research and reviews are required to fill the knowledge gap. This review discusses the use of EC for removing pharmaceuticals and focuses on removal mechanism and process parameters, the cost assessment, and the challenges involved in mitigation.
... The electric power (EP) applied in the laboratory reactor with either aluminum or iron electrodes was calculated using Eq. 5 as described elsewhere (Gu et al. 2009). The electric power applied in electroflocculation reactors is related with the ohmic resistance (OR Ω ) for the diffusion of metal ions through solution and Faradic resistance (FR F ). ...
... Operational parameters for the scale-up of the laboratory reactor Table 3 shows the electrode mass consumption, electric current, current density, ohmic, Faradic and total resistances, heat, calorie, and final temperature for the scale-up of the laboratory reactor to full-scale plant. A high mass consumption occurs when using iron electrodes as the iron atomic mass is higher than the aluminum atomic mass (Gu et al. 2009). For current densities from 10 to 1000 A m −2 , the scale-up of a laboratory reactor to full-scale plant is possible. ...
The aim of this work was to evaluate the scale-up of a laboratory reactor to full-scale plant for the electroflocculation of dairy food industry wastewater. The structural, operational and financial feasibilities were evaluated in reactors with either aluminum or iron electrodes. The laboratory reactor contained a beaker of 500.0 mL, two metal electrodes (thickness: 0.10 cm, length: 15.0 cm, width: 7.0 cm, distance between electrodes: 2.0 cm, total area for two electrodes in the laboratory reactor: 210.0 cm²), power source and magnetic stirring. The employed operational parameters included operation time of 1.0 h, applied potential intensity of 5.0 V, and electric currents of 0.94 A for aluminum electrodes and 0.71 A for iron electrodes. The scale-up was evaluated considering 110 m³ generated wastewater per day in a dairy food industry. The total applied electric power, electrode consumption, and final temperature after 1 h operation were 64.89 kWh, 1220 g m⁻³, and 32.19 °C using aluminum electrodes, whereas these values were 30.01 kWh, 1483 g m⁻³, and 25.64 °C using iron electrodes. Effective structural and operational costs higher than 65.0% in relation to the total costs of operation of the system were associated with the mass consumption of either aluminum or iron electrodes. In general, the scale-up of the laboratory reactor to full-scale plant was structurally, operationally and economically viable compared to the conventional wastewater treatment systems.
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... Generally, this term is smaller than 1 [42]; however, ϕ may be bigger than one if the chemical and the electrochemical oxidation routes of the metal happen concurrently. This final case is recurrent with Al [43,44]. The metal cations liberated inside the solution go through diverse equilibrium reactions that correspond to the acid/base, complexation, precipitation and redox reactions. ...
... As a result, several references mentioned that the Fe dissolution obeys to the Faraday's law with a faradic yield comprised in the range of 80 and 100% [42,43,75]. However, different authors affirm that there is a gap between the quantity of Fe theoretically solubilized evaluated using Faraday's law and the quantity of detected solubilized Fe founded on Z = 2 [5]. ...
During the two last decades, electrocoagulation method (EC) was the focus of many industrial applications and remains a fascinating domain of research. Most published researches concern uses in treating potable water and wastewaters to increase both the removal of dissolved and undissolved contamination. Significant achievements have been realized comprising participations to fundamental comprehension, electrode metals, working parameters, device conception, and economic aspects determinations. Despite the fact that there are several benefits mentioned through the specialized references, the EC large-scale use is not until now viewed as a recognized wastewater technique due to the absence of viable models used in designing device. The present review discusses the mechanisms involved in the EC process and opens a broad perspective on its modeling. The scientific community is near to suggest empirical/theoretical models to present the EC technology as a viable green process. However, more great efforts remain to be accomplished. Technological software developers such as COMSOL™ Multiphysics are invited to insert the EC process in their electrochemistry module to better commercialize this intensified technique and encourage its massive use through the world.
... This value is usually lower than 1 [12], but ϕ may be higher than 1 when the chemical and the electrochemical oxidation mechanisms of the metal proceed simultaneously. This last situation is frequent with aluminum [13,14]. The metal cations released in the bulk undergo various equilibrium reactions that correspond to acid/ base, complexation, precipitation and redox reactions in water. ...
... The consequence is that, on one hand, some studies report that the iron dissolution follows Faraday's law with a faradic yield between 80 and 100% [12,13,45]. On the other hand, others state that there is a difference between the amount of iron theoretically dissolved estimated by Faraday's law and the amount of observed dissolved iron based on Z = 2 [41]. ...
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.
... At the anode: 3 3 ...
... Table 1 and Figure 1 give a clear image of this tendency. It can be observed that the amount of produced aluminum grows as the current density decreases, fact that has been observed by other authors 1,3,4,5 , who reported that the total aluminum dose to the Faradic dose declined with the increased current density. We explain this behavior considering that as we apply the same intensity in every case, we needed to increase the number of electrodes in order to be able to have smaller values for j, increasing the cathodic area. ...
Studies at laboratory scale were carried out using a plug-flow electrochemical reactor with steel plates that produces iron hydroxide as coagulant in a continuous form. The goals were first to analyze the influence of turbulence over coagulation due to neutralization charges and second, to define the principal factors that are involved in obtaining high efficiencies of electrochemical iron production and in removing the formed flocs. The results revealed that these efficiencies were increased when the mixture velocity gradient (G) and its product by the reactor detention time (Gt) also rose. The iron production decreased according to the reactor operation time; however, the addition of NaCl to reach a conductivity of 6001tS-cm-1 avoided the reduction and increased electrochemical efficiency. The presence of chlorine in water raised considerably th e iron removal efficiency, but did not affect the iron production. In this study it was assumed that if more iron is removed after sedimentation the amount of eliminated arsenic in water will be higher The results showed that there is a good correlation between the elimination of both pollutants.
... Consequently, Fe(III) is preferred over Fe(II) as a coagulant for water purification applications. However, in the absence of significant NOM concentrations, Fe(II) can be potentially oxidized to precipitate Fe(OH) 3(s) in oxygenated waters by raising the pH (kinetics is first order in dissolved oxygen concentration and inverse second order in pH) to induce sweep coagulation and enmeshment [21,[59][60][61][62]: ...
... Along with anodic dissolution, hydrogen gas is released from the cathode due to water splitting explaining the observed bubble formation. These bubbles adhere to flocs, which can cause them to float to the top of the water column, which is sometimes referred to as EF [16,18,33,60,[64][65][66]. When the entire electrolyzed suspension is directly filtered (without intermediate liquid-solid separation), the process is referred to as EC [15,34,35,39,40]. ...
Electrocoagulation (EC) is the intentional corrosion of sacrificial anodes (typically aluminum or iron) by passing electricity to release metal-ion coagulant species and destabilize a wide range of suspended, dissolved, and macromolecular contaminants. It can be integrated ahead of microfiltration (MF) to effectively control turbidity, microorganisms, and disinfection by-products (DBPs) and simultaneously maintain a high MF specific flux. This manuscript summarizes the current knowledge on MF pretreatment by aluminum EC particularly focusing on mechanisms of (i) electrocoagulant dosing, (ii) (bio)colloid destabilization, (iii) fouling reductions, and (iv) enhanced removal of viruses, natural organic matter (NOM), and DBP precursors. Electrolysis efficiently removes hydrophobic NOM, viruses, and siliceous foulants. Aluminum effectively electrocoagulates viruses by physically encapsulating them in flocs, neutralizing their surface charge and reducing electrostatic repulsion, and increasing hydrophobic interactions between any sorbed NOM and free viruses. New results included herein demonstrate that EC achieves DBP control by removing NOM, reducing chlorine-reactivity of remaining NOM, and inducing a slight shift toward more brominated trihalomethanes and haloacetic acids. EC reduces MF fouling by forming large flocs that tend to deposit on the membrane surface, i.e. decrease pore penetration and forming more permeable cakes and by reducing foulant mass in case of significant floc-flotation.
... Electrocoagulant production Studies of electro-flocculation typically apply Al or Fe electrodes, voltage, and current directly into the culture (Vandamme et al. 2011;Xu et al. 2010;Gu et al. 2009;Uduman et al. 2010). This approach makes it difficult to determine or control the total dose, and also results in a nonuniform spatial dose distribution in the culture volume due to the concentration gradients surrounding the electrodes. ...
... Fig. 3 bottom plot), consistent with Faraday's law. More variation was observed at higher amperages and longer harvesting times, and the differences between theoretical and measured values increased, possibly indicating chemical dissolution of the electrodes as explained by Gu et al. (2009). In addition, washing to remove the adsorbed salts in the coagulant samples was not completed before drying, which likely contributed to increased differences between theoretical and measured values. ...
This research assessed the efficacy of three harvesting methods on a strain of Dunaliella viridis. While there is strong potential to use lipids from microalgae as a feedstock for biofuels to replace petroleum-based fuel, at present microalgal harvesting for biofuel production is not yet economically feasible or energy efficient. pH-induced flocculation (by adjusting the pH of exponentially growing cells), indirect electrocoagulation (applying aluminum hydroxide coagulant to culture), and hollow fiber filtration (separating biomass from medium using tangential flow) were compared as potential harvesting mechanisms for small-scale (3–10 L) and large-scale (30–150 L) volumes of D. viridis. Both pH-induced flocculation and electrocoagulation yielded significant biomass recovery (>95 %), but both methods required removal of added chemicals and/or coagulant before the medium could be reused. In contrast, hollow fiber filtration did not require added chemicals or coagulant, and as another advantage, the filtrate was successfully reused as culture medium without apparent detrimental effects on cell size, cell shape, or cell production. When high salinity stress was imposed on the concentrate produced from the filtration method, total fatty acids (FAs) did not increase. However, total FAs did significantly increase after hollow fiber filtration (49 %) in comparison to FA content before filtration (36 %). This research indicates that hollow fiber filtration as a commercial harvesting mechanism offers attractive advantages as a harvesting mechanism for microalgae such as Dunaliella, relative to pH-induced flocculation and indirect electrocoagulation.
... At the anode: 3 3 ...
... Table 1 and Figure 1 give a clear image of this tendency. It can be observed that the amount of produced aluminum grows as the current density decreases, fact that has been observed by other authors 1,3,4,5 , who reported that the total aluminum dose to the Faradic dose declined with the increased current density. We explain this behavior considering that as we apply the same intensity in every case, we needed to increase the number of electrodes in order to be able to have smaller values for j, increasing the cathodic area. ...
The design of an effective, efficient electrocoagulation reactor for an industrial scale application has being pursued in this job. The main parameters that guided the final design were the matrix velocity of the treated aqueous effluent inside the reactor and the current density, as they determine the energy requirements as well as steady state conditions that favor the total consumption of aluminium electrodes in an continuous, flocculator like, electrocoagulation reactor designed to remove silica from water. One of the important parameters to monitor the performance of the system is the Voltage as a function of time; when this variable increases means that something has changed, the most common cause is electrode passivation due to a solids film deposited over the electrodes, other causes are false contacts or exhausted electrodes. We got the profiles for Voltage as a function of time using different current densities under a galvanostatic regime. For our purposes, a current density of j=38 A/m2 was selected in scaling up an electrocoagulation unit as at this current density a good silica removal is reached, the electrodes could be totally consumed without an important increase in voltage and they kept free of deposits.
... Most available models of system cost and energy consumption neglect crucial scale-up issues. For example, the energy associated with the electrode dissolution processes can been estimated based on Faraday's law, but empirical models have not been validated at high current densities (> 10 mA/cm 2 ) [49]. Simply optimizing Faradaic efficiency does not translate to optimized target contaminant removal efficiency at pilot-scale due to confounding factors such as long residence times required for electrode cleaning [50]. ...
... The value of this factor is usually lower than 1 (Bagga, 2008), but it may be higher than 1 when there is a simultaneous occurrence of the chemical and the electrochemical oxidation mechanisms. This situation is common with aluminum (Gu, 2009;Mansouri, 2011) and sometimes ϕ can reach higher than 2 for aluminum electrodes (Mouedhen, 2008). ...
In recent years, the importance of water and wastewater treatment, especially the reuse of the treated industrial wastewater has been seriously taken into account. For this purpose, efficient and economical methods are essential. Electrochemical processes including electrocoagulation and electrocoagulation/flotation due to their intrinsic nature that chemicals are produced in-situ and thus do not produce secondary pollution, can be a new prospect in the treatment of water and wastewater. This paper attempts to present a brief useful review of the process nature and mechanism, advantages and disadvantages, suggestions and challenges in this area based on the previous works and studies.
... Bazrafshan et al. [11] found that electrocoagulation could be used to reduce COD in actual textile wastewater by more than 93.1%, and dye removal of more than 98.6% was achieved. Zheng et al. [12] developed a method to determine Faradaic power consumption as a function of current density and estimated the energy consumption per unit coagulant dose for electrocoagulation reactors that were operated over a wide range of conditions. Liu et al. [13] developed a multiple-stage treatment process by employing electrocoagulation with biogas pumping to simultaneously reclaim anaerobic digestion effluent and to clean biogas. ...
... En el ánodo, el metal se oxida en cationes (1) En el cátodo, el agua se reduce a hidrógeno (H 2 ) y aniones hidroxilo (OH -) (2) En solución (3) La cantidad de metal disuelto por oxidación anódica puede ser calculada usando la ley de Faraday 25, 26 : (4) Donde n son los moles del metal, por lo tanto es una función del tiempo de electrolisis t (s) y de la intensidad de corriente I (A), z es el número de oxidación del metal (material del electrodo) y F es la constante de Faraday (96500 C/mol) 20,22,27 . ...
... 17) [54], which value is usually lower than 1 [55]. However, when the electrode is attacked both chemically and electrochemically, φ can be higher than 1 [56], [57]. Thus, when determining the experimental mass (m exp ), it is necessary to multiply the value obtained (m theo ) from Eq. 16 by the φ value [53]. ...
Electrocoagulation (EC) was studied as an alternative treatment for Cork Boiling Wastewater (CBW). EC was performed in a bench-scale reactor, using aluminum and stainless-steel electrodes and a sodium chloride solution was used to increase conductivity. Different values of current density, electric tension and electrolyte concentration were tested to assess treatment efficiency and operational costs. The tested procedures achieved removal efficiencies of 93.5, 82.5, 88.9 and 99.0% for chemical oxygen demand (COD), total carbon (TC), total nitrogen (TN) and total suspended solids (TSS), respectively, using an electric tension of 15 V. Some experiments after 20 min reached the maximum COD removal, showing that reduction of the operation time can be feasible to maximize cost-efficiency. The prediction of COD removal in a batch treatment based on initial NaCl concentration was investigated during a reactional period of 60 min, demonstrating that higher electrolyte concentrations promote COD removal. Langmuir, Jovanovic Monolayer and Multilayer models were applied and studied to predict the effect of current density and total aluminium mass on COD removal efficiency after 60 min of reaction. The Jovanovic Multilayer model predicted the operating performance for the removal of COD from CBW with higher accuracy when considering the current density. Operational costs for 60 min of electrocoagulation reactional periods have been determined in correlation with current density, in terms of cost per m³, €/COD removed, €/TN removed, €/TC removed, and €/TSS removed. Costs vary between 2.78 and 25.35 €/m³ with 27.6 and 93.8%, respectively. Electrode wear was higher than predicted, suggesting that about 14% of the mass loss should correspond to chemical dissolution. Results show that higher current density and electrolyte concentration reduces electrode wear time but increase overall pollutant removal.
... Current efficiency is usually lower than 1 [50]. However, when the electrode is attacked both chemical and electrochemically, ϕ can be higher than 1 [51]. Figure 3 represents the relation between theoretical and experimental aluminum plate mass loss. ...
Cork boiling wastewater (CBW) is a highly polluted and difficult to treat effluent resultant from the cork manufacturing industry. This study aims to evaluate a new, reliable, efficient, and sustainable process to treat this effluent. This paper tested electrocoagulation as a pre- and post-treatment to improve the already existing physicochemical treatment in a cork production facility in Portugal. In the physicochemical procedures (PC), the addition of different volumes of coagulant (ferric chloride (III) 40% w/w), neutralizer (sodium hydroxide, 32% w/w), and flocculant (polyacrylamide, 0.2 g/L) were evaluated. Electrocoagulation (EC) was performed in a bench-scale reactor, using aluminum and stainless-steel electrodes. For EC, different initial pH, current density, and current tension values were tested. When electrocoagulation was used as a post-treatment, better performances were achieved. However, treatment costs were increased significantly. Coagulation/flocculation offers a viable and cheap treatment, achieving removal efficiencies of 88.2%, 81.0%, 76.9%, and 94.2% for total chemical oxygen demand (tCOD), total carbon (TC), total nitrogen (TN), and soluble chemical oxygen demand (sCOD), respectively. With a PC-EC combination, it is possible to achieve removal efficiencies of 92.4%, 88.0%, 91.4%, and 91.4% for tCOD, TC, TN, and sCOD, respectively. The increased TN removal efficiency can translate into great benefits for certain discharge conditions and should be taken into consideration for improving the sustainability of cork industry. On the other hand, when EC is used as a pre-treatment, there are no benefits either in terms of treatment performance or operating costs.
... In this case, a correction factor (ϕ) is required to compensate for the experimental and theoretical difference of anodic dissolution (Den and CJ, 2008;Hu et al., 2007). Usually, the value of the correction factor is lower than 1 but it may exceed 1 in the case when chemical and electrochemical oxidation of the metal occurs simultaneously (Gu et al., 2009;Mansouri et al., 2011). The generated metal cations in the system undergo several equilibrium reactions, e.g., complexation, redox reaction, acid/base, and precipitation. ...
Increasing discharge of saline wastewater (SWW) from different industries and environmental risks associated with it has compelled researchers to search for efficient treatment methods and safe disposal techniques. Unfortunately, several industries such as agro-food, oil & gas, tannery, and pulp & paper require brine solution units to obtain a finished product that further elevates the salinity of discharged wastewater to a magnitude of 1-3% by weight of NaCl. Among the conventional treatment procedures, electrochemical technologies proved to be more efficient, robust and cost-effective. Electrocoagulation (EC), an electrochemical based technology that produces in situ coagulant which ultimately assist in pollutant removal. It is even more suitable for the treatment of saline water as salinity increases conductivity which further enhances the EC process efficiency. However, the elevated anodic dissolution may increase the cost which can be reduced by using scrap metals as sacrificial electrodes out of iron and aluminum. The mechanism of salt removal from SWW using EC is similar to other pollutant removal mechanisms as salt species being coagulated by the metal hydroxides and are further removed as sludge. However, optimization of process parameters in EC is essential to maintain a balance between anodic passivation and higher metal dissolution so as to make the process efficient. This review paper highlights the theory of the EC technology, process parameters, potential application and recent developments of EC for the treatment of various types of SWW as well as economical assessment associated with this technology. Most of the recent research concerning EC for SWW treatment has been concentrated on the pollutant-specific evaluation without paying special attention to the process optimization, process modelling and commercial usage. This review further outlines the challenges with the recommendations for encouraging research options that can potentially enhance the EC performance, lower the operational costs and expand its range of applications for SWW treatment.
... 2-5. To observe the energy consumption and operating cost throughout the experiments following equations were adapted from literature [3][4][5][6][7] and the results are tabulated in Table 3. ...
The electrocoagulation setup must be optimized in order to design an economically feasible process. Therefore, in this work, the effect of the punched aluminum electrode on the performance of the electrocoagulation (EC) has been investigated. A series of experiments were performed for treatment of sewage wastewater using plane electrode and compare with punched electrodes. Effect of contact time, voltage, electrode spacing and stirring speed has been optimized for removal of Biochemical oxygen demand (BOD) and Total dissolved solids (TDS). It was observed that the performance of electrocoagulation process increased using punched electrode. Also, the less operating cost noticed in punched electrode as compared to a plane electrode for (70-80%) removal of BOD and TDS. These data would be useful in designing of an EC reactor to obtain high removal efficiency at low energy consumption .
... On the one hand, the faster the iron anode dissolves, the more ferric ions are produced per unit time, and the better reaction proceeds between phosphorus and ferric ions. On the other hand, micro-bubbles generated by the cathode could also enhance phosphorus removal by enhancing the agitation and the contact between ferric ions or its metal hydroxide complex species and phosphorus in water (Gu et al. 2009). . 6 The changes of the cell voltage with different anodes ...
Phosphorus removal from wastewater is very important in order to prevent water eutrophication. Although there are many ways to remove phosphorus, electrocoagulation (EC) is a promising method. However, the efficiency of conventional EC processes needs to be further improved. In this study, magnetized iron particle anodes used for EC were fabricated and batch experiments were conducted. The results showed that magnetized anode configuration (iron powder, iron filings, iron sheet), current density (i), as well as electrolysis time had significant effects on phosphorus removal. Particle electrodes (e.g., iron powder) with both large specific surface area and high current density were beneficial for phosphorus removal. Simultaneously, anode magnetization could also enhance the phosphorus removal to some extent based on the effect of magnetic field (MF) on water characteristics (e.g., conductivity). Combining the advantages of particle electrode and MF, magnetized particle anode was superior to other electrodes in phosphorus removal and cell voltage maintenance. Compared with the conventional plate anode, the magnetized iron particle anode was more economical and could reduce operating cost by more than 50%. The results are useful for the practical application of phosphorus removal by EC.
... Other parameters of importance such as nutrients, COD, turbidity, colour, pH and residual iron were also analysed (SI Table S4). Charge Dosage (CD) and Charge Dosage Rate (CDR) were selected as the main process-control parameters for the iron dosage, directly linked to the electrolysis time and current intensity, respectively ( Ghernaout et al., 2019, Delaire et al., 2015, Amrose et al., 2013, Gu et al., 2009. CD is defined as the total electric charge per unit volume applied to a given water sample, while CDR is defined as the speed of application of electric charge (Charge Dosage per unit time). ...
In this paper we analyse the feasibility of low voltage iron electrocoagulation as a means of municipal secondary effluent treatment with a focus on removal of microbial indicators, Antibiotic Resistant Bacteria (ARB) and nutrients. A laboratory scale batch unit equipped with iron electrodes was used on synthetic and real secondary effluent from a municipal wastewater treatment plant. Synthetic secondary effluent was separately assayed with spiked Escherichia coli WR1 and with bacteriophage ΦX174, while real effluent samples were screened before and after treatment for E. coli, Extended Spectrum Betalactamase-producing E. coli, Enterococci, Vancomycin Resistant Enterococci, Clostridium perfringens spores and somatic coliphages. Charge dosage (CD) and charge dosage rate (CDR) were used as the main process control parameters. Experiments with synthetic secondary effluent showed >4log10 and >5log10 removal for phage ΦX174 and for E. coli WR1, respectively. In real effluents, bacterial indicator removal exceeded 3.5log10, ARB were removed below detection limit (≥2.5log10), virus removal reached 2.3log10 and C. perfringens spore removal exceeded 2.5log10. Experiments in both real and synthetic wastewater showed that bacterial removal increased with increasing CD and decreasing CDR. Virus removal increased with increasing CD but was irresponsive to CDR. C. perfringens spore removal increased with increasing CD yet reached a removal plateau, being also irresponsive to CDR. Phosphate removal exceeded 99%, while total nitrogen and chemical oxygen demand removal were below 15% and 58%, respectively. Operational cost estimates were made for power and iron plate consumption, and were found to be in the range of 0.01 to 0.24€/m³ for the different assayed configurations. In conclusion, low voltage Fe-EC is a promising technology for pathogen reduction of secondary municipal effluents, with log10 removals comparable to those achieved by conventional disinfection methods such as chlorination, UV or ozonation.
... In the study of Gu et al., the energy consumption of electrocoagulation was estimated [10]. However, the effect of passivation layer formation was not included. ...
In some areas in Pampanga, arsenic concentration from handpumps reaches up to 300 μg/L, 10 times higher than the safe limit for drinking water. An efficient way of reducing elevated arsenic concentration is through electrocoagulation (EC) process with the use of iron electrodes. However due to several factors, the efficiency of the technique is decreased. This study focuses on determining the energy consumption and cost through time. The cost per cycle was estimated through the power consumption and projecting its growth with time. One 600 L cycle costs around $0.60 to $1.10 which is approximately $0.001 to $0.002 per liter of water. This value increases through each cycle until half of the electrode is consumed (500 cycles) and is to be replaced. The current processing time was set at 30 mins, charge dosage of 150 C/L, applied current of 16.67 mA, and an electrode area of 6.6 cm2. One factor examined which may have caused the increase is the formation of passivation layer on the electrode surface. It was described using linear sweep voltammetry (LSV) and Tafel extrapolation method. The resistance due to charge transfer was determined to be increasing per cycle.
... A simplified electrode dissolution known as electrochemical reactions occurs at anode are the following [27]. (2) ...
... Usually, anode water oxidation introduced H + , naturalization took place near the cathode regime, buffering the pH to a near neutral level by minimizing the EC's coagulation efficiency and leading to the partial formation of floc [19]. Furthermore, the non-faradaic contribution to anodic dissolution leads to a higher electrode material loss [20]. Therefore, overcoming the total effects of the prime residual electrode materials and the partial removal of F − in the final water become problematic when using the common single cell EC system. ...
A novel system for removing fluoride (F-) by electrolysis (ELC) was investigated as magnesium (Mg2+) ion assistive system with a sacrificial iron (Fe) electrode. To minimize and control the Fe leachate from the Fe electrode, ELC was performed in two stages. First stage: Fe dissociation (Fe/stainless steel (SS) electrodes); second stage: ELC electrocoagulation (SS/platinum (Pt) electrodes). The effect of initial ion concentrations on F- removal was investigated with different levels of Fe (0-486 mg/L), Mg2+(0–48 mg/L) and coexisting ions calcium (Ca2+), and carbonates (CO32-+HCO3-). Experimental results revealed that the proposed system’s Fe (486 mg/L) alone may remove 17% of F-. However, incorporating Fe (52 mg/L) and Mg2+ (46 mg/L) significantly increased the removal of F- to 77% for 5 mg/L initial F- level and the molar ratio of (0.24-0.94):1 of the Fe: Mg mixture showed maximum F- removal properties. The F- was removed by both co-precipitation and by Coulomb forces. It was found that F- was removed by co-precipitating with a mixture of Mg(OH)2 and Fe(OH)3 as F- was metathesis with the OH- ion due to the similar radius of both ions. To achieve 1.5 mg/L of F-, the desirable level recommended by the World Health Organization, minimum Mg2+ and Fe concentration ratios of 5:20, 10:20, and 50:50 mg/L were required, respectively, for the initial 2, 3, and 5 mg/L F- concentrations. The presence of Ca2+ ions and the presence of CO32-+HCO3- inhibited the system’s functionality significantly. The optimum operating cost was calculated as 0.56–1.50 US$/m3.
... 2-5. To observe the energy consumption and operating cost throughout the experiments following equations were adapted from literature [3][4][5][6][7] and the results are tabulated in Table 3. ...
... 2-5. To observe the energy consumption and operating cost throughout the experiments following equations were adapted from literature [3][4][5][6][7] and the results are tabulated in Table 3. ...
The electrocoagulation setup must be optimized in order to design an economically feasible process. Therefore, in this work, the effect of the punched aluminum electrode on the performance of the electrocoagulation (EC) has been investigated. A series of experiments were performed for treatment of sewage wastewater using plane electrode and compare with punched electrodes. Effect of contact time, voltage, electrode spacing and stirring speed has been optimized for removal of Biochemical oxygen demand (BOD) and Total dissolved solids (TDS). It was observed that the performance of electrocoagulation process increased using punched electrode. Also, the less operating cost noticed in punched electrode as compared to a plane electrode for (70–80%) removal of BOD and TDS. These data would be useful in designing of an EC reactor to obtain high removal efficiency at low energy consumption.
... This super-faradaic efficiency is explained in terms of a chemical dissolution process, which corresponds to the oxidation of the aluminum sheets with the simultaneous reduction of water to form hydrogen. It has also been mentioned that the amount of generated aluminum seems to depend on the pH, and this has been explained in terms of chemical (4) and (5) for the oxidation of water will decrease solution pH [30] and this was observed in this work, so, the super-faradaic efficiencies are greater for aluminum than those for iron [29]. The pKa of the remazol yellow dye is 3.77. ...
The feasibility of using photovoltaic modules to power a continuous 14 L electrochemical reactor applied to remove an azo dye with an efficiency of 70% is reported. The photovoltaic modules were directly connected, and the system efficiency was observed properly maintained when currents were applied in the range of 2.5 to 7.9 A. This value depends on solar radiation. Likewise, it was found that the efficiency depends mainly on the current density and the flow rate prevailing in the reactor.
... Despite the high efficiency and environmental friendliness of electrocoagulation, high capital and energy costs still remain the impediments to its application in industries for wastewater treatment in place of chemical coagulation (Gu et al., 2009). It is necessary to find out what can be done to minimize energy consumption while maximizing the performance of the process. ...
... Normally, the use of Al based sludges for fluoride removal process has shown adverse effect to human health. Moreover, non-Faradaic contribution to anodic dissolution of Al electrode leading to higher material loss during EC has also been examined [31]. Generally, Al electrodes are protected during EC by a passive layer and hence, it requires minimum chloride content in the water [32]. ...
... Once a small electrode surface fraction is free, the dissolution of aluminum would occur even at circumneutral pH (8,11): ...
The electrocoagulation technology has emerged as a suitable option for the treatment of different types of wastewater. However, one of the aspects that have limited its application is the passivation phenomena involved in aluminum dissolution. Hence, this paper analyzes the oxidation behavior of aluminum in an effluent from tissue paper industry, and synthetic solution. The effluent contains high concentrations of organic matter, chloride and sulfate ions. Through micro-electrolysis experiments, the energy necessary for oxidation of aluminum electrodes, and the zone of potential for the electrodes passivation were studied. Experiments using industrial solution showed no passivation of the aluminum electrodes and also that the anodic current involved is much higher than the observed in experiments where synthetic solutions were used.
... In addition to anodic dissolution, Al 3+ ions are released from the surface due to corrosion and pH of the aqueous solution (chemical dissolution). At high pH values, preferential dissolution of the protective oxide layer (boehmite) was suggested as per the following reaction [16]. ...
The effluents of gelatin production plant are highly complex and difficult to treat by conventional methods. The electrochemical techniques involving electrocoagulation and electrooxidation were attempted for the treatment of wastewater from gelatin production plant. Around 60% of TOC removal was achieved by electrocoagulation using aluminum as anode. However, the performance was severely affected due to scaling of the electrodes. The high concentration of dissolved calcium was found to be responsible for scaling of electrodes. To minimize the scaling, calcium was precipitated as CaCO3 using bicarbonate. After the calcium was precipitated, scaling was reduced and the performance of the electrodes was drastically improved. The effect of applied current density and flow rate on TOC removal was studied and the energy consumption for electrocoagulation was estimated. Since the removal of pollutants by electrocoagulation is only partial, the wastewater was processed further by electrooxidation using IrO2-Ta2O5 coated Ti electrode and TiO2 nanotubes grown on titanium sheet (TiO2 NT) as electrodes. The TOC removal was drastically improved in the presence of TiO2 NT electrode.
... The effect of initial concentration is to increase the charge loading required to reach the WHO MCL (see inset, Figure 1). Charge loading is directly related to the concentration of dissolved iron in solution by Faraday's law [30,31], and thus can be thought of as a proxy for the HFO adsorbent dosage. An increase in the initial concentration is expected to require an increase in HFO adsorbent dosage to reach the WHO MCL. ...
Bangladesh and neighboring areas face large health threats from drinking arsenic-contaminated ground water. Arsenic levels in Bangladesh ground water are typically several hundred µg/L (compared to WHO recommendation of 10 µg/L for the MCL). About 50 million people drink such water, with hundreds of thousands already showing serious adverse health effects in what is described as the largest mass poisoning in history. The challenge is to develop a method for arsenic remediation that is (1) technically effective for removing arsenic down to 10 µg/L in the presence of other competing ions in the water, (2) affordable to most of the local population, (3) robust and easy to operate and maintain, and (4) does not require use of other toxic or hazardous chemicals. We describe a novel method that aims to meet these goals. ElectroChemical Arsenic Removal (ECAR) uses a small DC current and ordinary steel electrodes to produce a specific type of iron rust in the arsenic-contaminated ground water that binds to the arsenic and can be removed by filtration. We describe results using synthetic groundwater prepared in the laboratory, and also preliminary results from real Bangladesh groundwaters. We describe the design of a small ECAR reactor to treat 100 L of water at time, for a technical trial in West Bengal (India). Lastly, we show results from Extended X-ray Absorption Fine Structure (EXAFS) analysis that suggests the structure of the iron precipitate and the dominant mode of arsenic surface complexation.
... ECF is an inherently versatile process involving several design and operation parameters, such as current density, electrode material, electrode spacing, electrolyte concentration, pH value, substrate concentration, all of which have to be optimized in order to achieve efficient removal of pollutants of interest (Tünay et al., 2010). However, ECF technique has many advantages when compared to the conventional methods: easier operation, simpler equipment, lower retention time, better safety, selectivity, flexibility, cost effectiveness, and lower sludge production (Chou, 2010;Gu et al., 2009;Merzouk et al., 2008). ...
The objective of this study was to investigate the possibility of heavy metals (copper, zinc and nickel) removal from the waste fountain solution by the electrocoagulation/flotation (ECF) treatment. After the printing process, the fountain solution changes its composition due to direct contact with different printing materials (plates, inks, etc.) and becomes enriched with metals. The effect of operational parameters, such as electrode materials and combinations, current density, interelectrode distance and operating time, was studied. Also, response surface methodology (RSM) was applied to evaluate the effect of main operational variables and to get a balanced removal efficiency of metals from waste fountain solution by ECF treatment. The iron/iron electrode combination yields a higher percentage of copper and zinc removal efficiency (>95% and >80%, respectively), while for nickel the aluminum/iron and iron/aluminum electrode combinations (>95 and >85%, respectively) proved to be more successful. The optimum interelectrode distance was 1.0 cm (for copper) and 1.5 cm (for zinc and nickel) for all current densities. Heavy metal removal efficiency increases with the increase of electrolysis time for all electrode combinations. Also, the increase of current density improves the ECF removal efficiency. Based on the results obtained through RSM, the optimized parameters for the ECF waste fountain solution treatment for metal removal were identified as: Fe(-)/Al(+) electrode with interelectrode distance of 1.5 cm, operating time of 60 minutes and current density of 8 mA cm−2. Overall, the ECF treatment was proven very efficient in the removal of heavy metals from the waste fountain solution under optimum conditions.
Millions of tons of heavy metals enter the ocean through estuaries each year. Estuaries can serve as the interconnection between the sea and the river, preventing the transfer of tons of heavy metals from the river to the sea. These heavy metals are flocculated during the estuarine process, but flocculation process enhancement in estuaries has received limited attention. This study examined the flocculation of dissolved heavy metals in mixtures of freshwater and seawater with varying salinities (0.7 ‰ to 2.49 ‰). The research objectives were first to examine the natural flocculation rate in one of the heavy metals contaminated sites, Namak-abrud River, in the world's largest lake, and then to compare electro-flocculation with self-purification of estuaries using aluminum and graphite electrodes. This multilateral strategy elucidates the practical enhancement of the natural flocculation process in greater detail. The mean removal efficiency of mixtures subjected to natural flocculation at various salinities is as follows: Fe (54.67 %) > Mn (47.82 %). The results indicated that salinity and the mean removal of metals were positively correlated. The most efficient removal of these metals, excluding Cd and Co, generally occurred between 1 and 2 %. Using aluminum electrodes has a negative impact on metal removal rates in comparison to natural flocculation. In contrast, the efficiency of a graphite electrode used for the first time is distinct. Graphite electrodes increased the Co, Cr, and V elimination rates compared to natural flocculation. By eliminating 36 % of metals, nature once again demonstrates its ecological role in estuaries' self-purification.
. In this study, an Enhanced Electro-Coagulation (En-EC) technique is described for removal of natural dissolved organic matter (DOM) from surface drinking water sources. Assessment of the En-EC technique included...
The aim of this manuscript was to investigate the electrogeneration of iron-based solids and their use in the adsorption of an azo dye. Experiments of electrochemical generation of iron hydr(oxides) were carried out in a Hoffman cell and in a well-stirred batch reactor at 25°C. The oxidation of iron metal at the anode and the reduction of water at the cathode were the electrochemical reactions confirmed to occur. A 2² factorial design of experiments was applied to investigate the effect of initial pH and current on the current efficiency for the production of ferrous ion at an electrolyte concentration of 300 g L⁻¹. The current efficiency for Fe²⁺ was much lower than unity (0.204±0.009) and it was statistically independent of the examined factors (p>0.05). An approximately 3:1 molar mixture of amorphous ferric and ferrous hydroxides was electrogenerated before being possibly converted to dehydrated hydroxides such as magnetite. The iron hydroxides were formed by precipitation reactions of soluble iron species at a rate constant higher than 0.072±0.013 s⁻¹. Additional experiments of electrogeneration of these solid adsorbents at electrolyte concentrations between 250 and 1.5 g L⁻¹ revealed a significant (p≤0.05) decrease in the current efficiency for Fe²⁺ formation from 0.180±0.006 to 0.118±0.008. Experiments of tartrazine adsorption on the electrogenerated iron oxyhydroxides were carried out batchwise at different initial concentrations of the dye at 25°C. Electrogeneration of oxyhydroxides and adsorption were described correctly by detailed kinetic models. The crystallinity of the electrogenerated adsorbent was examined by X-ray diffraction analysis, while its specific surface area, pore volume and average pore size were from BET analysis. SEM and EDX analyses were conducted to examine its morphology and elemental composition.
The waste effluents of two different dyes including one vat dye Indigo and one sulphur dye (Stay Black) were treated using continuous Electrocoagulation (EC) technique at denim dyeing plant. A coagulator reactor of 3 L capacity was designed to treat 7.9 L/h to 65.4 L/h of the dye wastewater. Process parameters like pH, flow rate, no of electrodes and material of electrodes were optimized to obtain maximum decrease in COD and color of the effluents before discharge. It was found that by controlling process parameters, COD can be reduced up to 79% and 90% for low concentrated Indigo and Sulphur Stay Black dyes respectively with a reduction of color value 98% and 70% respectively, while for higher effluent concentrations EC efficiency was reported for 81% and 72.3% color and COD removal respectively for indigo dye and 89.3% and 77.6% color and COD removal respectively for sulphur dye. Hence results of the proposed study could provide important information to design a scale up large reactor unit to commercially apply on denim dyeing discharge and control pollution limits of sulphur and sulfates during denim dyeing.
The presence of emerging pollutants in the environment can pose potential risks to the natural ecosystem. Thus, the efficacious removal of emerging pollutants, like pharmaceuticals from wastewater have recently been a major area of concern for the researchers; since, these biorefractory compounds can bio-accumulate in living beings and can also transform into other toxic compounds in the natural environment. Pharmaceuticals are not efficiently removed through conventional wastewater treatment technologies. Thus, the development of reliable and efficient treatment technologies for the removal of pharmaceuticals is imperative. One such plausible treatment technology is electrocoagulation (EC), which is an electrochemical process that works on the process of in-situ production of coagulants within the EC setup via metal electrodes due to the application of electric current. Therefore, in this review the application of EC for the removal of pharmaceuticals, critical parameters that influence the treatment efficiency, comparison of EC with chemical coagulation and the economics pertaining to EC have been discussed. The goal of this state-of-the-art review is to provide updated information on the application of EC for the removal of pharmaceuticals, which lacks in the previous review articles. Moreover, this would assist the readers to take this technology forward in terms of commercialization as well as removal of pharmaceuticals from contaminated water and thus to produce treated water safe for different reuse purpose.
Malaysia is one of the countries that is well known for its palm oil based products and exports all over the world. Over the years, palm oil mill has been rising at alarming rate in Malaysia, causing palm oil-based wastes to increase especially palm oil mill effluent (POME). POME in Malaysia are channelled into water bodies such as rivers after treated mostly with conventional biological method. However, with current technologies and knowledge, conventional POME treatments are seen to be outdated and require major improvements as greenhouse gaseous are emitted to the environment as well as being less cost effective. Integrated systems that combine two or more conventional methods are introduced and reviewed to provide insights on the advantages and disadvantages of the system if it is to be implemented in real life plant. Integrated systems that focus on combining conventional methods are compiled and reviewed specifically for POME treatment. Among the integrated methods that are reviewed includes biological with membrane, adsorption with magnetic field exposure, adsorption with membrane and electrocoagulation with membrane. The systems are seen to give excellent color, chemical oxygen demand (COD) and total suspended solids (TSS) removal with average of higher than 90%. Reduction in space utilization, improved treatment time as well as simplified operating system were reported when integrated systems are applied as compared to conventional treatment of POME.
The aim of this manuscript was to investigate indirectly the kinetics of formation of hydroxyl/hydroperoxyl radicals responsible for the degradation of persistent pollutants by electrochemical peroxidation. Experiments involving iron electrodes with and without H2O2 were initially carried out in a batch reactor at 0.2–0.6 A and 25 °C in the absence of any pollutants. Concentrations of Fe²⁺, H2O2, Fe³⁺, and H⁺ were determined experimentally as a function of time, and from them a detailed kinetic model comprising 25 electrolysis, dissociation, flotation and Fenton reactions was established. The tuned parameters were only the Faradaic yields for the reactions on the anode, the rate constant for the forward reaction of water dissociation, and flotation of Fe³⁺. A set of three kinetic experiments of electroperoxidation of trifluralin performed at 0.2 to 0.6 A and 25 °C was correctly described by the already presented subset of reactions, plus two others involving trifluralin and hydroxyl/hydroperoxyl radicals.
This paper deals with the study of suitability and efficiency of electrocoagulation (EC) coupled with adsorption to remove dye from synthetic dye solution. The EC cell consisted of mild steel (MS)/copper plates as electrodes and dye solution as electrolyte. The effects of operating time, concentration, supporting electrolyte, current density and pH have been investigated to find out the optimum operating conditions for EC. The concentration of dye was successfully reduced (EY) ?50% and Nigrosin dye ?99% during EC under the optimum operating conditions of initial concentration 0.5ppm, 20ppm, current density 0.04 A/cm2, 0.015 A/cm2, supporting electrolyte 4g, 4g, electrolysis time 20min, 10min, Eosin Yellow and Nigrosin dye respectively, the removal efficiency of the dyes were found 46.69% and 99%, electrical conductivity were 125.0 S/m and 105.7 S/m and TDS left in the EC treated solution were 82.0 and 69.3 ppt. Further proceedings with solution for adsorption process help to improve the dye removal. Results of the studies are electrical conductivity 20 S/m and TDS 30 ppt for EY, for Nigrosin 64.2 S/m and 42.1 ppt.
The efficacy of electrocoagulation at a pilot-scale as an alternative drinking water treatment technology to conventional coagulation is explored. A novel reactor was integrated into a pilot plant at the surface water supply of a small, remote community. Using iron anodes, the effect of metal loading (ML), current density and inter-electrode gap on the reduction of natural organic matter (NOM) was studied. Dissolved organics were characterized by large fractions of low molecular weight (<750Da) hydrophilic carbon structures with lower charge density. A greater reduction in UV254 was yielded compared to dissolved organic carbon, indicating better removal of larger molecular weight fractions NOM. As ML dosages increased from 27.8-60.8 mg/L, specific ultraviolet absorbance decreased from 1.92±0.14 to 1.60±0.10 L/m•mg respectively, from an initial raw water value of 2.21 L/m•mg. No clear trend was observed for the effect of current density and inter-electrode gap for NOM, however ML the primary variable dictating the process’ effectiveness. Energy requirements were observed to vary greatly and highly dependent on ML, current density and inter-electrode gap; variables that all effect the operating potential and resistance. In general, conditions that yielded the greatest reduction of NOM, 1 mm gap and 4-cell configuration, had energy requirements between 0.480-0.602 kWh/m³ of water treated.
In medium capacity, electroplating industry usually treats wastewater until 5 m³ per day. Heavy metal content becomes concern that should be reduced. Previous studies performed electrocoagulation method on laboratory scale, either batch or continuous. This study was aimed to compare the influence of voltage input variation into heavy metal removal in electroplating wastewater treatment using electrocoagulation process on laboratory-scale in order to determine the optimum condition for scaling up the reactor into pilot-scale. The laboratory study was performed in 1.5 L glass reactor in batch system using wastewater from electroplating industry, the voltage input varied at 20, 30 and 40 volt. The electrode consisted of aluminium 32 cm² as sacrifice anode and copper 32 cm² as cathode. During 120 min electrocoagulation process, the pH value was measured using pH meter, whereas the heavy metal of chromium, copper, iron, and zinc concentration were analysed using Atomic Absorption Spectrophotometer (AAS). Result showed that removal of heavy metals from wastewater increased due to the increasing of voltage input. Different initial concentration of heavy metals on wastewater, resulted the different detention time. At pilot-scale reactor with 30 V voltage input, chromium, iron, and zinc reached removal efficiency until 89-98%, when copper reached 79% efficiency. At 40V, removal efficiencies increased on same detention time, i.e. chromium, iron, and zinc reached 89-99%, whereas copper reached 85%. These removal efficiencies have complied the government standard except for copper that had higher initial concentration in wastewater. Kinetic rate also calculated in this study as the basic factor for scaling up the process.
This paper presents the results of a study carried out about the effect of water quality on the removal of dissolved silica using an electrocoagulation process with aluminum electrodes. Silica is found in replacement water (RW), usually known as make up water, and in cooling tower blowdown water (CTBW). Tests were conducted on a small pilot scale (∼2 lmin-3) with a continuous flow device. The treatment train consisted of electrocoagulation (EC), flocculation, sedimentation and sand filtration. Two distinct RW and two CTBW with different physicochemical characteristics were studied. The response variables analyzed were: efficiency of aluminum to remove silica (ratio mgl-1 of dosed Al3+/mgl-1 SiO2 removed), removal efficiency of dosed Al3+, hydraulic head loss throughout the electrochemical reactor and voltage. The cost of the treatment for the four types of water is discussed. The ratio mgl-1 Al3+ dosed /mgl-1 silica removed ranged from 1.09 ± 0.06 to 1.33 ± 0.05 when treating RW and 0.85 ± 0.1 when treating CTBW. The consumption costs of energy, chemicals and electrodes for RW treatment ranged from US$ 0.52 to 0.74 m-3, and was approximately US$0.53 m-3 for CTBW.
Research on a new electrochemical method with iron electrodes and aluminum electrodes for removal of lead, zinc, and copper from wastewater was studied. Several parameters such as initial pH, hydraulic retention time, mass of Fe/C, applied voltage, and particle diameter of Fe/C were studied to achieve a high removal capacity. The results indicated that the new electrochemical method using aluminum electrodes or iron electrodes for removal efficiency of lead, zinc, and copper are very high. But the lifetime of aluminum electrodes is smaller than 2.44 times the lifetime of iron electrodes. The optimal condition of the new electrochemical method was achieved in two iron electrodes, an initial pH of 4–6, a hydraulic retention time of 75 min, a mass of Fe/C of 125 g, an applied voltage of 10 V, and a particle diameter of Fe/C of 20–27 mesh. At this optimal condition and the initial concentration of ions of 50 mg/L, the residual concentration of lead, zinc, and copper are 0.548, 0.886, and 0.588 mg/L, respectively. The treated wastewater continues the use of chemical coagulation method to adjust the solution pH value of 9. After all treatment processes have been completed, the effluent wastewater is very clear and its quality exceeds the direct discharge standard.
We are faced with the problem of energy/carbon dioxide (CO2) in the coming decades. Microalgae has been considered as one of the most promising biomass feedstocks for biofuels production. Meanwhile, the productivity of these photosynthetic microorganisms in converting CO2 into carbon-rich lipids, only a step or two away from biodiesel, greatly exceed that of agricultural crops, without competing for arable land. Worldwide, research and demonstration programs are being carried out to develop the technologies needed to expand algal lipid production from a craft to a major industrial process. This paper narrates the recent advances on microalgae used for biofuels (e.g., biohydrogen, biodiesel and bioethanol) production, including their cultivation, harvesting, and processing. The various aspects associated with the design of microalgae production units are described as well, providing an overview of the current state of development of algae cultivation systems (photobioreactors and open ponds). Algal cultivation systems integrated with the algae-based biorefineries could yield a diversity of bioresources, such as biodiesel, green gasoline, bio-jet fuel, isolated proteins, food starches, textiles, organic fertilizers), which mitigate the costs of biofuels production. Utilizing the energy, nutrients and CO2 held within residual waste materials to provide all necessary inputs except for sunlight, the algae cultivation becomes a closed-loop engineered ecosystem. Consequently, developing this biotechnology is a tangible step towards a waste-free sustainable society.
An integrated electrolysis system was built to synthesize polyaluminum chloride with ultra high-basicity and even pure Al13. The system converts AlCl3 solution from aluminum electrode foil industry waste to Al13 chloride directly with reasonable cost, typically $1.09 per kilogram as Al2(OH)5Cl·2H2O at 25 °C. Electrolyte temperature and current density were investigated to optimize the process. Ferron assay and 27Al NMR results indicated that the purity of Al13 is over 99% in product solutions. Ion chromatogram analysis confirmed that Cl– ions accounted for about 96.5% in all counteranions. Our integrated system is the first instance to obtain pure Al13 polycations directly. Similar high purity products are only available after tedious purification. This effective and economic synthesis procedure has potential for mass production of Al13 for water treatment and catalyst as well as cosmetic industries.
A simplistic and systematic procedure has been developed for the design and upscaling of a multichannel, continuous-flow electrocoagulation reactor of monopolar configuration for the removal of submicron particles from wastewater. Using wastewater generated from the chemical-mechanical planarization process as the target wastewater, a series of laboratory-scale studies were conducted to determine the required operating conditions for the efficient removal of the ultrafine silica particles. These operating criteria included charge loading (≥8 F/m3), current density (ge;5.7 A/m2), hydraulic retention time (ge;60 min), as well as the initial pH (7-10). Furthermore, a steady-state transport equation with second-order reaction kinetics was employed to describe the rate of coagulation as the rate-limiting factor. The actual kinetic constant determined from the laboratory-scale experiments was approximately 1.2 × 10-21 m3/s, which was three orders of magnitude smaller than that calculated based on Brownian coagulation. The model was subsequently validated with a series of experiments using a pilot-scale electrocoagulation reactor geometrically similar to the laboratory-scale reactor with nearly 20 times volumetric scaleup.
All the authors working with aluminium electrodes in the electrocoagulation process have shown that a dissolution occurs at the cathode. This result cannot be explained by the electrochemical process in which only the anodes should be dissolved. The most probable reaction is a chemical attack by hydroxyl ions (generated during water reduction) on the aluminium cathode but nobody has proved it in the framework of the electrocoagulation process. So we are interested in determining what kind of reactions occurs at the cathode. For that, we have elaborated a batch pilot apparatus divided into two compartments, allowing measurement of gas formation taking place only in one compartment. The gases measurements were performed by mass spectrometry with helium as carrier gas. To validate our experimental protocol, the first experiments have been done with a stainless steel cathode: in this case, the results have indicated that the amount of created hydrogen is in good agreement with the values calculated using the second Faraday's law. The experiments realised with an aluminium cathode have shown that the hydrogen formation, in these conditions, was higher than those observed with the stainless steel cathode. All our investigations enable us to propose that with an aluminium cathode, hydrogen formation can be separated into two phenomena. The first one is due to an electrochemical reaction (water reduction), and the second one arises from a chemical reaction explaining the dissolution observed at the cathode.
In the present work, electrocoagulation process with aluminum electrodes was investigated. Different operational conditions such as composition of Na(2)SO(4) based solutions, pH and current density were examined in a systematic manner. Their influence on (i) electrode polarization phenomena, (ii) pH evolution during electrolysis and (iii) the amount of Al released (coagulant) was investigated. For this purpose, potentiodynamic tests and electrolyses using different electrochemical cell configurations were conducted. It is mainly found that (i) a minimum Cl(-) concentration of the electrolyte of about 60ppm is required to breakdown the anodic passive film and considerably reduce the cell voltage during electrolysis; (ii) the anodic dissolution efficiency is unit; (iii) the global amount of coagulant (Al(3+)) generated has two origins: electrochemical oxidation of the anode and "chemical" attack of the cathode and (iv) electrolysis with Al electrodes acts as pH neutralization of the electrolytic medium. Taking into account advantage of the pH evolution observed during electrolysis, electrocoagulation tests were performed to treat a synthetic wastewater containing heavy metallic ions (Ni(2+), Cu(2+), Zn(2+)). Removal efficiencies over 98% were reached. Furthermore, our results displayed prominently that an increase of current density notably reduces the treatment duration without inducing a strong increase of the charge loading.
The purification of water by the electro-removal process using different metal electrodes is widely used in different spheres of science and industry. The comparative characteristics under galvanostatic conditions of zinc (Zn), brass (Cu-Zn), copper (Cu) and iron (Fe) anodes for arsenic (As) removal from water by the electro-removal process in laboratory scale experiments were determined at current densities of 1.5, 3 and 12 mA cm(-2) for 60 min, from a solution containing different concentrations of As(v) (from 70 to 130 microg L(-1)). The results at these different current densities indicated that rapid arsenic removal was achieved at higher current densities (12 mA cm(-2)), with the chemical precipitation of arsenate complexes. The removal of As was relatively efficient, with the following tendency (at 1.5 mA cm(-2)): Fe (>93%) congruent with Zn (>93%) > Cu-Zn (>73%) >Cu (>67%), these efficiencies were relatively independent of the removal rate for all the initial arsenic concentrations investigated. This behaviour is attributed to the electrochemical intrinsic properties of the most active metals, and to the chemical precipitation reactions following the electrochemical process, iron being the most attractive metal for arsenic removal for practical applications.
The electrodissolution of aluminum electrodes in aqueous solutions containing sulfate or chloride ions is studied in this work. The results obtained are important in order to obtain a better understanding of the electrocoagulation process, as the electrodissolution of the anode surface is its first step. It has been determined that both chemical and electrochemical dissolution play an important role in the aluminum generation. The chemical dissolution of aluminum is strongly influenced by the pH. Alkaline pHs increase the dissolution rate by orders of magnitude. Within the experimental conditions used, the supporting media does not seem to influence greatly the chemical dissolution process. The electrochemical dissolution process depends mainly on the specific electrical charge passed. Salinity does not significantly affect the electrodissolution rate. Good fittings between experimental and modeled data are obtained by modeling the system with a simple model based on two assumptions: a highly segregated flow pattern and the calculation of aluminium species and pH from a pseudoequilibrium approach.
Protection of the global environment and, in particular, providing a sustainable source of clean water is a necessity for human survival. The wide use of heavy metals by modern industries has generated by-products containing heavy metals. Specifically, large quantities of chromium and arsenic containing compounds are being discharged into the environment. This study has been conducted to determine the feasibility of an electrocoagulation (EC) process using air injection to remove these inorganic elements with iron electrodes. Powder X-ray diffraction, scanning electron microscopy, and transmission Mössbauer spectroscopy were used to characterize the solid products formed at iron electrodes during EC. The results of this study suggest that magnetite particles and amorphous iron oxyhydroxides are present in the examined EC products. The field pilot-scale study demonstrated the removal of Cr(VI)/Cr(III) and As(III)/As(V) with an efficiency of more than 99 % from both wastewater and wells.
A renewed interest in electrocoagulation has been spurred by the search for reliable, cost-effective water treatment processes. This technology delivers the coagulant in situ as the sacrifcial anode corrodes, due to an applied potential, while the simultaneous evolution of hydrogen at the cathode allows for pollutant removal by flotation. By comparison, conventional chemical dosing typically adds a salt of the coagulant, with settling providing the primary pollutant removal path. This paper provides a quantitative comparison of these two approaches based on turbidity removal associated with a clay pollutant. Chemical coagulation was evaluated via jar tests using aluminium sulphate (alum). This proved more effective than electrocoagulation under acidic conditions (pH ∼4) and low coagulant levels (4 mg-Al l−1 being the minimum able to effectively destabilise the colloidal clay particles). Highly effective coagulation was observed at intermediate alum dosage levels (4–20 mg-Al l−1), where the isoelectric point occurred at pH ∼7.8. Three operating stages (lag, reactive and stable) were identified in a batch electrocoagulation reactor with the operating current determining the pollutant removal rate. At the isoelectric point, which occurs during the reactive stage, the greatest turbidity reduction occurs, indicating aggregation by a sorption mechanism (compared to the charge neutralisation as in the case of chemical coagulation). During the stable stage, continued precipitation of aluminium hydroxide and a decrease in turbidity indicated a sweep coagulation mechanism. The highest current (2 A) reduced the pollutant level in the shortest time, 1% residual turbidity after 30 min, though the highest efficiency (in terms of pollutant removed per unit of aluminium added) was achieved at the lowest current (0.25 A).
Continuous-flow electrocoagulation process with vertical flow-channels was investigated as a method to treat synthetic chemical–mechanical-planarization (CMP) wastewater containing highly charged ultrafine silica particles (ζ = −55 mV, mean Rp = 45 nm at pH 9.5). The parallel-plate, monopolar electrochemical cells resembled a series of closed electrical circuits such that the electrical field strength was highly dependent of the current density and aqueous conductivity, but independent of the inter-electrode gap. The residual turbidity of the CMP wastewater decreased with the increases in either hydraulic retention time or applied current density, and removal efficiency as high as 95% was achieved for wastewater with both low (70 NTU) and high (400 NTU) initial turbidities. The charge loading linearly correlated with turbidity removal efficiency up to a level of 8 F m−3, presenting an appropriate design parameter. Further analysis indicated that turbidity removal was limited by the quantity of liberated ferrous ions at lower range of current density, but seemingly reached a critical level of current density beyond which the process performance gradually deteriorated. Comparisons between the effective particle retention time and the estimated electrophoretic migration time revealed that the electrocoagulation process was predominantly controlled by the rate of particle aggregation occurring near the anodic surfaces. Furthermore, this process generates lesser amount of dry sludge as compared to chemical coagulation with polyaluminum chloride, and does not require pH adjustment prior to treatment.
In the present study electrocoagulation (EC) has been evaluated as a treatment technology for arsenite [As(III)] and arsenate [As(V)] removal from water. Laboratory scale experiments were conducted with three electrode materials namely, iron, aluminum and titanium to assess their efficiency. Arsenic removal obtained was highest with iron electrodes. EC was able to bring down aqueous phase arsenic concentration to less than 10 microgl(-1) with iron electrodes. Current density was varied from 0.65 to 1.53 mAcm(-2) and it was observed that higher current density achieved rapid arsenic removal. Experimental results at different current densities indicated that arsenic removal was normalized with respect to total charge passed and therefore charge density has been used to compare the results. Effect of pH on arsenic removal was not significant in the pH range 6-8. Comparative evaluation of As(III) and As(V) removal by chemical coagulation (with ferric chloride) and electrocoagulation has been done. The comparison revealed that EC has better removal efficiency for As(III), whereas As(V) removal by both processes was nearly same. The removal mechanism of As(III) by EC seems to be oxidation of As(III) to As(V) and subsequent removal by adsorption/complexation with metal hydroxides generated in the process.
The performance of electrocoagulation, with aluminium sacrificial anode, in the treatment of metal ions (Cu2+, Zn2+ and Cr(VI)) containing wastewater, has been investigated. Several working parameters, such as pH, current density and metal ion concentrations were studied in an attempt to achieve a higher removal capacity. Results obtained with synthetic wastewater revealed that the most effective removal capacities of studied metals could be achieved when the pH was kept between 4 and 8. In addition, the increase of current density, in the range 0.8-4.8 A dm(-2), enhanced the treatment rate without affecting the charge loading, required to reduce metal ion concentrations under the admissible legal levels. The removal rates of copper and zinc were found to be five times quicker than chromium because of a difference in the removal mechanisms. The process was successfully applied to the treatment of an electroplating wastewater where an effective reduction of (Cu2+, Zn2+ and Cr(VI)) concentrations under legal limits was obtained, just after 20 min. The electrode and electricity consumptions were found to be 1 g l(-1) and 32 A h l(-1), respectively. The method was found to be highly efficient and relatively fast compared to conventional existing techniques.
This research studied virus removal by iron electrocoagulation (EC) followed by microfiltration (MF) in water treatment using the MS2 bacteriophage as a tracer virus. In the absence of EC, MF alone achieved less than a 0.5-log removal of MS2 virus, but, as the iron-coagulant dosage increased, the log virus removal increased dramatically. More than 4-log virus removal, as required by the Surface Water Treatment Rule, was achieved with 6-9 mg/L Fe(3+). The experimental data indicated that at lower iron dosages and pH (< approximately 8 mgFe/L and pH 6.3 and 7.3) negatively charged MS2 viruses first adsorbed onto the positively charged iron hydroxide floc particles before being removed by MF. At higher iron dosages and pH (> approximately 9 mgFe/L and pH 8.3), virus removal was attributed predominantly to enmeshment and subsequent removal by MF. Additionally, the experimental data showed no obvious influence of ionic strength in the natural water range of 10(-7)-10(-2)M on MS2 virus removal by EC-MF. Finally, EC pretreatment significantly outperformed chemical coagulation pretreatment for virus removal. The proposed mechanism for this improved performance by EC is that locally higher iron and virus concentrations and locally lower pH near the anode improved MS2 enmeshment by iron flocs as well as adsorption of MS2 viruses onto the iron floc particles.
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