Fe Electrocoagulation Research Articles

Fate of calcium, magnesium, and phosphate during Fe electrocoagulation: An investigation for mitigating cathodic scaling in phosphate removal process

Fe electrocoagulation (Fe-EC) is efficient for the removal of phosphate (PO43−-P). The fate of Ca2+, Mg2+, and PO43−-P during the Fe-EC process is unclear, resulting in the difficulty for mitigating the cathodic scaling. After Fe-EC treatment for 10 min at 10 mA/cm2, PO43−-P was mainly distributed in the sediment (>90 %). Ca and Mg was mainly distributed in the solution (54 % − 97 %), followed by in the sediment (2 % − 44 %) and on the cathode (0 % − 6 %). Although only a small amount of Ca and Mg was precipitated on the cathode, with a long term operation, cathodic scaling would still occur. The precipitation of Ca on the cathode was mainly caused by the presence of HCO3− with other precipitates which directly precipitated with OH− as crystal seeds, because the precipitation of CaCO3 did not depend on the local pH near the cathode. The precipitation of Mg on the cathode was mainly caused by a lower applied current, because Mg(OH)2 which formed on the cathode would be prevented by H2 evolution with a higher current. Accordingly, the strategies for preventing cathode scaling are proposed. The precipitation of Ca can be prevented by increasing the current both with HCO3− and crystal seeds, and by increasing the current only with PO43−-P. It is hard to prevent the precipitation of Ca by controlling the current only with HCO3−. The precipitation of Mg can be prevented by increasing the current. With the initial concentrations of PO43−-P, HCO3−, Ca2+, and Mg2+ in the real wastewater 1.0 mg/L, 48 mg/L, 150 mg/L, and 30 mg/L, respectively, the amounts of Ca and Mg deposited on the cathode were much less at 10 mA/cm2 (5.8 ± 2.9 mg/L, 1.1 ± 0.3 mg/L) than those at 1 mA/cm2 (28.6 ± 4.6 mg/L, 5.0 ± 0.4 mg/L). With the above controlling strategies, the cathode scaling can be alleviated under different water quality conditions.

Importance of iron complexation and floc formation towards phosphonate removal with Fe–electrocoagulation

Phosphonates are widely used scale inhibitors, but the residual phosphonates in drainage are challenging to remove because of their chelating capacity and resistance to biodegradation. Here, we reported a highly efficient and robust Fe-electrocoagulation (Fe-EC) system for phosphonate removal. Surprisingly, we found for the first time that phosphonates like NTMP were more efficiently removed under anoxic conditions (80% of total soluble phosphorus (TSP) in 4 min) than oxic conditions (0% of TSP within 6 min) in NaCl solution. A similar phenomenon was observed when other phosphonates, such as EDTMP and DTPMP, were removed, highlighting the importance of iron complexation and floc formation toward phosphonate removal with Fe-EC. We also showed that the removal efficiency of NTMP by electrochemically in-situ formed flocs (97%) was much higher than post-adsorption systems (ex-situ, 40%), revealing that the growth of flocs consumed the active site for NTMP adsorption. Beyond the removal of TSP, 10 % of NTMP-P was also degraded after the electrolysis phase, evidenced by the evolution of phosphate-P. However, this did not happen in anoxic or chemical coagulation processes, which confirms the formation of reactive oxygen species via Fe(II) oxidation in the oxic Fe-EC system. The primary removal mechanism of phosphonates is due to their complexation with iron (hydr)oxide generated in the Fe-EC system by forming a Fe-O-P bond. Encouragingly, the Fe-EC system exhibits comparable or even better performance in treating phosphonate-laden wastewater (i.e., cooling water). Our preliminary cost calculation suggests the proposed system (€ 0.009/m3) has a much lower OPEX under oxic conditions than existing approaches. This study sheds light on the removal mechanism of phosphonate and the treatment of phosphonate-laden wastewater by playing with the iron complexion and flocs formation in classical Fe-EC systems.

Mn-assisted Fe-electrocoagulation strategy for enhanced efficient arsenic removal and its mechanism

Electrocoagulation (EC) is a facile technique for removing arsenic (As) pollutants from different water matrices with high efficiency. In this work, a novel strategy of Mn-assisted Fe EC was developed to further enhance the removal efficiency of arsenite [As(III)] from wastewater. When 1 mM of MnCl2 was added to an Fe-EC system, the As removal efficiency reached 99.99%, and the residual concentration was only 9 μg/L, which is lower than the World Health Organization’s limit for drinking water. The characteristics of the generated flocs by four different EC processes in Fe, Fe-Mn, Fe-As, and Fe-Mn-As systems were investigated. The results showed that Mn2+ promoted the formation of FeOOH, FeOx, MnOx, FeHAsO4, and MnHAsO4 through low crystallinity and a high surface area. Density functional theory simulation and crystal orbital hamiltonian population confirmed that the generated Fe-Mn flocs had a greater adsorption affinity for As(III) and arsenate [As(V)]. The possible reactions in the EC processes and reaction mechanisms were also hypothesised. The current work provides meaningful insights into understanding the mechanisms of Mn-assisted Fe-EC systems, and further confirms its potential for practical applications in As pollution treatment.

Fe electrocoagulation technology for effective removal of molybdate from water: Main influencing factors, response surface optimization, and mechanistic analysis

Excessive molybdate (MoO42–) in drinking water poses a potential hazard to human health. Herein, for the first time, Fe electrocoagulation (EC) was proposed for the removal of Mo(VI) from water. The effects of main aquatic and electrochemical factors on Mo(VI) removal were investigated. Results showed that, among the electrolytes (NaCl, Na2SO4, and NaNO3), NaNO3 obviously inhibited the anodic dissolution and Mo(VI) removal, and caused high energy consumption. NaCl was favorable for the reduction of energy consumption whereas its high concentrations inhibited Mo(VI) removal. Via using the response surface method with Box-Behnken design, the optimal process parameters for the maximum Mo(VI) removal were obtained as follows: pHi, 5.5–7.0; CD, 3.5–4.0 A/m²; ED, 0.5–0.9 cm. The analysis of variance demonstrated that initial pH, current density, and electrode distance had highly significant impacts on Mo(VI) removal (p-value < 0.01). The quadratic polynomial model was developed using the Mo(VI) removal efficiency as the response value. The Mo(VI) adsorption experiments demonstrated the effectiveness of adsorption during the Fe EC process. Results of flocs characterization by SEM-EDS, XPS, XRD, and FTIR showed that the main crystalline phases in the flocs included lepidocrocite (γ-FeOOH) and magnetite (Fe3O4), and no reduction reactions of Mo(VI) were observed. The mechanisms of Mo(VI) removal mainly involved flocculation, adsorption (electrostatic attraction and inner-sphere complexation), and co-precipitation. Continuous flow tests (172 h) using simulated groundwater showed an average Mo(VI) removal efficiency of 83.4 %. This study indicates that Fe EC is a promising water treatment technology for Mo(VI) removal.

Fe electrocoagulation technology for highly-efficient p-arsanilic acid removal from water: Feasibility and mechanisms

Conventional oxidation methods are effective for the removal of p-arsanilic acid (p-ASA) in water but are limited by complicated process. Herein, Fe electrocoagulation with Fe as anodes was used to efficiently remove p-ASA with 100% total arsenic removal within 60 min (1.75–20 A/m2). Current density significantly influenced sludge production, anode loss, and energy consumption (p-value < 0.05). Kinetic analyses showed a decline in arsenic removal rate with increasing initial pH (4.0–10.0). The changes in main elements of p-ASA (As and N) were analyzed to identify intermediate products using UPLC-Q-TOF-MS, HPLC-ICP-MS, and spectrometry. Hydroxyl radicals were confirmed as the primary reactive oxygen species. The active sites of p-ASA molecules were predicted by theoretical calculations and reaction paths were proposed. The toxicity of Fe-EC effluent was effectively reduced according to the analyses of ECOSAR and E. coli colonies method. The possible mechanisms of p-ASA removal, including oxidative degradation, electrostatic attraction, and ligand complexation, were proposed. Real water containing a p-ASA concentration of 250 μg/L was treated for 48 h using continuous-flow Fe-EC and arsenic concentrations of 2–30 μg/L in effluent were obtained. Overall, Fe-EC was a simple, cost-effective, and eco-friendly technology for the removal of p-ASA.

Faradaic efficiency and anodic electrochemical behavior of Fe electrocoagulation: The role of co-existing ions and ultrasonic assistance

Anodic passivation is a key factor affecting the Faradaic efficiency of Fe electrocoagulation. In practice the electrolyte nature of water matrix played a critical role in governing the Faradaic efficiency. In this study the effect of co-existing ions and ultrasonic field on the Faradaic efficiency and the electrochemical behavior of iron anodes was investigated. The results showed that in Cl− and SO42− solution Fe anode exhibited a typical characteristic of dissolution with a high Faradaic efficiency (>90 %), but severe passivation appeared in NO3− solution with a low Faradaic efficiency (4 %). However, adding Cl− can impair the passivation effect of NO3−. As the Cl−: NO3− ratio increased to 1:10, the Faradaic efficiency significantly increased to 90.65 %. Potentiodynamic polarization and electrochemical impedance spectroscopy analysis showed that the thickness of the passive film decreased and the corrosion rate increased, and thus promoting the anodic dissolution. In addition, ultrasonic field was introduced to assist electrocoagulation. In 50 mM NaNO3 + 2.5 mM NaCl solution, the Faradaic efficiency was only 12 % without ultrasonic assistance, but it increased to 60.9 % when the ultrasonic power was 180 W. Therefore, ultrasonic assistance was beneficial to reduce the anodic passivation and increase the Faradaic efficiency.

Inactivation of Escherichia Coli by mixed-valent nanoparticles in-situ generated during Fe electrocoagulation

Electrocoagulation (EC) is promising for the removal of chemical and microbial contaminants. Although the removal of pathogens from wastewater is efficient by conventional Fe-EC in the presence of dissolved oxygen (DO), the non-inactivated pathogens in the sediment still have a risk. Herein, the inactivation of Escherichia coli (E. coli) with the mixed-valent iron nanoparticles, magnetite and green rust (GR), in-situ generated from Fe-EC process in the absence of DO was investigated. The inactivation efficiency was significantly higher with magnetite (4.7 log cells) and GR (3.2 log cells) compared with FeOOH (0.7–1.7 log cells) generated at 50 mA in 10 min. The unstable in-situ generated magnetite with positive charges was prone to adsorb onto E. coli, damaging the cell membrane, inactivating the bacteria. The unstable in-situ generated GR was prone to coagulate with E. coli, delivering Fe2+ into the cell and inducing the generation of endogenous ROS, inactivating the bacteria. Fe-EC in the absence of DO was proved to be efficient for the inactivation of E. coli (4.2–4.3 log cells) in real wastewater. These findings identified the ignored inactivation effect and mechanism of E. coli with magnetite and GR generated in situ from Fe-EC process, which will provide theoretical support for real applications.

Influence of key cations and anions on phosphate removal by Fe(0) electrocoagulation

The electrocoagulation technology is efficient for the removal of phosphate. The removal efficiency of phosphate in the secondary effluent is higher than that of in the synthetic wastewater. In order to identify the key factors for promoting the removal of phosphate in Fe(0) electrocoagulation (EC), this study investigated typical coexisted substances in the secondary effluent, including Ca2+, Mg2+, NH4+, HCO3−, SO42−. The results indicated that Ca2+ and Mg2+ were the key factors promoting the removal of phosphate by Fe(0) EC both under normal (5–6 mg/L) and low dissolved oxygen (DO) (≤ 1 mg/L) conditions. Under low and normal DO conditions, the phosphate removal efficiency increased from 28 % to 98 % ± 2 % (in 5 min) at 10 mA/cm2 with the addition of Ca2+ (0.2–20 mM) or Mg2+ (0.2–2 mM) but decreased to approximately 70 % with the addition of a Mg2+ of 20 mM. Under low and normal DO conditions, the aggregation time of iron oxide flocs decreased from 10 min to 5 min when the concentration of Ca2+ increased from 0 to 20 mM and Mg2+ increased from 0 to 2 mM. The aggregation stability of flocs was not sufficient when the Mg2+ concentration was 20 mM at 5 mA/cm2. Our results confirmed that Fe(0) EC was suitable for the removal of phosphate in the secondary effluent, especially containing moderate amounts of Ca2+ and Mg2+ regardless of the concentration of DO.

Destabilization of polystyrene nanoplastics with different surface charge and particle size by Fe electrocoagulation

Nanoplastics (NPs) discharged from wastewater could pose a major threat to organisms in aquatic environments. Effective removal of NPs by the current conventional coagulation-sedimentation process is not yet satisfactory. This study aimed to investigate the destabilization mechanism of polystyrene NPs (PS-NPs) with different surface properties and sizes (i.e., 90 nm, 200 nm, and 500 nm) by Fe electrocoagulation (EC). Two types of PS-NPs were prepared by a nanoprecipitation method using sodium dodecyl sulfate and cetrimonium bromide solutions to produce negatively-charged SDS-NPs and positively-charged CTAB-NPs. For both NPs, obvious floc aggregation from 7 μm to 14 μm was observed only at pH 7 with particulate Fe accounted for >90 %. At pH 7, Fe EC removed 85.3 %, 82.8 %, and 74.7 % of the negatively-charged SDS-NPs at small-, mid-, and large-sizes from 90 nm, 200 nm, to 500 nm, respectively. Small-size SDS-NPs(90 nm) were destabilized through physical adsorption on the surface of Fe flocs, while the main removal mechanism of mid- and large-SDS-NPs(200 nm and 500 nm) involved the enmeshment of large Fe flocs. Compared to SDS-NPs(200 nm and 500 nm), Fe EC performed similar destabilization behavior to two CTAB-NPs(200 nm and 500 nm), but it resulted in much lower removal rates of 54.8 % - 77.9 %. The Fe EC also exhibited no removal (<1 %) ability toward the small-size and positively-charged CTAB-NPs(90 nm) due to insufficient formation of effective Fe flocs. Our results provide insight into the destabilization of PS in nano-scale with different sizes and surface properties, which clarifies the behavior of complex NPs in a Fe EC-system.

Arsenic immobilisation in soil using electricity-induced spreading of iron in situ

An in situ method for spreading iron amendments to arsenic (As)-contaminated soil has been investigated in the laboratory and field. This study tested the distribution of Fe from corroding electrodes through soil using a low-voltage direct current in a laboratory setting and validated the method in the field for As immobilisation in contaminated soil. Laboratory tests revealed that the corrosion of Fe electrodes in soil occurred in a way similar to that during the Fe electrocoagulation in water, which decreased the As concentrations in flow-through water from 150 μg L−1 to undetectable levels. Method validation over one year in the field using electric current pulses with reversing polarity revealed a decrease in As concentration in groundwater by 72–97% in five of the six groundwater wells within the experimental area. This method of introducing Fe amendments to soil can reduce the need for soil excavation upon chemical immobilisation of contaminants in soil.

Enhanced removal of phosphate by electrogenerated iron combined with mechanically activated calcite

Fe electrocoagulation is efficient for the removal of phosphate with low energy consumption, whereas suffers from the high concentrations of the total dissolved Fe (TDFe) in the effluent. In this study, mechanically activated calcite was used to combine with the electrogenerated Fe to improve the removal efficiency of phosphate and reduce the concentrations of TDFe. The removal efficiency of phosphate (initial concentration 1.0 mg/L) in 30 min was significantly increased (88 %) by mechanically activated calcite combined with electrogenerated Fe method, compared with mechanically activated calcite method (43 %) and electrogenerated Fe method (53 %) separately. The concentration of TDFe in the effluent reduced from 4.9 mg/L with electrogenerated Fe method to 0.2 ∼ 0.5 mg/L with mechanically activated calcite combined with the electrogenerated Fe method. The mechanically activated calcite combined with electrogenerated Fe method was confirmed by the efficient removal of phosphate in the biological treatment effluent from a municipal wastewater treatment plant reached a removal efficiency of approximately 100 % (reduced from 1.33 mg/L to 0.006 mg/L) and in the rainfall runoff from a fertilizer enterprise reached a removal efficiency of 98 % (reduced from 3.86 mg/L to 0.075 mg/L). The removal mechanism was proposed. The Fe-P polymer was formed in the dissolved phase. The mechanical activation improved the solubility of calcite and provided dissolved Ca2+, as well as increased the surface area of calcite and provided more adsorption sites. Therefore, the mechanical activation promoted the adsorption of the Fe-P polymer onto the surface of the mechanically activated calcite. This study provided an efficient method for the removal of phosphate in wastewater and simultaneously reducing the concentrations of TDFe in the effluent.

Effective removal of Sb(V) from aqueous solutions by electrocoagulation with composite scrap iron-manganese as an anode

Improving the removal rate of pentavalent antimony (Sb(V)) by electrocoagulation (EC) is of great significance to the environment. In this paper, the EC with composite scrap iron and manganese filings as an anode (Fe-Mn EC) was investigated for the high-efficiency elimination of Sb(V). The results showed that Fe-Mn EC can enhance the removal of Sb(V) by 11.18-17.36% compared with the traditional iron electrocoagulation (Fe EC). Meanwhile, Sb(V) removal increased with the growth of current concentration as well as Mn content in the anode. However, the Sb(V) removal rate was inhibited when Mn content exceeded 20%. Moreover, the flocs generated during the Fe and Fe-Mn EC (Fe flocs and Fe-Mn flocs) were analyzed both structurally and theoretically using XRD, SEM, BET, and adsorption experiment. The results indicated that the components of Fe-Mn flocs were mostly Mn-substituted FeOOH, which appeared as the structure of nanometer flakes and large internal surface areas. Meanwhile, the Fe-Mn flocs had the ability of much faster Sb(V) adsorption rate; its Sb(V) adsorption capacity was 2.5 times more than that of the Fe flocs. The thermodynamics constants of both Fe and Fe-Mn flocs proved that adsorption was associated with monolayer physical adsorption. To the best of our knowledge, this is the first report of the electrocoagulation with composite scrap iron-manganese as an anode to remove Sb, which provide a new idea and potential technical support for the removal of Sb(V).

Effects of coexisting ions on simultaneous removal of fluoride and arsenic from water by hybrid Al–Fe electrocoagulation

Effects of coexisting ions on simultaneous removal of fluoride and arsenic from water by hybrid Al–Fe electrocoagulation

Removal of fluoride and arsenic from groundwater by hybrid Al–Fe electrocoagulation: Adsorption isotherm and kinetics study of single and binary component systems

AbstractThis study reports on the adsorption isotherm and kinetics of arsenic and/or fluoride by the hybrid iron–aluminum electrocoagulation in a batch reactor. The experiments were performed at a condition of current densityJ = 9.9 mAcm−2; time = 50 min; and pH = 7.5, at variable initial concentrations. The flocs surfaces were characterized using Fourier transform infrared spectroscopy and X‐ray powder diffraction that revealed presence of AlAsO4·2(H2O), AlF2OH, and FeOOAs. Adsorption of fluoride and arsenic in both systems followed Freundlich and Langmuir models. The adsorption processes for fluoride and arsenic were spontaneous and physical in nature with monolayer maximum adsorption capacities of 76.4 and 1.14 mg/g, respectively in single systems. In a binary component system, the adsorption capacity of arsenic was 0.06 mg/g while that of fluoride became 75.6 mg/g as evaluated using extended Langmuir and extended Freundlich models. Moreover, the kinetics of fluoride and/or arsenic adsorption followed the pseudo second‐order model. The remediation of fluoride and arsenic from water by Al–Fe oxyhydroxide were found to be through ionic exchange and electrostatic attraction, respectively.

Efficient removal of Tetracycline-Cu complexes from water by electrocoagulation technology

Tetracycline (TC) and Cu2+ often coexist in water process and can form TC-Cu complexes. How to effectively remove them from water is becoming an exasperating problem. In current work, electrocoagulation (EC) via bipolar connection was developed to eliminate TC-Cu complexes from water and Fe anode was found to outperform Al anode. Characterization techniques such as XRD, FTIR, UV–vis spectra and UPLC-MS/MS analyses were carried out to explore possible mechanisms using Fe EC. The impacts of main factors including current density, conductivity and TC/Cu molar ratio (2:1, 1:1 and 1:2) were investigated. Results show that as for the three systems with different TC/Cu molar ratios, when the initial pH was 4.3, current density of 4.17 A/m2, conductivity of 1000 μS/cm, the removal of TC, TOC and Cu2+ all reached the maximum after the reaction of 15 min, which was separately 100%, 80.2% and 88.1%, implying excellent mineralization of organic contaminants. EC process displayed high electrodegradation efficiency towards TC-Cu complexes. Appropriate amount of Cu2+ could promote the TC degradation via its catalysis. TC and Cu2+ could be removed via adsorption, hydrogen bond association and coprecipitation by freshly-formed metal hydroxides (green rust, γ-FeOOH and Cu(OH)2). Electroreduction and flotation during EC process could also contribute to the partial removal of Cu2+. The operation cost under the optimum conditions was estimated as 0.050 USD/m3 of treated water. Current study indicates that Fe electrocoagulation was a promising technology for the removal of TC-Cu complexes in water and wastewater treatment.

Integrating biological As(III) oxidation with Fe(0) electrocoagulation for arsenic removal from groundwater

Arsenic (As) is a toxic element present in many (ground)water sources in the world. Most conventional As removal techniques require pre-oxidation of the neutral arsenite (As(III)) species to the negatively charged arsenate (As(V)) oxyanion to optimize As removal and minimize chemical use. In this work, a novel, continuous-flow As removal system was developed that combines biological As(III) oxidation by bacteria with Fe electrocoagulation (EC), an Fe(0)-based electrochemical technology that generates reactive Fe(III) precipitates to bind As. The bio-integrated FeEC system (bio-FeEC) showed effective oxidation and removal of 150 µg/L As(III), without the need of chemicals. To remove As to below the WHO guideline of 10 µg/L, 10 times lower charge dosage was required for the bio-FeEC system compared to conventional FeEC. This lower Fe dosage requirement reduced sludge production and energy consumption. The As(III) oxidizing biomass was found to consist of bacteria belonging to Comamonadaceae, Rhodobacteraceae and Acidovorax, which are capable of oxidizing As(III) and are common in drinking water biofilms. Characterization of the As-laden Fe solids by X-ray absorption spectroscopy indicated that both bio-FeEC and conventional FeEC produced solids consistent with a mixture of lepidocrocite and 2-line ferrihydrite. Arsenic bound to the solids was dominantly As(V), but a slightly higher fraction of As(V) was detected in the bio-FeEC solids compared to the conventional FeEC.

Advantage of selective production of green rusts for Sb(V) removal in Fe(0) electrocoagulation

The removal efficiency of pollutants in Fe(0) electrocoagulation (EC) has been associated closely with the speciation of generated Fe(II)/Fe(III) oxides during this process, which is very complicated and can be affected by various factors. In this work, in-situ Raman, X-ray diffraction and some other techniques have been used to study the speciation of Fe under different conditions and to establish a relationship between Fe speciation and Sb(V) removal efficiency. Results indicated that concentration of dissolved oxygen (DO) is a key factor influencing Fe(0) EC. It was found that green rusts (GRs) were formed and were then transformed into magnetite at lower DO concentration, and Sb(V) removal efficiency reached 99.9% after 30 min of EC. In contrast, γ-FeOOH was formed at high DO concentration, and the removal efficiency of Sb(V) after 30 min of EC was only 72.8%. In the presence of sulfite and phosphate with low concentrations, GRs can be stabilized and benefit the removal of Sb(V). We believe this work will provide some new insights on the mechanism of Fe(0) EC and the effective removal of other pollutants during Fe(0) EC process.

Coupled As and Mn Redox Transformations in an Fe(0) Electrocoagulation System: Competition for Reactive Oxidants and Sorption Sites.

Iron electrocoagulation (EC) can be used for the decentralized treatment of arsenic(As)-contaminated groundwater. Iron EC involves the electrolytic dissolution of an Fe(0) electrode to Fe(II). This process produces reactive oxidants, which oxidize As(III) and Fe(II) to As(V) and a range of Fe(III) (oxyhydr)oxide phases. Here, we investigated the impact of manganese (Mn) on As removal, since the two often co-occur in groundwater. In the absence of Mn(II), we observed rapid As(III) oxidation and the formation of As(V)-Fe(III) polymers. Arsenic removal was achieved upon aggregation of the As(V)-Fe(III) polymers. In the presence of Mn, the mechanism of As removal varied with pH. At pH 4.5, As(III) was oxidized rapidly by OH• and the aggregation of the resulting As(V)-Fe(III) polymers was enhanced by the presence of Mn. At pH 8.5, As(III) and Mn(II) competed for Fe(IV), which led As(III) to persist in solution. The As(V) that did form was incorporated into a mixture of As(V)-Fe(III) polymers and a ferrihydrite-like phase that incorporated 8% Mn(III); some As(III) was also sorbed by these phases. At intermediate pH values, As(III) and Mn(II) also competed for the oxidants, but Mn(III) behaved as a reactive intermediate that reacted with Fe(II) or As(III). This result can explain the presence of As(V) in the solid phase. This detailed understanding of the As removal mechanisms in the presence of Mn can be used to tune the operating conditions of Fe EC for As removal under typical groundwater conditions.

Electrocoagulants Characteristics and Application of Electrocoagulation for Micropollutant Removal and Transformation Mechanism.

Predominantly, the removal of dissolved contaminates via the Fe electrocoagulation (EC) process depends on the electrocoagulants stability, specific area, porosity, dissolution rate, and phase transformation kinetics. The present investigation elucidates the role of applied currents and electrolyte counteranions on the crystalline phase and surface topography of electrocoagulants generated from Fe EC. Moreover, the dissolved contaminant micropollutant removal efficiency was also evaluated by electrochemically produced coagulants. This study confirms that mixed-phase iron (oxyhydr) oxide nanostructures were consistently produced from Fe EC with predominant formation of the goethite phase. The applied current controls the morphology of the coagulants, with flake-like morphology observed with currents at and below 100 mA and spherical morphology observed with currents above 100 mA. The counteranions in the electrolyte also impacted the morphology with spherical, nanosheet, and nanorod morphologies produced by Cl- or SO42-, CO32-, and HCO3- counteranions, respectively. BET analysis revealed the formation of electrocoagulants with micro-, meso-, and macropores. Surface area was markedly reduced from 142.85 to 41.96 m2 g-1 by incident coagulation resulting from increased anodic dissolution. Applicability of the electrocoagulant was examined by different micropollutants (acetaminophen (AC), antipyrine (AT), and atenolol (AT)). Results suggest that >90% and >80% TOC reduction were achieved with Na2CO3 and NaHCO3 as electrolyte media. The lower TOC reduction was rationalized by the identified intermediate products, and possible micropollutant degradation pathways were proposed based on LC-MS/MS analysis.

Treatment of Sb(V) and Co(II) containing wastewater by electrocoagulation and enhanced Sb(V) removal with Co(II) presence

Antimony (Sb) and cobalt (Co) are toxic to human if present in high concentrations. The existence of Sb and Co pollution in some mining areas has generated the need for an effective Sb and Co treatment method. In this work, the removal of pentavalent antimony (Sb(V)) and bivalent cobalt (Co(II)) by iron (Fe) electrocoagulation (EC) was investigated. The interaction between Sb(V) removal and Co(II) removal in Fe EC was studied. Results indicated that both Sb(V) and Co(II) can be effectively removed in Fe EC process. At the current density of 5 mA cm−2, the concentration of Sb(V) and Co(II) can be reduced from 60 mg/L and 29 mg/L to below 0.1 mg/L within 20 min by EC process. Interestingly, the existence of Co(II) ions has promoted the removal of Sb(V) in EC. Through the characterization of the precipitates by Raman and XRD techniques, it was found that layered double hydroxides (LDHs) can be more steadily formed with the existence of Co(II) in EC, which has facilitated the removal of Sb(V). During the EC process, Co was primarily removed through precipitation (95.2%) and electrodeposition onto the cathode (4.8%), and Sb was mainly removed by the formed flocs from water.