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Włodarczyk-Makuła, M.; Myszograj, S.; Włodarczyk, M. Use of Electrocoagulation in Wastewater Treatment. Encyclopedia. Available online: https://encyclopedia.pub/entry/48029 (accessed on 08 May 2024).
Włodarczyk-Makuła M, Myszograj S, Włodarczyk M. Use of Electrocoagulation in Wastewater Treatment. Encyclopedia. Available at: https://encyclopedia.pub/entry/48029. Accessed May 08, 2024.
Włodarczyk-Makuła, Maria, Sylwia Myszograj, Maciej Włodarczyk. "Use of Electrocoagulation in Wastewater Treatment" Encyclopedia, https://encyclopedia.pub/entry/48029 (accessed May 08, 2024).
Włodarczyk-Makuła, M., Myszograj, S., & Włodarczyk, M. (2023, August 14). Use of Electrocoagulation in Wastewater Treatment. In Encyclopedia. https://encyclopedia.pub/entry/48029
Włodarczyk-Makuła, Maria, et al. "Use of Electrocoagulation in Wastewater Treatment." Encyclopedia. Web. 14 August, 2023.
Use of Electrocoagulation in Wastewater Treatment
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This entry is adapted from the peer-reviewed paper 10.3390/en16155591

Electrocoagulation (EC) is a wastewater treatment method based on chemical reactions between a coagulant formed under the influence of an electric current released from a given electrode. Electrocoagulation is a technology that properly combines electrochemistry, coagulation, and flotation (or sedimentation). This technology consists of four main stages: electrolytic reaction on the surface of the electrode, formation of metal hydroxides (coagulants), adsorption of soluble (colloidal) particles on coagulants, and removal by sedimentation or flotation. Reactions between the coagulant and pollutants lead to precipitation of sediments which are removed by sedimentation or flotation.

electrocoagulation wastewater coagulant coagulation flotation sediments

1. Introduction

The amount of organic micro-pollutants introduced into the aquatic environment from anthropogenic sources is much greater than that resulting from natural processes. This applies mainly to industrial activities in which coal and metal ores are processed, crude oil is refined, and chemicals, pharmaceuticals, textiles, or cosmetics are produced [1][2]. The concentration of organic micro-pollutants in the industrial wastewater depends on the type of industrial activity, type of raw materials, production technology, as well as the applied methods of wastewater treatment. Many processes are used to pre-treat the contaminated outflows before they are put into sewage systems or into an aquatic environment. However, even highly pre-treated wastewater contains organic compounds that are difficult to degrade and is characterised by high chemical oxygen demand (COD) values and relatively low biochemical oxygen demand (BOD) values. The low values of the ratio between these indicators shows a low susceptibility to biodegradation [3]. Persistent organic micro-pollutants (POPs) include polycyclic aromatic hydrocarbons (PAHs), halogenated organic compounds (AOX), di-2-ethylhexyl phthalates (DEHP), nonylphenols (NPE) and nonylphenol ethoxylates (NPEO), as well as selected surfactants such as linear alkylbenzene sulfonate (LAS), pharmaceuticals (PhACs), cosmetics (PPCPs—pharmaceuticals and personal care products), flame retardants (FRs), and many more [4][5][6]. POPs accumulate in the tissues of living organisms and display carcinogenic, mutagenic, and other undesirable health effects, such as endocrine disorders [7][8]. The removal rate of organic compounds from wastewater by biological methods used in conventional treatment plants is insufficient; thus, the treatment requires additional processes to ensure effective removal of organic compounds [9][10][11][12][13]. These include those that provide only the separation of pollutants but do not solve the problem of their occurrence, and those that ensure the degradation of compounds that are difficult to decompose [14]. Separation methods include coagulation, adsorption, flotation, and membrane separation. Among the membrane methods, pressure methods such as ultrafiltration, nanofiltration, and reverse osmosis are the most widely used in wastewater technology [15]. Methods ensuring degradation of persistent organic compounds include advanced oxidation processes (AOPs) [16][17][18][19]. These include chemical and catalytic processes, supported by an additional source of energy, as well as ones that do not use the latter. In these processes, as a result of subsequent chemical reactions, free radicals are generated, mainly hydroxyl radicals (HO•) with a high oxidizing potential, facilitating the destruction of most organic compounds. However, a disadvantage of these processes consists of the formation of intermediate products with different activity toward test organisms. Therefore, new solutions are currently being sought and research is being undertaken to modify known and used processes to ensure complete oxidation of organic compounds and reduce the toxicity of post-reaction solutions. In this respect, the proposed solutions concern, among others, supporting classic processes with solar, ultraviolet, or gamma radiation, as well as electricity. In relation to methods supported by electricity, such processes as electrocoagulation, electroflotation, and chemical and photochemical AOP (electro-Fenton, sono-electro-Fenton, photo-electro-Fenton) can be included [20][21][22][23][24][25][26].

2. Electrocoagulation

Flotation is caused by micro bubbles of gas released as a result of the redox reaction that takes place during the flow of electricity through the solution. The precipitates are collected in the form of scum on the surface and create sediments after degassing. The materials most often used for constructing electrodes utilized in the electrocoagulation process are aluminium and iron. As a result of the flow of electric current through the solution (sewage), Al3+ aluminium cations and Fe2+ iron cations are released—Reactions (1) and (2). Aluminium ions form hydroxide (Reaction (3)), while hydrogen is released on the cathode (Reaction (4)) [23][27].
Anode:
Fe0(s)→Fe2+(aq)+2e−Fe(s)0→Fe(aq)2++2e−                                                                       (1)
Al(s)→Al3+(aq)+3e−Al(s)→Al(aq)3++3e−                                                                               (2)
Al3+(aq)+3H2O→Al(OH)3(s)+3H+Alaq3++3H2O→Al(OH)3(s)+3H+                                      (3)
Cathode:
H2O(l)+3e−→1.5H+(g)+3OH−(aq)H2O(l)+3e−→1.5H(g)++3OH(aq)−                                    (4)
During electrocoagulation, iron hydroxides are formed as a result of Reactions (1) and (5)–(7).
Fe2++2OH−→Fe(OH)2Fe2++2OH−→Fe(OH)2                                                                      (5)
Fe2+−e−→Fe3+Fe2+−e−→Fe3+                                                                                            (6)
Fe2++OH−−e−→Fe(OH)3Fe2++OH−−e−→Fe(OH)3                                                             (7)
During the electrocoagulation process, depending on the reaction of the environment, transitional ionic forms of iron (Fe(OH)2+, Fe(OH)4–, Fe2(OH)24+, Fe(H2O)4(OH)2+) may be created, which then form iron (III) hydroxide [28]. The consumption of an aluminium electrode (C) in reference to the unit of treated wastewater (kg Al/m3) is calculated using the Faraday law according to Equation (8):
C=I·t·M·10−3z·F·VC=I·t·M·10−3z·F·V                                                                                    (8)
where
  • I the current intensity (A);
  • t the retention time (s);
  • V the volume of the treated wastewater (m3);
  • F the Faraday’s constant (96.487 C/mol);
  • M the mass of aluminium (26.98 g/mol) and mass of iron (55.847 g/mol);
  • z the number of electron transfer (e.g., zAl = zFe = 3).
Specific energy consumption, E, is calculated according to Equation (9) [27]:
E=U·I·t(COD0−CODt)·VE=U·I·tCOD0−CODt·V                                                                       (9)
where
  • E the specific energy consumption (kWh/kg of COD removed);
  • U the applied voltage (V);
  • I the current intensity (A);
  • t the retention time (h);
  • COD0 the chemical oxygen demand before treatment (g/L);
  • CODt the chemical oxygen demand after treatment (g/L);
  • V the volume of the treated wastewater (L).
The system consists of a reactor equipped with a stirrer (or allowing the solution to be mixed), a set of electrodes, a source of electricity, and a system for dosing and discharging the polluted solution. The possibility of removing the post-coagulation sediment, and in some cases changing the electrode connection to the power source, is also taken into account. The basic parameters that affect the process are electrode material and distance between them, electric current intensity and density, pH value of the solution, and initial concentration of pollutants. The literature data indicate that the electrocoagulation process was used to remove pollutants occurring in wastewater such as: tannery, galvanic, and dyeing wastewater, waste from metal processing plants, waste containing oil emulsions, textile wastewater, wastewater from oil presses, and laundry wastewater [17][29][30][31]. This method has been shown to be useful for removing arsenic, polyvinyl alcohol, 4-nitrophenol, dyes, fluorine, nitrates, petroleum derivative hydrocarbons, chromium, phosphates, as well as phenol and phenolic compounds [22][26][32][33][34][35][36][37][38][39].
Example studies concerning using the EC method to remove dyes from solutions, and the results of these studies demonstrated that the efficiency of removal of these xenobiotics can reach 97%. The decrease in the value of COD was at the level of 92%. Example studies examining the application of the electrocoagulation process concerned removal of pharmaceutical residues from actual sewage [33] also demonstrated that this method can be used for removal of fluorides from contaminated water. The research was carried out in a labyrinth reactor, where properly set partitions ensured flow between them, which extended the reaction time. The reactor included six alloy electrodes and was powered by a 30 V direct current. The initial fluoride concentration was at the level of 20 mg/L. Three process parameters were optimized: current density (1.5, 2.5, and 3.5 mA/cm2), pH (4, 7, and 10), and the distance between electrodes (5, 10, and 15 mm). After 30 min of the process, the fluoride concentration did not exceed the limit value for drinking water determined by the WHO (<1.5 mg/L) at pH 7, current density of 2.5 mA/cm2, and the distance between electrodes equal to 5 mm. The purification cost was estimated at 0.346 USD/m3 with energy consumption at the level of 5.03 kWh/m3. Smoczyński et al. conducted research concerning electrocoagulation of model wastewater using electrodes made of iron [28]. The research was carried out at a constant current intensity (0.3 A) analysing changes in pH, suspensions and turbidity, COD, and total phosphorus in the purified solutions. At fixed time intervals (256 s), the direction of current flow on the electrodes was changed in the system. Changing the role of the contaminated cathode into a soluble anode allowed it to be purified as a result of anodic dissolution. The efficiency of organic compound removal expressed by the COD index was 43%, and the removal of turbidity was equal to 62%. There was a decrease in the concentration of suspensions by 81% and phosphorus by 51–58%. It was determined that the most favourable conditions for phosphorus removal occur when the molar relationship Fe:P is greater than 1:3, which at the same time prevents the formation of post-coagulation sediments: Fe3(PO4)2, FePO4, (FeOH)3(PO4)2, and (FeOH)3PO4.
In the EC process, the amount of sediment is smaller than in the classical coagulation process, the system is not complicated, does not require any large objects to be provided, and can also be mobile. There is no thickener required as there would be in chemical classic coagulation, which reduces the operation cost. Other advantages include: no risk of residual chemicals in the effluent (toxins and odours), metals can be recovered from the solution. In most cases, this process does not require much energy to operate the coagulation equipment. This low level can easily be produced using green energy sources.

References

  1. Abdel-Shafy, J.H.I.; Mansour, M.S.M. A review on polycyclic aromatic hydrocarbons: Source, environmental impact, effect on human health and remediation. Egypt. J. Pet. 2016, 25, 107–123.
  2. Luo, Y.; Guo, W.; Ngo, H.H.; Nghiemb, L.D.; Hai, F.I.; Zhang, J.; Liang, S.; Wang, X.C. A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment. Sci. Total Environ. 2014, 473, 619–641.
  3. Samer, M. (Ed.) Biological and Chemical Wastewater Treatment Processes; IntechOpenLimited: London, UK, 2015; ISBN 978-953-51-6390-92014.
  4. European Community. European Community Regulation No. 850/2004, Persistent Organic Pollutants in the Environment, Information Materials; European Community: Warsaw, Poland, 2008.
  5. Włodarczyk-Makuła, M. Physical and Chemical Fates of Organic Micropollutants; Scholar Press, OmniScriptum GmbH & Co. KG: Saarbrucken, Germany, 2015; ISBN 978-3-639-85930-0.
  6. Płuciennik-Koropczuk, E.; Myszograj, M.; Myszograj, S. The influence of the Poles’ lifestyle on the quantity and quality of municipal wastewater. Civ. Environ. Eng. Rep. 2021, 31, 265–275.
  7. International Agency for Research on Cancer. Polychlorinated and Polybrominated Biphenyls, 107, Monographs on the Evaluation of Carcinogenic Risks to Humans; International Agency for Research on Cancer: Lyon, France, 2015; ISBN 978-92-832-0173-1.
  8. International Agency for Research on Cancer. Some Non-Heterocyclic Polycyclic Aromatic Hydrocarbons and Some Related Exposures, 92, Monographs on the Evaluation of Carcinogenic Risks to Humans; International Agency for Research on Cancer: Lyon, France, 2010; ISBN 978-92-832-1292-8.
  9. Petrie, B.; Barden, R.; Kacprzyk-Hordern, A. A review on emerging contaminants in wastewaters and the environment: Current knowledge, understudied areas and recommendations for future monitoring. Water Res. 2015, 72, 3–27.
  10. Gracia-Lor, E.; Sancho, J.V.; Serrano, R.; Hernández, F. Occurence and removal of pharmaceutical in wastewater treatment plants AT the Spanish Mediterranean area of Valencia. Chemosphere 2012, 87, 453–462.
  11. Gerrity, D.; Snyder, S. Wastewater and drinking water treatment technologies. In Human Pharmaceuticals in the Environment: Current and Future Perspectives, Emerging Topics in Ecotoxicology; Brooks, B.W., Huggett, D.B., Eds.; Springer: Berlin, Germany, 2012.
  12. Giannakis, S.; Vives, F.A.G.; Grandjean, D.; Magnet, A.; De Alencastro, L.F.; Pulgarin, C. Effect of advanced oxidation processes on the micropollutants and the effluent organic matter contained in municipal wastewater previously treated by three different secondary methods. Water Res. 2015, 84, 295–306.
  13. Köck-Schulmeyer, M.; Villagrasa, M.; López de Alda, M.; Céspedes-Sánchez, R.; Ventura, F.; Barceló, D. Occurrence and behavior of pesticides in wastewater treatment plants and their environmental impact. Sci. Total Environ. 2013, 458–460, 466–476.
  14. Włodarczyk-Makuła, M.; Wiśniowska, E.; Turek, A.; Obstój, A. Removal of PAHs from coking wastewater during photo degradation process. Desalination Water Treat. 2016, 57, 1262–1272.
  15. Bodzek, M. Membrane technologies for the removal of micropollutants in water treatment. In Advances in Membrane Technologies for Water Treatment: Materials, Processes and Applications; Basile, A., Cassano, A., Rastogi, N., Eds.; Elsevier Science: Amsterdam, The Netherlands; Woodhead Publishing Ltd.: Cambridge, UK, 2015; pp. 465–515.
  16. Andreozzi, R.; Caprio, V.; Insola, A.; Marotta, R. Advanced oxidation processes (AOP) for water purification and recovery. Catal. Today 1999, 53, 51–59.
  17. Santos-Juanes Jorda, L.; Ballesteros Martın, M.M.; Ortega Gomez, E.; Cabrera Reina, A.; Roman Sanchez, I.M.; Casas Lopez, J.L.; Sanches Perez, J.A. Economic evaluation of the photo-Fenton process. Mineralization level and reaction time: The keys for increasing plant efficiency. J. Hazard. Mater. 2011, 186, 1924–1929.
  18. Gopinath, A.; Pisharody, L.; Popat, A.; Nidheesh, P.V. Supported catalysts for heterogeneous electro-Fenton processes: Recent trends and future directions. Curr. Opin. Solid State Mater. Sci. 2022, 26, 100981.
  19. Cheng, M.; Guangming, Z.; Huang, D.; Lai, C. Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds-a review. Chem. Eng. J. 2016, 284, 582–598.
  20. Gzar, H.A.; Jasim, N.A.; Kseer, K.M. Electrocoagulation and chemical coagulation for treatment of Al-Kut textile wastewater: A comparative study. Period. Eng. Nat. Sci. 2020, 8, 1580–1590.
  21. Rafique, L.; Adnan, A.; Taha, A.; Bano, S.; Vambol, S.; Mushtaq, T.; Ilyas, N.; Hussain, S.; Borysova, L.; Kovalov, O. Application of copper and aluminium electrode in electro coagulation process for municipal wastewater treatment: A case study at Karachi. Ecol. Quest. 2023, 34.
  22. Nassar, S.O.A.; Yusoff, M.S.; Halim, H.; Kamal, N.H.M.; Bashir, M.J.K.; Manan, T.S.B.A.; Aziz, H.A.M.; Mojiri, A. Ultrasonic (US)-Assisted electrocoagulation (EC) process for oil and grease (O&G) removal from restaurant wastewater. Separations 2022, 10, 61.
  23. Mores, R.; Mello, P.D.A.; Zakrzevski, C.A.; Treichel, H.; Kunz, A.; Steffens, J.; Dallago, R.M. Reduction of soluble organic carbon and removal of total phosphorus and metals from swine wastewater by electrocoagulation. Braz. J. Chem. Eng. 2018, 35, 1231–1240.
  24. Can, O.T. COD removal from fruit-juice production wastewater by electrooxidation electrocoagulation and electro-Fenton processes. Desalination Water Treat. 2014, 52, 65–73.
  25. Marlina, E.; Purwanto, P. Electro-Fenton for industrial wastewater treatment: A review. In Proceedings of the 4th International Conference on Energy, Environment, Epidemiology and Information System (ICENIS 2019), Semarang, Indonesia, 7–8 August 2019; Volume 125, p. 03003.
  26. McGinnis, B.D.; Adams, V.D.; Middlebrooks, E.J. Degradation of ethylene glycol in photo Fenton systems. Water Res. 2000, 34, 2346–2354.
  27. Khaldi, S.; Lounici, H.; Drouiche, M.; Drouiche, N. Treatment of ointment pharmaceutical wastewater by electrocoagulation process. Desalination Water Treat. 2017, 71, 152–158.
  28. Smoczyński, L.; Muńska, K.M.; Pierożyński, B.; Kosobucka, M. Electrocoagulation of model wastewater on iron electrodes. Proc. ECOpole 2012.
  29. Posavcic, H.; Halkijevic, I.; Vouk, D. Oily wastewater treatment by hybrid ultrasound and electrocoagulation batch process. Desalination Water Treat. 2021, 235, 127–134.
  30. Özyonar, F.; Gökkuş, Ö.; Sabuni, M. Removal of disperse and reactive dyes from aqueous solutions using ultrasound-assisted electrocoagulation. Chemosphere 2020, 258, 127325.
  31. Pignatello, J.J.; Oliveros, E.; MacKay, A. Advanced oxidation processes for organic contaminant destruction based on the Fenton reaction and related chemistry. Crit. Rev. Environ. Sci. Technol. 2006, 36, 1–84.
  32. Comninellis, C.; Kapalka, A.; Malato, S.; Parsons, S.A.; Poulios, I.; Mantzavinos, D. Advanced oxidation processes for water treatment: Advances and trends for R&D. J. Chem. Technol. Biotechnol. 2008, 83, 769–776.
  33. Abdulredha, M.; Al-Samarrai, S.Y.; Hussein, A.H.; Samaka, I.; Al-Ansari, N.; Aldhaibani, O.A. Electrochemical defluorination of water: An experimental and morphological study. J. Water Sanit. Hyg. Dev. 2022, 12, 394.
  34. Medel, A.; Lugo, F.; Meas, Y. Application of electrochemical processes for treating effluents from hydrocarbon industries. In Electrochemical Water and Wastewater Treatment; Butterworth-Heinemann: Oxford, UK, 2018; pp. 365–392.
  35. Ai, Z.; Lu, L.; Li, J.; Zhang, L.; Qiu, J.; Wu, M. Fe2O3 core–shell nanowires as iron reagent. Efficient degradation of Rhodamine B by a noval sono-Fenton process. J. Phys. Chem. C 2007, 111, 4087–4093.
  36. Molina, R.; Martinez, F.; Melero, J.A.; Bremner, D.H.; Chakinala, A.G. Mineralization of phenol by a heterogeneous ultrasound/Fe-SBA-15/H2O2 process: Multivariate study by factorial design of experiments. Appl. Catal. B Environ. 2006, 66, 198–207.
  37. Sirtori, C.; Zapata, A.; Gernjaka, W.; Malato, S.; Lopez, A.; Agüera, A. Solar photo-Fenton degradation of nalidixic acid in waters and wastewaters of different composition. Analytical assessment by LC–TOF-MS. Water Res. 2011, 45, 1736–1744.
  38. Guivarch, E.; Trevin, S.; Lahitte, C.; Oturan, M.A. Degradation of azo dyes in water by electro-Fenton process. Environ. Chem. Lett. 2003, 1, 38–44.
  39. Da Rocha, O.R.S.; Dantas, R.F.; Bezerra, M.M.M.; Lima, M.M.; Lins, V. Solar photo-Fenton treatment of petroleum extraction wastewater. Desalination Water Treat. 2013, 51, 5785–5791.
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Maria Włodarczyk-Makuła
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Sylwia Myszograj
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Maciej Włodarczyk
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Entry Collection: Wastewater Treatment
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Update Date: 14 Aug 2023
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