Optimization of the Electrocoagulation Process with Aluminum Electrodes for Rainwater Treatment

Abstract

Rainwater collected in the Toluca region of Mexico with a pH of 6.25 was treated with an electrochemical process, and the efficiency of two supporting electrolytes were compared, one food grade (sea salt) and the other reagent grade (sodium sulfate). In the first stage, rainwater was characterized to detect the COD content, turbidity, metals such as zinc, iron, aluminum, and lead. Electrocoagulation treatment was performed with an electrochemical cell using aluminum electrodes to study the effect on COD and turbidity, as well as the removal of heavy metals present. The results obtained with response surface methodology and a central composite design reveal that the optimal conditions of the electrocoagulation treatment were a current density of 3.26 mA/cm2 and a time of 11.38 min. Using sodium sulfate, the percentage of turbidity removal is 99.27% and COD 70.83%. The use of sea salt as a support electrolyte in these conditions allowed the removal of COD at 100%, turbidity at 100%, and Al 100%, Mn 84.29%, Zn 97.97%, Pb 46%, Fe 21%. Energy costs that are low lead to proven savings when using this system, indicating that this treatment is an option to both improve rainwater conditions and be able to make use of it safely.

Electrocoagulation using aluminum electrodes as a sustainable and economic method for the removal of kinetic hydrate inhibitor (polyvinyl pyrrolidone) from produced wastewaters

“…In an electrochemical coagulation process, the metal cations are generated in situ and the elimination of pollutants from the water takes place. The electrocoagulation starts by the generation of coagulants by electrochemical dissolution of the anode material, followed by neutralization of the colloidal charges, co-precipitation of heavy metals, and breaking up of oil/water emulsions, and finally the formation of flocs that sediment (Mollah et al, 2001(Mollah et al, , 2004Akter et al, 2022;Morales-Figueroa et al, 2022;Othmani et al, 2022). The anodic dissolution of aluminum and iron electrodes generates the corresponding metal cations, which hydrolyze immediately and form hydroxo-metal complexes (Ghernaout, 2018;Morales-Figueroa et al, 2022;Othmani et al, 2022).…”

“…The electrocoagulation starts by the generation of coagulants by electrochemical dissolution of the anode material, followed by neutralization of the colloidal charges, co-precipitation of heavy metals, and breaking up of oil/water emulsions, and finally the formation of flocs that sediment (Mollah et al, 2001(Mollah et al, , 2004Akter et al, 2022;Morales-Figueroa et al, 2022;Othmani et al, 2022). The anodic dissolution of aluminum and iron electrodes generates the corresponding metal cations, which hydrolyze immediately and form hydroxo-metal complexes (Ghernaout, 2018;Morales-Figueroa et al, 2022;Othmani et al, 2022). Theses hydroxo-metal complexes (Ghernaout, 2018;Morales-Figueroa et al, 2022;Othmani et al, 2022) combine with the negative colloidal particles and destabilize them.…”

“…The anodic dissolution of aluminum and iron electrodes generates the corresponding metal cations, which hydrolyze immediately and form hydroxo-metal complexes (Ghernaout, 2018;Morales-Figueroa et al, 2022;Othmani et al, 2022). Theses hydroxo-metal complexes (Ghernaout, 2018;Morales-Figueroa et al, 2022;Othmani et al, 2022) combine with the negative colloidal particles and destabilize them. The water pollutants can be eliminated by different routes including adsorption on the surface of the coagulants, co-precipitation, or by incorporation inside the structure of the hydroxo-metal complexes (Al-Qodah and Al-Shannag, 2017;Hendaoui et al, 2021;Akter et al, 2022;Othmani et al, 2022;Hu et al, 2023).…”

“…These metal cations undergo further spontaneous reactions to produce hydroxides, oxyhydroxides and/or corresponding poly-hydroxides. (Khadir et al, 2021;Trompette and Lahitte, 2021;Zeng et al, 2021;Morales-Figueroa et al, 2022). These hydrolysis products have a high affinity for the dispersed particles and the charged particles to cause their coagulation.…”

“…The pitting corrosion of aluminum is much more vulnerable than other metals. The addition of certain supporting electrolytes such as NaCl, can reduce the passivation of the electrodes and improve ionic conductivity of the solution (Mansouri et al, 2011a(Mansouri et al, , 2012Acharya et al, 2022;Morales-Figueroa et al, 2022;Medina-Collana et al, 2023). The use of an alternating current source with variable pulse frequency can also prevent the formation of deposits on the surface of the electrodes (Asaithambi et al, 2021;Othmani et al, 2022).…”