Comparative evaluation of an advanced electrocoagulation treatment system versus a conventional lime softening treatment for removing Ca2+, SO42−, and Mn in groundwater

• Published in: Case studies in chemical and environmental engineering 2023-12, Vol.8, p.100448, Article 100448
• Main Authors: Mendez-Ruiz, Jonathan I., Medina-Toala, Angie N., Gutierrez, Leonardo, Valverde-Armas, Priscila E.
• Format: Article
• Language: English
• Subjects: Alum coagulation; Chemical precipitation; Electrochemical process; Sustainability; Vulnerable communities
• ISSN: 2666-0164; 2666-0164
• DOI: 10.1016/j.cscee.2023.100448

This research aims to evaluate the feasibility of a laboratory-scale batch electrocoagulation system for removing hardness, SO42−, and manganese from groundwater in San Cristobal, a rural community in the Austro region of Ecuador. The efficiency of the electrocoagulation process was compared to the conventional chemical precipitation with lime and alum coagulation. Various variables were analyzed to evaluate the performance of the electrocoagulation system, including initial pH, operating time, current density, and lime addition. The results showed that a basic environment (∼ pH 8.5) proved more effective in removing hardness and SO42− electrolytes by producing ferric flocs with high adsorption properties. Achieving reasonable removal efficiencies for hardness and SO42− under neutral or alkaline solution required a minimum of 80 min. Increasing the current density enhanced the removal of hardness and sulfate, and the addition of small amounts of lime (125 mg L−1) increased the hardness removal efficiency from approximately 35 to 50.5%. Under the operating conditions of pH 8.5, 80 min of operation, a current density of 1.0 mA cm−2, and a lime concentration of 75 mg L−1, the system achieved a removal efficiency of 37.6% for hardness, 14.7% for SO42−, and a 65.3% for manganese to comply with Ecuadorian drinking water criteria. While lime precipitation and alum coagulation reduced hardness to meet the Ecuadorian INEN 1108 Regulation requirements, the significant demand for treatment chemicals to reduce hardness content rendered the process unsustainable for implementation in the San Cristobal treatment plant. The conventional treatment method failed to reduce sulfate or manganese, and the excessive chemical consumption was not economically viable (1 kg of lime and 0.02 kg of alum per cubic meter of water). In conclusion, this study demonstrates that electrocoagulation, as a chemical-free system, minimizes the use of chemical additives to provide safe water to the population of San Cristobal.