Mechanisms behind pH changes during electrocoagulation

Electrocoagulation is a promising method for removing pollutants from surface water and industrial wastewater. The coagulation efficiency is dependent on pH but it is not fully understood how electrocoagulation affects pH of the treated water. Three series of experiments have been conducted to study how (1) chloride and sulfate anions, (2) negatively charged organic macromolecules, and (3) carbonate influence pH during electrocoagulation. It is found that dissolved carbonate has a significant influence on the pH change as CO₂ is stripped off during electrocoagulation due to formation of H₂ microbubbles at the cathode. The pH increased by (Formula presented.) 1 pH unit, which may significantly affect coagulation efficiency of iron. The pH increase depended strongly on the initial pH and the concentration of carbonate in the water. A secondary contribution to pH change was found to be ion exchange by sulfate and chloride ions into Fe(OH)₃ flocs, whereby OH⁻ was released into solution but only minor pH change was observed, not enough to affect the coagulation. The presence of charged organic macromolecules did not have any significant effect on pH.