Letter to the Editor: Regarding the “Simultaneous Removal of Turbidity and Humic Acid Using Electrocoagulation/Flotation Process in Aqua Solution”

We would like to comment on the above paper, which was published in Avicenna J Environ Health Eng 2(1) 2015 (1). The study is worthwhile in terms of its application of green methods for removing humic acid (HA) and turbidity. However, we would like to point out some deficiencies in the study design. The authors have claimed that they have employed an electrocoagulation process for the coagulation and flocculation of the pollutants and air spray through an air pump for floatation; the role of scarified anode of aluminum and iron is to produce metal ions and, in turn, coagulant agents Fe(OH)3 and Al(OH)3, but, in this study, the authors have not dealt with the role of cathodes because, based on the following reactions, water is reduced and hydrogen gas is created. This plays an important role in flotation. It should be noted that an air spray can only contribute to the electrocoagulation process. The process of electrocoagulation includes a series of reactions, such as coagulation, flocculation and floatation; the authors have not mentioned these reactions, as follows (2): Equilibrium 1. 2H2O + 2e− → H2 (g) + 2OH− Equilibrium 2. 2H3O + 2e− → 2H2O + H2 (g) The authors have applied the hybrid process of electrocoagulation/flotation to treat the pollutants and optimized only the variables of electrocoagulation: solution pH, electrical potentials, initial turbidity concentration, and reaction time with or without HA. It is also important to optimize flotation variables such as airflow rate and the size of gas bulbs. Another point to make here is to question why the authors have optimized the electrical potential. We believe that they should have optimized the current density. It is thought that current density is entirely important in industrial and economical applications. The use of fixed potential to make sure of oxidation or the reduction of a certain species is clear. Therefore, in order to optimize electrochemical methods, the fixed current phase is used. This enables us to study projects in terms of economic and energy consumption features and scaling up. In this study, the comparison of theoretical consumption and laboratorial consumption of the electrodes aluminum and iron, as well as energy consumption calculations, have not been tackled, though they are very important (3, 4).