Study of the Effects of the Use of Synthetic Domestic Water in an Electro-Fenton Reactor for the Discoloration of Brilliant Blue
Authors: Camacho Edgar , Godinez Mora-Tovar Luis Arturo , Robles Irma 
Published: February 2020

Biological methods are the most commonly used to treat effluents with high organic loads from sanitary water and industrial waste, mainly through aerobic fermentation. An effective alternative for water treatment are advanced oxidation methods, based on the Fenton reaction, where hydrogen peroxide (H2O2) reacts with iron ions (Fe2+) to obtain hydroxyl radicals (OH•), with a power of oxidation of 2.8 V vs ENH.

These methods have been used currently for the degradation of a wide range of pollutants, especially they have focused on the treatment of sanitary water in order to degrade pathogenic microorganisms. Therefore, the objective of this study was to evaluate the effect of the composition of a synthetic domestic wastewater, high in chlorides, which acts as an electrolyte in an electrochemical system named as electro-Fenton, where H2O2 is obtained by oxygen reduction reaction. Water composition effect was studied in an electro-Fenton (EF) (1.4V) laboratory scale system consisting of a device packed with activated carbon (previously saturated with brilliant blue as model pollutant), with graphite cloth and iron mesh electrodes;in order to evaluate EF efficiency, the adsorption (A) and electro-oxidation (Eox) was compared in separate systems to treat a solution of direct blue 1 [20 mg / L] in 20 minutes. A control system composed of distilled water was used, where the aforementioned effects were also compared. The color concentration at the output of the reactor was evaluated by means of UV-Vis spectrophotometry, as well as the iron Fe2+ and FeTOT concentrations by phenanthroline method. Activated activated carbon was also analyzed by scanning electron microscopy (SEM) to determine whether each treatment promotes a change in the morphology into the activated carbon.

As a result, it was obtained that the control system presented better discoloration results being: EF> EOx> A; unlike the system with synthetic residual water: A> EF> EOx with no significative difference between treatments. Distilled water showe 70% higher efficiency than synthetic water system. The pH and conductivity showed the same tendency as discoloration. The iron concentration at the system outlet was 5 mg/L of Fe2+ and 6 mg/L of FeTOT, for the control system; and 3 mg/L of Fe2+ and 4 mg/L of FeTOT in the synthetic wastewater system.

It is concluded that the composition of synthetic water, mostly chlorides, favors the accumulation of chlorine ions in activated carbon, which interferes with the discoloration process, since the destruction of the dye molecule is limited. There is a decrease in pH and conductivity that is attributed to the Fenton reaction.

SEM images showed differences between processes, as shown in the attached figure, which is attributed to the effect of formation of oxidizing species on the activated carbon surface. A greater difference is obscured in the Eox system, which suggests that the EF system is imitated by the high concentration of chlorine ions.

Figure 1