ANALYSIS OF THE EFFICIENCY OF THE ELECTROCOAGULATION PROCESS IN THE REMOVAL OF MICROPLASTICS

Purpose : The purpose of this study was to apply electrocoagulation with aluminum electrodes to evaluate the removal efficiency of microplastic in the form of Glitter. Method : This study consisted of an experimental system, composed of a benchtop scale reactor, with aluminum electrodes inside, connected to a direct current source, responsible for performing the water electrolysis process, forming microbubbles and the chemical coagulation process, contributing to the formation of microplastic aggregates Results and conclusion : The results showed high efficiency of microplastic removal in the form of glitter that increased proportionally with the increase in conductivity and current intensity. The maximum efficiency achieved was equal to 90.3%. Implications of the research : As demonstrated by the results of the experimental assays, the electrocoagulation technique proved to be very efficient to make the removal of microplastic in the form of glitter. Originality/value : It has been shown that it is possible to remove microplastic in an efficient way, without the need for the introduction of an external coagulant because it was generated within the system itself.


INTRODUCTION
Over the past century, the plastics industry has come to the fore and developed to the point where it is massively present in people's lives. According to the Sydney Environmental Protection Authority, the use of plastic has increased significantly, with the presence of the material expected to double in the coming decades, both on land and in water (EPA, 2016). Considering an assessment since the year 2016, there will be in the marine environment, more than 150 million tons of plastic waste, and from this estimate, about 1.5% of microplastic will be present (Gouin et al, 2015).
Microplastics (PMS) were recently included by the European scientific community in the list of global problems, as they are a type of pollutant from the use and disposal of plastic material. Currently, they are found in water bodies, soils, effluent treatment plants, drinking water and aquatic organisms (Massuga et al, 2022;Shen et al, 2021a).
Plastic materials can be categorized into primary and secondary, depending on their source (Jones, 2019). Those present in cosmetic products or toothpastes, for example, are considered to be of primary source. Those resulting from the degradation of plastics of greater proportion, such as textile materials, tires and plastic bags, are of secondary source.
In this paper authors present the results of microplastic removal by electrocoagulation with aluminum electrodes, in order to define current intensity, pH and efficiency of a benchscale system in the removal of microplastic in the form of glitter.

THEORETICAL FRAMEWORK
Due to their wide surface area, persistence and fluidity, MPs are easy to chemically adsorb organic pollutants, heavy metals and harmful bacteria, increasing their impact on the aquatic environment and human health. The toxic chemicals, adsorbed in the MP are also harmful to aquatic organisms that, as they serve as food for people, consequently, their health will be compromised (Shen et al, 2021b). The presence of PM in natural waters is worrisome because it has a potential impact on the marine biota, affecting the trophic chains of ecosystems. Due to their small size, below 5 mm, and low density, the MPs are not completely removed through conventional effluent treatment methods, and are then discarded in the water body, along with the final effluent (Elkhatib, Oyanedel-Craver & Carissimi, 2021).
Among the techniques used for the removal of PM is electrocoagulation (EC) (Picó & Barceló, 2019). The process is effective in the treatment of water and effluent, as well as industrial contaminants, by using simple, fast and cost-effective methodology (Elkhatib, Oyanedel-Craver & Carissimi, 2021), as it has the wide capacity in the removal of various pollutants, such as suspended solids, heavy metals, dyes and organic materials (Holt, 2003).
EC commonly uses electrochemical reactors with metal plates connected to a direct current source, creating electrical potential difference between the anode electrodes and cathodes. Those coming from the sacrificial metal, which is oxidized to cationic form, form hydroxides with the function of coagulating agent, constituting colloidal particles with pollutants (Crespilho & Rezende, 2004).
Three stages of consecutive occurrence, describe the functioning of the system: the formation of coagulant through the dissolution of anode ions; destabilization and then aggregation of particles and pollutants and finally the formation of flakes suspended by gases (Malakootian, Mansoorian & Moosazadeh, 2010). In this last stage, the microbubbles generated by the electrolysis of water, coming from cationic electrodes, will be responsible for the suspension of the particles, which will be agglomerated in the upper part of the reactor and under conditions to be removed (Elkhatib, Oyanedel-Craver & Carissimi, 2021).
In addition to requiring simple equipment that is easy to operate, the initial costs are low, requiring minimal maintenance. Because it is operated at low current, clean energies such as solar and wind can be used (Mollah et al, 2001).
The technique presents limitations, such as: the need for periodic replacement of the sacrificial cathodes; the high operating cost, due to the high value of electrical energy and the possibility of formation of films of impermeable oxides on the cathode, which causes resistance to the flow of electric current (Mollah et al, 2001). Also, the effectiveness of the process is reduced when the coagulant input into the solution is limited, because the formation of films on the surface of the electrode prevents the dissolution of the metal and the transfer of electrons (Holt, 2003) .
The present work aims to verify the efficiency of the electrocoagulation process in the removal of MPs, from the count made with stereoscopic magnifying glass with trinocular zoom.

METHODS
The experiments were carried out at the Sanitation and Microbiology Laboratory of the School of Civil and Environmental Engineering of the Federal University of Goiás, in the city of Goiânia.

Experimental System
The experimental system consists of a bench scale reactor with rectangular shape, consisting of glass, with volumetric capacity of 2 L, which was operated in sequential batches, a direct current source, responsible for generating the difference in electric potential between the electrodes, and a magnetic stirrer, with the function of homogenizing the liquid with the chemical components present. The schematic of the system is shown in Figure 1.  (2023) Inside the reactor, there were 4 aluminum electrodes that electrolyzed the water, when connected to the electrical source, with dimensions of length and width of, respectively, 10 cm and 5 cm. In each experiment, in the presence of distilled water, sodium chloride (NaCl) and microplastic in the form of glitter were added, as shown in Table 1. In order to promote coagulation by the mechanism of adsorption and neutralization of charges, the pH of the liquid was corrected by the addition of hydrochloric acid (HCl). When the electrical source had the current adjusted to 0.6A or 2.0A, during time intervals of 10 or 30 min, pH with values of 3 or 5 was used. When the current was 1.3A, the operating time was 20 min, with pH at 4. It was observed the conduction of the MPs, captured by the microbubbles when on their ascending path to the surface of the reactor.
The efficiency of the process was determined through the sampling and counting of MPs (Wang et al, 2020). First, samples with a 20 mL syringe were collected at the beginning and at the end of the process, for each of the experiments performed and, subsequently, the reading of these collected samples was performed, through a stereoscopic magnifying glass with trinocular zoom, in which the removal capacity was verified from the comparison of the present amount of MPs, before and after the treatment.

RESULTS AND DICUSSION
In principle, the experiments were repeated once, so for better representativeness, the arithmetic mean of both efficiency values was performed. Thus, the experiments carried out were presented, as shown in Table 2. The electric current and the efficiency in the removal of glitter are directly proportional parameters in the electrocoagulation process, since the higher the current, the greater the efficiency of glitter removal, influencing the process of electrolysis of water. When in a situation of low current, the lower the formation of microbubbles will be, these being the main allies to the process, because they capture the glitter that will then suffer the flotation process. From interpretative analyses of Figure 1, it was possible to illustrate the importance of electric current control in the experiments. According to the results presented, it is noted that the value of the coefficient of variation, for all experiments, was low, according to the statistical parameters. Table 3 presents this comparison between the experiments. All experiments were classified as low, which was established when the values of the coefficient of variation were below 10 units, so the average efficiency was considered ideal for removal of PMS. After the electrocoagulation process, the pH became alkaline in most of the experiments performed, contributing to the removal of MPs, due to the generation of hydroxyl ions.

CONCLUSIONS
In view of the results obtained, it was concluded that the process of removing MPs through the electrocoagulation process is efficient, thanks to the difference in its concentration, at the beginning and end of the experiments. So, in view of this, the eighth experiment performed, with an average efficiency of 90.3%, had better results, because there was a greater difference between the concentrations, and this parameter was the best for analysis of removal of MPs.
Further studies suggested are Electrocoagulation using other metal electrodes like iron, titanium, etc. Comparison with alum coagulation results and effects of surfactants on coagulation of microplastic. Electrocoagulation of polystyrene or polypropylene.