PRELIMINARY RESULTS OF SPADNS TREATMENT BY LECTROFLOCCULATION WITH IRON ELECTRODES

Objective: The objective of this work is to present the results obtained from the removal of color from SPADNS effluent by electroflocculation treatment. Theoretical framework: The dyes used for analysis methods such as SPADNS are released into nature without any treatment, even in low concentrations affecting the aesthetics of rivers. Dyes are considered common pollutants in effluents and color removal is a major challenge for the industry. Method: Iron nails (Fe) were used as cathode and anode, dipped in a sodium chloride solution with the SPADNS effluent, connected to an ATX (advanced technology extended) computer source at a voltage of 12 volts (v) with maximum current of 15 amps (a). Mass balance of the nails used was carried out to determine the mass dissolved in the effluent. After dissolving the iron, the pH is corrected. Results and conclusion: It was determined that the samples achieved 98% color removal. The results indicate a slight increase in turbidity, within the maximum allowed value. The use of Fe as an electrode is economically viable. The use of sodium chloride to pass current did not prove to be satisfactory.


INTRODUCTION
Water pollution has been a hotly debated issue in society, as it is an essential resource for practically all human activities.Released into nature even in low concentrations, the color associated with dyes affects not only the aesthetics, but also the transparency of water, interfering with photosynthesis and the solubilization of gases in lakes, rivers and other bodies of surface water, as well as containing considerable quantities of toxic compounds (Cerqueira et al., 2009;Daneshvar et al., 2007;Kunz et al., 2002).Dyes are common pollutants in a wide variety of industrial effluents (Cañizares et al., 2006).
Removing color from effluents is a major challenge for industry due to the strict water quality parameters imposed by environmental agencies.For this reason, conventional treatment processes are constantly being applied, such as adsorption, precipitation, chemical degradation, photochemical degradation, biodegradation, flocculation, and so on (Paschoal & Tremiliosi-Filho, 2005).
Another less widespread process is electroflocculation (EF).It is based on electrocoagulation and electroflotation caused by the passage of electric current through an electrolytic cell.In the process, hydroxides of the metal that makes up the electrode are released into the aqueous medium, constituting the coagulating agent (Moreno-Casillas et al., 2007).This technology is based on an electrochemical reaction between pollutants and a metal supplied by a working electrode (Chen, 2004;Butler, 2011) and has the same purpose as chemical coagulants.
The aim of this work is to present the results obtained with the removal of color from SPADNS effluent by electroflocculation treatment, evaluating turbidity, conductivity and dissolved iron content together.

THEORETICAL BACKGROUND
The irregular discharge of dyes into the environment significantly alters the chemical and biological characteristics of the water, negatively influencing photosynthetic processes and the infiltration of light into the water column.According to Neto et al. (2011), although the exact amount of dyes produced by industry is not known, it is estimated that around 100,000 types of dyes and pigments are used in industrial activities.

Spadns
Monitoring the concentration of fluoride in public water supplies aims to ensure a balance between the benefit (caries prevention) and risk (dental fluorosis) of water fluoridation programs (Lins-Cardeiro et al., 2020).The main advantages of water fluoridation are the lifelong prevention of dental caries, the large number of people who benefit from this process and the fact that it is considered affordable compared to other means (Whelton et al., 2019).To this end, analytical methods are used to determine the concentration of fluoride added to water treatment.
This method, which is widely used, is intended for the analysis of fluoride in drinking water and effluents with low turbidity and color, in a range from 0 to 2 mg.L -1 .4 Source: Jayaweera et al. (2007), Greluk and Hubicki (2009).
Fluoride forms a colorless anionic complex with the dye.The amount of fluoride is inversely proportional to the color produced, i.e., the color becomes progressively lighter as the fluoride concentration increases.The most common interferents are alkalinity (in the form of CaCO2), aluminum, chloride, free residual chlorine, color and turbidity, iron, hexametaphosphate, phosphate and sulfate, according to (APHA, 2005).

Electroflocculation
The electroflocculation process consists of metal pairs called electrodes, which are arranged in pairs of two -anodes (negative) and cathodes (positive).Using the principles of electrochemistry, the cathode is oxidized (loses electrons), while the water is reduced (gains electrons), making the effluent better treated.When the cathode electrode comes into contact with the wastewater, the metal is ionized (Butler, 2011).
In other words, it consists of separating suspended materials (solids or liquids) from an aqueous solution by aggregating these pollutants with the hydrogen gas bubbles produced at the cathode by the water hydrolysis reaction.Once formed, these aggregates move towards the surface of the solution, allowing it to be separated from the medium and, consequently, removing these materials from the solution (Grecco, 2021;Kyzas & Matis, 2015).
According to Ding et al. (2018) and Cardonha et al. (2018), the assembly model is shown below in Figure 2. When this happens, the particulates are neutralized by the formation of hydroxide complexes in order to form agglomerates.The main advantage of electroflocculation technology is the short residence time (hours) and high pollutant removal efficiency can also be achieved (Chen, 2004).
The most commonly used anode materials for the process are iron and aluminum, which always hydrolyze into polymeric iron and aluminum hydroxides.The iron electrode material is considered more appropriate in the tertiary treatment of leachates because it is less toxic and more acceptable in the environment (Bouhezila et al., 2011).Lacasa et al. (2013) also indicated that the cost of iron is lower than that of aluminum.Electroflotation always occurs, since hydrogen bubbles are produced at the cathode and some flocculated pollutants are floated by natural buoyancy to the surface.Operational factors Important factors influencing performance include electrode distance, mechanical agitation, current density, pH and conductivity (Orkun & Kuleyin, 2012).Brillas et al. (2009) presented a comprehensive review on the application of the EF process and various electrochemical technologies based on the chemical Fenton reaction for wastewater treatment.In addition to the electroflocculation generated, this type of treatment can be considered an advanced oxidation process, since it releases oxygen gas in the presence of iron ions.The electrochemical production of H2O2 with the addition of Fe 2+ to the volume gives rise to the common and widely studied electro-Fenton process, in which additional -OH is produced in the volume from the Fenton reaction.This treatment has gained increasing attention over the last two decades as a promising class of advanced oxidation process.Cavalcanti (2019), in his study, evaluated the generation of hydrogen from the treatment of residual effluents from the biodiesel manufacturing process.In addition to significant reductions in BOD and COD in the effluent, hydrogen was obtained at a flow rate of 1 L.h -1 .Many benefits can be found in the technique.

MATERIALS AND METHODS
An experimental methodology was developed to enable an understanding of the various parameters that influence the electroflocculation process.Subsequently, an electroflocculation experiment was designed and repeated to evaluate the treatment method and its removal efficiency.
Nails were used as cathodes and anodes (as a source of Fe +2 and Fe +3 ions), supported on a copper wire, mounted in a glass beaker, slightly immersed in the sample.The electrolysis was carried out using an ATX computer power supply with a voltage of 12 v and a maximum continuous current of 15 a.For operation, a piece of paperclip was placed on the connector linking the green wire to the black wire, so that the power supply could be operated without the motherboard.The mass of the sacrificial nail was measured every 2 min so as not to heat up the wiring, up to a total of 6 min, dissolving approximately 1.1 g of Fe.This measurement of 1.1 g for every 180 mL of effluent plus 20 g of salt was used as a reference for removing color from the effluent.The amount of salt used is the approximate saturation value of the solution.
The nails used were 18 x 27 and 17 x 27, each weighing approximately 4.00 g to 4.32 g and with a contact area of 5.8 to 5.84 cm².The volume of the samples was treated in a 200 mL beaker with dissolved NaCl (sodium chloride) to facilitate the passage of electric current.The nails were weighed before, during and after the experiment to determine the mass used.The average color parameter in the effluent was 1200 PCU and the turbidity parameter (which analyzes the concentration of suspended solids) was 0 NTU.
After the electroflocculation process lasting a total of 6 min, a 5% lime solution was used to form clots which were filtered with paper towels and absorbent cotton for rapid separation.
The reading equipment used was a precision analytical balance, portable pH meter, conductivity meter, Dellab bench turbidimeter and multi-parameter bench photometer and COD model HI 83099.
The results were collected after each experiment and organized in a spreadsheet for statistical study of the samples.The results for color, turbidity and Fe concentration were obtained from the laboratory of SAAETRI, the sanitation company in Três Rios.The statistical studies were carried out using the R Studio software (2018), to check the trend of the data and the statistical reliability of future experiments.

RESULTS AND DISCUSSION
After positioning the nails, it was noted that at a voltage of 12 v and a current of up to 15 a, the anode nail did not show any apparent bubbling, but dissolved over time, while the cathode generated a boil in the solution.According to Grecco et al. (2021), the generation of gases at the cathode is hydrogen, which has energy potential during treatment and is considered by Bezerra (2021) to be a solution for decarbonizing the economy, with a view to reducing greenhouse gases (GHG) in the atmosphere.
According to Fogarcs et al. ( 2004) and Robinson et al. (2001), the reactions that take place at the anode are: The reactions that take place at the cathode can be represented as follows (Papic et al., 2004;Jae-Wook et al., 2006).

M n+
(aq) + ne -→ M(s) eq. 2 2H2O(l) + 2e -→ 2OH - (aq) + H2(g) How the treatment works can be seen in Figure 3 below (Cerqueira et al., 2009).The loss of iron over a period of 6 min in all the samples followed a pattern.Sample 7 showed low dissolution of iron in the effluent, but did not obtain unsatisfactory color removal results.The variation can be seen in Figure 4.It can be seen that over time, the dissolved iron values increased, and that in the same unit of time, most of the samples remained with similar results.The difference between 2 min, 4 min and 6 min can be seen in Figure 5.Although some values differ, the iron concentration increases, up to the desired value of 1.1 g of dissolved iron.The effluent from SPADNS has an acidic pH due to its mixture with hydrochloric acid, with no change in pH after using electric current.After treatment, its physical and chemical characteristics change slightly due to the presence of iron, which darkens the effluent, leaving it with high turbidity and pH.
To remove the color and form flocs, it was necessary to add an alkaline solution to neutralize the dissolved Fe and form agglomerates.Lime at 5% m.v -1 was added to an average volume of 102.3 mL.After raising the pH, the solution began to form colloidal flakes and change color from a cloudy reddish hue to a greenish hue.Iron hydroxide (Fe(OH)n(s)) remains in the aqueous phase as a gelatinous suspension, which can remove pollutants from wastewater by either complexation or electrostatic attraction followed by coagulation (Cerqueira et  The change in color can be seen in Figure 6.After the color change, the solution was left to stand for phase separation.The solid part was separated using 2-stage filtration.The filter used was ordinary paper and another using a cotton wad in the narrowest part of a funnel (Figure 7).After filtration, the treatment came out looking clear, transparent and with a final pH close to 10.27.There was a need to correct the pH for discharge into a water body.Another parameter monitored was the electrical conductivity of the solution due to the presence of salt.The bench conductivity meter scored an initial average of 285.2 mS.cm -1 and according to Cardonha et al. (2005) and Matthess (1982), the electrical conductivity of seawater is lower than the prepared effluent, with values between 45 mS.cm -1 and 55 mS.cm -1 .Despite being partially removed, one point observed in the study was that the conductivity of the treated effluent was still high, with an average of 194.3 mS.cm -1 , preventing it from being discharged into a water body.The conductivity values can be seen in Table 1 below: The positive point of the project is its color removal.The effluent has its color analyzed in the 1200 PCU range.The values found after treatment were very low compared to the initial one.According to the R Studio software (2018), the average final color is 24.89PCU and the maximum value is 45 PCU, demonstrating a removal of close to 98%.Samples 3 and 4 in this study showed results that differed from the statistical method, which is believed to be a consequence of changing the lime solution used.The lime had solubility problems and was replaced.Some of the parameters obtained after treatment showed results lower than the VMP (maximum permitted value) for drinking water, in accordance with ordinance GM/MS 888 (Brasil, 2021).These values can be seen in Table 2.The turbidity results in the effluent were different.Initially, the effluent had no turbidity and no Fe ions.After electroflocculation and the dissolution of iron in the medium, the level of turbidity increased and was removed together with the filtration stage.Although there was an insignificant increase in turbidity, the clarified results were in the range of 0.77 NTU, below the VMP -maximum permitted value.All the values listed are within the legal limit, except for samples 3 and 4. The results obtained for this parameter are shown in Table 3.The comparison between the turbidity and color results, related to the mass of iron inserted by electroflocculation, shows that in most of the samples, the amount of Fe introduced into the system helped to reduce color and slightly increased turbidity.
As for the use of iron as a sacrificial anode, its residual was analyzed in the samples clarified by electrochemical treatment.The Fe values analyzed were an average of 1.35 mg.L - 1 .Samples 3 and 4 had higher values, while the rest of the samples had iron below the level established in GM/MS Ordinance 888.However, all the values in Table 4 remain within the permitted limit for release into water bodies, as established by CONAMA 430 (Brasil, 2011).

FINAL CONSIDERATIONS
Electroflocculation treatment proved to be effective in removing color from the effluent generated by SPADNS.Color removal was 98% on average, which is satisfactory as it meets the limits for discharge into water bodies.The increase in turbidity was insignificant and did not exceed the VMP.
The use of iron electrodes may be an economically viable solution for this type of effluent, but more information is needed.The dissolution of iron was completely removed in the treatment, establishing limits below the water potability ordinance GM/MS 888, and not harming public welfare.
Energy data was not collected in this study, but is important for sizing pilot systems.The use of sodium chloride to obtain a preliminary treatment result was not satisfactory due to the increase in conductivity.
It is recommended that another substance be used to favor the passage of electric current, which can be removed at the same time as the treatment.The use of sodium chloride made the treated water saline, making it difficult to dispose of.
It is also highly recommended that an energy cost survey be carried out to evaluate the economics of the method applied, to evaluate the generation of hydrogen in the process for possible use in energy generation and to apply this promising treatment to other types of effluent such as leachate.

Figure 2 -
Figure 2-Assembly diagram Source: Adapted by the author from Ding et al. (2018).

Figure 3 -
Figure 3-Adsorption process and formation of the colloidal particles that generate the flakes with the dye molecules.IS = sacrificial ion: Al(OH)3 or Fe(OH)3, depending on the scheme used.Note.Source: Neto et al. (2011).

Figure 4 -
Figure 4-Mass of iron dissolved in a solution of 180 mL of effluent with 20 g of salt.Note.Source: Authors, (2024)

Table 1 -
Conductivity values of treated effluent SAMPLES Final conductivity Final mS.cm -1

Table 2 -
Color level of the samples analyzed.

Table 3 -
Color level of the samples analyzed.

Table 4 -
Residual iron concentration