ABSTRACT
Purpose: This study aims to evaluate the efficiency of electro-oxidation as a treatment option for textile effluents containing industrial dyes, with the goal of minimizing their environmental impact.
Theoretical framework: The textile industry is known for its high water demand and generation of effluents containing dyes, posing an environmental challenge. Electro-oxidation is a promising technology for the degradation of pollutants that are difficult to mineralize.
Method: The treatment process and operational conditions were described, utilizing a Boron-Doped Diamond (BDD) electrode. Three ranges of electric current (6, 12, and 18 mA cm-2) were tested to degrade the Procion Yellow (PY) dye. The removal of the dye, energy consumption, reduction in Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and effluent toxicity were evaluated.
Results and conclusion: The treatment resulted in the removal of 91.4% of the dye, with an energy consumption of 88.4 kWh/m3 for a concentration of 150 mg/L of PY, following a first-order kinetics. Significant reductions in COD (74%) and TOC (85.2%) were observed. The effluent toxicity decreased at currents of 6 and 12 mA cm-2 but increased at 18 mA cm-2. Electro-oxidation proved to be a promising option for treating textile effluents containing industrial dyes.
Research implications: The results contribute to the advancement of science and socio-environmental management practices in the textile industry, providing a viable option for effluent treatment and reduction of environmental impact.
Originality/value: This study highlights the efficiency of electro-oxidation in the degradation of industrial dyes present in textile effluents, presenting relevant results on dye removal, energy consumption, COD and TOC reduction, as well as the evaluation of treated effluent toxicity.
Keywords: Industrial Dyes, Electro-Oxidation, Dye Absorbance, Textile Industry.
RESUMO
Objetivo: Avaliar a eficiência da eletro-oxidação como tratamento de efluentes têxteis com corantes industriais, visando reduzir o impacto ambiental.
Referencial teórico: A indústria têxtil gera efluentes com corantes, representando um desafio ambiental. A eletrooxidação é uma tecnologia promissora para degradar poluentes de difícil mineralização.
Método: Utilizou-se um eletrodo de Diamante Dopado com Boro (DDB) para degradar o corante Procion Yellow (PY), testando três faixas de corrente elétrica (6, 12 e 18 mA cm-2 ). Avaliaram-se remoção do corante, consumo de energia, redução da Demanda Química de Oxigênio (DQO), Carbono Orgânico Total (TOC) e toxicidade do efluente.
Resultados e conclusão: A eletro-oxidação removeu 91,4% do corante, com consumo de energia de 88,4 kWh/m para 150 mg/L de PY, seguindo cinética de primeira ordem. Houve redução significativa de DQO (74%) e TOC (85,2%). A toxicidade diminuiu nas correntes de 6 e 12 mA cm-2 , mas aumentou a 18 mA cm-2 . A eletro-oxidação é promissora para tratar efluentes têxteis com corantes industriais.
Implicações da pesquisa: Os resultados contribuem para avanços científicos e gestão socioambiental na indústria têxtil, oferecendo uma opção viável para o tratamento de efluentes e redução do impacto ambiental.
Originalidade/valor: O estudo destaca a eficiência da eletro-oxidação na degradação de corantes industriais em efluentes têxteis, com relevância na remoção do corante, consumo de energia, redução de DQO e TOC, além da avaliação da toxicidade do efluente tratado.
Palavras-chave: Corantes Industriais, Eletro-oxidação, Absorbância de Corante, Indústria Têxtil.
(ProQuest: ... denotes formulae omitted.)
1INTRODUCTION
Water is an essential natural resource for the survival of all living organisms. In addition to playing a key role in maintaining the planet's climate, it is necessary for most means of production. Ensuring the availability of water is crucial for the maintenance of life on the planet, both in terms of quantity and quality (Fikri, Fauzi & Firmansyah, 2023). In the industrial context, water plays a vital role in several industries, including the textile industry, contributing to dyeing, washing and cooling processes (Chen et al. 2021). However, it is worrying to note that the private sector often prioritizes financial issues over social and environmental perspectives, which is detrimental to sustainable development (Arag&acaron;o; da Silva & Pereira, 2022).
The textile industry is one of the largest and most important industries in the world, with significant representation in the global economy. According to the United Nations Industrial Development Organization (United Nations, 2022), the textile and clothing industry employs about 60 million people worldwide and accounts for about 2% of global gross domestic product (GDP). In addition, it accounts for a large share of world exports, accounting for about 7% of global exports of goods, according to World Trade Organization (WTO, 2022) data.
From the environmental point of view, constituents from the textile industry are considered to be difficult to treat by common treatment plants. In most cases, these substances end up in waste water, inducing serious health problems for human, plant and animal life of all aquatic biota involved, being few controllable (Hussain, 2020; Ahmad, 2021). This new class of contaminants of different chemical natures is known as "Emerging Contaminants" (CE) (Carrasco; Delgado; Cobos, 2017).
Ecosystems are threatened by various pollutants, but emerging contaminants (EC) have received special attention from the scientific community since the 1990s. At that time, it was found that these substances were not regulated and their environmental impact was unknown. CEs are substances that occur in low concentrations (qg L-1 and ng L-1) but that can cause significant impacts on ecology and human health (Montagner, 2017).
Waste water from the textile industry, containing substances such as Procion Yellow dye, is often discharged without proper treatment into sewage treatment plants (ETEs), which are not prepared to deal with these pollutants (Meléndez-Marmolejo et al., 2020). The textile industry is one of the largest in the world, generating an annual revenue of about $1 trillion and employing millions of workers globally (Lellis, 2019). However, due to the high water consumption in the coloring and finishing process, textile production generates a significant volume of highly polluted waste water, representing one of the major environmental challenges of the 21st century (Kant, 2012).
In addition, synthetic dyes such as Procion Yellow, often used in the textile industry, can be toxic to aquatic life and an irritant to skin and eyes if not treated properly. For Hussain (2019), it is essential that companies adopt responsible waste management and effluent treatment practices to ensure that dyes and other chemicals are treated before being disposed of into the environment.
Among the various dyes used in the textile industry, Procion Yellow (PY) stands out, a synthetic dye widely used to dye fabrics of cotton, viscose, silk and wool. Due to its high water solubility and affinity with textile fibers, PY is often combined with other dyes to produce a wide range of colors. However, like many other synthetic dyes, PY can have negative impacts on the environment if it is not treated properly. It can be toxic to aquatic life and irritating to skin and eyes (Abit, 2020).
Environmental concern with waste water is intensified by improper disposal of organic and inorganic compounds, resulting in significant ecological impacts (Rasheed et al., 2019). Among the control strategies, the advanced electrochemical oxidation (POEA) process stands out as an innovative treatment technology. This method is not only simple to operate, low cost and high efficiency, but also stands out for the ability to effectively control pollutants that are difficult to degrade and protect water resources from pollution. Its unique ability to mineralize most non-biodegradable organic compounds has attracted significant attention from the scientific community (Usepa, 2014; Monge et al., 2018).
Electrochemistry is the study of the chemical processes that cause electrons to move; it is a very relevant theme in the scientific world because it has advantages over other oxidation processes, such as ease of operation, high efficiency, operation at low temperatures and the possibility of coupling with other traditional treatment processes (Hussein, 2020). Advanced oxidation processes have gained increasing attention as an emerging clean and efficient technology for air and water treatment. The main advantage of this technology is that it can totally or partially destroy organic substances at room temperature and convert them into various harmless intermediates and end products, such as carboxylic acids, carbon dioxide and halides ions (Angelo et al, 2013; Fayazi, 2020; Khajouei et al., 2019).
For Brillas and Martínez-Huitle (2015) advanced oxidation processes are a reliable means of meeting new environmental standards. They also offer lower operating and investment costs compared to conventional treatment processes. This new process is very effective in demanding applications such as toxic pollutants and non-biodegradable organic compounds, Total Organic Carbon/TOC, Reduction of toxicity, removal of color and odor.
The justification for the relevance of this work is the urgent need for environmental preservation, a topic of great importance in the current context. The study aims to contribute to the development of wastewater treatment technologies, aiming at minimizing the environmental impacts caused by organic and inorganic compounds in the effluents. The main objective is to use the electrochemical degradation method to reduce the concentration of Procion Yellow dye in water, using a batch-type reactor with dye recirculation in the system and the use of the Boron Doped Diamond (DDB) electrode.
By obtaining the UV/VIS spectra of the Procion Yellow dye and characterizing it by means of spectrophotometric curves, it will be possible to quantify the dye and evaluate the effectiveness of electrochemical treatment. In parallel, we will carry out statistical analyzes to identify the conditions that provide a satisfactory rate of dye degradation and assess possible toxic effects on the aquatic environment.
This study, by establishing spectrophotometric curves for the reading of the Procion Yellow dye and by analyzing the ecotoxicity of the treated effluent, aims to contribute effectively to the reduction of water pollution, one of the biggest environmental problems faced at the moment. Therefore, the promotion of sustainable technologies in waste water treatment is essential to ensure the preservation of the environment and the quality of life of the population.
2METHODOLOGY
In this work, the treatment used was electrochemistry, for the degradation of organic dye used in the textile industry and its toxicity before and after the decomposition process. The electrochemical experiments were carried out in batches and conducted into a flow cell containing anode (Ti/RuO0.3TiO0jO22) and cathode (stainless steel) with an effective surface area of 14 cm224 separated by Viton® and Teflon® spacers. During all degradation experiments, the temperature of the reactor was always monitored starting from the ambient temperature close to 25°C, the magnetic stirrer was used for the continuous stirring of the solution passing through the reactor, as illustrated in Fig. 1(a).
2.1Proposed Electrochemical System
An electrolytic cell consumes electrical energy from an external source, using it to cause a non-spontaneous redox reaction (AG > 0). These type cells contain two electrodes, which are solid metals connected to an external circuit that provides an electrical connection between the two parts of the system (Fig. 1(b) "Electrochemical Reactor").
The electrochemical treatment system of synthetic dyes consists of various equipment. A beaker (1) is used as a dye reservoir, connected to a peristaltic pump (2) that feeds the flow electrochemical cell (3). A DC power supply (4) is used to supply the current needed for the electrochemical reaction. A digital thermometer and a pH meter (5) are used to monitor solution conditions. A magnetic stirrer (6) keeps the solution homogeneous during treatment. The electrochemical cell contains a DDB electrode and a mixed dioxide cathode of Iridium/Ruthenium Oxide, with a total area of 48 cm2 and an effective sample volume of 250 mL.
During the treatment process, the dye is pumped from the reservoir (1) to the electrochemical cell (3) by the peristaltic pump (2), where it is treated and returns to the reservoir (1). The pH, temperature and concentration of the dye are constantly monitored. The magnetic stirrer (6) is used to keep the solution homogeneous during the treatment process, which occurs in cyclic batches.
Batch flow is commonly used in electrochemical treatment systems. It involves recirculating the effluent at a specific rate for a given period of time. A reservoir is attached to the reaction system and a peristaltic pump propels the effluent to the electrolyte cell, where degradation occurs.
The hydraulic holding time (TDH) is calculated according to Equations 1 and 2, and the reaction time (Tr) is determined by Equation 3
... (1) (2)
Where:
HRT = Hydraulic holding time
Vr = reactor volume;
Q = recirculation flow;
... (1)
Where:
Tt = recirculation time at collection intervals;
Vt = total sample volume;
Previous studies (Oliveira et al., 2011; Fujishima, 2005; Badawi, Harisson, & Argun, 2019) evaluated the DDB electrocatalyst, demonstrating its excellent characteristics, such as wide potential range (-1.0 to +2.5 V), low background currents and high stability under oxidizing conditions. This makes DDB electrodes suitable for oxidation of complex mixtures of organic components and sewage treatment systems. Furthermore, studies have observed that these DDB electrodes have good resistance to fouling for long periods.
2.2Instrumentation and Analytical Measurement
Experiments were carried out to evaluate the degradation of the Procion Yellow dye by means of Advanced Oxidative Processes (POA) with an emphasis on electrochemistry. The toxicity of the by-products formed during degradation has also been verified.
The experiments investigated the effect of the variation in the current and concentration of the dye. Analyzes of parameters of total organic carbon, pH and dye concentration were performed using analytical techniques recommended by Standard Methods.
An adjustable DC power supply was used to change the currents applied in the system. Current ranges of 6, 12 and 18 mA cm-2 were establisheď with a maximum duration of one hour.
The initial tests were performed with an electrolyte concentration of 0.065 mol L-1 of Na2SO44. Energy efficiency was assessed using different dye concentrations.
For dye recirculation, a peristaltic pump was used with a maximum flow rate of 225 mL/min. The dye was added to a 250 mL beaker as a reservoir for recirculation.
It is important to note that the starting parameters were not adjusted. The dye concentrations were established by dilution and checked against a prior spectrophotometric calibration curve. Tests were conducted with four concentrations within the reading range of the calibration curve for the three established current ranges.
2.3Energy Consumption
Energy consumption is crucial for the feasibility and practical implementation of electrochemical dye degradation techniques. In this study, energy consumption was expressed in terms of Wh (Watt-hour). Calculation of energy consumption can be performed using Equation 1 (Brillas & Martinez-Huitle, 2015).
... (3)
U is the mean voltage, given in V;
I is the applied current, given in A;
T is the electrolysis time, given in h;
Vs is the volume of the solution, given in dm3.
The electrical energy consumed in this process is a very important factor as it directly affects the cost, so in some cases using modeling to optimize parameters is important to obtain the maximum degradation effect with the lowest energy consumption.
2.4Spectroscopic Determination UV-Visible Dye Procion Yellow H-E3G
The absorption spectrum is a graph of absorbance as a function of wavelength in UVVisible spectrophotometry. The maximum absorption wavelength, called Xmax, is where a substance, such as a dye, shows the maximum absorption of electromagnetic radiation. To determine Xmax of the dye PY, solutions of different concentrations were prepared in the range of 190 to 1100 nm. Each solution was tested at various wavelengths, and the absorbances were recorded. These absorbances were plotted with respect to the wavelength, allowing the determination of Xmax for the dye PY.
2.5Calibration Curve
The calibration curve is an analytical chemistry tool for determining unknown sample concentrations. It is constructed by plotting concentration versus absorbance, using samples prepared at different concentrations. The calibration curve allows estimating the concentration of unknown samples by comparing them with the curve. Beer's law is applied to relate the amount of light absorbed to concentration. By measuring the absorbance of the unknown sample in the spectrophotometer, it is possible to determine its concentration by comparing it to the calibration curve. This allows a simple graphical deduction of the concentration based on the measured absorbance.
2.6 Dye Removal
The main objective of this study was to remove pollutants from dyes from the aqueous solution, so % dye removal is a key factor in evaluating the effectiveness of the experiments. The percentage of dye removal for all experiments was calculated using Eq. (1) (Sartaj et al., 2020).
... (4)
Where:
Dye removal is given as % degradation of PY, Ci (mg L-1) is the pre-treatment PY concentration, i.e. time t = 0 and Ce (mg L-1) is the post-treatment PY concentration, i.e. time t.
2.7 Kinetic Studies
In the present study, three electric currents with densities of 6, 12 and 18 mA cm-2 were used, in a reator containing an electrolytic cell, for the degradation of the dye (PY) present in solution. The solution was dissolved in ultrapure water, and then the solutions were submitted to electrochemical treatment, for one hour, with the pre-established currents. PY concentrations were assessed at regular intervals of time by means of a UV-Vis spectrophotometer.
In order to determine the order of reaction of the dye and obtain the degradation constant k for each electric current, the method of adjusting the best line between the zero order, first order and second order velocity equations was used. The quality of the kinetic adjustment to the experimental data was evaluated by calculating the R2 values for each reagent. The Equations. (5), (6) and (7) represent the linearized models of order zero (Connors, 1990), first order (Connors, 1990), and second order (Connors, 1990), respectively
... (5)
... (6)
... (7)
In which:
c0 is the initial dye concentration (mg. L -1), cis the dye concentration at any time (mg. L -1), t is the time and k is the reaction rate constant.
The results obtained will make it possible to check the kinetic order of the degradation of the dye and whether the electric current used affects the rate of degradation. The equation of reagent degradation kinetics can be used to predict future concentrations of these compounds in solution, which may be useful in optimizing degradation processes or determining safety limits for the release of effluents containing these reagents.
2.8 Toxicity
An acute toxicity bioassay was conducted with Artemia Salina following NBR ABNT 16530:2021. The objective was to evaluate the toxic effect of the dye Procion Yellow H-E3G after electrochemical treatment in aquatic organisms and possible risks to human health. Different dye concentrations were tested to determine the concentration range with mortality ranging from 0% to 100%. Nauplii of Artemia Salina were exposed to dye concentrations and incubated in the dark for 48 hours. Mortality of the Nauplians was recorded and compared with the control group. The LC50 was determined to evaluate the effect of the dye on mortality of the nauplii of Artemia Salina, using K2&2O7 as positive control.
2.9 Data Statistics
The statistical analysis of the collected data was carried out using three statistical software programs: jamovi (The jamovi project, 2022), R (R Core Team, 2021) and Minitab (Minitab Inc., 2022). Jamovi was used for descriptive analysis, normality testing and graphics generation. R was used for multiple linear regression, significance testing, and graph creation. Minitab was used to create 3D graphics, such as surface graphics. The graphic results were generated by exporting the jamovi and R data to import them into Minitab. The graphic results were discussed and interpreted in relation to the objectives of the research.
3RESULTS AND DISCUSSION
The dye PY is an azo dye, therefore a wide absorption band attributed to UV-Visible by chromophore, i.e. the azo group -N=N- of the dye PY is the main reason behind its color.
3.1UV-Visible Analysis of Xmax for Dye PY
In Fig. 2(a), two absorption bands were observed in the ultraviolet region at 270 nm and 320 nm, similar to Hussain's study (2021). These bands are attributed to the ...-transition absorption of conjugated electrons in benzene rings attached to the primary chromophore sides of the dye PY. The Xmax of the dye PY, as shown in Fig. 2(b), was calculated from the UV- Visible absorption curves and found at 270 nm, representing the wavelength with the highest absorbance response.
The energy content of light varies inversely with wavelength, making violet light (wavelength = 270 nm) more energetic than red light (wavelength = 350 nm). This fact is due to the presence of several double bonds in the compound, favoring the presented formation.
Within the above, suggested by (Rosa & Gonçalves, 2013), light is composed of energy particles called photons, and the energy content of these photons is closely related to the wavelength of light. When light is absorbed by matter, the energy contained in the photon is incorporated into the structure of the absorbing molecules.
3.2Calibration Curve
The process of selecting the best wavelength was carried out through the analysis of test solutions at different wavelengths, identifying the wavelength in which the solution showed the greatest absorption. Based on this result, the calibration curve of the dye PY at a wavelength of 270 nm was constructed. Figure 3(a) shows the spectra of the concentrations that presented the best absorption responses, while Figure 3(b) presents the calibration curve with these concentrations.
For the quantification of the dye Procion Yellow, established concentrations were used during spectral scanning, including 10 mg L-1, 20 mg L-1, 30 mg L-1, 40 mg L-1, 50 mg L-1, 100 mg L-12, 150 mg L-14 and 200 mg L-14. The resulting calibration curve showed a favorable linear regression with a coefficient of determination R2 = 0,9981, allowing quantitative analysis of the dye concentration. This curve was used in the experiments to verify the removal of color in each test.
In the intermediate condition with a current of 12 mA cm-2, a similar response was observed at concentrations of 100, 150 and 200 mg L-1, with significantly higher values compared to the previous condition, resulting in a removal of 81.4% at the concentration of 100 mg L-1. Already in the condition of 18 mA cm-2, a good degradation response of the dye was observed, with a linear relationship in all concentration ranges tested and a maximum removal of approximately 90%. These results indicate that the DDB electrode is suitable for the degradation of this dye, with room for adjustments in the current to improve removal at different concentrations.
In the intermediate condition of the tests, with a current of 12 mA cm-2, the response was similar for concentrations of 100, 150 and 200 mg L-1, with values significantly higher than in the previous condition. Removal was 81.4% at the concentration of 100 mg L-1. In the current condition of 18 mA cm-2, the Procion Yellow H-E3G dye showed a good response to degradation, remaining linear in all concentration ranges and achieving a maximum removal of approximately 90%. These three dye treatment conditions demonstrate that the DDB electrode is suitable for degrading this dye, allowing adjustments in the current to obtain better removals at different concentrations.
According to the statistical analysis presented in Figure 5, current is the variable that most influences the removal of color during the electrochemical oxidation process. It was observed that the percentage of removal increases as the current applied to the system increases. This is because, at higher potentials, the electrode is more efficient at oxidizing PY dye species, which aids in solution discoloration due to the species generated.
As for the removal of the dye PY, a better response was obtained in the condition of 18 mA cm2, indicating that the increased current degrades the dye PY. However, in relation to the chemical oxygen demand (COD), the current condition of 12 mA cm2 obtained the best removal results for this parameter, as shown in Figures 6(a) and 4(b).
To evaluate PY dye degradation, several parameters were monitored, including COD and TOC, to determine the most effective concentration ranges. This is confirmed by the removal of the TOC, whose best removal efficiency is shown in Figures 7(a) and 5(b).
Electric current is the most important variable in color removal during electrochemical oxidation of dye PY. Increasing the current results in greater efficiency in oxidation and color removal. The current of 18 mA cm2 was the most efficient in the removal of the dye, while the current of 12 mA cm2 presented better results in the removal of COD. These results are useful for the development of effluent treatment processes with dyes, emphasizing the efficiency of electrochemical oxidation when ideal conditions are applied.
3.3Kinetic Studies
A kinetic analysis of the degradation processes was performed on three currents (6, 12 and 18 mA cm-2) based on experimental data. The degradation constant k was calculated using linear regressions of the linear transformation of the equation. Results for the zero, first order, and second order kinetics are summarized in Table 1.
The table presents the results of a chemical kinetics experiment with Procion Yellow, measuring the electric current at different concentrations of the dye. The parameters of the equations of order zero, first order and second order were calculated based on this data. Values of r2 indicate the quality of the equations adjustment to the experimental data. In general, the first-order equations presented better adjustments than the second-order and zero-order equations.
To represent the data more adequately, the median of each experimental condition was calculated, considering the concentrations of 50, 100, 150 and 200 mg/L for each current. This median represents the chemical kinetics for each current condition, encompassing all concentration ranges studied. The median was chosen due to the considerable magnitude of concentrations in degradation.
Figure 5, 6 and 7 show the reaction kinetics equations for each current, using the median values to plot the corresponding points. It can be observed that the first-order equations presented better agreement with the experimental data compared with the zero and second-order equations.
Zero order is characterized by a constant reaction rate, independent of the reagent concentration. The values of r2 for the zero order equation were high for all electric currents studied, indicating a good fit of the equation to the experimental data. The k (speed constant) values for the zero-order equation were greater than the values for the first-order and secondorder equations, suggesting a rapid reaction of Procion Yellow with respect to electric current. In Figure 6 we can observe the reactions to order 1.
The first order is characterized by a reaction rate proportional to the concentration of the reagent. The values of r2 for the first-order equation were greater than the values for the zero and second-order equations, indicating a better fit of the equation to the experimental data. The k values for the first-order equation were lower than the values for the zero-order equation, suggesting that the reaction is slower but still occurs efficiently with respect to the electric current. Figure 7 shows the second-order kinetics of dye degradation (PY).
The degradation kinetics of Procion Yellow was best described by a first-order equation, where the rate of reaction is proportional to the reagent concentration. Linear regression models adjusted well to experimental data, explaining the variability in measured concentrations. The degradation kinetics in the three currents tested were first order, with high coefficients of determination, indicating a good fit of the kinetic equation to the data. The degradation constant k is a measure of the reagent degradation rate, and the 12 mA cm-2 current showed the highest degradation constant (0.027 min-1), suggesting faster degradation compared to the other currents tested.
These results indicate that the degradation of dyes follows first order kinetics and that the current used affects the degradation rate. These findings are relevant for future studies on the degradation of dyes and for the optimization of effluent treatment processes containing these compounds.
3.4Dye ecotoxicity
Based on the calculations made, we can infer that the experiments conducted exhibited different lethal concentrations (LC50) for the organisms examined. The test conducted with an electric current of 6, 12 and 18mA cm-2 showed an estimated LC50 of 122.7; 108.33; 13.58 mg L-1 respectively by the Trimmed Sperman Karber (TSK) statistical method, (1938). A concentration (LC50) of 73.9 mg L-1 was measured in the raw effluent, indicating that removal of effluent toxicity was reduced in tests with electrical currents of 6 and 12 mA cm-2. On the other hand, under the condition of 18 mA cm-2, the ecotoxicity of the raw effluent increased compared to the initial condition. The survival ratio of the test organisms used in the toxicity test, as shown in Figure 8, is a clear indication of this variation.
The concentration of the dye (PY) is related to the mortality rate of the tested organisms. Higher concentrations of the dye resulted in higher mortality of organisms, regardless of the electric current applied (6mA, 12mA and 18mA cm-2). In addition, different electrical currents have also affected the mortality of organisms, suggesting that the electric current may influence the toxicity of the substance.
The data also indicate that the lethal concentration (LC50) of the dye is affected by the electric current used in the treatment of the effluent. For example, in the electric current of 18mA cm-2, the estimated LC50 was 13.58 mg L-1, indicating higher toxicity. However, in the electric currents of 6mA and 12mA cm-2, the estimated LC50 was higher, suggesting lower toxicity.
However, it is important to stress that the ecotoxicity of a substance cannot be assessed by the LC50 alone, but that other factors need to be considered for a full assessment. Therefore, further studies are needed to fully understand the effects of electric current on effluent treatment and on the ecotoxicity of the substances present.
4FINAL CONSIDERATIONS
The electrochemical process with the DDB electrode was efficient in the removal of the Procion Yellow H-E3G dye at different concentrations and electrical currents, suggesting its application in the remediation of textile effluents. However, additional studies are needed to assess the effects of other compounds and pollutants on the effluent, as well as the costs and scalability of the process.
The applied electric current is a determining factor for the efficiency of the process, but the removal of the dye can also vary in relation to parameters such as DQO and TOC. The degradation kinetics were described by the pseudo-first-order model, with good adjustments to the experimental data.
The three currents tested showed first-order degradation kinetics, indicating reaction efficiency. The current of 12mA cm-2 showed the highest degradation constant k, indicating greater ease of degradation in all applied current situations. The zero and second order equations showed faster and slower behavior, respectively.
These results are important for understanding the degradation kinetics of Procion Yellow and may contribute to the development of more efficient effluent treatment processes containing this dye.
The use of electric currents to treat effluents can have varied effects on the toxicity of the treated effluent. The currents of 6 and 12 mA cm-2 reduced toxicity, while the current of 18 mA cm-2 increased ecotoxicity. This highlights the importance of evaluating the effectiveness of the treatment in relation to the toxicity of aquatic organisms and highlights the need for testing for each electric current used.
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Abstract
Objetivo: Avaliar a eficiência da eletro-oxidação como tratamento de efluentes têxteis com corantes industriais, visando reduzir o impacto ambiental. Referencial teórico: A indústria têxtil gera efluentes com corantes, representando um desafio ambiental. A eletrooxidação é uma tecnologia promissora para degradar poluentes de difícil mineralização. Método: Utilizou-se um eletrodo de Diamante Dopado com Boro (DDB) para degradar o corante Procion Yellow (PY), testando três faixas de corrente elétrica (6, 12 e 18 mA cm-2 ). Avaliaram-se remoção do corante, consumo de energia, redução da Demanda Química de Oxigênio (DQO), Carbono Orgânico Total (TOC) e toxicidade do efluente. Resultados e conclusão: A eletro-oxidação removeu 91,4% do corante, com consumo de energia de 88,4 kWh/m para 150 mg/L de PY, seguindo cinética de primeira ordem. Houve redução significativa de DQO (74%) e TOC (85,2%). A toxicidade diminuiu nas correntes de 6 e 12 mA cm-2 , mas aumentou a 18 mA cm-2 . A eletro-oxidação é promissora para tratar efluentes têxteis com corantes industriais. Implicações da pesquisa: Os resultados contribuem para avanços científicos e gestão socioambiental na indústria têxtil, oferecendo uma opção viável para o tratamento de efluentes e redução do impacto ambiental. Originalidade/valor: O estudo destaca a eficiência da eletro-oxidação na degradação de corantes industriais em efluentes têxteis, com relevância na remoção do corante, consumo de energia, redução de DQO e TOC, além da avaliação da toxicidade do efluente tratado.