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Application of heterogeneous photo-fenton process using chitosan beads for textile wastewater treatment
Journal of Environmental Chemical Engineering 8 (2020) 103893
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Application of heterogeneous photo-fenton process using chitosan beads for textile wastewater treatment
T
Beatriz Lima Santos Klienchen Dalari*, Cristiane Lisboa Giroletti, Leonardo Dalri-Cecato, Dayane Gonzaga Domingos, Maria Eliza Nagel Hassemer Federal University of Santa Catarina, Sanitary and Environmental Engineering Department, Trindade University Campus, Delfino Conti Street., PO Box 476, 88040-970, Florianópolis, Santa Catarina, Brazil
A R T I C LE I N FO
A B S T R A C T
Editor: GL Dotto
Among the Advanced Oxidative Processes (AOPs) applied in the degradation of toxic and resistant organic compounds such as dyes, the heterogeneous photo-Fenton process stands out, once it has high discoloration efficiency and operational simplicity. Given that, this study evaluated the efficiency of the heterogeneous photoFenton process in real textile wastewater treatment using chitosan beads as a solid catalyst. Laboratory-scale beads production and tests were carried out to monitor a photochemical reactor equipped with a mercury bulb of 125 W. Samples were collected at different reaction times, equal to 15, 30, 45, 60, 75, 90, and 105 min. The H2O2 concentration applied was 400 mg L−1. The chitosan beads weighed 2 g and were coated with iron, presenting an average diameter of approximately 4 mm. The results presented 91.92 % of effluent discoloration. It was possible to verify the process efficiency without iron precipitation when working with pH values above 6. Furthermore, the determination of other parameters behaviors, such as color, aromatic compounds, dissolved and total solids, as well as toxicity, was accomplished.
Keywords: Heterogeneous photo-Fenton Chitosan beads Textile effluent
1. Introduction Textile industries are the fifth largest industrial sector in the world and the fourth largest in clothing manufacturing [1]. This segment is crucial in Vale do Itajaí region, located in the State of Santa Catarina, as well as in the whole Brazilian country. This type of business is known worldwide as one of the biggest consumers of water in its production processes (80–100 m3/ton of finished fabric) and, consequently, one of the biggest generators of industrial effluents [2]. The large volume of effluent generated in the dyeing process has high organic load, elevated inorganic salts content, and substantial concentration of suspended solids, as well as a variable pH, surfactants, and, mainly, high concentration of dyes [3]. Dyes usually have complex structures, which make them resistant to physical-chemical and biological degradation, resulting in their long presence in water bodies [4]. About 10–15% of dyes applied during the manufacturing process are released into the environment due to its incomplete adherence to the fabric fibers [5]. Given that, the removal of textile dyes is one of the main issues in wastewater treatment technology [6]. Advanced oxidative processes have been researched in order to
solve this problem, as they are efficient in toxic and resistant organic compounds degradation, such as dyes [7]. These processes are based on hydroxyl radical generation (●OH), which is a powerful non-selective oxidation agent that reacts with various types of organic compounds, including the recalcitrant ones [8]. Among the several existing AOPs, Fenton process is credited as being one of the most efficient processes for color removal from wastewater produced by dyeing, textile manufacturing, and other industrial processes [9]. It is characterized by the reaction between ferrous ion (Fe2+) and hydrogen peroxide (H2O2) to generate the hydroxyl radical (●OH), which is highly oxidant [10]. Although the Fenton process itself already promotes the degradation of many pollutants, its treatment efficiency can be significantly improved if the system is assisted by ultraviolet or visible radiation, which consists in the photo-Fenton system [11]. However, there are operational conditions that limit its applicability, such as the need to operate under acidic conditions (pH < 3) to avoid the precipitation of Fe3+ hydroxides and the reduction of their catalytic capacity. However, Souza, Peralta-Zamora, and Zawadzki [12] indicate that it is possible to solve this inconvenience by using immobilized forms of iron.
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Corresponding author. E-mail addresses: [email protected] (B. Lima Santos Klienchen Dalari), [email protected] (C. Lisboa Giroletti), [email protected] (L. Dalri-Cecato), [email protected] (D. Gonzaga Domingos), [email protected] (M.E. Nagel Hassemer). https://doi.org/10.1016/j.jece.2020.103893 Received 5 February 2020; Received in revised form 21 March 2020; Accepted 22 March 2020 Available online 29 March 2020 2213-3437/ © 2020 Elsevier Ltd. All rights reserved.
Journal of Environmental Chemical Engineering 8 (2020) 103893
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distilled water to remove the crosslinker excess. Fe+2 was adsorbed on the crosslinked chitosan beads. Approximately 20 g of beads were added in an aqueous solution of ferrous sulfate heptahydrate (0,1 mol. L−1) under stirring. After 4 days, analyses of iron content remaining in solution were made. Eq. (1) was applied in order to determine the adsorption capacity of each sphere.
One of the materials used for iron immobilization is chitosan, which originates from chitin and consists of a natural polymer presented as the main constituent of the exoskeleton of aquatic crustaceans, insects, and the cell wall of fungi [13]. It has great environmental relevance, since Brazil produced 57.142 tons of crustaceans in 2010, and more than 50 % of this amount turned into waste [14]. Given its polycatalytic nature, it is possible to use chitosan in a wide range of applications with a variety of polymeric forms, such as powders, nanoparticles, membranes, sponges, fibers, and beads, since it is applied with acidic solutions [15–18]. Therefore, the objective of this study was to evaluate the efficiency of the heterogeneous photo-Fenton process in the treatment of textile wastewater using chitosan beads as a supporting matrix for ferrous ion immobilization.
qe =
(C 0 − Ceq) ×V m
(1)
where: Qe = quantity of sorbed Fe2+ (mg g−1) C0 = initial iron concentration (mg L−1) Ceq = concentration of iron in equilibrium (mg L−1) V = Fe2+ solution volume (L) m = mass of beads (g). The structural stability of the beads was evaluated as a function of different pH (1–14) and temperature (20 °C–100 °C) conditions. For both tests, 1 g of beads was placed in beakers with distilled water. Then, visual observations were made during the process, and samples were collected for the quantification of iron, according to the methodology described in the analytical control.
2. Material and methods Textile wastewater samples were collected from the effluent treatment plant of a textile dyeing company located in Brusque, Santa Catarina/BR. The effluent treatment system consisted of screening, heat exchanger, equalization, activated sludge biological process, and physical-chemical processes. The collection of samples was carried at the outlet of the secondary clarifier of the activated sludge process. Therefore, the system proposed in this study aimed at the post-treatment of the effluent (E2). The experiments were carried in a benchtop scale photochemical reactor assembled with a useful volume of 1.2 L and constant stirring. It had a double wall in order to recirculate cooling water, thus maintaining isothermal conditions for the reactions to happen. The conduction of radiation was given by the introduction of a mercury vapor lamp (125 W) into the solution. A quartz tube protected the lamp and allowed UV radiation into the liquid medium (Fig. 1). The chitosan used had a 90% deacetylation degree and a mean molar mass of 1.2 x 105 g mol−1 (determined by viscosimetry), obtained from Purifarma Company (São Paulo, Brazil). Chitosan beads production followed the methodology proposed by Souza; Zamora and Zawadzki [12]. Initially, 5 g of chitosan were dissolved in 100 mL of a 5 % (w/v) acetic acid aqueous solution. The viscous solution resulted from this process was put to rest for 24 h at room temperature in order to achieve complete chitosan solubilization. Then, this polymer solution was dripped with a syringe into a 2 mol L−1 NaOH solution in order to form the beads. After that, the beads rested inside this solution for 24 h to complete their precipitation. After being prepared, the chitosan beads underwent a crosslinking reaction. This process consisted of placing 20 g of beads in a beaker with 250 mL of a 0.1 % (v/v) glutaraldehyde aqueous solution. The mixture was maintained under the effect of the crosslinker (glutaraldehyde) with constant stirring for 24 h at room temperature. Finally, the beads were washed extensively with
2.1. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) Scanning electron microscopy analyses were performed using a JEOL JSM-6390LV microscope installed at the Central Electron Microscopy Laboratory of the Federal University of Santa Catarina (UFSC). The samples were supported on a copper tape in order to do the analysis. In parallel to the SEM analysis, the beads underwent an energy dispersive X-ray spectrometry (EDS). This procedure took place by using the Noran System Six program, which is coupled to the scanning electron microscope. The chitosan beads were analyzed without crosslinking, with crosslinking, and with iron adsorbed. Each situation was monitored with an applied voltage of 10 kV, followed by a voltage increase of 30, 65, and 500 times. 2.2. Heterogeneous photo-Fenton process experiment The heterogeneous photo-Fenton process experiment took place under optimum conditions of hydrogen peroxide concentration (400 mg L−1) and iron-modified beads dosage (2 g of beads), as previously optimized based on a factorial design, which considered the E2 natural pH of 8.30 [19]. The tests were made with approximately 750 mL of effluent and lasted for 105 min. Aliquots were removed at the established times (15, 30, 45, 60, 75, 90, and 105 min) to be submitted to the analyses later described in the analytical control. 2.3. Analytical control The color was evaluated spectrophotometrically, considering the higher wavelength of effluent absorption (455 nm) by using the spectrophotometer Hach model DR/2500. The aromatic compounds were also analyzed with the spectrophotometer, by reading the absorbance of the effluent at 280 nm in the UV band using a quartz cuvette with 1 cm of optical path. The residual peroxide was determined following the methodology proposed by Nogueira [20], which is based on the reaction between the vanadate ion and hydrogen peroxide, which leads to a red coloration due to the formation of the peroxovanadium cation. The samples were analyzed with a spectrophotometer at a wavelength of 446 nm. The biochemical oxygen demand (BOD5), the measurement of solids, and pH analytical methods employed followed the Standard Methods for the Examination of Water and Wastewater [21]. The colorimetric method was applied to measure Fe2+, by using Kits Hach Ferrous Iron band 0.02–3.00 mg L−1. The samples were read in a
Fig. 1. Schematic representation of the photochemical reactor. 1) Magnetic stirrer; 2) Quartz tube; 3) Mercury vapor lamp; 4) Sample collector; 5) Cooling water inlet and outlet; 6) Recirculation system with thermostat. 2
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size and structure, but they still had fragile physical conditions. After that, the beads were then subjected to a crosslinking reaction with glutaraldehyde (Fig. 2B). Neto et al. [26] indicate that the crosslinking objective is to modify properties such as chemical and thermal stability, structural rigidity, permeability, and resistance to chemical and biological degradation. According to Favere [27], such modifications occur when chitosan is subjected to a reagent with two or more carbonyl reactive functional groups (aldehyde groups) and can form bonds between the amino groups of the polymer and aldehyde of the reagent, resulting in a crosslinked polymer with a three-dimensional structure. The crosslinked beads (CBG) had an average diameter of 4 mm. Souza, Zamora, Zawadzki [12] reported the same measure with a standard deviation of 0.3 mm. Visually, the beads with or without the crosslinking did not differ from each other. However, regarding the structural aspect, the crosslinked beads were significantly more resistant. The crosslinked and iron-adsorbed chitosan beads (CBGI) remained structurally resistant. A value of 1.8 mg of adsorbed iron/gram of sample was obtained. Fig. 2C shows the beads after 4 days in contact with iron. pH was maintained at 3 to avoid iron precipitation. Ngah, Ghani, Kamari [18] studied the sorption behavior of Fe2+ and Fe3+ ions in aqueous solution in pure chitosan spheres without crosslinking and in glutaraldehyde and other crosslinked spheres and found that the maximum adsorption of the crosslinked sphere was at pH 3. In the leaching studies according to pH and temperature variation, it was observed that the spheres maintained their structure during all the variations, and did not present changes in their consistency, suggesting that the crosslinking reaction happened satisfactorily. They also did not present significant alterations in iron leaching.
spectrophotometer Hach model DR/2500. Total iron concentrations were determined by using Kits Hach Ferrous Iron band 0.02–3.00 mg L−1. Then, the samples were read in a spectrophotometer Hach model DR/2010. The temperature was directed measured with a thermometer. 2.4. Toxicity evaluation performed with Daphnia magna Acute toxicity was assessed following the NBR 12.713 with the freshwater crustacean Daphnia magna. Newborns of Daphnia magna with ages from 2 to 26 h were exposed to a range of different dilutions of the same sample over 48 h. The assays were carried in duplicates, using 20 organisms for each dilution, without providing any feeding or illumination, under a temperature between 20 °C and 22 °C. The organisms were observed after 24 and 48 h, in order to verify their immobility/ mortality. The results were expressed by the Effective Concentration that affects 50 % of the population of the organisms (EC50), and the Dilution Factor (DF), which represents the lowest sample concentration in which there was no immobility in more than 10% of the organisms. 3. Results and discussion 3.1. Biological treatment effluent (E2) characterization Table 1 shows the parameters analyzed and their values regarding the biological treatment effluent (E2) characterization. The effluent presented a strong purple coloration, due to the diversity of dyes used in the textile process and the biological treatment inefficiency in removing color. Metcalf and Eddy [22] indicate that the effluent increases in concentration and anaerobic conditions over time, resulting in color modifications, which becomes gray, then dark gray, and latter presents black coloration. The effluent characterization evidenced basic pH, high conductivity, salinity, and chloride concentrations, due to the addition of salt in the dyeing process, which is necessary to fix the color onto the fabric. High concentration of chlorides can compromise some analyses, such as chromatography, once it is necessary to make a substantial sample dilution, which can mask other compounds. Interferences in COD analysis are also mentioned [23]. Total dissolved solids (TDS) represented a large part of the total solids (TS). It can be explained due to the high concentration of dyes presented in the textile effluent. The activated sludge biological process reduced the organic matter in relation to the raw effluent, resulting in low values of BOD5. Justino [24] and Menon [25] found BOD5 reductions of 87 % and 97 %, respectively, when analyzing a similar effluent from the same company.
3.3. Morphology assessment of the beads by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) SEM analysis showed that the CB had spherical size and regular surface with an average diameter of 4 mm. Dantas et al. [28] studied the production of chitosan-hydroxyapatite spheres and observed that as the hydroxyapatite substance increases, the surface of the sphere reveals a more rough morphology, however, their spheres had diameters equal to 1.9 and 2.2 mm. The CBG presented a visually more rigid surface, corroborating with the results of Silva [29], who obtained more uniform surfaces, probably due to the crosslinking agent used, which was also glutaraldehyde. The CBGI revealed a structure with a rough and uneven surface. This shape is resulted by the adsorption of the iron on the surface. Fig. 3A1, B1 and C1 show the non-crosslinked sphere, the crosslinked sphere, and the iron adsorbed sphere, respectively, with 30-fold magnification. Fig. 3A2, B2 and C2 show the same spheres with a magnification of 65 times. Fig. 3A3, B3 and C3 show the spheres with a 500fold magnification. In the EDS analysis, elements such as carbon, oxygen, and sodium were found. The high peak next to the sodium element represents gold, derived from the material used for the analysis. Other elements not represented in the graph were found, such as silicon, phosphorus, chlorine, and calcium. Their presence could be due to the location where the crustaceans (used to obtain chitosan) were extracted, as well as their exoskeleton. Regarding the CB, carbon, oxygen, and sodium elements, as well as other elements not presented in the graph, such as calcium, silicon, and phosphorus were observed (similar to those found in CBG). Dantas et al. [28] also evidenced sodium and phosphorus in their spheres. However, they came from sodium tripolyphosphate, which was used as a crosslinker. EDS analysis confirmed the high iron presence in the CBGI structure, proving that the beads adsorbed the compound, as well as the other elements previously presented. Table 2 shows the EDS analysis for CB, CBG, and CBGI.
3.2. Production of chitosan beads Fig. 2A shows the chitosan beads (CB) before they went through the crosslinking process. It was observed that the beads presented similar Table 1 Characterization of the biological effluent (E2). Parameter
Unit
E2 ± standard deviation
Aromatic compounds Color Chlorides Conductivity pH TS TSS TDS Salinity BOD5
λ = 280 nm/Absorbance mg L-1 PtCo mg L-1 mS cm-1 – mg L-1 mg L-1 mg L-1 % mg L-1
2.431 ± 0.07 825 ± 0.19 3251 ± 32 13.5 ± 0.9 8.18 ± 0.19 6638.18 ± 223.55 31.87 ± 3.38 6606.31 ± 220.33 8.0 ± 0.01 37.14 ± 1.39
3
Journal of Environmental Chemical Engineering 8 (2020) 103893
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Fig. 2. Chitosan beads. A- Chitosan beads formed after reacting with NaOH; B- Glutaraldehyde crosslinked beads; C- Crosslinked and iron-adsorbed chitosan beads.
3.4. Results of the analytical parameters assessed
Table 2 EDS analysis for CB, CBG and CBGI.
The effluent characterization revealed that the biological treatment process efficiency of the industry, regarding color reduction, does not meet the values required by the Brazilian legislation, presenting a value of 825 mg L−1 PtCo. After 105 min of testing, a reduction percentage of 91.92 % was achieved. Fig. 4 shows the percentage of discoloration over time. Souza, Zamora, Zawadzki [12] achieved 90 % of discoloration of the
Elements
CB
CBG
CBGI
C O Na Fe
41.68 ± 0.88 30.12 ± 0.49 28.20 ± 0.31 —
21.76 ± 0.87 41.10 ± 0.48 37.14 ± 0.36 —
10.63 ± 0.58 32.19 ± 0.55 — 57.18 ± 4.41
Fig. 3. Micrograph of the chitosan beads. A1- non-crosslinked sphere with 30-fold magnification; A2- with 65-fold magnification; A3- with 500-fold magnification. B1- the crosslinked sphere with 30-fold magnification; B2- with 65-fold magnification; B3- with 500-fold magnification. C1- the iron adsorbed sphere with 30-fold magnification; C2-with 65-fold magnification; C3 with 500-fold magnification. 4
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Fig. 6. Box plot graphic of TS concentrations highlighting the average values of TS in E2 and after the treatment. Fig. 4. Percentage of discoloration of samples over time.
sludge) submitted to the photo-Fenton process, Guimarães [32] reported a BOD reduction of 30.2 % after 1 h of treatment. Affirming that although the effluent biodegradability increased, which indicates that contaminant molecules were broken down into smaller fragments, the textile effluent still had molecules that were unable to be biologically oxidated. Braile and Cavalcanti [33] reported that the mean composition of a textile industry effluents can be given by total solids ranging from 1000 to 1600 mg L−1, and suspended solids from 30 to 50 mg L−1. However, this characterization only defines the orders of magnitude of the effluent characteristics, since the composition of the effluent depends on the process and the type of fiber processed. The average TS concentration found in the biological post-treatment effluent studied was 6638.18 mg L−1 on average. Fig. 6 shows a box plot of TS concentrations before and after the photooxidative treatment. After treatment, a value of 6017.5 mg L−1 was obtained, indicating that there was a reduction of only 9.70 %. However, most of the solids evidenced are composed of TDS, which are expressed in the box plot shown in Fig. 7. The TDS parameter indicates that part of the organic and inorganic matter presented in the effluent is dissolved, besides representing a more difficult portion of removal, since it corresponds to the recalcitrant matter of the textile effluent [34]. After the application of the treatment, the effluent still presented an average TDS concentration of 5993.88 mg L−1, corresponding to a reduction of 12.70 %. The mean biological concentration after treatment was 31.9 mg L−1. According to Hassan and Hameed [35], the ideal pH value in the photo-Fenton process should be in the range of 2.5–3.5, in order to avoid the precipitation of iron. However, this study addressed the heterogeneous reaction, which uses a solid catalyst, and therefore does not require rigid pH control, since the iron is impregnated in the catalyst, avoiding coagulation and complexation. The pH during the experiment was 8.30, equivalent to the natural pH of the textile effluent studied. The results show that it was possible to increase the operational range of the pH, maintaining it at high values throughout the process, without interfering in the color removal efficiency, proving the efficiency of the beads as solid catalysts. After 105 min, the effluent had an average pH of 6.87. Fig. 8 shows the variation of pH in the 3 tests performed over time.
reactive dye QR-19 Blue, using a photo-Fenton process with chitosan beads. Gusmão [30] evaluated the photooxidation adsorption process with chitosan-titanium dioxide-iron oxide for the removal of textile dyes in aqueous media and obtained a discoloration of 94.8 % of Remazol Blue, 83.0 % of Orange 16, and 85.6 % of Yellow 3-GP (85.6 %), at the times of 80, 105, and 40 min, respectively. The textile effluent studied initially showed a high absorbance. After treatment (105 min), a reduction of 70.87% of the aromatic compounds was observed. These results indicate that the process modified the structure of these compounds into smaller fragments. The initial concentration of hydrogen peroxide was 400 mg L−1. During the treatment, there was no need for replacement of H2O2, since, at the end of the test, its mean concentration in the solution was 70 mg L−1 (Fig. 5). Souza [31] monitored the peroxide concentration in a similar study regarding the photo-Fenton process applied to a paper and cellulose effluent and observed a peroxide reduction of 90 % in 60 min of treatment, which required peroxide replacement. However, the initial concentration used was 100 mg L−1. As for the parameter BOD5, after the application of the photoFenton Heterogeneous process, there was a reduction of approximately 58 %. However, according to the Brazilian Resolution CONAMA N°. 430, of May 13, 2011, the minimum removal of BOD for discharge is 60 %. In a study using biologically pretreated textile effluent (activated
3.5. D. magna toxicity results D. magna toxicity assays were performed with the post-biological effluent (E2) and the post-oxidative effluent samples from the time of 105 min, as shown in Table 3. The pH of both effluents remained neutral, and according to the NBR 12.713 [36], at neutral pH (between 6 and 9), their adjustment is
Fig. 5. H2O2 consumption over time of treatment. 5
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Fig. 7. Box plot graphic of TDS concentrations highlighting the average values of TS in E2 and after the treatment. Table 4 Toxicity classification in relation to EC50 %. Source: Adapted from Tonkes et al. (1999).
Table 3 Characteristics of effluents and their toxicity concerning EC 50 %. pH
Temperature °C
Average EC50,48 h ± SD (%)
Raw (Post-biologic) Post photooxidative process
7.84 ± 0.02 7.9 ± 0.06
20 ± 2 20 ± 2
63.12 ± 2.21 76.57 ± 6.84
Sample classification
<1 1–10 10–100 > 100
Very toxic Moderately toxic Slightly toxic Non-toxic
establishes a maximum acute toxicity threshold tested with D. magna for textile effluent equal to a DF of 2. The post-process photooxidative effluent did not meet the Ordinance and presented DF equal to 4, higher than what is required by IMA. According to Lanzer et al. [38], the removal of color does not necessarily imply that the effluent is not toxic. Possibly, the degraded textile dyes were converted into intermediate products, which can sometimes present toxic characteristics. Besides that, by the end of the treatment, the residual hydrogen peroxide concentration was lower (70 mg L−1) than the initial one (400 mg L−1). This may have influenced the D. magna organisms, which could lead to the DF values that could not comply with the Brazilian legislation. Zanella [39] applied the photo-Fenton process in dyebaths and, despite the almost complete removal of color and efficiency in the removal of organic compounds from the effluent, it still presented slight toxicity when evaluated by D. magna.
Fig. 8. pH variation along the photooxidative process in the 3 tests performed.
Sample
EC 50 % value
4. Conclusions The study of the application of the chitosan beads in the heterogeneous photo-Fenton process showed that these beads were more resistant, bearing variations in temperature and pH satisfactorily after their crosslinking with glutaraldehyde. The beads had an average diameter of approximately 4 mm and showed a stiffer structure when crosslinked with glutaraldehyde. It was observed that the beads are a good solid catalyst for the heterogeneous process, and the operational range of pH can be increased. Regarding the analyzed parameters, the coloration disappeared progressively. At the time of 105 min of treatment, the average value of 91.92 % of color removal was reached. The initial concentration of hydrogen peroxide was 400 mg L−1, and it was not necessary to perform its replacement during the tests. Although there was little
not necessary. Also, the temperature must be between 18 and 22 °C to be considered optimal. As observed in Table 3, the photooxidative process caused lower toxicity in relation to EC 50%. The effluent E2 presented a mean EC50 % equal to 63.12 %. However, after 105 min of treatment, the EC 50 % was 76.57 %. Tonkes et al. [37] did similar evaluations, in which the two effluents analyzed presented characteristics considered to be slightly toxic, as presented in Table 4. Brazilian Institute of Environment (IMA) Ordinance Nº 017/2002 6
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significant removal of solids, the proposed treatment presented a reduction of approximately 70 % of aromatic compounds, indicating that the process modified the structure of these compounds, transforming them into smaller fragments. The toxicity tested with the test organism D. magna showed that the proposed treatment reduced the toxicity of the effluent. However, it was not enough to reach the Brazilian standards for toxicity proposed by IMA Ordinance N°. 017/02 for the emission of textile effluent, presenting DF equal to 4. Thus, the authors indicate that future studies investigate and identify the presence of possible intermediate compounds formed during the application of the heterogeneous photofenton process, as well as to increase the test time to verify if the toxicity reaches the standards of Brazilian legislation in terms of dilution factor.
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[13]
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Declaration of Competing Interest [19]
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[20]
[21]
CRediT authorship contribution statement [22]
Beatriz Lima Santos Klienchen Dalari: Conceptualization, Methodology, Investigation, Writing - original draft. Cristiane Lisboa Giroletti: Writing - review & editing, Validation. Leonardo DalriCecato: Writing - review & editing, Validation. Dayane Gonzaga Domingos: Writing - review & editing, Validation. Maria Eliza Nagel Hassemer: Supervision, Resources, Validation.
[23] [24]
[25] [26]
Acknowledgements [27]
The funds for this research were provided by the scholarship from the Coordination of Improvement of Higher Education Personnel (CAPES).
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Guibal, Interactions of metal ions with chitosan-based sorbents: a review, Sep. Purif. Technol. 38 (2004) 43–74. K. Okuyama, K. Noguchi, M. Kanenari, et al., Structural diversity of chitosan and its complexes, Carbohydr. Polym. V. 41 (2000) 237–247. W.S.W. Ngah, S.A. Ghani, A. Kamari, Adsorption behaviour of Fe (II) and Fe (III) ions in aqueous solution on chitosan and cross-linked chitosan beads, Bioresour. Technol. 96 (2005) 443–450. B.L.S.K. Dalari, Treatment and study of the effluent toxicity of the process-based textile industry (fenton heterogeneous), Revista Dae 68 (06-19) (2018) 2020. R.F.P. Nogueira, M.R.A. Silva, A.G. Trovó, Influence of the iron source on the solar photo-fenton degradation of different classes oforganic compounds, Sol. Energy 79 (2005) 384–392. APHA, American Public Health Association – Standard Methods for the Examination of Water and Wastewater, wef. 21. ed., APHA, AWWA, Washington, 2005. Metcalf, Eddy, Wastewater Engineering – Treatment, Disposal and Reuse, 3. ed., McGraw-Hill, New York, 1991. SABESP – Companhia de Saneamento Básico do Estado de São Paulo, Norma Técnica Interna, NTS 004. Demanda Química de Oxigênio, São Paulo, 1997. N.M. Justino, Seasonal degradation of textile effluents through the solar photoFenton process mediated by ferrioxalate: discoloration and behavior of solids, Eng. Sanit. Ambient 24 (33-43) (2016) 2019. B.C. Menon, Evaluation of the electrocoagulation process in the treatment of textile effluents, Revista Dae 68 (141-152) (2017) 2020. C.G.T. Neto, T.N.C. Dantas, J.L.C. Fonseca, M.R. Pereira, Permeability studies in chitosan membranes. Effects of crosslinking and poly(ethylene oxide) addition, Carbohydr. Res. 340 (2005) 2630–2636. V.T. Fávere, Aadsorption of the Ions (ii), Cd (Ii), Ni (Ii), Pb (ii) and Zn (Ii) by the Biopolymer Chitin, Chitosan and Modified Chitosan. Thesis (Doctorate) Graduate Program in Chemistry, Federal University of Santa Catarina- SC, 1994. M.J.L. Dantas, T.B. Fidéles, R.G. Carrodeguas, M.V.L. Fook, Obtaining and characterization of chitosan / hydroxyapatite spheres generated in: electronic, J. Mater. Processes 11 (1) (2016) 18–24. A.C.O. Silva, Adsorption Study of the Reactive Dye Orange 16 With Chitosan and Its Derivatives, Thesis (Doctorate in Chemistry), Federal University of Alagoas-MA, 2017. L.L. Gusmão, Treatment of Effluents From The Textile Industry By The AdsorptionPhotooxidation Process Using The Magnetic Composite Chitosan-Thio2-Iron Oxide, Dissertation (master’s degree in agrochemistry). Federal University of Viçosa-MG, 2014. K.V. Souza, E.O. Lopes, D. Bartiko, C.M.S. Vidal, J.B. Souza, Use of biopolymer in pulp and paper industry wastewater treatment by advanced oxidative process, Scientia Forestalis 45 (2017) 363–372. J.R. Guimarães, M.G. Maniero, R.N. Araújo, A comparative study on the degradation of RB-19 dye in an aqueous medium by advanced oxidation processes, J. Environ. Manage. 110 (2012) 33–39. P. Braile, J.E.W.A. M., Cavalcanti, Manual of Treatment of Industrial Wastewater, 18 ed., São Paulo: Cetesb, 1993. G. Giordano, Treatment and control of industrial effluents, Book of Abes, Mato Grosso-MG, 2009. H. Hassan, B.H. Hameed, Fe–clay as effective heterogeneous fenton catalyst for the decolorization of reactive blue 4, Chem. Eng. J. 171 (912-) (2011) 918. ABNT, Associação brasileira de normas técnicas, Ecotoxicologia aquática – Toxicidade aguda - Método de ensaio com Daphnia spp. (Cladocera, Crustacea): NBR 12.713, ABNT, Rio de Janeiro, 2003. M. Tonkes, P.J.F. Graaf, J. Graansma, Assessment of complex industrial effluents in the Netherlands using a whole effluent toxicity (or WET) approach, Water Sci. Technol. 39 (1999) 55–61. R. Lanzer, M. Müller, M. Dumcke, K. Rasera, Comparison of ecotoxicological tests with biomaphylaria tenagophila (orbigny, 1835) and daphnia magna (straus, 1820) using remazol brilliant blue r and urban stream water, J. Brazilian Soc. Ecotoxicol. 2 (1) (2007) 27–32. G. Zanella, M. Scharf, G.A. Vieira, P. Peralta-Zamora, Tratamento de banhos de tingimento têxtil por processos foto-fenton e avaliação da potencialidade de reuso, Quím. Nova 33 (2010) 1039–1043.
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Application of heterogeneous photo-fenton process using chitosan beads for textile wastewater treatment
T
Beatriz Lima Santos Klienchen Dalari*, Cristiane Lisboa Giroletti, Leonardo Dalri-Cecato, Dayane Gonzaga Domingos, Maria Eliza Nagel Hassemer Federal University of Santa Catarina, Sanitary and Environmental Engineering Department, Trindade University Campus, Delfino Conti Street., PO Box 476, 88040-970, Florianópolis, Santa Catarina, Brazil
A R T I C LE I N FO
A B S T R A C T
Editor: GL Dotto
Among the Advanced Oxidative Processes (AOPs) applied in the degradation of toxic and resistant organic compounds such as dyes, the heterogeneous photo-Fenton process stands out, once it has high discoloration efficiency and operational simplicity. Given that, this study evaluated the efficiency of the heterogeneous photoFenton process in real textile wastewater treatment using chitosan beads as a solid catalyst. Laboratory-scale beads production and tests were carried out to monitor a photochemical reactor equipped with a mercury bulb of 125 W. Samples were collected at different reaction times, equal to 15, 30, 45, 60, 75, 90, and 105 min. The H2O2 concentration applied was 400 mg L−1. The chitosan beads weighed 2 g and were coated with iron, presenting an average diameter of approximately 4 mm. The results presented 91.92 % of effluent discoloration. It was possible to verify the process efficiency without iron precipitation when working with pH values above 6. Furthermore, the determination of other parameters behaviors, such as color, aromatic compounds, dissolved and total solids, as well as toxicity, was accomplished.
Keywords: Heterogeneous photo-Fenton Chitosan beads Textile effluent
1. Introduction Textile industries are the fifth largest industrial sector in the world and the fourth largest in clothing manufacturing [1]. This segment is crucial in Vale do Itajaí region, located in the State of Santa Catarina, as well as in the whole Brazilian country. This type of business is known worldwide as one of the biggest consumers of water in its production processes (80–100 m3/ton of finished fabric) and, consequently, one of the biggest generators of industrial effluents [2]. The large volume of effluent generated in the dyeing process has high organic load, elevated inorganic salts content, and substantial concentration of suspended solids, as well as a variable pH, surfactants, and, mainly, high concentration of dyes [3]. Dyes usually have complex structures, which make them resistant to physical-chemical and biological degradation, resulting in their long presence in water bodies [4]. About 10–15% of dyes applied during the manufacturing process are released into the environment due to its incomplete adherence to the fabric fibers [5]. Given that, the removal of textile dyes is one of the main issues in wastewater treatment technology [6]. Advanced oxidative processes have been researched in order to
solve this problem, as they are efficient in toxic and resistant organic compounds degradation, such as dyes [7]. These processes are based on hydroxyl radical generation (●OH), which is a powerful non-selective oxidation agent that reacts with various types of organic compounds, including the recalcitrant ones [8]. Among the several existing AOPs, Fenton process is credited as being one of the most efficient processes for color removal from wastewater produced by dyeing, textile manufacturing, and other industrial processes [9]. It is characterized by the reaction between ferrous ion (Fe2+) and hydrogen peroxide (H2O2) to generate the hydroxyl radical (●OH), which is highly oxidant [10]. Although the Fenton process itself already promotes the degradation of many pollutants, its treatment efficiency can be significantly improved if the system is assisted by ultraviolet or visible radiation, which consists in the photo-Fenton system [11]. However, there are operational conditions that limit its applicability, such as the need to operate under acidic conditions (pH < 3) to avoid the precipitation of Fe3+ hydroxides and the reduction of their catalytic capacity. However, Souza, Peralta-Zamora, and Zawadzki [12] indicate that it is possible to solve this inconvenience by using immobilized forms of iron.
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Corresponding author. E-mail addresses: [email protected] (B. Lima Santos Klienchen Dalari), [email protected] (C. Lisboa Giroletti), [email protected] (L. Dalri-Cecato), [email protected] (D. Gonzaga Domingos), [email protected] (M.E. Nagel Hassemer). https://doi.org/10.1016/j.jece.2020.103893 Received 5 February 2020; Received in revised form 21 March 2020; Accepted 22 March 2020 Available online 29 March 2020 2213-3437/ © 2020 Elsevier Ltd. All rights reserved.
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distilled water to remove the crosslinker excess. Fe+2 was adsorbed on the crosslinked chitosan beads. Approximately 20 g of beads were added in an aqueous solution of ferrous sulfate heptahydrate (0,1 mol. L−1) under stirring. After 4 days, analyses of iron content remaining in solution were made. Eq. (1) was applied in order to determine the adsorption capacity of each sphere.
One of the materials used for iron immobilization is chitosan, which originates from chitin and consists of a natural polymer presented as the main constituent of the exoskeleton of aquatic crustaceans, insects, and the cell wall of fungi [13]. It has great environmental relevance, since Brazil produced 57.142 tons of crustaceans in 2010, and more than 50 % of this amount turned into waste [14]. Given its polycatalytic nature, it is possible to use chitosan in a wide range of applications with a variety of polymeric forms, such as powders, nanoparticles, membranes, sponges, fibers, and beads, since it is applied with acidic solutions [15–18]. Therefore, the objective of this study was to evaluate the efficiency of the heterogeneous photo-Fenton process in the treatment of textile wastewater using chitosan beads as a supporting matrix for ferrous ion immobilization.
qe =
(C 0 − Ceq) ×V m
(1)
where: Qe = quantity of sorbed Fe2+ (mg g−1) C0 = initial iron concentration (mg L−1) Ceq = concentration of iron in equilibrium (mg L−1) V = Fe2+ solution volume (L) m = mass of beads (g). The structural stability of the beads was evaluated as a function of different pH (1–14) and temperature (20 °C–100 °C) conditions. For both tests, 1 g of beads was placed in beakers with distilled water. Then, visual observations were made during the process, and samples were collected for the quantification of iron, according to the methodology described in the analytical control.
2. Material and methods Textile wastewater samples were collected from the effluent treatment plant of a textile dyeing company located in Brusque, Santa Catarina/BR. The effluent treatment system consisted of screening, heat exchanger, equalization, activated sludge biological process, and physical-chemical processes. The collection of samples was carried at the outlet of the secondary clarifier of the activated sludge process. Therefore, the system proposed in this study aimed at the post-treatment of the effluent (E2). The experiments were carried in a benchtop scale photochemical reactor assembled with a useful volume of 1.2 L and constant stirring. It had a double wall in order to recirculate cooling water, thus maintaining isothermal conditions for the reactions to happen. The conduction of radiation was given by the introduction of a mercury vapor lamp (125 W) into the solution. A quartz tube protected the lamp and allowed UV radiation into the liquid medium (Fig. 1). The chitosan used had a 90% deacetylation degree and a mean molar mass of 1.2 x 105 g mol−1 (determined by viscosimetry), obtained from Purifarma Company (São Paulo, Brazil). Chitosan beads production followed the methodology proposed by Souza; Zamora and Zawadzki [12]. Initially, 5 g of chitosan were dissolved in 100 mL of a 5 % (w/v) acetic acid aqueous solution. The viscous solution resulted from this process was put to rest for 24 h at room temperature in order to achieve complete chitosan solubilization. Then, this polymer solution was dripped with a syringe into a 2 mol L−1 NaOH solution in order to form the beads. After that, the beads rested inside this solution for 24 h to complete their precipitation. After being prepared, the chitosan beads underwent a crosslinking reaction. This process consisted of placing 20 g of beads in a beaker with 250 mL of a 0.1 % (v/v) glutaraldehyde aqueous solution. The mixture was maintained under the effect of the crosslinker (glutaraldehyde) with constant stirring for 24 h at room temperature. Finally, the beads were washed extensively with
2.1. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) Scanning electron microscopy analyses were performed using a JEOL JSM-6390LV microscope installed at the Central Electron Microscopy Laboratory of the Federal University of Santa Catarina (UFSC). The samples were supported on a copper tape in order to do the analysis. In parallel to the SEM analysis, the beads underwent an energy dispersive X-ray spectrometry (EDS). This procedure took place by using the Noran System Six program, which is coupled to the scanning electron microscope. The chitosan beads were analyzed without crosslinking, with crosslinking, and with iron adsorbed. Each situation was monitored with an applied voltage of 10 kV, followed by a voltage increase of 30, 65, and 500 times. 2.2. Heterogeneous photo-Fenton process experiment The heterogeneous photo-Fenton process experiment took place under optimum conditions of hydrogen peroxide concentration (400 mg L−1) and iron-modified beads dosage (2 g of beads), as previously optimized based on a factorial design, which considered the E2 natural pH of 8.30 [19]. The tests were made with approximately 750 mL of effluent and lasted for 105 min. Aliquots were removed at the established times (15, 30, 45, 60, 75, 90, and 105 min) to be submitted to the analyses later described in the analytical control. 2.3. Analytical control The color was evaluated spectrophotometrically, considering the higher wavelength of effluent absorption (455 nm) by using the spectrophotometer Hach model DR/2500. The aromatic compounds were also analyzed with the spectrophotometer, by reading the absorbance of the effluent at 280 nm in the UV band using a quartz cuvette with 1 cm of optical path. The residual peroxide was determined following the methodology proposed by Nogueira [20], which is based on the reaction between the vanadate ion and hydrogen peroxide, which leads to a red coloration due to the formation of the peroxovanadium cation. The samples were analyzed with a spectrophotometer at a wavelength of 446 nm. The biochemical oxygen demand (BOD5), the measurement of solids, and pH analytical methods employed followed the Standard Methods for the Examination of Water and Wastewater [21]. The colorimetric method was applied to measure Fe2+, by using Kits Hach Ferrous Iron band 0.02–3.00 mg L−1. The samples were read in a
Fig. 1. Schematic representation of the photochemical reactor. 1) Magnetic stirrer; 2) Quartz tube; 3) Mercury vapor lamp; 4) Sample collector; 5) Cooling water inlet and outlet; 6) Recirculation system with thermostat. 2
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size and structure, but they still had fragile physical conditions. After that, the beads were then subjected to a crosslinking reaction with glutaraldehyde (Fig. 2B). Neto et al. [26] indicate that the crosslinking objective is to modify properties such as chemical and thermal stability, structural rigidity, permeability, and resistance to chemical and biological degradation. According to Favere [27], such modifications occur when chitosan is subjected to a reagent with two or more carbonyl reactive functional groups (aldehyde groups) and can form bonds between the amino groups of the polymer and aldehyde of the reagent, resulting in a crosslinked polymer with a three-dimensional structure. The crosslinked beads (CBG) had an average diameter of 4 mm. Souza, Zamora, Zawadzki [12] reported the same measure with a standard deviation of 0.3 mm. Visually, the beads with or without the crosslinking did not differ from each other. However, regarding the structural aspect, the crosslinked beads were significantly more resistant. The crosslinked and iron-adsorbed chitosan beads (CBGI) remained structurally resistant. A value of 1.8 mg of adsorbed iron/gram of sample was obtained. Fig. 2C shows the beads after 4 days in contact with iron. pH was maintained at 3 to avoid iron precipitation. Ngah, Ghani, Kamari [18] studied the sorption behavior of Fe2+ and Fe3+ ions in aqueous solution in pure chitosan spheres without crosslinking and in glutaraldehyde and other crosslinked spheres and found that the maximum adsorption of the crosslinked sphere was at pH 3. In the leaching studies according to pH and temperature variation, it was observed that the spheres maintained their structure during all the variations, and did not present changes in their consistency, suggesting that the crosslinking reaction happened satisfactorily. They also did not present significant alterations in iron leaching.
spectrophotometer Hach model DR/2500. Total iron concentrations were determined by using Kits Hach Ferrous Iron band 0.02–3.00 mg L−1. Then, the samples were read in a spectrophotometer Hach model DR/2010. The temperature was directed measured with a thermometer. 2.4. Toxicity evaluation performed with Daphnia magna Acute toxicity was assessed following the NBR 12.713 with the freshwater crustacean Daphnia magna. Newborns of Daphnia magna with ages from 2 to 26 h were exposed to a range of different dilutions of the same sample over 48 h. The assays were carried in duplicates, using 20 organisms for each dilution, without providing any feeding or illumination, under a temperature between 20 °C and 22 °C. The organisms were observed after 24 and 48 h, in order to verify their immobility/ mortality. The results were expressed by the Effective Concentration that affects 50 % of the population of the organisms (EC50), and the Dilution Factor (DF), which represents the lowest sample concentration in which there was no immobility in more than 10% of the organisms. 3. Results and discussion 3.1. Biological treatment effluent (E2) characterization Table 1 shows the parameters analyzed and their values regarding the biological treatment effluent (E2) characterization. The effluent presented a strong purple coloration, due to the diversity of dyes used in the textile process and the biological treatment inefficiency in removing color. Metcalf and Eddy [22] indicate that the effluent increases in concentration and anaerobic conditions over time, resulting in color modifications, which becomes gray, then dark gray, and latter presents black coloration. The effluent characterization evidenced basic pH, high conductivity, salinity, and chloride concentrations, due to the addition of salt in the dyeing process, which is necessary to fix the color onto the fabric. High concentration of chlorides can compromise some analyses, such as chromatography, once it is necessary to make a substantial sample dilution, which can mask other compounds. Interferences in COD analysis are also mentioned [23]. Total dissolved solids (TDS) represented a large part of the total solids (TS). It can be explained due to the high concentration of dyes presented in the textile effluent. The activated sludge biological process reduced the organic matter in relation to the raw effluent, resulting in low values of BOD5. Justino [24] and Menon [25] found BOD5 reductions of 87 % and 97 %, respectively, when analyzing a similar effluent from the same company.
3.3. Morphology assessment of the beads by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) SEM analysis showed that the CB had spherical size and regular surface with an average diameter of 4 mm. Dantas et al. [28] studied the production of chitosan-hydroxyapatite spheres and observed that as the hydroxyapatite substance increases, the surface of the sphere reveals a more rough morphology, however, their spheres had diameters equal to 1.9 and 2.2 mm. The CBG presented a visually more rigid surface, corroborating with the results of Silva [29], who obtained more uniform surfaces, probably due to the crosslinking agent used, which was also glutaraldehyde. The CBGI revealed a structure with a rough and uneven surface. This shape is resulted by the adsorption of the iron on the surface. Fig. 3A1, B1 and C1 show the non-crosslinked sphere, the crosslinked sphere, and the iron adsorbed sphere, respectively, with 30-fold magnification. Fig. 3A2, B2 and C2 show the same spheres with a magnification of 65 times. Fig. 3A3, B3 and C3 show the spheres with a 500fold magnification. In the EDS analysis, elements such as carbon, oxygen, and sodium were found. The high peak next to the sodium element represents gold, derived from the material used for the analysis. Other elements not represented in the graph were found, such as silicon, phosphorus, chlorine, and calcium. Their presence could be due to the location where the crustaceans (used to obtain chitosan) were extracted, as well as their exoskeleton. Regarding the CB, carbon, oxygen, and sodium elements, as well as other elements not presented in the graph, such as calcium, silicon, and phosphorus were observed (similar to those found in CBG). Dantas et al. [28] also evidenced sodium and phosphorus in their spheres. However, they came from sodium tripolyphosphate, which was used as a crosslinker. EDS analysis confirmed the high iron presence in the CBGI structure, proving that the beads adsorbed the compound, as well as the other elements previously presented. Table 2 shows the EDS analysis for CB, CBG, and CBGI.
3.2. Production of chitosan beads Fig. 2A shows the chitosan beads (CB) before they went through the crosslinking process. It was observed that the beads presented similar Table 1 Characterization of the biological effluent (E2). Parameter
Unit
E2 ± standard deviation
Aromatic compounds Color Chlorides Conductivity pH TS TSS TDS Salinity BOD5
λ = 280 nm/Absorbance mg L-1 PtCo mg L-1 mS cm-1 – mg L-1 mg L-1 mg L-1 % mg L-1
2.431 ± 0.07 825 ± 0.19 3251 ± 32 13.5 ± 0.9 8.18 ± 0.19 6638.18 ± 223.55 31.87 ± 3.38 6606.31 ± 220.33 8.0 ± 0.01 37.14 ± 1.39
3
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Fig. 2. Chitosan beads. A- Chitosan beads formed after reacting with NaOH; B- Glutaraldehyde crosslinked beads; C- Crosslinked and iron-adsorbed chitosan beads.
3.4. Results of the analytical parameters assessed
Table 2 EDS analysis for CB, CBG and CBGI.
The effluent characterization revealed that the biological treatment process efficiency of the industry, regarding color reduction, does not meet the values required by the Brazilian legislation, presenting a value of 825 mg L−1 PtCo. After 105 min of testing, a reduction percentage of 91.92 % was achieved. Fig. 4 shows the percentage of discoloration over time. Souza, Zamora, Zawadzki [12] achieved 90 % of discoloration of the
Elements
CB
CBG
CBGI
C O Na Fe
41.68 ± 0.88 30.12 ± 0.49 28.20 ± 0.31 —
21.76 ± 0.87 41.10 ± 0.48 37.14 ± 0.36 —
10.63 ± 0.58 32.19 ± 0.55 — 57.18 ± 4.41
Fig. 3. Micrograph of the chitosan beads. A1- non-crosslinked sphere with 30-fold magnification; A2- with 65-fold magnification; A3- with 500-fold magnification. B1- the crosslinked sphere with 30-fold magnification; B2- with 65-fold magnification; B3- with 500-fold magnification. C1- the iron adsorbed sphere with 30-fold magnification; C2-with 65-fold magnification; C3 with 500-fold magnification. 4
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Fig. 6. Box plot graphic of TS concentrations highlighting the average values of TS in E2 and after the treatment. Fig. 4. Percentage of discoloration of samples over time.
sludge) submitted to the photo-Fenton process, Guimarães [32] reported a BOD reduction of 30.2 % after 1 h of treatment. Affirming that although the effluent biodegradability increased, which indicates that contaminant molecules were broken down into smaller fragments, the textile effluent still had molecules that were unable to be biologically oxidated. Braile and Cavalcanti [33] reported that the mean composition of a textile industry effluents can be given by total solids ranging from 1000 to 1600 mg L−1, and suspended solids from 30 to 50 mg L−1. However, this characterization only defines the orders of magnitude of the effluent characteristics, since the composition of the effluent depends on the process and the type of fiber processed. The average TS concentration found in the biological post-treatment effluent studied was 6638.18 mg L−1 on average. Fig. 6 shows a box plot of TS concentrations before and after the photooxidative treatment. After treatment, a value of 6017.5 mg L−1 was obtained, indicating that there was a reduction of only 9.70 %. However, most of the solids evidenced are composed of TDS, which are expressed in the box plot shown in Fig. 7. The TDS parameter indicates that part of the organic and inorganic matter presented in the effluent is dissolved, besides representing a more difficult portion of removal, since it corresponds to the recalcitrant matter of the textile effluent [34]. After the application of the treatment, the effluent still presented an average TDS concentration of 5993.88 mg L−1, corresponding to a reduction of 12.70 %. The mean biological concentration after treatment was 31.9 mg L−1. According to Hassan and Hameed [35], the ideal pH value in the photo-Fenton process should be in the range of 2.5–3.5, in order to avoid the precipitation of iron. However, this study addressed the heterogeneous reaction, which uses a solid catalyst, and therefore does not require rigid pH control, since the iron is impregnated in the catalyst, avoiding coagulation and complexation. The pH during the experiment was 8.30, equivalent to the natural pH of the textile effluent studied. The results show that it was possible to increase the operational range of the pH, maintaining it at high values throughout the process, without interfering in the color removal efficiency, proving the efficiency of the beads as solid catalysts. After 105 min, the effluent had an average pH of 6.87. Fig. 8 shows the variation of pH in the 3 tests performed over time.
reactive dye QR-19 Blue, using a photo-Fenton process with chitosan beads. Gusmão [30] evaluated the photooxidation adsorption process with chitosan-titanium dioxide-iron oxide for the removal of textile dyes in aqueous media and obtained a discoloration of 94.8 % of Remazol Blue, 83.0 % of Orange 16, and 85.6 % of Yellow 3-GP (85.6 %), at the times of 80, 105, and 40 min, respectively. The textile effluent studied initially showed a high absorbance. After treatment (105 min), a reduction of 70.87% of the aromatic compounds was observed. These results indicate that the process modified the structure of these compounds into smaller fragments. The initial concentration of hydrogen peroxide was 400 mg L−1. During the treatment, there was no need for replacement of H2O2, since, at the end of the test, its mean concentration in the solution was 70 mg L−1 (Fig. 5). Souza [31] monitored the peroxide concentration in a similar study regarding the photo-Fenton process applied to a paper and cellulose effluent and observed a peroxide reduction of 90 % in 60 min of treatment, which required peroxide replacement. However, the initial concentration used was 100 mg L−1. As for the parameter BOD5, after the application of the photoFenton Heterogeneous process, there was a reduction of approximately 58 %. However, according to the Brazilian Resolution CONAMA N°. 430, of May 13, 2011, the minimum removal of BOD for discharge is 60 %. In a study using biologically pretreated textile effluent (activated
3.5. D. magna toxicity results D. magna toxicity assays were performed with the post-biological effluent (E2) and the post-oxidative effluent samples from the time of 105 min, as shown in Table 3. The pH of both effluents remained neutral, and according to the NBR 12.713 [36], at neutral pH (between 6 and 9), their adjustment is
Fig. 5. H2O2 consumption over time of treatment. 5
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Fig. 7. Box plot graphic of TDS concentrations highlighting the average values of TS in E2 and after the treatment. Table 4 Toxicity classification in relation to EC50 %. Source: Adapted from Tonkes et al. (1999).
Table 3 Characteristics of effluents and their toxicity concerning EC 50 %. pH
Temperature °C
Average EC50,48 h ± SD (%)
Raw (Post-biologic) Post photooxidative process
7.84 ± 0.02 7.9 ± 0.06
20 ± 2 20 ± 2
63.12 ± 2.21 76.57 ± 6.84
Sample classification
<1 1–10 10–100 > 100
Very toxic Moderately toxic Slightly toxic Non-toxic
establishes a maximum acute toxicity threshold tested with D. magna for textile effluent equal to a DF of 2. The post-process photooxidative effluent did not meet the Ordinance and presented DF equal to 4, higher than what is required by IMA. According to Lanzer et al. [38], the removal of color does not necessarily imply that the effluent is not toxic. Possibly, the degraded textile dyes were converted into intermediate products, which can sometimes present toxic characteristics. Besides that, by the end of the treatment, the residual hydrogen peroxide concentration was lower (70 mg L−1) than the initial one (400 mg L−1). This may have influenced the D. magna organisms, which could lead to the DF values that could not comply with the Brazilian legislation. Zanella [39] applied the photo-Fenton process in dyebaths and, despite the almost complete removal of color and efficiency in the removal of organic compounds from the effluent, it still presented slight toxicity when evaluated by D. magna.
Fig. 8. pH variation along the photooxidative process in the 3 tests performed.
Sample
EC 50 % value
4. Conclusions The study of the application of the chitosan beads in the heterogeneous photo-Fenton process showed that these beads were more resistant, bearing variations in temperature and pH satisfactorily after their crosslinking with glutaraldehyde. The beads had an average diameter of approximately 4 mm and showed a stiffer structure when crosslinked with glutaraldehyde. It was observed that the beads are a good solid catalyst for the heterogeneous process, and the operational range of pH can be increased. Regarding the analyzed parameters, the coloration disappeared progressively. At the time of 105 min of treatment, the average value of 91.92 % of color removal was reached. The initial concentration of hydrogen peroxide was 400 mg L−1, and it was not necessary to perform its replacement during the tests. Although there was little
not necessary. Also, the temperature must be between 18 and 22 °C to be considered optimal. As observed in Table 3, the photooxidative process caused lower toxicity in relation to EC 50%. The effluent E2 presented a mean EC50 % equal to 63.12 %. However, after 105 min of treatment, the EC 50 % was 76.57 %. Tonkes et al. [37] did similar evaluations, in which the two effluents analyzed presented characteristics considered to be slightly toxic, as presented in Table 4. Brazilian Institute of Environment (IMA) Ordinance Nº 017/2002 6
Journal of Environmental Chemical Engineering 8 (2020) 103893
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significant removal of solids, the proposed treatment presented a reduction of approximately 70 % of aromatic compounds, indicating that the process modified the structure of these compounds, transforming them into smaller fragments. The toxicity tested with the test organism D. magna showed that the proposed treatment reduced the toxicity of the effluent. However, it was not enough to reach the Brazilian standards for toxicity proposed by IMA Ordinance N°. 017/02 for the emission of textile effluent, presenting DF equal to 4. Thus, the authors indicate that future studies investigate and identify the presence of possible intermediate compounds formed during the application of the heterogeneous photofenton process, as well as to increase the test time to verify if the toxicity reaches the standards of Brazilian legislation in terms of dilution factor.
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Declaration of Competing Interest [19]
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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CRediT authorship contribution statement [22]
Beatriz Lima Santos Klienchen Dalari: Conceptualization, Methodology, Investigation, Writing - original draft. Cristiane Lisboa Giroletti: Writing - review & editing, Validation. Leonardo DalriCecato: Writing - review & editing, Validation. Dayane Gonzaga Domingos: Writing - review & editing, Validation. Maria Eliza Nagel Hassemer: Supervision, Resources, Validation.
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Acknowledgements [27]
The funds for this research were provided by the scholarship from the Coordination of Improvement of Higher Education Personnel (CAPES).
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