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flocculation process of textile wastewater
Accepted Manuscript Performance of different coagulants in the coagulation/flocculation process of textile wastewater Juliana Dotto, Márcia Regina Fagundes-Klen, Márcia Teresinha Veit, Soraya Moreno Palácio, Rosangela Bergamasco PII:
S0959-6526(18)33126-3
DOI:
10.1016/j.jclepro.2018.10.112
Reference:
JCLP 14514
To appear in:
Journal of Cleaner Production
Received Date: 30 May 2018 Revised Date:
1 October 2018
Accepted Date: 10 October 2018
Please cite this article as: Dotto J, Fagundes-Klen MáRegina, Veit MáTeresinha, Palácio SM, Bergamasco R, Performance of different coagulants in the coagulation/flocculation process of textile wastewater, Journal of Cleaner Production (2018), doi: https://doi.org/10.1016/j.jclepro.2018.10.112. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Performance
of
different
coagulants
in
the
coagulation/flocculation process of textile wastewater Juliana Dottoa, Márcia Regina Fagundes-Klenb, Márcia Teresinha Veitc, Soraya Moreno Paláciod and Rosangela Bergamascoe a
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Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]; corresponding author. b Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. c Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. d Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. e Chemical Engineering Department, State University of Maringá, Maringá-Paraná 87020900, Brazil. [email protected].
ACCEPTED MANUSCRIPT ABSTRACT
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A comparative study of the efficiency of different coagulants in the textile wastewater treatment was carried out. The utilization of natural coagulants instead of the synthetic ones has demonstrated significant advantages since it provides a low cost and environmentally friendly technology for removing dyes. This study aimed at evaluating the performance of different coagulants in the removal of the apparent colour, turbidity, absorbance, and COD of textile wastewater samples from an industrial laundry. Two organic coagulants (Moringa oleifera Lam seeds extracted in saline solutions of NaCl and KCl 1 mol L-1) and an inorganic coagulant (aluminium sulphate) were used. Initially, the influence of the pH was evaluated for each coagulant. Then, a factorial design was applied in order to determine the coagulant concentration and the sedimentation time needed for the textile wastewater treatment. All the parameters obtained their best results with acidic pH values for the studied coagulants. The organic coagulants presented the best results, in general, reaching removals of 82.2 % for the apparent colour, 83.05 % for COD, 78.4 % for RP-HE7B, and 89.7 % for OP-HER using the Moringa coagulant extracted in KCl. This study demonstrated the applicability of the Moringa oleifera Lam seeds to the textile wastewater treatment.
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Keywords: organic coagulant; colour removal; Moringa oleifera Lam; experimental planning; COD removal.
ACCEPTED MANUSCRIPT 1. Introduction
In the textile industry, water consumption varies greatly according to different sectors, such as the colouring process, which may need more than 100 L kg-1 of processed fabric. Besides the consumption, another determining factor is the composition of the wastewater in
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relation to the seasonality that can widely differ from one industry to another (Vajnhandl and Valh, 2014).
Textile production requires a high concentration of different types of organic dyes, additives, and salts, generating wastewaters with high turbidity, chemical oxygen demand,
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suspended solids, pH varying from 2 to 12, and usually high temperatures (Merzouk et al., 2011; Yeap et al., 2014). The discharge of textile wastewaters has a negative aesthetic effect on water supplies, reducing the light penetration, and consequently changing the dynamics of
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the aquatic ecosystem (Pathania et al., 2016; Kakoi et al., 2017).
Dyes and some intermediary products from their degradation can be potentially mutagenic and carcinogenic (Levin et al., 2012; Prola et al., 2013; Katheresan et al., 2018). Even in low concentrations, the presence of dyes in wastewater is not desired since they can cause esthetic and dangerous effects on living beings when discharged into the aquatic ecosystems
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(Morghaddam et al., 2010; Florenza et al., 2014). A significant number of textile wastewater treatment processes have been described in the literature, such as the electrochemical (Palácio et al., 2009; Aquino et al., 2013), biological (Türgay et al., 2011), adsorption (Fagundes-Klen et al., 2012; Sathishkumar et al., 2012; Cao et al., 2014), coagulation (Beltrán-Heredia et al.,
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2009a; Zhao et al., 2014) and advanced oxidation processes (Módenes et al., 2012; Palácio et al., 2012). The coagulation-flocculation process is usually used in wastewater treatment due to its high efficiency and low cost, proving to be effective in the removal of dyes (Huang et
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al., 2014). The coagulation process is related to the addition of chemical products to the wastewater in order to change the physical state of the dissolved and suspended solids and promote their removal through sedimentation (Verma et al., 2012). In the coagulation/flocculation process, the choice of coagulant has a significant role in contaminant removal. There are many categories of coagulants, including inorganic and organic (Huang et al., 2014). Inorganic coagulants, such as iron and aluminium salts, were extensively used in textile wastewater treatment (Furlan et al., 2010; Huang et al., 2014; Liang et al., 2014). However, the sludge generated from an inorganic coagulant is toxic, produced in large quantities and, considerably affects the pH of the treated water according to Vijayaraghavan et al. (2011). Moreover, aluminium is a neurotoxic product and can 1
ACCEPTED MANUSCRIPT contribute to Alzheimer’s disease (Huang et al., 2014; Lau et al., 2014). Therefore, the use of the traditional coagulants is uncertain, and the polymeric macromolecules derived from plants, known as organic coagulants have received a particular interest in textile wastewater treatment due to their biodegradability, non-toxicity, wide variety and availability (Elkady et al., 2011; Huang et al., 2014; Lau et al., 2014).
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The use of natural coagulants from vegetal sources has been recently reported in the literature for the treatment of surface and industrial waters, highlighting the tannins (Hameed et al., 2018), Jatropha curcas (Abidin et al., 2013), Maize (Patel and Vashi, 2012), and Moringa oleifera (De Paula et al., 2018). Particularly, the Moringa oleifera Lam, a member of
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the Moringaceae family, is a plant that has been thoroughly studied as one of the most promising natural coagulants (Madrona et al., 2010; Pritchard et al., 2010; Mangale et al., 2012).
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The present study aimed at evaluating the efficiency of the natural coagulant obtained from the Moringa oleifera Lam extracted from different saline solutions (NaCl and KCl), in addition to the aluminium sulphate inorganic coagulant as a primary textile wastewater treatment. In this study, the influence of the pH on the coagulant capacity of removing colour, turbidity, chemical oxygen demand (COD) and absorbance has been evaluated. The response
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surface methodology (RSM) was applied to study the effects of the coagulant concentration, the sedimentation time, and the interaction between them in the COD removal by the coagulants,
as
well
as
determine
the
optimal
operating
conditions
of
the
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coagulation/flocculation process.
2. Materials and methods
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2.1. Textile Wastewater
The textile wastewater was obtained from an industrial laundry and contained the reactive dyes RP-HE7B and OP-HER, according to the industry. The wastewater characterization was performed, determining the pH (DIGIMED DM-22), apparent colour (HACH DR 2010, mg Pt-Co L-1), and turbidity (HACH 2100 P, NTU). The chemical oxygen demand (COD) was established consistent with the closed reflux colorimetric method and measured in quintuplicate, utilizing a stock solution (COMBICHECK 20) with 750 ± 75 mg O2 L-1. The mean result acquired was 710 ± 23.7 mg O2 L-1. All the analytical measurements were performed according to the Standard Methods for the Examination of Water and Wastewater 2
ACCEPTED MANUSCRIPT (APHA, 2005). The molecular absorption spectra of the reactive dyes RP-HE7B and OP-HER were achieved in a spectrophotometer (SHIMADZU UV 1800), operating between 300 and 700 nm to determine the wavelength of maximum absorption (λmax) of each dye. The absorbance in the λmax was ascertained for the textile wastewater. The results of the physico-
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chemical characterization are presented in Table 1.
Table 1. Physico-chemical properties of the textile wastewater used in the study.
The textile wastewater with an alkaline pH (10.9) presented an intense blue-purplish colour, verified by the high values of apparent colour (4500 mg Pt-Co L-1) and observed
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absorbance. The high COD value (5820 mg O2 L-1) indicates the presence of a large quantity of organic matter.
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The chemical structures of the dyes contained in the industrial textile wastewater are presented in Figure 1. Table 2 shows the molar mass and λmax found according to the literature and experimentally obtained for these dyes. The molecular absorption spectra are shown in Figure 2.
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Figure 1. Chemical structures of the reactive dyes: (a) RP-HE7B (Stringhini, 2013) and (b) OP-HER (Chatterjee et al., 2008).
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Table 2. Physical properties of the dyes present in the textile wastewater. Figure 2. Molecular absorption spectra of the dyes (- - -) RP-HE7B and (___) OP-HER.
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The experimental λmax values were used in the study of the absorbance (A) decay of the effluent in relation to the treatment that was applied.
2.2. Preparation of the Coagulants
The coagulants used in the coagulation/flocculation experiments were: a) Aluminium sulphate solution (AS) (Al2(SO4)3.18H2O), VETEC) was prepared in a concentration of 10.0 g L-1 and dissolved in distilled water; b) The extract from the Moringa oleifera Lam seeds in potassium chloride (MO-KCl) was prepared by triturating 5.0 g of seeds in 100 mL of a KCl 1.0 mol L-1 saline solution. This mixture was kept under magnetic stirring for 30 minutes as 3
ACCEPTED MANUSCRIPT well as vacuum filtered on qualitative filter paper. The extract was obtained immediately after separation and c) The extract of Moringa oleifera Lam seeds in sodium chloride (MO-NaCl) had a similar preparation procedure to the MO-KCl coagulant, substituting the KCl with sodium chloride 1.0 mol L-1. The preparation of the extracts followed the methodology
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described by Beltrán-Heredia et al. (2009a).
2.3. Coagulation/Flocculation Tests
Coagulation/flocculation tests were carried out in a Jar test (Milan, JT-103) in order to
concentration and sedimentation time.
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2.3.1. Determination of the coagulation/flocculation pH
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evaluate the efficiency of the different coagulants, varying the pH values, coagulant
In this experiment, the best coagulation/flocculation pH value was determined according to each coagulant studied. A fixed amount of each coagulant (AS = 1000 mg L-1, MO-NaCl and MO-KCl= 1600 mg L-1) was added to 1.0 L of the textile wastewater, stirring for 2 minutes
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with a rapid mixing gradient of 100 rpm and for 20 minutes with a slow mixing gradient of 20 rpm (Golob et al., 2005). The initial wastewater pH was adjusted, using HCl and NaOH 1 mol L-1 solutions, to a value between 1 and 10. After 60 minutes of sedimentation, aliquots of 50 mL of the supernatant of each sample were collected in order to evaluate the apparent colour,
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COD and turbidity in triplicate.
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2.3.2. Experimental factorial design: concentration of coagulant and sedimentation time
To establish the ideal concentration and the optimal sedimentation time of each coagulant, a 32 full factorial experimental design (FED) was applied, based on the Response Surface Methodology (RSM) (Myers and Montgomery, 2002; Khuri and Mukhopadhyay, 2010). The chemical oxygen demand (COD) was used as the response variable. In the experimental design, two levels were used to represent the variables (coagulant concentration and sedimentation time) and a centre point, previously selected in preliminary experiments (Table 3).
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ACCEPTED MANUSCRIPT Table 3. Actual and coded values of the independent variables used in the experimental design.
The experiments were performed at the best pH obtained for each coagulant. Then, the coagulants were added to 1.0 L of the textile wastewater, and the sedimentation time varied
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according to the experimental design (Table 3). The rapid and slow operating conditions have been previously described. Aliquots of 50 mL of the supernatant were collected to determine the COD.
Based on the achieved results from the 32 factorial experimental design (FED), presented
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in Table 3, the RSM was applied to develop the polynomial regression equations and to corroborate the connection between the response (COD) and the optimal values of the two operating parameters of the coagulation process (POP): coagulant concentration (q1) and
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sedimentation time (q2). The second order response surface models for each of the evaluated coagulants were developed as follows (Myers and Montgomery, 2002; Khayet et al., 2011):
N
N N
i =1
i =1 j =1
N N
R = k0 + ∑ ai qi + ∑∑ bij qi + ∑∑ cij qi q j i −1 j =1
(1)
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2
Where R is the response predicted by the model, qi and qj are the independent variables, k0, aj, bij, and cij are the regression coefficients that represent the types of interactions among the POP values, and N is the number of POP.
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In order to evaluate the error of the models related to the experimental values, the effluent
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was treated in the best operating conditions obtained from the factorial designs.
2.3.3. Effect of sedimentation time
For 1.0 L of wastewater, the best concentration of each coagulant was used at the optimal pH and under the rapid and slow mixing gradients previously described, varying the sedimentation time (15, 30, 45, and 60 minutes). Aliquots of 50 mL of the supernatant were collected to determine the parameters: apparent colour, COD, turbidity, Abs 541 and Abs 493.5 nm, in triplicate.
3. Results and discussion 5
ACCEPTED MANUSCRIPT 3.1. Effect of the Initial pH on the Performance of the Coagulants
Figure 3 shows the effect of the initial pH of the wastewater on the performance of the AS, MO-NaCl, and MO-KCl coagulants when reducing the apparent colour, turbidity, COD and
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absorbance (493.5 and 541 nm). Figure 3. Removal of (a) apparent colour (mg Pt-Co L-1), (b) turbidity (NTU), (c) absorbance 541 nm (RP-HE7B), (d) absorbance 493.5 nm (OP-HER) and (e) COD (mg L-1) after the treatment with MO-KCl, MO-NaCl and AS at different initial pH values and coagulant
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concentrations (AS-1000 mg L-1, MO-NaCl/MO-KCl-1600 mg L-1).
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According to Figure 3a-e, the highest reduction in the evaluated parameters occurred at an acidic pH for the coagulants studied. The aluminium sulphate (AS) inorganic coagulant presented the best results at pH values between 5 and 6, showing a maximum turbidity removal of 87.6% (Figure 3b) and a COD of 73.6% (Figure 3e).
For the AS, the maximum reduction of absorbance was 31.4% for RP-HE7B (Figure 3c)
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and 12.5% for OP-HER (Figure 3d) at a pH of 5. Merzouk et al. (2011) utilized the same coagulant when treating a synthetic solution of the disperse dye, obtaining a more efficient discolouration within a pH range from 4.0 to 7.8, and a colour removal between 86.0 and 93.6%, reaching the highest value at a pH value close to 5.5. Khayet et al. (2011) used an AS
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coagulant concentration of 820 mg L-1 and attained a maximum absorbance removal of the Acid Black 210 dye at a pH of 5.61. The studies previously mentioned confirmed the optimal pH range of the AS coagulant for removing colour and absorbance in dyes of different
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fixation methods (reactive, disperse and acidic). The study of El-Gohary and Tawfik (2009) with textile wastewater derived from different industries and containing diverse classes of coagulants presented the maximum results of colour removal with the AS coagulant at a pH of 5.3, confirming the optimal pH range for this coagulant. The authors attribute this result to the fact that, within the optimal pH range, the particles of the dye retain negative charges, which promotes a better performance of the AS coagulant, of a cationic nature. The MO-NaCl organic coagulant presented its best results at a pH of 2, as shown in Figure 3a-e. Beltrán-Heredia et al. (2009b) obtained similar results when studying the removal of the Alizarin Violet 3R dye at an acidic pH, confirming the cationic protein nature of the MO, which can enhance the coagulant activity at low pH values. The MO-NaCl, at a pH of 2, 6
ACCEPTED MANUSCRIPT presented a removal of 76.0% for apparent colour, 60.2% for COD, and 32.8% for turbidity. At a pH of 1, a higher reduction of the apparent colour was realised. Nevertheless, it presents a disadvantage due to the use of a greater quantity of the acidic solution in order to adjust the treated sample. The MO-KCl coagulant exhibited a result similar to the MO-NaCl at a pH of 2, which can
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be verified in Figure 3a-e, showing a removal of 76.0% for apparent colour, 62.9% for COD and 27.1% for turbidity.
Both coagulants extracted from the MO seeds presented an increase of the treated textile wastewater turbidity when compared to the untreated sample in most of the evaluated pH
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values. A similar behaviour was achieved by Muthuraman and Sasikala (2014), utilizing the Moringa oleifera Lam seeds extracted with NaCl when treating synthetic turbid water to obtain drinking water. The authors verified that as long as the pH of the reaction increased,
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the turbidity removal efficiency decreased.
According to Table 1, the initial turbidity value of the effluent (66.8 NTU) and its low removal efficiency (Figure 3b) confirmed the observations of Suleyman and Evison (1995) and Katayon et al. (2007), who attribute this behaviour to a low rate of inter-particle contact of MO and the particles in the reaction medium, reducing flake formation and its
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sedimentation.
In Figure 3c-d, the removals of the RP-HE7B and OP-HER dyes with MO-NaCl were higher when compared to the MO-KCl coagulant. As observed, the similar parameters that were evaluated, apparent colour and the absorbance of the two dyes, accomplished the same
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or better removal results with MO-NaCl. According to Zhao et al. (2014), the colour removal may be related to the macromolecules that form the natural coagulant, such as polysaccharides and cellulose. Therefore, a higher quantity of these macromolecules provided
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a more efficient coagulation process, as observed.
3.2 Influence of the Coagulant Concentration and Sedimentation Time The COD results attained from the 32 full factorial design, carried out at the best pH value for each coagulant (pH=2 for MO-NaCl and MO-KCl; pH=5 for AS) in the coagulation/flocculation process, in triplicate, are presented in Table 4. Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MO-NaCl, MO-KCl and AS at the best pH. 7
ACCEPTED MANUSCRIPT The COD values achieved for the wastewater treated by the coagulation/flocculation process using the MO-NaCl, MO-KCl and AS coagulants varied between 1080 to 5550 mg O2 L-1 with MO-NaCl, 1332 to 5590 mg O2 L-1 with MO-KCl and 912 to 3068 mg O2 L-1 with AS.
of variance (ANOVA). The results are indicated in Table 5.
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The response surface models for each coagulant were statistically validated by the analysis
Table 5. Analysis of variance (ANOVA) for the COD removal models realised in the
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coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval of 95% (p<0.05)
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The statistical significance of the second order regression models was determined by the F value. If the models provide an adequate prediction of the experimental data, the values of F should be higher than the Ftable = 2.68 (Myers and Montgomery, 2002). In this context, the F values for the three coagulants studied were greater than the Ftable, statistically validating the models.
The models presented an excellent fit for the observed COD values (Table 4), with R2 of
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0.98 for MO-NaCl, 0.99 for MO-KCl and 0.99 for AS. The values of R2 indicate that the experimental data acquired could be described by the models developed at 98% (MO-NaCl – Equation 2), 99% (MO-KCl – Equation 3), and 99% (AS – Equation 4).
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According to the effect of the interactions presented in Table 6, it can be verified that the results of the t-statistic (tstat) from the coefficients (k0, a1, b12, a2, b22, and c1) for all the coagulants was higher than 2, in absolute values. It confirms that the intercept, the coagulant
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concentration (linear and quadratic terms), the sedimentation time (linear and quadratic), and the interaction between the coagulant concentration and the sedimentation time of the process presented a statistical significance, which is confirmed by the p-value < 0.05.
Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95% (p<0.05)
The negative effects of a1 and a2 for the MO-NaCl and MO-KCl coagulants suggest that the highest coagulant concentrations and sedimentation time values provided the greatest 8
ACCEPTED MANUSCRIPT efficiency of the coagulation/flocculation process concerning the COD reduction. For the AS coagulant, the positive a1 and negative a2 values indicate that low coagulant concentrations and high sedimentation times benefit the COD reduction. The empirical models for the COD values obtained by the coagulation/flocculation process
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were written according to Equations 2 (MO-NaCl), 3 (MO-KCl) and 4 (AS).
(2)
CODMO-KCl= 2576.54 - 2468.95C - 1545.98T - 879.23C2 - 498.48T2 + 838.45CT
(3)
CODAS= 2606.46 +1151.40C - 1094.13T - 1151.78C2 - 158.85T2 + 165.60CT
(4)
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CODMO-NaCl= 2961.69 - 1459.72C - 2792.70 T - 362.99C2 - 663.04T2 + 387.53CT
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Where 200 ≤ C ≤ 2800 mg L-1 for MO-NaCl; 200 ≤ C ≤ 2600 mg L-1 for MO-KCl and 600 ≤ C ≤ 2800 mg L-1 for AS, and 15 ≤ T ≤ 60 for the three evaluated coagulants (C = concentration = q1 and T = sedimentation time = q2).
The graphical representations of the models (contour plots) were plotted based on Equations 2-4. The plots are shown in Figure 4 and indicate the influence of the coagulant
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concentration and sedimentation time on the COD removal, where the black/green region represents the lowest values of COD.
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Figure 4. Contour plots for COD predicted as a function of the coagulant concentration and sedimentation time in the coagulation/flocculation process utilizing the coagulants a) MO-
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NaCl; b) MO-KCl and c) AS
The MO-NaCl and MO-KCl coagulants (Figure 4a and 4b) presented a similar behaviour, i.e. the increase of coagulant concentration and sedimentation time caused a decrease in the COD values. The aluminium sulphate (Figure 4c) differed from the organic coagulants regarding the concentration influence on the COD values, in this case, intermediary coagulant concentration values provided higher COD reduction values. A higher sedimentation time possibly indicates a more efficient COD reduction when using the AS coagulant. In order to maximize the COD removal from the wastewater studied, it is essential to establishthe optimal operating conditions of the coagulation/flocculation process. The values 9
ACCEPTED MANUSCRIPT of the operating parameters that provided the maximum COD reduction efficiency and were determined through the models for the evaluated coagulants are shown in Table 7.
Table 7. Values of the operating parameters of the coagulation/flocculation process that provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl and AS
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coagulants
It can be observed that, for the organic coagulants (MO-NaCl and MO-KCl), the sedimentation process was quicker when compared to the inorganic coagulant (AS) according
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to Table 7. The effluent was treated with the optimal experimental conditions of the coagulant and sedimentation time in order to evaluate the error (%) of the applied models. All the models presented errors of up to 5%, as MO-NaCl, MO-KCl, and AS were 2.01, 3.71, and
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5.01, respectively, confirming their applicability (Table 7). For the AS coagulant, the COD at a sedimentation time of 60 min was determined as well. The results demonstrated that, in spite of the fact that the statistic model presented the best sedimentation time as 74 min with a predicted COD of 872 mg L-1, the COD decreased to 835 mg L-1 in 60 min. Thus, for comparison purposes, the maximum sedimentation time used was 60 minutes, and the effect
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of the flake sedimentation time on the treatment efficiency was also evaluated.
3.3. Effect of the Sedimentation Time
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The effect of the sedimentation time on the coagulation/flocculation process was analysed with the optimal conditions at a pH of 2 (MO-NaCl and MO-KCl) and 5 (AS) and coagulant concentrations of 2086 mg L-1 (MO-KCl), 2461 mg L-1 (MO-NaCl), and 1531 mg L-1 (AS).
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The maximum sedimentation time was 60 minutes. The obtained results are presented in Figure 5.
Figure 5. Variation of the parameters a) COD; b) Apparent Colour; c) Turbidity; d) Abs 541 nm and e) Abs 493.5 nm, using 2086 mg L-1 of MO-KCl, 2461 mg L-1 of MO-NaCl and 1531 mg L-1 of AS
It can be confirmed that, in general, the organic coagulants presented the best removal results for all the evaluated parameters (Figure 5). Whereas, lower removals were achieved with the AS coagulant. The removal of apparent colour was 23.6%, absorbance at a wavelength of 10
ACCEPTED MANUSCRIPT 493.5 was 30.5% and a wavelength of 541 nm was 29.5% after 15 min since there was not an increase in the removal with the increment in sedimentation time (Figure 5b, 5d and 5e). The COD removal (Figure 5a) increased with time, 82.9% in 60 min. The turbidity reduced 23.6% after 30 min of sedimentation, and modifications after this period were not verified (Figure 5c). De Paula et al. (2014) demonstrated that the utilization of the coagulant mixture of
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aluminum sulfate and Moringa oleifera Lam removed the turbidity with a higher performance compared to the inorganic coagulant when treating wastewater from concrete. In their experiments, the authors verified a reduction of 99.3% of turbidity in 60 minutes using 1850 mg L-1 of coagulant (80% aluminum sulfate and 20% of powdered Moringa oleifera Lam).
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However, when using just aluminum sulfate, 97.9% of removal in 60 minutes was realised. A similar behavior was obtained by De Paula et al. (2018). The authors achieved a turbidity removal higher than 99% using 1010 mg L-1 of the coagulant solution (53.5% of aluminum
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sulfate and ferric chloride and 46.5% of powdered Moringa oleifera Lam) in 60 minutes. The results confirmed that the organic coagulants can enhance the action of chemical coagulants.Wong et al. (2007) utilized the AS coagulant when treating a reactive dye synthetic solution, acquiring a removal of 78.0% of colour and 75.0% of COD with a coagulant concentration of 6000 mg L-1, and a pH within 3.9-4.1. The lowest value of colour removal
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observed for the AS coagulant in this study is possibly related to the fact that industrial effluents present different characteristics as compared to a synthetic solution. For a real effluent, the interactions between coagulant and dye are differentiated when compared to a solution that was produced in a laboratory since the real effluent contains some components
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that are not present in the synthetic solution. Nonetheless, the COD removal accomplished in this study, using a lower coagulant concentration (82.9%), was higher than the one achieved by Wong et al. (2007) (75%) (1531 mg L-1 versus 6000 mg L-1).
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For the MO-NaCl and MO-KCl coagulants, a higher colour removal when compared to the AS was substantiated (Figure 5b). The MO-KCl coagulant had a colour removal of 82.2% after 60 min, whereas the MO-NaCl coagulant removed 70.2%. Patel and Vashi (2013) utilized the MO for treating textile wastewater at a neutral pH with concentrations higher than the ones used in this study (5000 – 30000 mg L-1), and obtained lower colour removals, even in the greatest coagulant concentration (58.4%) along with a higher sedimentation time (120 minutes). Therefore, the relevance of the preparation method of the coagulant solution and its pH can be verified, which increased the colour removal in conditions that represented an economical treatment process (lower coagulant concentration and sedimentation time).
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ACCEPTED MANUSCRIPT The decrease in the absorbance (90%) at 493.5 nm (OP-HER) occurred in the first 15 minutes of sedimentation for both organic coagulants (Figure 5e). For the wavelength of 541 nm (RP-HE7B), there was a reduction of 75.3% with MO-NaCl and 78.4% with MO-KCl in the absorbance after 30 min, without any changes after this period (Figure 5d). Vilaseca et al. (2014) treated a textile effluent using the MO-NaCl organic coagulant and attained a removal
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of 80% of the Orange Procion MX-2R dye, a similar behaviour achieved for the Orange Procion dye. The coagulant concentration used in the treatment was 1250 mg L-1, and the obtained results were close to the ones from this current study.
When adding the MO-NaCl and MO-KCl coagulants to the coagulation/flocculation
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process to treat the textile wastewater, it was verified that the initial turbidity increased. Nevertheless, it decreased at a minimum sedimentation time of 45 minutes, for both coagulants (Figure 5c). There was a reduction of 50% for the MO-NaCl and 62% for the MO-
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KCl. De Paula et al. (2014) utilized crushed Moringa oleifera Lam seeds as a coagulant for the turbidity removal of wastewater from concrete. The results from the coagulation process showed a turbidity reduction of the real effluent from 132 to 13.04 NTU in 60 minutes, corresponding to a removal of approximately 90%. Byreducing the processing time to 30 minutes, it impacted the turbidity removal, which reached 78%. Sánchez-Martín et al. (2010),
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aiming at reducing the turbidity of river waters, proposed the purification of the MO extract to remove the proteins that do not present a coagulant effect, only retaining the active ones. The results indicated that the purification procedure of the Moringa oleifera Lam enhanced the efficiency of the coagulant protein. The authors cited in their study that, during the
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coagulation process, the inactive proteins initially promote an increased turbidity of the river waters, and is then reduced according to the increment in the sedimentation time. This behaviour is in agreement with the achieved results, since the MO extract used in the
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treatment was not submitted to a purification process. Katayon et al. (2007) stated that low turbidity effluents, such as the one in this present study, provide flake formation with a low sedimentation capability, reducing the coagulation/flocculation performance of the coagulant. The COD removal (Figure 5a) was also higher with an increased sedimentation time for the MO-NaCl and MO-KCl coagulants. For the MO-NaCl, there was a lower removal (72.8%) when compared to the AS coagulant (82.9%) in 60 minutes of coagulation. However, the inorganic coagulant removal was similar to the one realised by MO-KCl (83.0%). Patel and Vashi (2013) evaluated the sedimentation time when studying the COD removal, and acquired results similar to the ones in this study, confirming that the increased sedimentation time is crucial to the COD removal. The sedimentation time varied from 15 to 150 minutes, 12
ACCEPTED MANUSCRIPT and the best COD removal result was achieved in 120 minutes (75.6%), with a coagulant concentration of 20000 mg L-1. Meanwhile, it was observed that the coagulant concentration and the sedimentation time were higher, raising the cost of the treatment process. Consequently, the extraction method of the coagulant agent from the MO seeds is a key factor in the process efficiency, enabled by the use of a saline solution, which was confirmed by
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Madrona et al. (2010).
4. Conclusions
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The present study compared the efficiency of the MO-NaCl, MO-KCl and AS coagulants for treating textile wastewaters. It was verified that, for the coagulants applied to the treatment, the pH of the wastewater influences the coagulation/flocculation process when
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removing the colour, turbidity, COD and absorbance of the dyes. The response surfaces realised demonstrated that the physicochemical parameters indicated different optimal coagulant concentration and sedimentation time values, according to each coagulant studied. The best sedimentation time values were reached with the MO-NaCl and MO-KCl coagulants when compared to the AS. Among the coagulants studied, MO-KCl and MO-NaCl presented
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a higher efficiency when compared to the AS coagulant, highlighting the MO-KCl performance, indicating the applicability of the organic coagulants derived from Moringa oleifera Lam for treating textile wastewaters.
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Acknowledgments
The authors acknowledge the Coordination for the Improvement of Higher Education
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Personnel (CAPES) for the financial support and the Environmental Institute of Paraná (IAP) for the laboratory infrastructure.
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ACCEPTED MANUSCRIPT Yeap, K.L.,Teng, T.T., Poh, B.T., Morad, N., Lee, K.E., 2014. Preparation and characterization of coagulation/flocculation behavior of a novel inorganic–organic hybrid polymer for reactive and disperse dyes removal. Chem Eng J. 243, 305-314. Zhao, S., Gao, B., Yue, Q., Wang, Y., 2014. Effect of Enteromorpha polysaccharides on coagulation performance and kinetics for dye removal. Colloids Surf A Physicochem Eng
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ACCEPTED MANUSCRIPT Table list
Table 1. Physico-chemical properties of the textile wastewater used in the study. Table 2. Physical properties of the dyes present in the textile wastewate. Table 3. Actual and coded values of the independent variables used in the experimental
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design. Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MO-NaCl, MO-KCl and AS at the best pH.
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Table 5. Analysis of variance (ANOVA) for the COD removal models obtained in the coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval
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of 95 % (p<0.05).
Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95 % (p<0.05). Table 7. Values of the operating parameters of the coagulation/flocculation process that
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AS coagulants.
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provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl, and
ACCEPTED MANUSCRIPT Table 1. Physico-chemical properties of the textile wastewater used in the study. Parameters
Units
pH
-
Initial values 10.9 -1
mg Pt-Co L
4500
Turbidity
NTU
66.8
COD
mg O2 L-1
5820
Absorbance 541 nm*
-
Absorbance 493.5 nm**
-
2.267 3.311
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*(RP- HE7B); **(OP-HER)
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Apparent colour
ACCEPTED MANUSCRIPT Table 2. Physical properties of the dyes present in the textile wastewater. Molar mass Dye
Literature
Experimental
1596
543.5*
541.0
OP-HER
1850
496.0**
493.5
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Garcia-Montaño et al., 2006 and **Chatterjee et al., 2008
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RP- HE7B
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*
g mol
λmax (nm)
-1
ACCEPTED MANUSCRIPT Table 3. Actual and coded values of the independent variables used in the experimental design.
MO-KCl
MO-NaCl
Symbol Real values of coded levels -1
0
+1
Coagulant concentration (mg L-1)
q1
200
1200
2600
Sedimentation time (min)
q2
15
30
60
Coagulant concentration (mg L-1)
q1
200
1800
2800
Sedimentation time (min)
q2
15
30
60
Coagulant concentration (mg L )
q1
600
1200
2800
Sedimentation time (min)
q2
15
30
60
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Variable
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Coagulant
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Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MONaCl, MO-KCl and AS at the best pH. MO-NaCl
(min)
1
200
15
2
200
30
3
200
4
COD Removal (%)
q1 (mg L )
(min)
4.7
200
15
Residual COD (mg L-1) 5586±4
(mg L )
(min)
4.0
600
15
Residual COD (mg L-1) 3056±12
3876±6
33.4
200
30
4185±9
28.1
600
30
2627±5
54.9
60
2545±6
56.3
200
60
2939±3
49.5
600
60
1771±5
69.6
1200
15
4182±5
28.1
1200
15
3017±7
48.2
1200
15
2081±4
64.2
5
1200
30
2838±5
6
51.2
1200
30
2083±5
64.2
1200
30
1929±3
66.9
1200
60
1085±5
81.4
1200
7
2800
15
3795±5
34.8
2600
8 9
2800
30
2059±5
64.6
2600
2800
60
1605±6
72.4
2600
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q2 -1
COD Removal (%)
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Residual COD (mg L-1) 5547±4
q1
q2
AS
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q2 -1
-1
COD Removal (%) 47.5
60
1770±4
69.6
1200
60
916±5
84.3
15
2220±3
61.9
2600
15
3941±5
32.3
30
1467±2
74.8
2600
30
3879±5
33.4
60
1336±5
77.0
2600
60
3033±5
47.9
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q1
MO-KCl
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Run
ACCEPTED MANUSCRIPT Table 5. Analysis of variance (ANOVA) for the COD removal models obtained in the coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval of 95 % (p<0.05). Source
SS
DF
MS
F
Ftable
R2
p-value
MO-NaCl
Regression
46961496
5
9392299
199.41
2.68
0.98
< 0.05
Residual
989103
21
47100
Total
47950599
26
Regression
46145267
5
9229053
Residual
467914
21
22282
Total
46613181
26
Regression
24136905
5
4827381
Residual
74104
21
3529
Total
24211009
26
AS
414.19
2.68
0.99
< 0.05
1367.91
2.68
0.99
< 0.05
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ACCEPTED MANUSCRIPT Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95 % (p<0.05).
parameters
MO-KCl
q0
k0
q1
a1
(q1)2
b1 2
q2
a2
(q2)2
b2 2
q1 x q2
c1
q0
k0
q1
SE
tstat
p-value
42.34
69.95 < 0.05
-1459.72 103.20 -14.14 < 0.05 -362.99
89.38
-4.06 < 0.05
-2792.70 102.74 -27.18 < 0.05 -663.04
90.23
-7.35 < 0.05
387.53 121.96
3.18 < 0.05
2576.54
29.06
88.67 < 0.05
a1
-2468.95
70.99 -34.78 < 0.05
b1 2
-879.23
61.22 -14.36 < 0.05
a2
-1545.98
70.52 -21.92 < 0.05
b2 2
-498.48
62.06
-8.03 < 0.05
q1 x q2
c1
838.45
84.24
9.95 < 0.05
q0
k0
2606.46
11.73 222.12 < 0.05
a1
1151.40
28.24
b1 2
-1151.78
25.07 -45.94 < 0.05
q2
a2
-1094.13
28.43 -38.49 < 0.05
(q2)2
b2 2
158.85
24.70
6.43 < 0.05
q1 x q2
c1
165.60
32.57
5.08 < 0.05
(q1)2 q2
q1
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(q1)2
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(q2)2
AS
2961.69
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Regression coefficients Effect
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Actions of
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q1 = coagulant concentration (mg L-1); q2 = sedimentation time (min)
40.78 < 0.05
ACCEPTED MANUSCRIPT Table 7. Values of the operating parameters of the coagulation/flocculation process that provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl, and AS coagulants. MO-NaCl
MO-KCl
AS
Coagulant concentration (mg L-1)
2461
2086
1531
Sedimentation time (min)
56
48
74
Predicted COD (mg L-1)
1318
1034
872
Experimental COD (mg L-1)
1345
997
918
Model error (%)
2.01
3.71
5.01
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ACCEPTED MANUSCRIPT Highlights •
The efficiency of the coagulants is dependent on the pH, preferably acid.
•
High natural coagulant concentrations and settling times resulted in COD removals. The natural coagulants provided a more significant COD removal.
•
Moringa oleifera Lam has potential as a coagulant for treating textile
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•
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wastewater.
S0959-6526(18)33126-3
DOI:
10.1016/j.jclepro.2018.10.112
Reference:
JCLP 14514
To appear in:
Journal of Cleaner Production
Received Date: 30 May 2018 Revised Date:
1 October 2018
Accepted Date: 10 October 2018
Please cite this article as: Dotto J, Fagundes-Klen MáRegina, Veit MáTeresinha, Palácio SM, Bergamasco R, Performance of different coagulants in the coagulation/flocculation process of textile wastewater, Journal of Cleaner Production (2018), doi: https://doi.org/10.1016/j.jclepro.2018.10.112. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Performance
of
different
coagulants
in
the
coagulation/flocculation process of textile wastewater Juliana Dottoa, Márcia Regina Fagundes-Klenb, Márcia Teresinha Veitc, Soraya Moreno Paláciod and Rosangela Bergamascoe a
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Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]; corresponding author. b Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. c Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. d Postgraduate Program of Chemical Engineering, State University of Western Paraná, Toledo-Paraná 85903000, Brazil. [email protected]. e Chemical Engineering Department, State University of Maringá, Maringá-Paraná 87020900, Brazil. [email protected].
ACCEPTED MANUSCRIPT ABSTRACT
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A comparative study of the efficiency of different coagulants in the textile wastewater treatment was carried out. The utilization of natural coagulants instead of the synthetic ones has demonstrated significant advantages since it provides a low cost and environmentally friendly technology for removing dyes. This study aimed at evaluating the performance of different coagulants in the removal of the apparent colour, turbidity, absorbance, and COD of textile wastewater samples from an industrial laundry. Two organic coagulants (Moringa oleifera Lam seeds extracted in saline solutions of NaCl and KCl 1 mol L-1) and an inorganic coagulant (aluminium sulphate) were used. Initially, the influence of the pH was evaluated for each coagulant. Then, a factorial design was applied in order to determine the coagulant concentration and the sedimentation time needed for the textile wastewater treatment. All the parameters obtained their best results with acidic pH values for the studied coagulants. The organic coagulants presented the best results, in general, reaching removals of 82.2 % for the apparent colour, 83.05 % for COD, 78.4 % for RP-HE7B, and 89.7 % for OP-HER using the Moringa coagulant extracted in KCl. This study demonstrated the applicability of the Moringa oleifera Lam seeds to the textile wastewater treatment.
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Keywords: organic coagulant; colour removal; Moringa oleifera Lam; experimental planning; COD removal.
ACCEPTED MANUSCRIPT 1. Introduction
In the textile industry, water consumption varies greatly according to different sectors, such as the colouring process, which may need more than 100 L kg-1 of processed fabric. Besides the consumption, another determining factor is the composition of the wastewater in
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relation to the seasonality that can widely differ from one industry to another (Vajnhandl and Valh, 2014).
Textile production requires a high concentration of different types of organic dyes, additives, and salts, generating wastewaters with high turbidity, chemical oxygen demand,
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suspended solids, pH varying from 2 to 12, and usually high temperatures (Merzouk et al., 2011; Yeap et al., 2014). The discharge of textile wastewaters has a negative aesthetic effect on water supplies, reducing the light penetration, and consequently changing the dynamics of
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the aquatic ecosystem (Pathania et al., 2016; Kakoi et al., 2017).
Dyes and some intermediary products from their degradation can be potentially mutagenic and carcinogenic (Levin et al., 2012; Prola et al., 2013; Katheresan et al., 2018). Even in low concentrations, the presence of dyes in wastewater is not desired since they can cause esthetic and dangerous effects on living beings when discharged into the aquatic ecosystems
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(Morghaddam et al., 2010; Florenza et al., 2014). A significant number of textile wastewater treatment processes have been described in the literature, such as the electrochemical (Palácio et al., 2009; Aquino et al., 2013), biological (Türgay et al., 2011), adsorption (Fagundes-Klen et al., 2012; Sathishkumar et al., 2012; Cao et al., 2014), coagulation (Beltrán-Heredia et al.,
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2009a; Zhao et al., 2014) and advanced oxidation processes (Módenes et al., 2012; Palácio et al., 2012). The coagulation-flocculation process is usually used in wastewater treatment due to its high efficiency and low cost, proving to be effective in the removal of dyes (Huang et
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al., 2014). The coagulation process is related to the addition of chemical products to the wastewater in order to change the physical state of the dissolved and suspended solids and promote their removal through sedimentation (Verma et al., 2012). In the coagulation/flocculation process, the choice of coagulant has a significant role in contaminant removal. There are many categories of coagulants, including inorganic and organic (Huang et al., 2014). Inorganic coagulants, such as iron and aluminium salts, were extensively used in textile wastewater treatment (Furlan et al., 2010; Huang et al., 2014; Liang et al., 2014). However, the sludge generated from an inorganic coagulant is toxic, produced in large quantities and, considerably affects the pH of the treated water according to Vijayaraghavan et al. (2011). Moreover, aluminium is a neurotoxic product and can 1
ACCEPTED MANUSCRIPT contribute to Alzheimer’s disease (Huang et al., 2014; Lau et al., 2014). Therefore, the use of the traditional coagulants is uncertain, and the polymeric macromolecules derived from plants, known as organic coagulants have received a particular interest in textile wastewater treatment due to their biodegradability, non-toxicity, wide variety and availability (Elkady et al., 2011; Huang et al., 2014; Lau et al., 2014).
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The use of natural coagulants from vegetal sources has been recently reported in the literature for the treatment of surface and industrial waters, highlighting the tannins (Hameed et al., 2018), Jatropha curcas (Abidin et al., 2013), Maize (Patel and Vashi, 2012), and Moringa oleifera (De Paula et al., 2018). Particularly, the Moringa oleifera Lam, a member of
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the Moringaceae family, is a plant that has been thoroughly studied as one of the most promising natural coagulants (Madrona et al., 2010; Pritchard et al., 2010; Mangale et al., 2012).
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The present study aimed at evaluating the efficiency of the natural coagulant obtained from the Moringa oleifera Lam extracted from different saline solutions (NaCl and KCl), in addition to the aluminium sulphate inorganic coagulant as a primary textile wastewater treatment. In this study, the influence of the pH on the coagulant capacity of removing colour, turbidity, chemical oxygen demand (COD) and absorbance has been evaluated. The response
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surface methodology (RSM) was applied to study the effects of the coagulant concentration, the sedimentation time, and the interaction between them in the COD removal by the coagulants,
as
well
as
determine
the
optimal
operating
conditions
of
the
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coagulation/flocculation process.
2. Materials and methods
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2.1. Textile Wastewater
The textile wastewater was obtained from an industrial laundry and contained the reactive dyes RP-HE7B and OP-HER, according to the industry. The wastewater characterization was performed, determining the pH (DIGIMED DM-22), apparent colour (HACH DR 2010, mg Pt-Co L-1), and turbidity (HACH 2100 P, NTU). The chemical oxygen demand (COD) was established consistent with the closed reflux colorimetric method and measured in quintuplicate, utilizing a stock solution (COMBICHECK 20) with 750 ± 75 mg O2 L-1. The mean result acquired was 710 ± 23.7 mg O2 L-1. All the analytical measurements were performed according to the Standard Methods for the Examination of Water and Wastewater 2
ACCEPTED MANUSCRIPT (APHA, 2005). The molecular absorption spectra of the reactive dyes RP-HE7B and OP-HER were achieved in a spectrophotometer (SHIMADZU UV 1800), operating between 300 and 700 nm to determine the wavelength of maximum absorption (λmax) of each dye. The absorbance in the λmax was ascertained for the textile wastewater. The results of the physico-
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chemical characterization are presented in Table 1.
Table 1. Physico-chemical properties of the textile wastewater used in the study.
The textile wastewater with an alkaline pH (10.9) presented an intense blue-purplish colour, verified by the high values of apparent colour (4500 mg Pt-Co L-1) and observed
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absorbance. The high COD value (5820 mg O2 L-1) indicates the presence of a large quantity of organic matter.
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The chemical structures of the dyes contained in the industrial textile wastewater are presented in Figure 1. Table 2 shows the molar mass and λmax found according to the literature and experimentally obtained for these dyes. The molecular absorption spectra are shown in Figure 2.
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Figure 1. Chemical structures of the reactive dyes: (a) RP-HE7B (Stringhini, 2013) and (b) OP-HER (Chatterjee et al., 2008).
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Table 2. Physical properties of the dyes present in the textile wastewater. Figure 2. Molecular absorption spectra of the dyes (- - -) RP-HE7B and (___) OP-HER.
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The experimental λmax values were used in the study of the absorbance (A) decay of the effluent in relation to the treatment that was applied.
2.2. Preparation of the Coagulants
The coagulants used in the coagulation/flocculation experiments were: a) Aluminium sulphate solution (AS) (Al2(SO4)3.18H2O), VETEC) was prepared in a concentration of 10.0 g L-1 and dissolved in distilled water; b) The extract from the Moringa oleifera Lam seeds in potassium chloride (MO-KCl) was prepared by triturating 5.0 g of seeds in 100 mL of a KCl 1.0 mol L-1 saline solution. This mixture was kept under magnetic stirring for 30 minutes as 3
ACCEPTED MANUSCRIPT well as vacuum filtered on qualitative filter paper. The extract was obtained immediately after separation and c) The extract of Moringa oleifera Lam seeds in sodium chloride (MO-NaCl) had a similar preparation procedure to the MO-KCl coagulant, substituting the KCl with sodium chloride 1.0 mol L-1. The preparation of the extracts followed the methodology
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described by Beltrán-Heredia et al. (2009a).
2.3. Coagulation/Flocculation Tests
Coagulation/flocculation tests were carried out in a Jar test (Milan, JT-103) in order to
concentration and sedimentation time.
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2.3.1. Determination of the coagulation/flocculation pH
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evaluate the efficiency of the different coagulants, varying the pH values, coagulant
In this experiment, the best coagulation/flocculation pH value was determined according to each coagulant studied. A fixed amount of each coagulant (AS = 1000 mg L-1, MO-NaCl and MO-KCl= 1600 mg L-1) was added to 1.0 L of the textile wastewater, stirring for 2 minutes
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with a rapid mixing gradient of 100 rpm and for 20 minutes with a slow mixing gradient of 20 rpm (Golob et al., 2005). The initial wastewater pH was adjusted, using HCl and NaOH 1 mol L-1 solutions, to a value between 1 and 10. After 60 minutes of sedimentation, aliquots of 50 mL of the supernatant of each sample were collected in order to evaluate the apparent colour,
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COD and turbidity in triplicate.
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2.3.2. Experimental factorial design: concentration of coagulant and sedimentation time
To establish the ideal concentration and the optimal sedimentation time of each coagulant, a 32 full factorial experimental design (FED) was applied, based on the Response Surface Methodology (RSM) (Myers and Montgomery, 2002; Khuri and Mukhopadhyay, 2010). The chemical oxygen demand (COD) was used as the response variable. In the experimental design, two levels were used to represent the variables (coagulant concentration and sedimentation time) and a centre point, previously selected in preliminary experiments (Table 3).
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ACCEPTED MANUSCRIPT Table 3. Actual and coded values of the independent variables used in the experimental design.
The experiments were performed at the best pH obtained for each coagulant. Then, the coagulants were added to 1.0 L of the textile wastewater, and the sedimentation time varied
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according to the experimental design (Table 3). The rapid and slow operating conditions have been previously described. Aliquots of 50 mL of the supernatant were collected to determine the COD.
Based on the achieved results from the 32 factorial experimental design (FED), presented
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in Table 3, the RSM was applied to develop the polynomial regression equations and to corroborate the connection between the response (COD) and the optimal values of the two operating parameters of the coagulation process (POP): coagulant concentration (q1) and
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sedimentation time (q2). The second order response surface models for each of the evaluated coagulants were developed as follows (Myers and Montgomery, 2002; Khayet et al., 2011):
N
N N
i =1
i =1 j =1
N N
R = k0 + ∑ ai qi + ∑∑ bij qi + ∑∑ cij qi q j i −1 j =1
(1)
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2
Where R is the response predicted by the model, qi and qj are the independent variables, k0, aj, bij, and cij are the regression coefficients that represent the types of interactions among the POP values, and N is the number of POP.
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In order to evaluate the error of the models related to the experimental values, the effluent
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was treated in the best operating conditions obtained from the factorial designs.
2.3.3. Effect of sedimentation time
For 1.0 L of wastewater, the best concentration of each coagulant was used at the optimal pH and under the rapid and slow mixing gradients previously described, varying the sedimentation time (15, 30, 45, and 60 minutes). Aliquots of 50 mL of the supernatant were collected to determine the parameters: apparent colour, COD, turbidity, Abs 541 and Abs 493.5 nm, in triplicate.
3. Results and discussion 5
ACCEPTED MANUSCRIPT 3.1. Effect of the Initial pH on the Performance of the Coagulants
Figure 3 shows the effect of the initial pH of the wastewater on the performance of the AS, MO-NaCl, and MO-KCl coagulants when reducing the apparent colour, turbidity, COD and
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absorbance (493.5 and 541 nm). Figure 3. Removal of (a) apparent colour (mg Pt-Co L-1), (b) turbidity (NTU), (c) absorbance 541 nm (RP-HE7B), (d) absorbance 493.5 nm (OP-HER) and (e) COD (mg L-1) after the treatment with MO-KCl, MO-NaCl and AS at different initial pH values and coagulant
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concentrations (AS-1000 mg L-1, MO-NaCl/MO-KCl-1600 mg L-1).
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According to Figure 3a-e, the highest reduction in the evaluated parameters occurred at an acidic pH for the coagulants studied. The aluminium sulphate (AS) inorganic coagulant presented the best results at pH values between 5 and 6, showing a maximum turbidity removal of 87.6% (Figure 3b) and a COD of 73.6% (Figure 3e).
For the AS, the maximum reduction of absorbance was 31.4% for RP-HE7B (Figure 3c)
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and 12.5% for OP-HER (Figure 3d) at a pH of 5. Merzouk et al. (2011) utilized the same coagulant when treating a synthetic solution of the disperse dye, obtaining a more efficient discolouration within a pH range from 4.0 to 7.8, and a colour removal between 86.0 and 93.6%, reaching the highest value at a pH value close to 5.5. Khayet et al. (2011) used an AS
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coagulant concentration of 820 mg L-1 and attained a maximum absorbance removal of the Acid Black 210 dye at a pH of 5.61. The studies previously mentioned confirmed the optimal pH range of the AS coagulant for removing colour and absorbance in dyes of different
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fixation methods (reactive, disperse and acidic). The study of El-Gohary and Tawfik (2009) with textile wastewater derived from different industries and containing diverse classes of coagulants presented the maximum results of colour removal with the AS coagulant at a pH of 5.3, confirming the optimal pH range for this coagulant. The authors attribute this result to the fact that, within the optimal pH range, the particles of the dye retain negative charges, which promotes a better performance of the AS coagulant, of a cationic nature. The MO-NaCl organic coagulant presented its best results at a pH of 2, as shown in Figure 3a-e. Beltrán-Heredia et al. (2009b) obtained similar results when studying the removal of the Alizarin Violet 3R dye at an acidic pH, confirming the cationic protein nature of the MO, which can enhance the coagulant activity at low pH values. The MO-NaCl, at a pH of 2, 6
ACCEPTED MANUSCRIPT presented a removal of 76.0% for apparent colour, 60.2% for COD, and 32.8% for turbidity. At a pH of 1, a higher reduction of the apparent colour was realised. Nevertheless, it presents a disadvantage due to the use of a greater quantity of the acidic solution in order to adjust the treated sample. The MO-KCl coagulant exhibited a result similar to the MO-NaCl at a pH of 2, which can
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be verified in Figure 3a-e, showing a removal of 76.0% for apparent colour, 62.9% for COD and 27.1% for turbidity.
Both coagulants extracted from the MO seeds presented an increase of the treated textile wastewater turbidity when compared to the untreated sample in most of the evaluated pH
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values. A similar behaviour was achieved by Muthuraman and Sasikala (2014), utilizing the Moringa oleifera Lam seeds extracted with NaCl when treating synthetic turbid water to obtain drinking water. The authors verified that as long as the pH of the reaction increased,
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the turbidity removal efficiency decreased.
According to Table 1, the initial turbidity value of the effluent (66.8 NTU) and its low removal efficiency (Figure 3b) confirmed the observations of Suleyman and Evison (1995) and Katayon et al. (2007), who attribute this behaviour to a low rate of inter-particle contact of MO and the particles in the reaction medium, reducing flake formation and its
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sedimentation.
In Figure 3c-d, the removals of the RP-HE7B and OP-HER dyes with MO-NaCl were higher when compared to the MO-KCl coagulant. As observed, the similar parameters that were evaluated, apparent colour and the absorbance of the two dyes, accomplished the same
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or better removal results with MO-NaCl. According to Zhao et al. (2014), the colour removal may be related to the macromolecules that form the natural coagulant, such as polysaccharides and cellulose. Therefore, a higher quantity of these macromolecules provided
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a more efficient coagulation process, as observed.
3.2 Influence of the Coagulant Concentration and Sedimentation Time The COD results attained from the 32 full factorial design, carried out at the best pH value for each coagulant (pH=2 for MO-NaCl and MO-KCl; pH=5 for AS) in the coagulation/flocculation process, in triplicate, are presented in Table 4. Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MO-NaCl, MO-KCl and AS at the best pH. 7
ACCEPTED MANUSCRIPT The COD values achieved for the wastewater treated by the coagulation/flocculation process using the MO-NaCl, MO-KCl and AS coagulants varied between 1080 to 5550 mg O2 L-1 with MO-NaCl, 1332 to 5590 mg O2 L-1 with MO-KCl and 912 to 3068 mg O2 L-1 with AS.
of variance (ANOVA). The results are indicated in Table 5.
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The response surface models for each coagulant were statistically validated by the analysis
Table 5. Analysis of variance (ANOVA) for the COD removal models realised in the
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coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval of 95% (p<0.05)
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The statistical significance of the second order regression models was determined by the F value. If the models provide an adequate prediction of the experimental data, the values of F should be higher than the Ftable = 2.68 (Myers and Montgomery, 2002). In this context, the F values for the three coagulants studied were greater than the Ftable, statistically validating the models.
The models presented an excellent fit for the observed COD values (Table 4), with R2 of
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0.98 for MO-NaCl, 0.99 for MO-KCl and 0.99 for AS. The values of R2 indicate that the experimental data acquired could be described by the models developed at 98% (MO-NaCl – Equation 2), 99% (MO-KCl – Equation 3), and 99% (AS – Equation 4).
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According to the effect of the interactions presented in Table 6, it can be verified that the results of the t-statistic (tstat) from the coefficients (k0, a1, b12, a2, b22, and c1) for all the coagulants was higher than 2, in absolute values. It confirms that the intercept, the coagulant
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concentration (linear and quadratic terms), the sedimentation time (linear and quadratic), and the interaction between the coagulant concentration and the sedimentation time of the process presented a statistical significance, which is confirmed by the p-value < 0.05.
Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95% (p<0.05)
The negative effects of a1 and a2 for the MO-NaCl and MO-KCl coagulants suggest that the highest coagulant concentrations and sedimentation time values provided the greatest 8
ACCEPTED MANUSCRIPT efficiency of the coagulation/flocculation process concerning the COD reduction. For the AS coagulant, the positive a1 and negative a2 values indicate that low coagulant concentrations and high sedimentation times benefit the COD reduction. The empirical models for the COD values obtained by the coagulation/flocculation process
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were written according to Equations 2 (MO-NaCl), 3 (MO-KCl) and 4 (AS).
(2)
CODMO-KCl= 2576.54 - 2468.95C - 1545.98T - 879.23C2 - 498.48T2 + 838.45CT
(3)
CODAS= 2606.46 +1151.40C - 1094.13T - 1151.78C2 - 158.85T2 + 165.60CT
(4)
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CODMO-NaCl= 2961.69 - 1459.72C - 2792.70 T - 362.99C2 - 663.04T2 + 387.53CT
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Where 200 ≤ C ≤ 2800 mg L-1 for MO-NaCl; 200 ≤ C ≤ 2600 mg L-1 for MO-KCl and 600 ≤ C ≤ 2800 mg L-1 for AS, and 15 ≤ T ≤ 60 for the three evaluated coagulants (C = concentration = q1 and T = sedimentation time = q2).
The graphical representations of the models (contour plots) were plotted based on Equations 2-4. The plots are shown in Figure 4 and indicate the influence of the coagulant
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concentration and sedimentation time on the COD removal, where the black/green region represents the lowest values of COD.
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Figure 4. Contour plots for COD predicted as a function of the coagulant concentration and sedimentation time in the coagulation/flocculation process utilizing the coagulants a) MO-
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NaCl; b) MO-KCl and c) AS
The MO-NaCl and MO-KCl coagulants (Figure 4a and 4b) presented a similar behaviour, i.e. the increase of coagulant concentration and sedimentation time caused a decrease in the COD values. The aluminium sulphate (Figure 4c) differed from the organic coagulants regarding the concentration influence on the COD values, in this case, intermediary coagulant concentration values provided higher COD reduction values. A higher sedimentation time possibly indicates a more efficient COD reduction when using the AS coagulant. In order to maximize the COD removal from the wastewater studied, it is essential to establishthe optimal operating conditions of the coagulation/flocculation process. The values 9
ACCEPTED MANUSCRIPT of the operating parameters that provided the maximum COD reduction efficiency and were determined through the models for the evaluated coagulants are shown in Table 7.
Table 7. Values of the operating parameters of the coagulation/flocculation process that provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl and AS
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coagulants
It can be observed that, for the organic coagulants (MO-NaCl and MO-KCl), the sedimentation process was quicker when compared to the inorganic coagulant (AS) according
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to Table 7. The effluent was treated with the optimal experimental conditions of the coagulant and sedimentation time in order to evaluate the error (%) of the applied models. All the models presented errors of up to 5%, as MO-NaCl, MO-KCl, and AS were 2.01, 3.71, and
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5.01, respectively, confirming their applicability (Table 7). For the AS coagulant, the COD at a sedimentation time of 60 min was determined as well. The results demonstrated that, in spite of the fact that the statistic model presented the best sedimentation time as 74 min with a predicted COD of 872 mg L-1, the COD decreased to 835 mg L-1 in 60 min. Thus, for comparison purposes, the maximum sedimentation time used was 60 minutes, and the effect
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of the flake sedimentation time on the treatment efficiency was also evaluated.
3.3. Effect of the Sedimentation Time
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The effect of the sedimentation time on the coagulation/flocculation process was analysed with the optimal conditions at a pH of 2 (MO-NaCl and MO-KCl) and 5 (AS) and coagulant concentrations of 2086 mg L-1 (MO-KCl), 2461 mg L-1 (MO-NaCl), and 1531 mg L-1 (AS).
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The maximum sedimentation time was 60 minutes. The obtained results are presented in Figure 5.
Figure 5. Variation of the parameters a) COD; b) Apparent Colour; c) Turbidity; d) Abs 541 nm and e) Abs 493.5 nm, using 2086 mg L-1 of MO-KCl, 2461 mg L-1 of MO-NaCl and 1531 mg L-1 of AS
It can be confirmed that, in general, the organic coagulants presented the best removal results for all the evaluated parameters (Figure 5). Whereas, lower removals were achieved with the AS coagulant. The removal of apparent colour was 23.6%, absorbance at a wavelength of 10
ACCEPTED MANUSCRIPT 493.5 was 30.5% and a wavelength of 541 nm was 29.5% after 15 min since there was not an increase in the removal with the increment in sedimentation time (Figure 5b, 5d and 5e). The COD removal (Figure 5a) increased with time, 82.9% in 60 min. The turbidity reduced 23.6% after 30 min of sedimentation, and modifications after this period were not verified (Figure 5c). De Paula et al. (2014) demonstrated that the utilization of the coagulant mixture of
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aluminum sulfate and Moringa oleifera Lam removed the turbidity with a higher performance compared to the inorganic coagulant when treating wastewater from concrete. In their experiments, the authors verified a reduction of 99.3% of turbidity in 60 minutes using 1850 mg L-1 of coagulant (80% aluminum sulfate and 20% of powdered Moringa oleifera Lam).
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However, when using just aluminum sulfate, 97.9% of removal in 60 minutes was realised. A similar behavior was obtained by De Paula et al. (2018). The authors achieved a turbidity removal higher than 99% using 1010 mg L-1 of the coagulant solution (53.5% of aluminum
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sulfate and ferric chloride and 46.5% of powdered Moringa oleifera Lam) in 60 minutes. The results confirmed that the organic coagulants can enhance the action of chemical coagulants.Wong et al. (2007) utilized the AS coagulant when treating a reactive dye synthetic solution, acquiring a removal of 78.0% of colour and 75.0% of COD with a coagulant concentration of 6000 mg L-1, and a pH within 3.9-4.1. The lowest value of colour removal
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observed for the AS coagulant in this study is possibly related to the fact that industrial effluents present different characteristics as compared to a synthetic solution. For a real effluent, the interactions between coagulant and dye are differentiated when compared to a solution that was produced in a laboratory since the real effluent contains some components
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that are not present in the synthetic solution. Nonetheless, the COD removal accomplished in this study, using a lower coagulant concentration (82.9%), was higher than the one achieved by Wong et al. (2007) (75%) (1531 mg L-1 versus 6000 mg L-1).
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For the MO-NaCl and MO-KCl coagulants, a higher colour removal when compared to the AS was substantiated (Figure 5b). The MO-KCl coagulant had a colour removal of 82.2% after 60 min, whereas the MO-NaCl coagulant removed 70.2%. Patel and Vashi (2013) utilized the MO for treating textile wastewater at a neutral pH with concentrations higher than the ones used in this study (5000 – 30000 mg L-1), and obtained lower colour removals, even in the greatest coagulant concentration (58.4%) along with a higher sedimentation time (120 minutes). Therefore, the relevance of the preparation method of the coagulant solution and its pH can be verified, which increased the colour removal in conditions that represented an economical treatment process (lower coagulant concentration and sedimentation time).
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ACCEPTED MANUSCRIPT The decrease in the absorbance (90%) at 493.5 nm (OP-HER) occurred in the first 15 minutes of sedimentation for both organic coagulants (Figure 5e). For the wavelength of 541 nm (RP-HE7B), there was a reduction of 75.3% with MO-NaCl and 78.4% with MO-KCl in the absorbance after 30 min, without any changes after this period (Figure 5d). Vilaseca et al. (2014) treated a textile effluent using the MO-NaCl organic coagulant and attained a removal
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of 80% of the Orange Procion MX-2R dye, a similar behaviour achieved for the Orange Procion dye. The coagulant concentration used in the treatment was 1250 mg L-1, and the obtained results were close to the ones from this current study.
When adding the MO-NaCl and MO-KCl coagulants to the coagulation/flocculation
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process to treat the textile wastewater, it was verified that the initial turbidity increased. Nevertheless, it decreased at a minimum sedimentation time of 45 minutes, for both coagulants (Figure 5c). There was a reduction of 50% for the MO-NaCl and 62% for the MO-
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KCl. De Paula et al. (2014) utilized crushed Moringa oleifera Lam seeds as a coagulant for the turbidity removal of wastewater from concrete. The results from the coagulation process showed a turbidity reduction of the real effluent from 132 to 13.04 NTU in 60 minutes, corresponding to a removal of approximately 90%. Byreducing the processing time to 30 minutes, it impacted the turbidity removal, which reached 78%. Sánchez-Martín et al. (2010),
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aiming at reducing the turbidity of river waters, proposed the purification of the MO extract to remove the proteins that do not present a coagulant effect, only retaining the active ones. The results indicated that the purification procedure of the Moringa oleifera Lam enhanced the efficiency of the coagulant protein. The authors cited in their study that, during the
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coagulation process, the inactive proteins initially promote an increased turbidity of the river waters, and is then reduced according to the increment in the sedimentation time. This behaviour is in agreement with the achieved results, since the MO extract used in the
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treatment was not submitted to a purification process. Katayon et al. (2007) stated that low turbidity effluents, such as the one in this present study, provide flake formation with a low sedimentation capability, reducing the coagulation/flocculation performance of the coagulant. The COD removal (Figure 5a) was also higher with an increased sedimentation time for the MO-NaCl and MO-KCl coagulants. For the MO-NaCl, there was a lower removal (72.8%) when compared to the AS coagulant (82.9%) in 60 minutes of coagulation. However, the inorganic coagulant removal was similar to the one realised by MO-KCl (83.0%). Patel and Vashi (2013) evaluated the sedimentation time when studying the COD removal, and acquired results similar to the ones in this study, confirming that the increased sedimentation time is crucial to the COD removal. The sedimentation time varied from 15 to 150 minutes, 12
ACCEPTED MANUSCRIPT and the best COD removal result was achieved in 120 minutes (75.6%), with a coagulant concentration of 20000 mg L-1. Meanwhile, it was observed that the coagulant concentration and the sedimentation time were higher, raising the cost of the treatment process. Consequently, the extraction method of the coagulant agent from the MO seeds is a key factor in the process efficiency, enabled by the use of a saline solution, which was confirmed by
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Madrona et al. (2010).
4. Conclusions
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The present study compared the efficiency of the MO-NaCl, MO-KCl and AS coagulants for treating textile wastewaters. It was verified that, for the coagulants applied to the treatment, the pH of the wastewater influences the coagulation/flocculation process when
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removing the colour, turbidity, COD and absorbance of the dyes. The response surfaces realised demonstrated that the physicochemical parameters indicated different optimal coagulant concentration and sedimentation time values, according to each coagulant studied. The best sedimentation time values were reached with the MO-NaCl and MO-KCl coagulants when compared to the AS. Among the coagulants studied, MO-KCl and MO-NaCl presented
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a higher efficiency when compared to the AS coagulant, highlighting the MO-KCl performance, indicating the applicability of the organic coagulants derived from Moringa oleifera Lam for treating textile wastewaters.
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Acknowledgments
The authors acknowledge the Coordination for the Improvement of Higher Education
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Personnel (CAPES) for the financial support and the Environmental Institute of Paraná (IAP) for the laboratory infrastructure.
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ACCEPTED MANUSCRIPT Aquino, J.M., Rocha-Filho, R.C., Bocchi, N., Biaggio, S.R., 2013. Electrochemical degradation of the Disperse Orange 29 dye on a β-PbO2 anode assessed by the response surface methodology. J Environ Chem Eng. 1, 954-961. Beltrán-Heredia, J., Sánchez-Martín, J., Delgado-Regalado, A., 2009a. Removal of Carmine Indigo Dye with Moringa oleifera Seed Extract. Ind. Eng.Chem. 48, 6512-6520.
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Hameed, Y.T., Idris, A., Hussain, S.A., Abdullah, N., Man, H.C., Suja, F., 2018. A tanninbased agent for coagulation and flocculation of municipal wastewater as a pretreatment for biofilm process. J Clean Prod. 182, 198-205.
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Huang, X., Bo, X., Zhao, Y., Gao, Y., Wang, Y., Sun, S., Yue, Q., Li, Q., 2014. Effects of compound bioflocculant on coagulation performance and floc properties for dye removal. Bioresour Technol. 165, 116-121.
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Katheresan, V., Kansedo, J., Yon-Lau, S., 2018. Efficiency of various recent wastewater dye removal methods: A review. J. Environ. Chem. Eng. 6, 4676-4697. Khayet, M., Zahrim, A.Y., Hilal, N., 2011. Modelling and optimization of coagulation of
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ACCEPTED MANUSCRIPT Liang, C.-Z., Sun, S.-P., Li, F.-Y., Ong, Y.-K., Chung, T.-S., 2014. Treatment of highly concentrated wastewater containing multiple synthetic dyes by a combined process of coagulation/flocculation and nanofiltration. J Membr Sci Technol. 469, 306-315. Madrona, G., Serpelloni, G., Salcedo Vieira, A., Nishi, L., Cardoso, K., Bergamasco, R., 2010. Study of the Effect of Saline Solution on the Extraction of the Moringa oleifera Seed’s
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Active Component for Water Treatment. Water Air Soil Pollut. 211, 409-415. Mangale, M.S., Chonde, S.G., Jadhav, A.S., Raut, P.D., 2012. Study of Moringa oleifera (Drumstick) seed as natural Absorbent and Antimicrobial agent for River water treatment. J Nat Prod Plant Resour. 2, 89-100.
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Merzouk, B., Gourich, B., Madani, K., Vial, C., Sekki, A., 2011. Removal of a disperse red dye from synthetic wastewater by chemical coagulation and continuous electrocoagulation. A comparative study. Desalination. 272, 246-253.
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Módenes, A.N., Espinoza-Quiñones, F.R., Borba, F.H., Manenti, D.R., 2012. Performance evaluation of an integrated photo-Fenton – Electrocoagulation process applied to pollutant removal from tannery effluent in batch system. Chem. Eng. J. 197, 1-9. Moghaddam, S.S., Moghaddam, A.M.R., Arami, M., 2010. Coagulation/flocculation process for dye removal using sludge from water treatment plant: Optimization through response
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Palácio, S.M., Espinoza-Quiñones, F.R., Módenes, A.N., Oliveira, C.C., Borba, F.H., Silva Jr, F.G., 2009. Toxicity assessment from electro-coagulation treated-textile dye wastewaters by bioassays. J Hazard Mater. 172, 330-337. Palácio, S.M., Espinoza-Quiñones, F.R., Módenes, A.N., Manenti, D.R., Oliveira, C.C., Garcia, J.C., 2012. Optimised photocatalytic degradation of a mixture of azo dyes using a TiO2/H2O2/UV process. Water Sci. Technol 65, 1392-1398. Patel, H., Vashi, R.T., 2012. Removal of Congo Red dye from its aqueous solution using natural coagulants., J Saudi Chem Soc. 16, 131-136. Patel, H., Vashi, R.T., 2013. Comparison of naturally prepared coagulants for removal of COD and color from textile wastewater. Global NEST J. 15, 522-528. 16
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ACCEPTED MANUSCRIPT Yeap, K.L.,Teng, T.T., Poh, B.T., Morad, N., Lee, K.E., 2014. Preparation and characterization of coagulation/flocculation behavior of a novel inorganic–organic hybrid polymer for reactive and disperse dyes removal. Chem Eng J. 243, 305-314. Zhao, S., Gao, B., Yue, Q., Wang, Y., 2014. Effect of Enteromorpha polysaccharides on coagulation performance and kinetics for dye removal. Colloids Surf A Physicochem Eng
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ACCEPTED MANUSCRIPT Table list
Table 1. Physico-chemical properties of the textile wastewater used in the study. Table 2. Physical properties of the dyes present in the textile wastewate. Table 3. Actual and coded values of the independent variables used in the experimental
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design. Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MO-NaCl, MO-KCl and AS at the best pH.
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Table 5. Analysis of variance (ANOVA) for the COD removal models obtained in the coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval
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of 95 % (p<0.05).
Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95 % (p<0.05). Table 7. Values of the operating parameters of the coagulation/flocculation process that
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AS coagulants.
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provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl, and
ACCEPTED MANUSCRIPT Table 1. Physico-chemical properties of the textile wastewater used in the study. Parameters
Units
pH
-
Initial values 10.9 -1
mg Pt-Co L
4500
Turbidity
NTU
66.8
COD
mg O2 L-1
5820
Absorbance 541 nm*
-
Absorbance 493.5 nm**
-
2.267 3.311
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*(RP- HE7B); **(OP-HER)
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Apparent colour
ACCEPTED MANUSCRIPT Table 2. Physical properties of the dyes present in the textile wastewater. Molar mass Dye
Literature
Experimental
1596
543.5*
541.0
OP-HER
1850
496.0**
493.5
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Garcia-Montaño et al., 2006 and **Chatterjee et al., 2008
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RP- HE7B
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*
g mol
λmax (nm)
-1
ACCEPTED MANUSCRIPT Table 3. Actual and coded values of the independent variables used in the experimental design.
MO-KCl
MO-NaCl
Symbol Real values of coded levels -1
0
+1
Coagulant concentration (mg L-1)
q1
200
1200
2600
Sedimentation time (min)
q2
15
30
60
Coagulant concentration (mg L-1)
q1
200
1800
2800
Sedimentation time (min)
q2
15
30
60
Coagulant concentration (mg L )
q1
600
1200
2800
Sedimentation time (min)
q2
15
30
60
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Variable
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Coagulant
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Table 4. Experimental results of the COD values obtained from the 32 full factorial design in the coagulation/flocculation process using MONaCl, MO-KCl and AS at the best pH. MO-NaCl
(min)
1
200
15
2
200
30
3
200
4
COD Removal (%)
q1 (mg L )
(min)
4.7
200
15
Residual COD (mg L-1) 5586±4
(mg L )
(min)
4.0
600
15
Residual COD (mg L-1) 3056±12
3876±6
33.4
200
30
4185±9
28.1
600
30
2627±5
54.9
60
2545±6
56.3
200
60
2939±3
49.5
600
60
1771±5
69.6
1200
15
4182±5
28.1
1200
15
3017±7
48.2
1200
15
2081±4
64.2
5
1200
30
2838±5
6
51.2
1200
30
2083±5
64.2
1200
30
1929±3
66.9
1200
60
1085±5
81.4
1200
7
2800
15
3795±5
34.8
2600
8 9
2800
30
2059±5
64.6
2600
2800
60
1605±6
72.4
2600
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q1 = Coagulant concentration; q2 = Sedimentation time
q2 -1
COD Removal (%)
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(mg L )
Residual COD (mg L-1) 5547±4
q1
q2
AS
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q2 -1
-1
COD Removal (%) 47.5
60
1770±4
69.6
1200
60
916±5
84.3
15
2220±3
61.9
2600
15
3941±5
32.3
30
1467±2
74.8
2600
30
3879±5
33.4
60
1336±5
77.0
2600
60
3033±5
47.9
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q1
MO-KCl
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Run
ACCEPTED MANUSCRIPT Table 5. Analysis of variance (ANOVA) for the COD removal models obtained in the coagulation/flocculation using MO-NaCl, MO-KCl and AS with a confidence interval of 95 % (p<0.05). Source
SS
DF
MS
F
Ftable
R2
p-value
MO-NaCl
Regression
46961496
5
9392299
199.41
2.68
0.98
< 0.05
Residual
989103
21
47100
Total
47950599
26
Regression
46145267
5
9229053
Residual
467914
21
22282
Total
46613181
26
Regression
24136905
5
4827381
Residual
74104
21
3529
Total
24211009
26
AS
414.19
2.68
0.99
< 0.05
1367.91
2.68
0.99
< 0.05
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MO-KCl
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ACCEPTED MANUSCRIPT Table 6. Values of the regression parameters and the interaction among the POP that allow modelling the efficiency of the coagulation/flocculation process in reducing the textile wastewater COD, with a confidence interval of 95 % (p<0.05).
parameters
MO-KCl
q0
k0
q1
a1
(q1)2
b1 2
q2
a2
(q2)2
b2 2
q1 x q2
c1
q0
k0
q1
SE
tstat
p-value
42.34
69.95 < 0.05
-1459.72 103.20 -14.14 < 0.05 -362.99
89.38
-4.06 < 0.05
-2792.70 102.74 -27.18 < 0.05 -663.04
90.23
-7.35 < 0.05
387.53 121.96
3.18 < 0.05
2576.54
29.06
88.67 < 0.05
a1
-2468.95
70.99 -34.78 < 0.05
b1 2
-879.23
61.22 -14.36 < 0.05
a2
-1545.98
70.52 -21.92 < 0.05
b2 2
-498.48
62.06
-8.03 < 0.05
q1 x q2
c1
838.45
84.24
9.95 < 0.05
q0
k0
2606.46
11.73 222.12 < 0.05
a1
1151.40
28.24
b1 2
-1151.78
25.07 -45.94 < 0.05
q2
a2
-1094.13
28.43 -38.49 < 0.05
(q2)2
b2 2
158.85
24.70
6.43 < 0.05
q1 x q2
c1
165.60
32.57
5.08 < 0.05
(q1)2 q2
q1
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(q1)2
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(q2)2
AS
2961.69
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MO-NaCl
Regression coefficients Effect
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Actions of
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q1 = coagulant concentration (mg L-1); q2 = sedimentation time (min)
40.78 < 0.05
ACCEPTED MANUSCRIPT Table 7. Values of the operating parameters of the coagulation/flocculation process that provided the maximum COD reduction efficiency utilizing the MO-NaCl, MO-KCl, and AS coagulants. MO-NaCl
MO-KCl
AS
Coagulant concentration (mg L-1)
2461
2086
1531
Sedimentation time (min)
56
48
74
Predicted COD (mg L-1)
1318
1034
872
Experimental COD (mg L-1)
1345
997
918
Model error (%)
2.01
3.71
5.01
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ACCEPTED MANUSCRIPT Highlights •
The efficiency of the coagulants is dependent on the pH, preferably acid.
•
High natural coagulant concentrations and settling times resulted in COD removals. The natural coagulants provided a more significant COD removal.
•
Moringa oleifera Lam has potential as a coagulant for treating textile
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•
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wastewater.