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Discoloration test of a slaughterhouse effluent by adsorption on two adsorbents produced from sawdust of Khaya senegalensis and Pinus sp
Results in Engineering 4 (2019) 100068
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Discoloration test of a slaughterhouse effluent by adsorption on two adsorbents produced from sawdust of Khaya senegalensis and Pinus sp Weldi Gnowe Djonga a, b, Eric Noubissie a, *, Guy Bertrand Noumi b a b
Laboratory of Chemical Engineering and Environment, BP 455 University Institute of Technology (IUT), University of Ngaoundere, Cameroon Department of Chemistry, BP 454 Faculty of Science, University of Ngaoundere, Cameroon
A R T I C L E I N F O
A B S T R A C T
Keywords: Adsorption Sawdust Slaughterhouse effluent Turbidity Organic matter
The aim of this work is to valorise wood waste in the discoloration of slaughterhouse effluent by the adsorption principle. To achieve this, two adsorbents were made from sawdust species Kaïcedra (Khaya senegalensis) and Pin (Pinus sp). A slaughterhouse effluent of cows was sampled in the town of Ngaoundere and characterized. An experimental design was used to determine the minimum values of adsorbent mass and agitation time required for better turbidity reduction of the slaughterhouse effluent. The results obtained reveal that the two adsorbents produced are more microporous than macroporous with specific surface areas ranging from 39.40 m2/g to 79.65 m2/g for Kaïcedra and Pin, respectively. The effluent of the slaughterhouse to be treated is turbid, conductible and rich in sulphate. The discoloration tests of this effluent with the two adsorbents produced made it possible to reduce more than 75% of all the above-mentioned polluting loads. Under the optimum pair of factors (adsorbent mass - agitation time), it is possible on an industrial scale to use almost 200 g of Kaïcedra adsorbent or 550 g of Pin adsorbent to remove more than 90% of the turbidity of 100 L of slaughterhouse effluent stirred for 1 h.
1. Introduction The consumption of water in the industrial sector is a major issue. The animal slaughter industry is one of the industrial sectors that consume a lot of water. In slaughterhouses of cows, water is mainly used for cleaning. This generates large quantities of effluents that considerably pollute the aquatic environment when this liquid discharged are not treated. With its heavy load of organic matter, sulphated and phosphated molecules, slaughterhouse effluents are likely to destabilize aquatic ecosystems by causing eutrophication of lakes and rivers [1]. These wastewaters discharged into the nature without treatment are also responsible for the proliferation of microorganisms such as Staphylococcus spp., Escherichia coli, Salmonella typhi and others microorganisms that are potentially harmful to human health [2,3]. Despite the various dangers presented by slaughterhouse effluents, their management remains problematic in several countries, including Cameroon. The slaughterhouse effluents that contain a high load of pollutant organic material [2] are in most cases treated by biological processes
[3–5]. But this technique has limits related to efficiency and also to the residence time or treatment time considered too long [2]. To overcome these problems, the exploitation of the adsorption principle can be an effective solution. Because adsorption is one of the most efficient and easy-to-implement wastewater treatment techniques [4,6]. However, the idea of this work is not to consider substituting the biological treatment that is most suitable for slaughterhouse effluents by the principle of adsorption, but rather to combine the two principles to improve the quality and processing time. Several types of adsorbents have been produced and tested in the treatment of wastewater [7–9]. But we have not found much available scientific work that would have treat on the use of an adsorbent for the treatment of slaughterhouse effluents of cows. The present work aims to test a non-timber forest species, locally available which are Kaïcedra (Khaya senegalensis) and Pin (Pinus sp), as adsorbent materials to improve the discoloration of effluent slaughterhouse by the principle of adsorption. It will be specifically question to produce and characterize two Kaïcedra and Pin adsorbents, to carry out adsorption tests first on a water contaminated with Methylene Blue (organic pollutant model) and on an effluent from
* Corresponding author. University Institute of Technology (IUT), BP. 455 University of Ngaoundere, Cameroon E-mail addresses: [email protected] (W.G. Djonga), [email protected] (E. Noubissie), [email protected] (G.B. Noumi). https://doi.org/10.1016/j.rineng.2019.100068 Received 15 August 2019; Received in revised form 13 November 2019; Accepted 20 November 2019 2590-1230/© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
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2.1.2.3. Methylene blue index. The determination of the Methylene Blue Index was inspired by Kra et al. [10]. Indeed, 0.2 g of each adsorbent was mixed in a beaker with 100 ml of a methylene blue solution at 20 mg/L. After 1h30min of stirring in the jar-test (at 250 rpm), representing the maximum time to reach equilibrium, the adsorbent was separated from the solution by filtration. The absorbance of the filtrate was measured on a UV/visible spectrophotometer (Jenway brand) at 664 nm. But before, a range of calibration solutions had been prepared with concentrations varying from 0 to 10 mg/L of methylene blue in steps of 1 mg/L and analysed at the same wavelength. The residual dye concentration was determined using the calibration line. The methylene blue number or the adsorption capacity of the adsorbent was calculated from the formula below.
the abattoir taken from a slaughterhouse of cows in the town of Ngaounder e. 2. Material and methods 2.1. Adsorbent materials 2.1.1. Substrate sampling and production of adsorbent materials The adsorbents used in this work are produced from two species of sawdust, Kaïcedra (Khaya senegalensis) and Pin (Pinus sp). They are part of the most manipulated wood species in the sawmills of city of Ngaounder e. The choice of these substrates also comes within the framework of the valorisation of local waste. Both adsorbent materials were produced following the modified method of Kra et al. [10]. Indeed, the samples were dried in an oven for 24 h, then ground and sieved with a sieve of 1 mm mesh diameter. They were then mixed with a solution of 1 N H3PO4 with a ratio 3.5 g per 20 ml. The mixture remained at room temperature for 24 h and the resulting solutions were filtered. The solid fractions were oven dried at 105 C for 24 h. The dry substrates were introduced into reformable porcelain crucibles and introduced into a furnace (brand Nabertherm) where they were pyrolyzed for 1h30 at a maximum temperature of 500 C. At the outlet of the oven, the adsorbents obtained were cooled in a desiccator and then washed several times with deionized water to remove the maximum H3PO4 which served as an activator, until the pH stabilized. At the end of the wash, the pH of the adsorbent materials was 3.7 for Kaïcedra and 4.0 for Pin. After washing, the adsorbent materials were again dried in an oven at 105 C for 24 h, then crushed and sieved using a 200 μm sieve. The adsorbents obtained were packaged in glass jars.
MB index ðmg = gÞ ¼
Ci ¼ initial concentration of methylene blue (MB) in the solution; Cf ¼ concentration of MB in the solution after adsorption; V ¼ volume of MB solution; mA ¼ mass of adsorbent. 2.1.2.4. Determination of the specific surface area of the adsorbent materials produced. The determination of the specific surface (SMB) area of the adsorbents is conventionally based on measurements of adsorbent adsorption capacity for adsorbates of known characteristics. In this case, it has been decided to determine the adsorption capacity of SMB on the monolayer of our adsorbents from the adsorption isotherm. Indeed, for the determination of SMB (m2/g), 1 g of Kaïcedra and 0.6 g of Pin were brought into contact with a solution of methylene blue of varied concentration (15–150 mg/L in steps of 15 mg/L) in a series of beakers. After 1h30min of stirring time in the jar-test, the residual MB absorbance of each solution in the series was measured by UV–Visible spectrophotometer at 664 nm. The results obtained, made it possible to draw the equilibrium adsorbed quantity curve (Qe) as a function of the equilibrium concentration (Ce). From the following Langmuir equation in the linear form:
2.1.2. Characterization of adsorbents 2.1.2.1. Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscope (SEM) and surface functions. The SEM of the two adsorbents was determined according to the modified method used by Tsamo and Kamga [11]. Indeed, 2 mg of the dry adsorbent was mixed with 1 ml of chloroform. After stirring, the solution obtained was analysed by SEM, brand FEI QUANTA 200. The Infra-Red of the adsorbents was performed according to the modified method of Kibami et al. [12]. For this purpose, 2 mg of dry adsorbent was directly analysed by Fourier transform infra-red spectrometry (iS50RAMAN brand). Each sample were recorded in the waver number range of 4000–400 cm1. The determination of the acidic surface functions of the adsorbents was made according to the Boehm method implemented by Bamba et al. [4].
Ce Ce 1 þ ¼ Q∞:KL Qe Q∞ The maximum adsorption capacity of the monolayer Q∞ was deduced from the slope and the intercept at the origin Ce/Qe ¼ f (Ce). The specific surface (SMB) area is given by the following relationship: SBM ¼
Q∞ :s NA MBM
Q∞ ¼ ultimate adsorption capacity (mg/g); Ce ¼ equilibrium concentration (mg/L); Qe ¼ equilibrium adsorption capacity (mg/g); KL ¼ Langmuir constant, S ¼ the area occupied by a MB molecule (175 Å2); NA ¼ Avogadro's number (6,02 1023 mol-1) and MMB ¼ molar mass of methylene blue (319.5 g/mol).
2.1.2.2. Iodine index. The iodine index of the adsorbents was determined according to the method used by Soleimani and Kaghazchi [13]. In fact, 0.5 g of each dry adsorbent was mixed with 50 ml of an iodine solution (0.1 N) in a beaker. After stirring in a jar-test (Raypa brand) at 250 rpm for 5 min, the mixture was filtered and 10 ml of the filtrate were pipetted and introduced into a conical flask with 0.5 ml of a 1% prepared starch solution. The solution tinted to dark blue and the reaction between iodine and starch was titrated with sodium thiosulfate (Na2S2O3 at 0.1 N) until complete bleaching of the mixture. The iodine index was calculated from the following formula. Iodine index ¼
Ci Cf V mA
2.2. Sampling and characterization of the slaughterhouse effluent of cows to be treated The effluent was taken at the exit of the slaughterhouse of cows of Ngaoundere (7 190 5800 N; 13 340 1100 E; 1110 m). The sample was then transported to the Chemical and Environmental Engineering Laboratory at the University of Ngaoundere where it was first sieved to remove particles and suspended solids larger than 2 mm, before undergoing a physico-chemical characterization. Organic matter was determined by oxidation with potassium dichromate (K2Cr2O7) in an acidic medium using the method of the Quebec Centre of Expertise for Environmental Analysis [14]. The iron, sulphate and phosphate contents were determined according to the methods of Rodier et al. [15].
ðVb Ve ÞNthio x MI2 x 1; 5 mA
Vb ¼ volume of sodium thiosulfate used for the blank (mL); Ve ¼ volume of sodium thiosulfate used to determine the iodine solution after adsorption (mL); Nsthio ¼ normality of sodium thiosulfate (0.1 N); MI2 ¼ molecular mass of Iodine (253.81 g/mol) and mA ¼ mass of adsorbent used (0.5 g).
2
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Results in Engineering 4 (2019) 100068
adsorption of the organic material (biological dye) on the adsorbent material, the turbidity of the effluent before adsorption and that of the effluent after adsorption were measured using a Hanna brand turbidimeter.
Table 1 Experimental matrix of the centred composite plane. Coded Variables
Real Variables
Tests
A
B
A
B
1 2 3 4 5 6 7 8 9 10 11 12 13
1 0 0 0 1 1.414214 0 1.414214 1 0 0 0 1
1 0 1.41421 0 1 0 0 0 1 0 0 1.414214 1
103.9 65.0 65.0 65.0 26.1 120.0 65.0 10.0 103.9 65.0 65.0 65.0 26.1
0.46 1.10 0.20 1.10 0.46 1.10 1.10 1.10 1.74 1.10 1.10 2.00 1.74
2.3.2. Influence of adsorption on other parameters of the effluent The experience matrix allowed to determine a couple of factors consisting of the agitation time (A) and the mass of each optimum adsorbent (B) to be used for a better discoloration of the effluent from the slaughterhouse. It is this pair of factors that has been used to perform effluent bleaching test. Turbidity and therefore organic matter are the most important parameters of this work. But at the end of these experiments, other physico-chemical parameters were monitored on the treated effluent whose time-mass pair gave the lowest turbidity after adsorption. The physico-chemical parameters monitored on the effluent are pH, 3 electrical conductivity, organic matter, Fe2þ, SO2 3 and PO4 .
A ¼ Stirring time (min) and B ¼ mass of the adsorbent (g).
3. Results 2.3. Discoloration test of the effluent from the slaughterhouse with products adsorbents
3.1. Characterization of the adsorbents produced 3.1.1. Scanning electron microscopy (SEM) Fig. 1 presents the results of the scanning electron microscopy (SEM) obtained from the two adsorbents produced at different scales (1 mm, 50 μm and 20 μm) of observation. Both adsorbents are porous and of more or less similar structure. The pores are of various sizes, oval and relatively deep textures. Their porous structure gives them an ability to fix pollutants of different sizes.
2.3.1. Agitation time and the amount of adsorbents effective for discoloration of the effluent In order to find the amount of adsorbents to be used and the agitation time for optimum discoloration of the effluent, a composite plan centred experiment was used. The matrix of experiments presented in Table 1 shows the number of experiments performed and the variety of factors taken into consideration in this work. Indeed, it was a question of introducing for each experiment in a beaker, the mass of the corresponding adsorbent in 100 ml of the diluted effluent (1/100 dilution factor). The mixture was stirred at 250 rpm using a test jar during the time corresponding to each experiment proposed by the matrix. Then the mixture was allowed to stand for about 20 min to promote decantation. In order to avoid the influence of the adsorbent microparticles on the turbidity, the mixture was precautionarily filtered using a wattman filter paper (0.45 μm). Each experiment was repeated three times. To assess the
3.1.2. Fourier transform infra-red spectroscopy The infra-red absorption spectra obtained on the two adsorbents produced are shown in Fig. 2. The IR spectra highlight three common elongation vibrations in the two adsorbents produced. These are first the bands 471.98 cm1 and 413.83 cm1 observed respectively in Kaïcedra and Pin, which correspond to the C–I bond; then bands observed precisely at 959 cm1
Fig. 1. Scanning Electron Microscopy of Kaïcedra adsorbent (a, b, c) and Pin adsorbent (d, e, f). 3
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Results in Engineering 4 (2019) 100068
Fig. 2. IR absorption spectra obtained on Kaïcedra and Pin adsorbents.
adsorbents increases with the increase in the concentration of methylene blue until a stabilization which reflects the occupation of all the adsorption sites available on adsorbents. These adsorption capacities, which are a function of the specific surface area of the adsorbent, are maximum at 11.95 mg/g and 24.15 mg/g for Kaizedra and Pin, respectively (Table 2). The correlation coefficients close to unity show that the Langmuir model describes the adsorption of methylene blue on the two adsorbents produced. This means that the adsorption on the adsorbents takes place in monolayer.
certainly corresponding to the C–F bond. The third common elongation is a band observed between 1510 cm1 and 1600 cm1 probably corre– O acid and N– – O bonds. A specific elongation to the sponding to the C– Kaïcedra adsorbent is observed at 1082.95 cm1 (C–O bond). The only vibration of deformation detected is observed in the Kaïcedra adsorbent on a band between 735 cm1 and 770 cm1 corresponding to the O-disubstituted aromatic Ctri-H bond. 3.1.3. Porosity of the adsorbents produced The values relating to the porosity of the two adsorbents produced are presented in Table 2. The iodine index (Iiode) gives information on the microporosity of the adsorbents while the methylene blue index (IMB) gives information on their macroporosity. On this basis, Kaïcedra adsorbent is significantly more microporous than Pin. If they are relatively close macroporosity, the specific surfaces and the maximum adsorption capacities show that the Pin adsorbent is still more predisposed to a better elimination of large molecules such as methylene blue in water.
3.2. Treatment test of the slaughterhouse effluent with adsorbents produced Some physicochemical characteristics of the slaughterhouse effluent to be treated are summarized in Table 5 of the additional equipment. The effluent from the slaughterhouse to be treated is slightly basic and highly conductive. It is dark red with turbidity ranging from 3825 to 8280 NTU. It is phosphated and its organic material is estimated at 4%. Only its colour, its turbidity and its phosphate content confer to it characteristics of a water which requires a treatment before its rejection in the nature.
3.1.4. Adsorption isotherm of methylene blue in water The methylene blue adsorption isotherms on the adsorbents produced and their Langmuir models are shown in Fig. 3. The adsorption isotherm expresses the amount of adsorbate present on the adsorbent Qe (mg/g) as a function of the concentration of adsorbate remaining in solution Ce (mg/L). It is apparent from the adsorption isotherms shown in Fig. 3 that the adsorption capacity of the
3.2.1. Minimum stirring time and mass of adsorbents for optimal discoloration of slaughterhouse effluent Table 3 presents the matrix of the actual values of the experimental design, composite centred plane model and the results of the influence of stirring time and mass of adsorbents on the discoloration of the slaughterhouse effluent. From this table, it is clear that the pairs of adsorbent mass and stirring time factors “minimum” for a maximum discoloration of the effluent of the slaughterhouse are 0.2 g and 65 min for the Kaïcedra adsorbent; and 1.1 g and 120 min for the Pin adsorbent. The summary of this excerpt is presented in Table 3 of the supplementary material. The mathematical models of the elimination of turbidity by Kaïcedra (1) and Pin (2) adsorbents from the experimental design are presented below.
Table 2 Porosity of adsorbents and Langmuir parameters after adsorption of Methylene Blue on both adsorbents. Porosities
Langmuir parameters
Absorbants
Iiode (mg/g)
IMB (mg/g)
R2
Qmax
KL
SBM (m2/g)
Kaïcedra Pin
859.2 11,6 701.8 4.4
9.47 0.00 9.85 0.03
0.975 0.981
11.95 24.15
2.790 2.978
39.40 79.65
Iiodine ¼ iodine Index; IMB ¼ Methylene Blue Index; R2 ¼ correlation coefficient; KL ¼ Langmuir constant; Qmax ¼ maximum adsorption capacity; SMB ¼ specific surface of the adsorbents obtained by the adsorption of the BM.
Y ¼ 1296:8 94:5A þ 1485:7B þ 757:7A2 344:3B2 318A B
(1)
Y ¼ 773 651:2 A þ 382:5B þ 154A2 153:5B2 þ 172:5A B
(2)
where Y ¼ response (turbidity); A ¼ stirring time; B ¼ mass of adsorbent. These mathematical equations reveal that unlike the stirring time 4
Results in Engineering 4 (2019) 100068
12.00
(a) Isotherme d’adsorption de Kaïcedra
Ce/Qe (g/L)
Qe (mg/g)
W.G. Djonga et al.
10.00 8.00
(b) Modèle de Langmuir (Kaïcedra)
0.25 0.20 0.15
6.00
y = 0.0837x + 0.03 R² = 0.9754
0.10
4.00
0.05
2.00
0.00
0.00 0.0
0.5
1.0
1.5
2.0
2.5
0.0
3.0
1.0
2.0
Ce (mg/L)
Ce/Qe (g/L)
Ce/Qe (g/L)
Ce (mg/L)
(c) Isotherme d’adsorption de Pin
25.0
3.0
20.0 15.0 10.0 5.0 0.0
(d) Modèle linéaire de Langmuir (Pin)
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
y = 0.0414x + 0.0139 R² = 0.9809
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
1.0
2.0
Ce (mg/L)
3.0
4.0
Ce (mg/L)
Fig. 3. Adsorption isotherms and Langmuir linear model of the adsorption of methylene blue on the various adsorbents produced. Table 3 Influences of the mass of adsorbents (Kaïcedra and Pin) and agitation time on the reduction of the turbidity of the effluent of the slaughterhouse according to the implemented experimental design. Kaïcedra
Pin
Test
Agitation Time (min)
Mass of adsorbent (g)
Turbidity before adsorption (NTU)
Turbidity after adsorption (NTU)
Despondency (%)
Turbidity before adsorption (NTU)
Turbidity after adsorption (NTU)
Despondency (%)
01 02 03 04 05 06 07 08 09 10 11 12 13
65.00 65.00 65.00 65.00 65.00 65.00 65.00 103.90 103.90 26.10 26.10 120.00 10.00
2.00 0.20 1.10 1.10 1.10 1.10 1.10 0.46 1.74 1.74 0.46 1.10 1.10
3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825
2283 605 270 60 1193 370 1026 247 1493 110 1309 445 1463 160 464 117 1694 673 2213 127 347 131 2387 121 2370 132
40.31 92.94 68.82 73.19 60.96 65.79 61.74 87.88 55.72 42.14 90.93 37.60 38.04
8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280
960 104 327 261 781 197 946 650 1099 366 634 231 405 124 324 167 814 115 1002 211 857 422 285 137 1617 395
88.41 96.05 90.56 88.57 86.73 92.35 95.11 96.08 90.17 87.90 89.65 96.56 80.48
(A2), the quadratic effect of the mass of Kaïcedra and Pin (B2) adsorbents globally has a negative influence on the elimination of the turbidity of the effluent (discoloration). Which means in both cases of adsorption (with Kaicedra and Pin), that the prolongation of the stirring time in the reactor contributes more favourably to the elimination of the turbidity of the effluent than the increase of the mass of adsorbent. This observation is, moreover, more appreciable on the estimated response surfaces presented on Fig. 4. It should be noted, however, that with the minimum mass of adsorbent (<0.4 g), the Kaicedra adsorbent requires less agitation time (approximately 60 min (Fig. 4a)) to be as effective for the removal of turbidity, that will have been the adsorbent Pin (about 120 min (Fig. 4b)). But taking into account the relevance of the information conveyed by these mathematical models, it is essential to validate them. The validation indicators for the different mathematical models are presented in Table 4. Table 4 shows that all validation indicators (R2, Bf, Af and AAMD) are
positive with Kaïcedra adsorbent. As for the adsorbent Pin, only the R2 is negative, but the model is still validated because it has three positive indicators (Bf, Af and AAMD) out of four.
Table 4 Validation indicators of the mathematical models resulting from the experimental plan. Validation indicators
Kaïcedra
Pin
Acceptable values
References
R2
85.2
72.78%
80%
Bias factor (Bf) Accuracy factor (Af) AAMD
1.02 1.07
1.01 1.12
[0.75–1.25] [0.75–1.25]
Joglekar et May [16] Dalgaard et Jorgesen [17]
0.16
0.27
[0–0.3]
Baș et Boyac [18]
AAMD ¼ Absolute Analysis of Mean Deviation.
5
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Table 5 Some physico-chemical parameters of the slaughterhouse effluent before and after adsorption treatment on the two adsorbents produced. Physico-chemical parameters Raw effluent Treated effluent with
Kaïcedra Pin
pH
EC (μS/cm)
PO3 4 (mg/L)
SO2 3 (mg/L)
Fe2þ (mg/L)
MO (%)
7,73 5,8 6,04
6200 1600 2200
354 6 174 99 326 181
4388 272 831 136 504 163
248 4 54 1 116 3
4,15 0,18 1,47 0,09 0,90 0,16
EC ¼ electrical conductivity; OM ¼ organic matter.
4. Discussion 4.1. Characteristics of adsorbents products Kaïcedra and Pin adsorbents are more microporous than macroporous (Table 2). This means that they will be better able to adsorb micropollutants such as ions than macropollutants such as dyes and MB [10, 19] and even OM contained in an effluent. They effectively adsorb MB in monolayer according to the Langmuir adsorption isotherms of which they faithfully describe the model [20]. They are characterized by phenolic surface functions and lactones which gives them an acidic property as shown by the results in Table 6. These two surface functions have moreover been confirmed by the IR spectra, respectively through – O bonds [12]. These are the characteristics of the the C–O [21] and C– two adsorbents produced which were used according to well-defined parameters (mass and agitation time) following an experimental design, to carry out the treatment test of slaughterhouse effluent by adsorption.
4.2. Effectiveness of the two adsorbent materials on the treatment of slaughterhouse effluent At the end of the test treatment, the treated effluent has a pH decreased from 7.73 to nearly 6 because of the surface pH of different adsorbents are acid when they are introduced into the reactor. Indeed, the two adsorbents produced are characterized by acidic surface functions. It is therefore obvious that their introduction in a slightly basic medium induces decrease of the pH towards acidity. The effectiveness of the Kaïcedra adsorbent on the reduction of the electrical conductivity compared to the Pin adsorbent is explained by their difference in microporous structure. Indeed, the Kaïcedra adsorbent is more microporous than the Pin adsorbent (Table 2). The electrical conductivity of the effluent being induced by cationic micropollutants of the effluent such as metals (Ca2þ, Mg2þ, Fe2þ, Mn2þ …), the elimination of these as the Fe2þ cation (78.23%) will greatly reduce the electrical conductivity of the effluent. In contrast, the more macroporous Pin adsorbent was already predisposed for effective removal of molecules whose OM compared to the Kaïcedra adsorbent. The various efficiencies of the adsorbents produced on the removal of phosphates and sulphates were a function of the concentration of these two pollutants in the raw effluent. Indeed, it was observed above that the two adsorbents had been very effective on the removal of sulphates but less effective on the elimination of phosphates. Thus, the high sulphate adsorption rates achieved by the two adsorbents are certainly due to the high concentration of sulphate in the effluent before treatment. It is established that the adsorption rate of a pollutant on an adsorbent increases with its concentration in the effluent as long as there are sites available on the adsorbent [22–25]. Thus, the low adsorption rates of phosphates are also due to the low concentration of phosphate in the raw
Fig. 4. The estimated response surfaces from the experimental design with the agitation time and mass of adsorbent for the two adsorbents produced that are (a) Kaicedra and (b) Pin.
3.2.2. Influence of adsorption on some physico-chemical parameters of slaughterhouse effluent in the optimum condition of stirring time and mass of adsorbent The residual concentrations of some chemical parameters of the effluent from the slaughterhouse treated by adsorption are presented in Table 5. The pH of the treated effluent decreased until a value around 6. Globally, the treatment allowed to reduce the pollutant load of the raw effluent. The efficiency of the reduction of parameters by adsorption varies from one adsorbent to another. For example, the Kaïcedra adsorbent was more effective in reducing the electrical conductivity (74.19%) and iron (78.23%) while the Pin adsorbent was more effective in reducing the OM (Organic Matter). If both adsorbents were effective for the removal of sulphates (88.51% with Pin and 81.1% with Kaedecra) contained in the effluent, they were less for the removal of phosphates (51% with Kaïcedra and 8% with Pin).
Table 6 Surface functions of the two adsorbents produced. Adsorbents
RM (%)
pH
Carboxylic groups (meq/g)
Lactone groups (meq/g)
Phenolics groups (meq/g)
Total acidity (meq/g)
Basics groups (meq/g)
Kaïcedra Pin
21.18 15.17
3.70 4.02
0.000 0.000
0.015 0.010
0.146 0.148
0.161 0.158
0.000 0.000
RM ¼ residual moisture. 6
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slaughterhouse effluent of cows by adsorption on two adsorbents produced from sawdust of Khaya senegalensis and Pinus sp”, and we declare that no conflict of interest exited among us.
effluent. The main parameter targeted in this slaughterhouse effluent treatment test is turbidity which in this case is characterized by the red colour caused by bovine red blood cells and which is also primarily related to the OM. In the end, the Pin adsorbent was more effective (97% abatement rate) than the Kaïcedra adsorbent on the elimination of the colour of the effluent from the slaughterhouse. This performance is on the other hand due to its specific surface and its high macropore richness and thus to its ability to adsorb larger molecules [10,19] such as OM than Kaïcedra adsorbent. As mentioned previously, the strong coloration of the slaughterhouse effluent is mainly due to its high loading OM. This performance is also due to the mass of the Pin adsorbent (1.10 g) introduced into the effluent, which was greater than the mass of the Kaïcedra adsorbent (0.2 g). Because as long as there is pollutant in the effluent, the adsorption rate of a pollutant will increase with the increase of the mass of the adsorbent [9,24,26,27]. It is also important not to neglect the influence of the agitation time on the efficiency of the Pin adsorbent as shown by the estimated response surfaces in Fig. 4a. Indeed, the extension of the agitation time increases the probability of contact between the pollutant and the adsorbent still having available sites which causes progressive augmentation of the amount of pollutant adsorbed over time. The results of the experimental design showed at the end of the treatment, that with 0.20 g of Kaïcedra adsorbent, it is possible to reduce 93% of the turbidity of 100 ml of a slaughterhouse effluent after 65 min agitation. In the same logic, with 1.10 g of the Pin adsorbent and 2 h of agitation would be required to reduce the turbidity of 100 ml of slaughterhouse effluent by 97%. This would mean that it is possible on a large scale to remove more than 90% of the turbidity of 100 L of slaughterhouse effluent with only 200 g of Kaïcedra adsorbent or 550 g of Pin adsorbent, and this after 1 h of agitation. They are therefore two adsorbent materials that can be fully exploited by the technicians responsible for wastewater treatment in slaughterhouses around the world. The energy consumption for the production of the adsorbent material may be considered as a disadvantage in this project, but the cost of production will be completely negligible compared to the results of the effluent treatment that the company will obtain. This satisfaction will be observed at the level of the treatment time which will be reduced by more than half and especially the quality of the effluent treated downstream. Especially when you know what a company spends as a penalty, when it discharges into the nature its untreated effluent.
Acknowledgments The authors of this work address their gratitude to Prof. ALI Ahmed, Head of Department of Chemical Engineering and Responsible of the Laboratory of Chemical Engineering and Environment of the University Institute of Technology (IUT) of Ngaoundere. Thank you to the Department of Chemistry of the Faculty of Sciences of the University of Ngaoundere in Cameroon. Our thanks also go to ASONGAZI NJUAKA Isidore, future engineer of ENSAI at the University of Ngaounere for his participation in the review of this article. References [1] O. Chukwu, Analysis of groundwater pollution from abattoir waste in Minna, Nigeria, Res. J. Dairy Sci. 2 (4) (2008) 74–77. [2] A. Khennoussi, M. Chaouch, A. Chahlaoui, Traitement d’effluents d’abattoir de viande rouge par electrocoagulation-flottation avec des electrodes en fer, Rev. Sci. Eau 26 (2) (2013) 81–171. [3] A.B. Umaru, A.H. Hong, B.R. Burmamu, S.M. Bala, The effects of abattoir waste on groundwater quality at Yola main slaugter slab, Adamawa State, Nigeria, Int. J. Renew. Energy Technol. 6 (2018) 37–48. [4] D. Bamba, B. Dongui, A. Trokourey, Z.E. Guessan, G.P. Atheba, D. Robert, J.V. Weber, Etudes comparees des methodes de preparation du charbon actif, suivies d’un test de depollution d’une eau contaminee au diuron, J. Soc. Ouest Afr. Chim. 028 (2009) 41–52. [5] N.T. Manjunath, I. Mehrotra, R.P. Mathur, Treatment of wastewater from slaughterhouse by DAF-UASB system, Water Res. 34 (6) (2000) 1930–1936. [6] F. Sakr, A. Sennaoui, M. Elouardi, M. Tamimi, A. Assabbane, Adsorption study of Methylene Blue on biomaterial using cactus, J. Mater. Environ. Sci. 6 (2) (2014) 397–406. [7] S. Zeroual, K. Guerfi, S. Hazourli, C. Charnay, Estimation de l’heterogeneite d’un charbon actif oxyde a differentes temperatures a partir de l’adsorption des molecules sondes, Revue des Energies Renouvelables 14 (4) (2011) 581–590. [8] M. Daoud, O. Benturki, L'Activation d’un Charbon a Base de Noyaux de Jujubes et Application a l'Environnement. Adsorption d’un Colorant de Textile, Revue des Energies Renouvelables SIENR’14 Ghardaïa (2014) 155–162. [9] M. Trachi, N. Bourfis, S. Benamara, H. Gougam, Preparation et caracterisation d’un charbon actif a partir de la coquille d’amande (Prunus amygdalus) amere, Biotechnologie, Agronomie, societe et environnement (BASE) 18 (4) (2014) 492–502. [10] D.O. Kra, N.A. Kouadio, G.P. Atheba, B. Coulibaly, N.B. Allou, K.G. Grassi, A. Trokouerey, Modelin of the adsorbent properties of activated carbons resulting from two varieties of Acacia (auriculoformis and mangium), Int. J. Innov. Sci. Res. 13 (2) (2015) 542–553. [11] C. Tsamo, R. Kamga, Variation of physico-chemical and textural properties of laboratory prepared red-mud through acid and thermal activations, Adv. Mater. 6 (2) (2017) 11–19, https://doi.org/10.11648/j.am.20170602.12. [12] D. Kibami, C. Pongener, K.S. Rao, D. Sinha, Surface characterization and adsorption studies of Bambusa vulgaris-a low cost adsorbent, J. Mater. Environ. Sci. 8 (7) (2017) 2494–2505. [13] M. Soleimani, T. Kaghazchi, Low-Cost adsorbents from agricultural by-products impregnated with phosphoric acid, Adv. Chem. Eng. Res. 3 (2014) 34–41 [Online] Available: https://www.academia.edu/27856628. [14] Centre d’expertise en analyse environnementale du Quebec, MA. 405-C 1.0 Edition : 2003-03-03, in: Methode d’analyse : Determination du carbone organique total dans les solides : dosage par titrage, Revision, 2006, 10-06 (3). [15] J. Rodier, B. Legube, N. Merlet, L’analyse de l’eau. 9eme edition, Dunod, Paris, 2009, p. 1526pp. [16] A.M. Joglekar, A.T. May, Product excellence through design of experiments, Cereal Foods World 32 (1987) 857–868. [17] P. Dalgaard, J.V. Jorgensen, Predicted and observed growth of Listeria monocytogenes in seafood challenge tests and in naturally contaminated coldsmoked salmon, Int. J. Food Microbiol. 40 (1–2) (1998) 105–115, https://doi.org/ 10.1016/S0168-1605(98)00019-1. [18] D. Bas, I.H. Boyacı, Modeling and optimization II: comparison of estimation capabilities of response surface methodology with artificial neural networks in a biochemical reaction, J. Food Eng. 78 (2007) 846–854, https://doi.org/10.1016/ j.jfoodeng.2005.11.025. [19] G. Enaime, K. Ennaciri, A. Oumas, A. Baçaoui, M. Seffen, T. Selmi, A. Yaacoubi, Preparation and characterization of activated carbons from olive wastes by physical and chemical activation: application to Indigo carmine adsorption, J. Mater. Environ. Sci. 8 (11) (2017) 4125–4137. [20] C. Yang, A. Girma, T. Lei, Y. Liu, C. Ma, Study on simultaneous adsorption of Zn(II) and methylene blue on waste-derived activated carbon for efficient applications in wastewater treatment, Cogent Environ. Sci. 2 (2016) 1–9, 1151983.
5. Conclusion It emerges from this work that sawdust from Kaïcedra and Pin species are exploitable substrates for the production of good adsorbent materials. During their application in the treatment of the slaughterhouse effluent, the rate of reduction of the turbidity of the effluent is as much influenced by the agitation time as by the mass of the adsorbent. Both adsorbents have been shown to be effective in removing the most important pollutants from the slaughterhouse effluent. In a perspective of implementation on an industrial scale, we can now try the treatment of slaughterhouse effluent combining the principles of biological treatment (activated sludge for example) with adsorption on the adsorbent materials. Author contribution (author). He This work is part of a project initiated by Eric Noubissie carried out physico-chemical analyses in the laboratory with the master student who is Weldi Djonga Gnowe under the supervision of I (Pr Guy Bertrand Noumi). Declaration of competing interest We are the authors of the manuscript entitled “Discoloration test of a 7
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Results in Engineering 4 (2019) 100068 [25] B.K. Asmaa, M. Badia, H. Mohsine, B. Mina, Y. Abdelghani, Elimination du colorant basique « Bleu de Methylene » en solution aqueuse par l’argile de Safi, Rev. Sci. Eau 23 (4) (2010). [26] A.H.A. Dabwan, N. Yuki, N.A.M. Asri, H. Katsumata, T. Suzuki, S. Kaneco, Removal of methylene blue, rhodamine B and ammonium ion from aqueous solution by adsorption onto sintering porous materials prepared from coconut husk waste, Open J. Inorg. Non-Metallic Mater. 5 (2015) 21–30. http://dx.org/10.42 36/ojinm.2015.52003. [27] D. Bendaho, T.D. Ainad, D. Bassou, Adsorption du Cu(II) en solution par l’argile brut et activee de la region de Tiout-Naama sud-ouest algerien, Revue Sci. des materiaux (2014) 23–34. Laboratoire LARHYSS N 02.
[21] O.Y. Abdelaziz, C.P. Hulterberg, Physochemical characterisation of technical Lignins for potential valorisation, Waste Biomass Valor. 8 (2017) 859–869, https:// doi.org/10.1007/s12649-016-9643-9. [22] R. Domga, M. Harouna, C. Tcheka, J.B. Tchatchueng, A. Tsafam, K.N. Dama, D. Dikdim, Batch equilibrium, kinetic and thermodynamic studies on adsorption of methylene blue in aqueous solution onto activated carbon prepared from Bos Indicus Gudali bones, Chem. J. 1 (6) (2015) 172–181. http://www.aiscience.org/j ournal/cj. [23] M. Faisal, R. Atmani, I. Maghri, M. Elkouali, M. Talbi, M.L. Bouamrani, M. Salouhi, A. Kenz, Elimination of methylene blue dye with natural adsorbent « banana peels powder », Global J. Inc 14 (1) (2014) 39–44, 2014. [24] I. Youcef, A. Ouakouak, D. Boulanouar, S. Achour, Etude du pouvoir adsorbant du charbon actif en poudre pour l’elimination des phosphates des eaux naturelles, Larhyss J. 17 (2014) 35–46.
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Discoloration test of a slaughterhouse effluent by adsorption on two adsorbents produced from sawdust of Khaya senegalensis and Pinus sp Weldi Gnowe Djonga a, b, Eric Noubissie a, *, Guy Bertrand Noumi b a b
Laboratory of Chemical Engineering and Environment, BP 455 University Institute of Technology (IUT), University of Ngaoundere, Cameroon Department of Chemistry, BP 454 Faculty of Science, University of Ngaoundere, Cameroon
A R T I C L E I N F O
A B S T R A C T
Keywords: Adsorption Sawdust Slaughterhouse effluent Turbidity Organic matter
The aim of this work is to valorise wood waste in the discoloration of slaughterhouse effluent by the adsorption principle. To achieve this, two adsorbents were made from sawdust species Kaïcedra (Khaya senegalensis) and Pin (Pinus sp). A slaughterhouse effluent of cows was sampled in the town of Ngaoundere and characterized. An experimental design was used to determine the minimum values of adsorbent mass and agitation time required for better turbidity reduction of the slaughterhouse effluent. The results obtained reveal that the two adsorbents produced are more microporous than macroporous with specific surface areas ranging from 39.40 m2/g to 79.65 m2/g for Kaïcedra and Pin, respectively. The effluent of the slaughterhouse to be treated is turbid, conductible and rich in sulphate. The discoloration tests of this effluent with the two adsorbents produced made it possible to reduce more than 75% of all the above-mentioned polluting loads. Under the optimum pair of factors (adsorbent mass - agitation time), it is possible on an industrial scale to use almost 200 g of Kaïcedra adsorbent or 550 g of Pin adsorbent to remove more than 90% of the turbidity of 100 L of slaughterhouse effluent stirred for 1 h.
1. Introduction The consumption of water in the industrial sector is a major issue. The animal slaughter industry is one of the industrial sectors that consume a lot of water. In slaughterhouses of cows, water is mainly used for cleaning. This generates large quantities of effluents that considerably pollute the aquatic environment when this liquid discharged are not treated. With its heavy load of organic matter, sulphated and phosphated molecules, slaughterhouse effluents are likely to destabilize aquatic ecosystems by causing eutrophication of lakes and rivers [1]. These wastewaters discharged into the nature without treatment are also responsible for the proliferation of microorganisms such as Staphylococcus spp., Escherichia coli, Salmonella typhi and others microorganisms that are potentially harmful to human health [2,3]. Despite the various dangers presented by slaughterhouse effluents, their management remains problematic in several countries, including Cameroon. The slaughterhouse effluents that contain a high load of pollutant organic material [2] are in most cases treated by biological processes
[3–5]. But this technique has limits related to efficiency and also to the residence time or treatment time considered too long [2]. To overcome these problems, the exploitation of the adsorption principle can be an effective solution. Because adsorption is one of the most efficient and easy-to-implement wastewater treatment techniques [4,6]. However, the idea of this work is not to consider substituting the biological treatment that is most suitable for slaughterhouse effluents by the principle of adsorption, but rather to combine the two principles to improve the quality and processing time. Several types of adsorbents have been produced and tested in the treatment of wastewater [7–9]. But we have not found much available scientific work that would have treat on the use of an adsorbent for the treatment of slaughterhouse effluents of cows. The present work aims to test a non-timber forest species, locally available which are Kaïcedra (Khaya senegalensis) and Pin (Pinus sp), as adsorbent materials to improve the discoloration of effluent slaughterhouse by the principle of adsorption. It will be specifically question to produce and characterize two Kaïcedra and Pin adsorbents, to carry out adsorption tests first on a water contaminated with Methylene Blue (organic pollutant model) and on an effluent from
* Corresponding author. University Institute of Technology (IUT), BP. 455 University of Ngaoundere, Cameroon E-mail addresses: [email protected] (W.G. Djonga), [email protected] (E. Noubissie), [email protected] (G.B. Noumi). https://doi.org/10.1016/j.rineng.2019.100068 Received 15 August 2019; Received in revised form 13 November 2019; Accepted 20 November 2019 2590-1230/© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
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2.1.2.3. Methylene blue index. The determination of the Methylene Blue Index was inspired by Kra et al. [10]. Indeed, 0.2 g of each adsorbent was mixed in a beaker with 100 ml of a methylene blue solution at 20 mg/L. After 1h30min of stirring in the jar-test (at 250 rpm), representing the maximum time to reach equilibrium, the adsorbent was separated from the solution by filtration. The absorbance of the filtrate was measured on a UV/visible spectrophotometer (Jenway brand) at 664 nm. But before, a range of calibration solutions had been prepared with concentrations varying from 0 to 10 mg/L of methylene blue in steps of 1 mg/L and analysed at the same wavelength. The residual dye concentration was determined using the calibration line. The methylene blue number or the adsorption capacity of the adsorbent was calculated from the formula below.
the abattoir taken from a slaughterhouse of cows in the town of Ngaounder e. 2. Material and methods 2.1. Adsorbent materials 2.1.1. Substrate sampling and production of adsorbent materials The adsorbents used in this work are produced from two species of sawdust, Kaïcedra (Khaya senegalensis) and Pin (Pinus sp). They are part of the most manipulated wood species in the sawmills of city of Ngaounder e. The choice of these substrates also comes within the framework of the valorisation of local waste. Both adsorbent materials were produced following the modified method of Kra et al. [10]. Indeed, the samples were dried in an oven for 24 h, then ground and sieved with a sieve of 1 mm mesh diameter. They were then mixed with a solution of 1 N H3PO4 with a ratio 3.5 g per 20 ml. The mixture remained at room temperature for 24 h and the resulting solutions were filtered. The solid fractions were oven dried at 105 C for 24 h. The dry substrates were introduced into reformable porcelain crucibles and introduced into a furnace (brand Nabertherm) where they were pyrolyzed for 1h30 at a maximum temperature of 500 C. At the outlet of the oven, the adsorbents obtained were cooled in a desiccator and then washed several times with deionized water to remove the maximum H3PO4 which served as an activator, until the pH stabilized. At the end of the wash, the pH of the adsorbent materials was 3.7 for Kaïcedra and 4.0 for Pin. After washing, the adsorbent materials were again dried in an oven at 105 C for 24 h, then crushed and sieved using a 200 μm sieve. The adsorbents obtained were packaged in glass jars.
MB index ðmg = gÞ ¼
Ci ¼ initial concentration of methylene blue (MB) in the solution; Cf ¼ concentration of MB in the solution after adsorption; V ¼ volume of MB solution; mA ¼ mass of adsorbent. 2.1.2.4. Determination of the specific surface area of the adsorbent materials produced. The determination of the specific surface (SMB) area of the adsorbents is conventionally based on measurements of adsorbent adsorption capacity for adsorbates of known characteristics. In this case, it has been decided to determine the adsorption capacity of SMB on the monolayer of our adsorbents from the adsorption isotherm. Indeed, for the determination of SMB (m2/g), 1 g of Kaïcedra and 0.6 g of Pin were brought into contact with a solution of methylene blue of varied concentration (15–150 mg/L in steps of 15 mg/L) in a series of beakers. After 1h30min of stirring time in the jar-test, the residual MB absorbance of each solution in the series was measured by UV–Visible spectrophotometer at 664 nm. The results obtained, made it possible to draw the equilibrium adsorbed quantity curve (Qe) as a function of the equilibrium concentration (Ce). From the following Langmuir equation in the linear form:
2.1.2. Characterization of adsorbents 2.1.2.1. Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscope (SEM) and surface functions. The SEM of the two adsorbents was determined according to the modified method used by Tsamo and Kamga [11]. Indeed, 2 mg of the dry adsorbent was mixed with 1 ml of chloroform. After stirring, the solution obtained was analysed by SEM, brand FEI QUANTA 200. The Infra-Red of the adsorbents was performed according to the modified method of Kibami et al. [12]. For this purpose, 2 mg of dry adsorbent was directly analysed by Fourier transform infra-red spectrometry (iS50RAMAN brand). Each sample were recorded in the waver number range of 4000–400 cm1. The determination of the acidic surface functions of the adsorbents was made according to the Boehm method implemented by Bamba et al. [4].
Ce Ce 1 þ ¼ Q∞:KL Qe Q∞ The maximum adsorption capacity of the monolayer Q∞ was deduced from the slope and the intercept at the origin Ce/Qe ¼ f (Ce). The specific surface (SMB) area is given by the following relationship: SBM ¼
Q∞ :s NA MBM
Q∞ ¼ ultimate adsorption capacity (mg/g); Ce ¼ equilibrium concentration (mg/L); Qe ¼ equilibrium adsorption capacity (mg/g); KL ¼ Langmuir constant, S ¼ the area occupied by a MB molecule (175 Å2); NA ¼ Avogadro's number (6,02 1023 mol-1) and MMB ¼ molar mass of methylene blue (319.5 g/mol).
2.1.2.2. Iodine index. The iodine index of the adsorbents was determined according to the method used by Soleimani and Kaghazchi [13]. In fact, 0.5 g of each dry adsorbent was mixed with 50 ml of an iodine solution (0.1 N) in a beaker. After stirring in a jar-test (Raypa brand) at 250 rpm for 5 min, the mixture was filtered and 10 ml of the filtrate were pipetted and introduced into a conical flask with 0.5 ml of a 1% prepared starch solution. The solution tinted to dark blue and the reaction between iodine and starch was titrated with sodium thiosulfate (Na2S2O3 at 0.1 N) until complete bleaching of the mixture. The iodine index was calculated from the following formula. Iodine index ¼
Ci Cf V mA
2.2. Sampling and characterization of the slaughterhouse effluent of cows to be treated The effluent was taken at the exit of the slaughterhouse of cows of Ngaoundere (7 190 5800 N; 13 340 1100 E; 1110 m). The sample was then transported to the Chemical and Environmental Engineering Laboratory at the University of Ngaoundere where it was first sieved to remove particles and suspended solids larger than 2 mm, before undergoing a physico-chemical characterization. Organic matter was determined by oxidation with potassium dichromate (K2Cr2O7) in an acidic medium using the method of the Quebec Centre of Expertise for Environmental Analysis [14]. The iron, sulphate and phosphate contents were determined according to the methods of Rodier et al. [15].
ðVb Ve ÞNthio x MI2 x 1; 5 mA
Vb ¼ volume of sodium thiosulfate used for the blank (mL); Ve ¼ volume of sodium thiosulfate used to determine the iodine solution after adsorption (mL); Nsthio ¼ normality of sodium thiosulfate (0.1 N); MI2 ¼ molecular mass of Iodine (253.81 g/mol) and mA ¼ mass of adsorbent used (0.5 g).
2
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adsorption of the organic material (biological dye) on the adsorbent material, the turbidity of the effluent before adsorption and that of the effluent after adsorption were measured using a Hanna brand turbidimeter.
Table 1 Experimental matrix of the centred composite plane. Coded Variables
Real Variables
Tests
A
B
A
B
1 2 3 4 5 6 7 8 9 10 11 12 13
1 0 0 0 1 1.414214 0 1.414214 1 0 0 0 1
1 0 1.41421 0 1 0 0 0 1 0 0 1.414214 1
103.9 65.0 65.0 65.0 26.1 120.0 65.0 10.0 103.9 65.0 65.0 65.0 26.1
0.46 1.10 0.20 1.10 0.46 1.10 1.10 1.10 1.74 1.10 1.10 2.00 1.74
2.3.2. Influence of adsorption on other parameters of the effluent The experience matrix allowed to determine a couple of factors consisting of the agitation time (A) and the mass of each optimum adsorbent (B) to be used for a better discoloration of the effluent from the slaughterhouse. It is this pair of factors that has been used to perform effluent bleaching test. Turbidity and therefore organic matter are the most important parameters of this work. But at the end of these experiments, other physico-chemical parameters were monitored on the treated effluent whose time-mass pair gave the lowest turbidity after adsorption. The physico-chemical parameters monitored on the effluent are pH, 3 electrical conductivity, organic matter, Fe2þ, SO2 3 and PO4 .
A ¼ Stirring time (min) and B ¼ mass of the adsorbent (g).
3. Results 2.3. Discoloration test of the effluent from the slaughterhouse with products adsorbents
3.1. Characterization of the adsorbents produced 3.1.1. Scanning electron microscopy (SEM) Fig. 1 presents the results of the scanning electron microscopy (SEM) obtained from the two adsorbents produced at different scales (1 mm, 50 μm and 20 μm) of observation. Both adsorbents are porous and of more or less similar structure. The pores are of various sizes, oval and relatively deep textures. Their porous structure gives them an ability to fix pollutants of different sizes.
2.3.1. Agitation time and the amount of adsorbents effective for discoloration of the effluent In order to find the amount of adsorbents to be used and the agitation time for optimum discoloration of the effluent, a composite plan centred experiment was used. The matrix of experiments presented in Table 1 shows the number of experiments performed and the variety of factors taken into consideration in this work. Indeed, it was a question of introducing for each experiment in a beaker, the mass of the corresponding adsorbent in 100 ml of the diluted effluent (1/100 dilution factor). The mixture was stirred at 250 rpm using a test jar during the time corresponding to each experiment proposed by the matrix. Then the mixture was allowed to stand for about 20 min to promote decantation. In order to avoid the influence of the adsorbent microparticles on the turbidity, the mixture was precautionarily filtered using a wattman filter paper (0.45 μm). Each experiment was repeated three times. To assess the
3.1.2. Fourier transform infra-red spectroscopy The infra-red absorption spectra obtained on the two adsorbents produced are shown in Fig. 2. The IR spectra highlight three common elongation vibrations in the two adsorbents produced. These are first the bands 471.98 cm1 and 413.83 cm1 observed respectively in Kaïcedra and Pin, which correspond to the C–I bond; then bands observed precisely at 959 cm1
Fig. 1. Scanning Electron Microscopy of Kaïcedra adsorbent (a, b, c) and Pin adsorbent (d, e, f). 3
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Fig. 2. IR absorption spectra obtained on Kaïcedra and Pin adsorbents.
adsorbents increases with the increase in the concentration of methylene blue until a stabilization which reflects the occupation of all the adsorption sites available on adsorbents. These adsorption capacities, which are a function of the specific surface area of the adsorbent, are maximum at 11.95 mg/g and 24.15 mg/g for Kaizedra and Pin, respectively (Table 2). The correlation coefficients close to unity show that the Langmuir model describes the adsorption of methylene blue on the two adsorbents produced. This means that the adsorption on the adsorbents takes place in monolayer.
certainly corresponding to the C–F bond. The third common elongation is a band observed between 1510 cm1 and 1600 cm1 probably corre– O acid and N– – O bonds. A specific elongation to the sponding to the C– Kaïcedra adsorbent is observed at 1082.95 cm1 (C–O bond). The only vibration of deformation detected is observed in the Kaïcedra adsorbent on a band between 735 cm1 and 770 cm1 corresponding to the O-disubstituted aromatic Ctri-H bond. 3.1.3. Porosity of the adsorbents produced The values relating to the porosity of the two adsorbents produced are presented in Table 2. The iodine index (Iiode) gives information on the microporosity of the adsorbents while the methylene blue index (IMB) gives information on their macroporosity. On this basis, Kaïcedra adsorbent is significantly more microporous than Pin. If they are relatively close macroporosity, the specific surfaces and the maximum adsorption capacities show that the Pin adsorbent is still more predisposed to a better elimination of large molecules such as methylene blue in water.
3.2. Treatment test of the slaughterhouse effluent with adsorbents produced Some physicochemical characteristics of the slaughterhouse effluent to be treated are summarized in Table 5 of the additional equipment. The effluent from the slaughterhouse to be treated is slightly basic and highly conductive. It is dark red with turbidity ranging from 3825 to 8280 NTU. It is phosphated and its organic material is estimated at 4%. Only its colour, its turbidity and its phosphate content confer to it characteristics of a water which requires a treatment before its rejection in the nature.
3.1.4. Adsorption isotherm of methylene blue in water The methylene blue adsorption isotherms on the adsorbents produced and their Langmuir models are shown in Fig. 3. The adsorption isotherm expresses the amount of adsorbate present on the adsorbent Qe (mg/g) as a function of the concentration of adsorbate remaining in solution Ce (mg/L). It is apparent from the adsorption isotherms shown in Fig. 3 that the adsorption capacity of the
3.2.1. Minimum stirring time and mass of adsorbents for optimal discoloration of slaughterhouse effluent Table 3 presents the matrix of the actual values of the experimental design, composite centred plane model and the results of the influence of stirring time and mass of adsorbents on the discoloration of the slaughterhouse effluent. From this table, it is clear that the pairs of adsorbent mass and stirring time factors “minimum” for a maximum discoloration of the effluent of the slaughterhouse are 0.2 g and 65 min for the Kaïcedra adsorbent; and 1.1 g and 120 min for the Pin adsorbent. The summary of this excerpt is presented in Table 3 of the supplementary material. The mathematical models of the elimination of turbidity by Kaïcedra (1) and Pin (2) adsorbents from the experimental design are presented below.
Table 2 Porosity of adsorbents and Langmuir parameters after adsorption of Methylene Blue on both adsorbents. Porosities
Langmuir parameters
Absorbants
Iiode (mg/g)
IMB (mg/g)
R2
Qmax
KL
SBM (m2/g)
Kaïcedra Pin
859.2 11,6 701.8 4.4
9.47 0.00 9.85 0.03
0.975 0.981
11.95 24.15
2.790 2.978
39.40 79.65
Iiodine ¼ iodine Index; IMB ¼ Methylene Blue Index; R2 ¼ correlation coefficient; KL ¼ Langmuir constant; Qmax ¼ maximum adsorption capacity; SMB ¼ specific surface of the adsorbents obtained by the adsorption of the BM.
Y ¼ 1296:8 94:5A þ 1485:7B þ 757:7A2 344:3B2 318A B
(1)
Y ¼ 773 651:2 A þ 382:5B þ 154A2 153:5B2 þ 172:5A B
(2)
where Y ¼ response (turbidity); A ¼ stirring time; B ¼ mass of adsorbent. These mathematical equations reveal that unlike the stirring time 4
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12.00
(a) Isotherme d’adsorption de Kaïcedra
Ce/Qe (g/L)
Qe (mg/g)
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10.00 8.00
(b) Modèle de Langmuir (Kaïcedra)
0.25 0.20 0.15
6.00
y = 0.0837x + 0.03 R² = 0.9754
0.10
4.00
0.05
2.00
0.00
0.00 0.0
0.5
1.0
1.5
2.0
2.5
0.0
3.0
1.0
2.0
Ce (mg/L)
Ce/Qe (g/L)
Ce/Qe (g/L)
Ce (mg/L)
(c) Isotherme d’adsorption de Pin
25.0
3.0
20.0 15.0 10.0 5.0 0.0
(d) Modèle linéaire de Langmuir (Pin)
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
y = 0.0414x + 0.0139 R² = 0.9809
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
1.0
2.0
Ce (mg/L)
3.0
4.0
Ce (mg/L)
Fig. 3. Adsorption isotherms and Langmuir linear model of the adsorption of methylene blue on the various adsorbents produced. Table 3 Influences of the mass of adsorbents (Kaïcedra and Pin) and agitation time on the reduction of the turbidity of the effluent of the slaughterhouse according to the implemented experimental design. Kaïcedra
Pin
Test
Agitation Time (min)
Mass of adsorbent (g)
Turbidity before adsorption (NTU)
Turbidity after adsorption (NTU)
Despondency (%)
Turbidity before adsorption (NTU)
Turbidity after adsorption (NTU)
Despondency (%)
01 02 03 04 05 06 07 08 09 10 11 12 13
65.00 65.00 65.00 65.00 65.00 65.00 65.00 103.90 103.90 26.10 26.10 120.00 10.00
2.00 0.20 1.10 1.10 1.10 1.10 1.10 0.46 1.74 1.74 0.46 1.10 1.10
3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825 3825
2283 605 270 60 1193 370 1026 247 1493 110 1309 445 1463 160 464 117 1694 673 2213 127 347 131 2387 121 2370 132
40.31 92.94 68.82 73.19 60.96 65.79 61.74 87.88 55.72 42.14 90.93 37.60 38.04
8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280 8280
960 104 327 261 781 197 946 650 1099 366 634 231 405 124 324 167 814 115 1002 211 857 422 285 137 1617 395
88.41 96.05 90.56 88.57 86.73 92.35 95.11 96.08 90.17 87.90 89.65 96.56 80.48
(A2), the quadratic effect of the mass of Kaïcedra and Pin (B2) adsorbents globally has a negative influence on the elimination of the turbidity of the effluent (discoloration). Which means in both cases of adsorption (with Kaicedra and Pin), that the prolongation of the stirring time in the reactor contributes more favourably to the elimination of the turbidity of the effluent than the increase of the mass of adsorbent. This observation is, moreover, more appreciable on the estimated response surfaces presented on Fig. 4. It should be noted, however, that with the minimum mass of adsorbent (<0.4 g), the Kaicedra adsorbent requires less agitation time (approximately 60 min (Fig. 4a)) to be as effective for the removal of turbidity, that will have been the adsorbent Pin (about 120 min (Fig. 4b)). But taking into account the relevance of the information conveyed by these mathematical models, it is essential to validate them. The validation indicators for the different mathematical models are presented in Table 4. Table 4 shows that all validation indicators (R2, Bf, Af and AAMD) are
positive with Kaïcedra adsorbent. As for the adsorbent Pin, only the R2 is negative, but the model is still validated because it has three positive indicators (Bf, Af and AAMD) out of four.
Table 4 Validation indicators of the mathematical models resulting from the experimental plan. Validation indicators
Kaïcedra
Pin
Acceptable values
References
R2
85.2
72.78%
80%
Bias factor (Bf) Accuracy factor (Af) AAMD
1.02 1.07
1.01 1.12
[0.75–1.25] [0.75–1.25]
Joglekar et May [16] Dalgaard et Jorgesen [17]
0.16
0.27
[0–0.3]
Baș et Boyac [18]
AAMD ¼ Absolute Analysis of Mean Deviation.
5
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Results in Engineering 4 (2019) 100068
Table 5 Some physico-chemical parameters of the slaughterhouse effluent before and after adsorption treatment on the two adsorbents produced. Physico-chemical parameters Raw effluent Treated effluent with
Kaïcedra Pin
pH
EC (μS/cm)
PO3 4 (mg/L)
SO2 3 (mg/L)
Fe2þ (mg/L)
MO (%)
7,73 5,8 6,04
6200 1600 2200
354 6 174 99 326 181
4388 272 831 136 504 163
248 4 54 1 116 3
4,15 0,18 1,47 0,09 0,90 0,16
EC ¼ electrical conductivity; OM ¼ organic matter.
4. Discussion 4.1. Characteristics of adsorbents products Kaïcedra and Pin adsorbents are more microporous than macroporous (Table 2). This means that they will be better able to adsorb micropollutants such as ions than macropollutants such as dyes and MB [10, 19] and even OM contained in an effluent. They effectively adsorb MB in monolayer according to the Langmuir adsorption isotherms of which they faithfully describe the model [20]. They are characterized by phenolic surface functions and lactones which gives them an acidic property as shown by the results in Table 6. These two surface functions have moreover been confirmed by the IR spectra, respectively through – O bonds [12]. These are the characteristics of the the C–O [21] and C– two adsorbents produced which were used according to well-defined parameters (mass and agitation time) following an experimental design, to carry out the treatment test of slaughterhouse effluent by adsorption.
4.2. Effectiveness of the two adsorbent materials on the treatment of slaughterhouse effluent At the end of the test treatment, the treated effluent has a pH decreased from 7.73 to nearly 6 because of the surface pH of different adsorbents are acid when they are introduced into the reactor. Indeed, the two adsorbents produced are characterized by acidic surface functions. It is therefore obvious that their introduction in a slightly basic medium induces decrease of the pH towards acidity. The effectiveness of the Kaïcedra adsorbent on the reduction of the electrical conductivity compared to the Pin adsorbent is explained by their difference in microporous structure. Indeed, the Kaïcedra adsorbent is more microporous than the Pin adsorbent (Table 2). The electrical conductivity of the effluent being induced by cationic micropollutants of the effluent such as metals (Ca2þ, Mg2þ, Fe2þ, Mn2þ …), the elimination of these as the Fe2þ cation (78.23%) will greatly reduce the electrical conductivity of the effluent. In contrast, the more macroporous Pin adsorbent was already predisposed for effective removal of molecules whose OM compared to the Kaïcedra adsorbent. The various efficiencies of the adsorbents produced on the removal of phosphates and sulphates were a function of the concentration of these two pollutants in the raw effluent. Indeed, it was observed above that the two adsorbents had been very effective on the removal of sulphates but less effective on the elimination of phosphates. Thus, the high sulphate adsorption rates achieved by the two adsorbents are certainly due to the high concentration of sulphate in the effluent before treatment. It is established that the adsorption rate of a pollutant on an adsorbent increases with its concentration in the effluent as long as there are sites available on the adsorbent [22–25]. Thus, the low adsorption rates of phosphates are also due to the low concentration of phosphate in the raw
Fig. 4. The estimated response surfaces from the experimental design with the agitation time and mass of adsorbent for the two adsorbents produced that are (a) Kaicedra and (b) Pin.
3.2.2. Influence of adsorption on some physico-chemical parameters of slaughterhouse effluent in the optimum condition of stirring time and mass of adsorbent The residual concentrations of some chemical parameters of the effluent from the slaughterhouse treated by adsorption are presented in Table 5. The pH of the treated effluent decreased until a value around 6. Globally, the treatment allowed to reduce the pollutant load of the raw effluent. The efficiency of the reduction of parameters by adsorption varies from one adsorbent to another. For example, the Kaïcedra adsorbent was more effective in reducing the electrical conductivity (74.19%) and iron (78.23%) while the Pin adsorbent was more effective in reducing the OM (Organic Matter). If both adsorbents were effective for the removal of sulphates (88.51% with Pin and 81.1% with Kaedecra) contained in the effluent, they were less for the removal of phosphates (51% with Kaïcedra and 8% with Pin).
Table 6 Surface functions of the two adsorbents produced. Adsorbents
RM (%)
pH
Carboxylic groups (meq/g)
Lactone groups (meq/g)
Phenolics groups (meq/g)
Total acidity (meq/g)
Basics groups (meq/g)
Kaïcedra Pin
21.18 15.17
3.70 4.02
0.000 0.000
0.015 0.010
0.146 0.148
0.161 0.158
0.000 0.000
RM ¼ residual moisture. 6
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Results in Engineering 4 (2019) 100068
slaughterhouse effluent of cows by adsorption on two adsorbents produced from sawdust of Khaya senegalensis and Pinus sp”, and we declare that no conflict of interest exited among us.
effluent. The main parameter targeted in this slaughterhouse effluent treatment test is turbidity which in this case is characterized by the red colour caused by bovine red blood cells and which is also primarily related to the OM. In the end, the Pin adsorbent was more effective (97% abatement rate) than the Kaïcedra adsorbent on the elimination of the colour of the effluent from the slaughterhouse. This performance is on the other hand due to its specific surface and its high macropore richness and thus to its ability to adsorb larger molecules [10,19] such as OM than Kaïcedra adsorbent. As mentioned previously, the strong coloration of the slaughterhouse effluent is mainly due to its high loading OM. This performance is also due to the mass of the Pin adsorbent (1.10 g) introduced into the effluent, which was greater than the mass of the Kaïcedra adsorbent (0.2 g). Because as long as there is pollutant in the effluent, the adsorption rate of a pollutant will increase with the increase of the mass of the adsorbent [9,24,26,27]. It is also important not to neglect the influence of the agitation time on the efficiency of the Pin adsorbent as shown by the estimated response surfaces in Fig. 4a. Indeed, the extension of the agitation time increases the probability of contact between the pollutant and the adsorbent still having available sites which causes progressive augmentation of the amount of pollutant adsorbed over time. The results of the experimental design showed at the end of the treatment, that with 0.20 g of Kaïcedra adsorbent, it is possible to reduce 93% of the turbidity of 100 ml of a slaughterhouse effluent after 65 min agitation. In the same logic, with 1.10 g of the Pin adsorbent and 2 h of agitation would be required to reduce the turbidity of 100 ml of slaughterhouse effluent by 97%. This would mean that it is possible on a large scale to remove more than 90% of the turbidity of 100 L of slaughterhouse effluent with only 200 g of Kaïcedra adsorbent or 550 g of Pin adsorbent, and this after 1 h of agitation. They are therefore two adsorbent materials that can be fully exploited by the technicians responsible for wastewater treatment in slaughterhouses around the world. The energy consumption for the production of the adsorbent material may be considered as a disadvantage in this project, but the cost of production will be completely negligible compared to the results of the effluent treatment that the company will obtain. This satisfaction will be observed at the level of the treatment time which will be reduced by more than half and especially the quality of the effluent treated downstream. Especially when you know what a company spends as a penalty, when it discharges into the nature its untreated effluent.
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5. Conclusion It emerges from this work that sawdust from Kaïcedra and Pin species are exploitable substrates for the production of good adsorbent materials. During their application in the treatment of the slaughterhouse effluent, the rate of reduction of the turbidity of the effluent is as much influenced by the agitation time as by the mass of the adsorbent. Both adsorbents have been shown to be effective in removing the most important pollutants from the slaughterhouse effluent. In a perspective of implementation on an industrial scale, we can now try the treatment of slaughterhouse effluent combining the principles of biological treatment (activated sludge for example) with adsorption on the adsorbent materials. Author contribution (author). He This work is part of a project initiated by Eric Noubissie carried out physico-chemical analyses in the laboratory with the master student who is Weldi Djonga Gnowe under the supervision of I (Pr Guy Bertrand Noumi). Declaration of competing interest We are the authors of the manuscript entitled “Discoloration test of a 7
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