Original Article

Optimization and Isothermal Studies of Antibiotics Mixture Biosorption From Wastewater Using Palm Kernel, Chrysophyllum albidum, and Coconut Shells Biocomposite

Please cite this article as follows: Opeoluwa OS, Kayode LG, Ajani AO, Afolabi TJ, Okeowo IO, Olaitan AR, et al. Optimization and isothermal studies of antibiotics mixture biosorption from wastewater using palm kernel, Chrysophyllum albidum, and coconut shells biocomposite. Avicenna J Environ Health Eng. 2023; 10(1):44-56. doi:10.34172/ajehe.2023.5316

1. Introduction

Pollution of water resources by different pollutants is a global environmental issue (1). For several decades, pharmaceutical constituents have been used in veterinary and human medicine; nevertheless, these compounds have potential risks for organisms when released into the environment. An essential source of these organic compounds is the discharge of effluents from wastewater treatment plants into surface water bodies (2). These recalcitrant pollutants in urban wastewater have turned into a severe environmental concern because they threaten aquatic ecosystems and human health (3). The presence of antibiotics in aquatic systems is of concern since their toxicity may cause a long-term effect on ecological sustainability even if they are present at trace levels (4). Antibiotics are essential as they have been used to treat infection-related diseases in humans and animals (5). The significant sources of antibiotics in the aqueous environment mainly originate from hospital effluents, pharmaceutical industries, and municipal wastewater. Antibiotics are widely used in human, veterinary medicine, and aquaculture to prevent or treat microbial infections (6). Tetracycline (TC), ampicillin (AMP), and amoxicillin (AMOX) are prominent antibiotics found in the environment. AMP and AMOX are penicillin-type antibiotics used to treat bacterial bladder infections, pneumonia, gonorrhea, stomach or intestine infections, and bacterial infections in the ear, nose, throat, skin, and lower respiratory tract, respectively (7,8). TC is a bacteriostatic agent that inhibits the synthesis of bacterial protein and is widely used as an antibiotic for animals and humans (9). These antibiotics are discharged continuously in the water bodies in the concentration range between ng/L-µg/L (10). Thus, removing these non-biodegradable pollutants from the aquatic environment becomes unavoidable. Conventional wastewater treatment technologies based on biological treatment, membrane separation, coagulation, flocculation, and sedimentation are ineffective in completely removing antibiotics and can only lead to partial elimination (11-13). Advanced oxidation technologies such as ultraviolet (UV) photolysis and Fenton’s reagent produce ^•OH radicals to actively and non-selectively decompose contaminants to completely remove antibiotics from wastewater (14). However, the main constraints of advanced oxidation are application cost, catalyst management, and residual toxicity in treated effluents (15). Such issues have motivated active research in recent years to develop new, simple, and efficient alternative technologies for eliminating antibiotics from bodies of water, of which adsorption is no exception.

The adsorption approach, among the numerous techniques, provides various advantages compared to other treatment technologies such as low initial investment, more straightforward construction, and easy operation (16). Unlike other more expensive methods, this method of removing antibiotics is preferable in terms of cost, efficiency, and lack of hazard. The proper comprehension and interpretation of adsorption isotherms are essential to the design and improvement of the adsorption system and the improvement of adsorption mechanism pathways (17). The most common isotherm models include Langmuir, Freundlich, Temkin, and Dubinin–Kaganer–Radushkevich (DKR) (18). Other isotherm models reported in the literature are Halsey, Jovanovic, Elovich, Jossen, Flory–Huggins, Kiselev, Harkins–Jura, Fowler–Guggenheim, and Redlich–Peterson to predict and compare adsorption performances (19).

Accordingly, this study aimed to investigate the potential of the biocomposite produced from the mixture of palm kernel shell (PKS), Chrysophyllum albidum shell (CAS), and coconut shell (CS) for the removal of TC, AMP, and AMOX in simulated wastewater. The simple-centroid design feature of the Design Expert Software (version 12.0.1) was deployed to optimize the mixing ratio of PKS, CAS, and CS in the development of a composite biosorbent. To the best of our knowledge, this is the first time biosorbent from a mixture of PKS, CAS, and CS is reported for the removal of antibiotics. Furthermore, unlike most previous studies on biosorbents for removing antibiotics, this research focused on investigating 12 different isotherm models to generate detailed isotherm parameters, which could essentially help understand the adsorption process and the generation of detailed isotherm parameters for reactor design and create a significant research gap at universal interest.

2. Methods

2.1. Materials and Equipment

The CAS and PKS were obtained from Odo-Oba Market in Ogbomoso in Oyo State, while the CS was obtained from Ogere-Remo in Ogun State. The reagents used included TC (C₂₂H₂₄N₂O₈), AMP (C₁₆H₁₉N₃O₄S), and AMOX (C₁₆H₁₉N₃O₅S, 90% purity), and their physicochemical properties and chemical structure are presented in Table 1. Other reagents are sodium hydroxide (NaOH), nitric acid, hydrogen peroxide, and distilled water. All chemicals were of analytical grade. The equipment used includes a weighing balance, beaker, measuring cylinder, crucible, volumetric flask, reagent bottle, desiccator, microwave oven (SAISHO), pH meter, rotary shaker (HZ- 300), centrifuge, and UV-visible spectrophotometer (AXIOM MEDICAL 752D).

Table 1. Physicochemical Properties of Selected Pharmaceutical Drugs

Trade Name	Chemical Formula	Chemical Structure	Molecular Mass (g/mol)	Log K ow	pKa
Tetracycline	C22H24N2O8	Close .	444.435	-1.37	7.68 (Basic) 3.3
Ampicillin	C16H18N3NaO4S	Close .	349.406	1.35	2.5 (-COOH) 7.3 (-NH2)
Amoxicillin	C16H19N3O5S	Close .	365.4	0.87	7.22

Source. DrugBank (20).

2.2. Preparation of Biocomposite from Coconut Shell, Palm Kernel Shell, and Chrysophyllum albidum Cell

The CS, PKS, and CAS were thoroughly washed with water to remove mud, dust, and other dirt. Afterward, these precursors were sun-dried for three weeks before being oven-dried at 105 °C to constant weight (21). Some of the dried samples were pulverized and then sieved to different sizes of 0.016-0.0937 inches. Each sample size was weighed, packed in separate polythene bags, and labeled accordingly, and the part with a particle size of 3.31 µm Granular activated carbon (GAC) was used for this study. PKS (400 g), CS (300 g), and CAS (300 g) were immersed in 1000 mL of 0.1 M NaOH and kept in the oven for 24 hours to aid the activation process. Excess NaOH was removed, and the activated samples were decolorized with 0.5 M H₂O₂, by soaking 400 g of activated CAS and CS in 500 mL H₂O₂ and 400 grams of PKS in 600 mL H2O2. Later, the decolorized activated samples were neutralized to pH 6.9-7.1 and oven-dried at 110 °C for 2 hours.

2.3. Simple Centroid Design and Statistical Analysis for the Preparation of Palm Kernel Shell-Chrysophyllum albidum Cell-Coconut Shell Biocomposite

The composition of the activated biocomposite materials, including PKS, CAS, and CS was formed through the matrix generated by the Design Expert software (v. 12.0.1.0). The composition of the input parameters (i.e., PKS, CAS, and CS) was varied as shown in Table 2. The output variables adsorption capacities and removal efficiencies were used as the dependent variables, the optimized input parameters of which were varied. Then, the analysis of variance (ANOVA) and other statistical components such as adequate precision, coefficient of determination (R²), coefficient of variation, adjusted R², predicted R², and standard deviation of the model equations and their terms were evaluated. The effect of the levels of the selected components was verified with contour and three-dimensional plots.

2.4. Biosorption Studies

Batch adsorption studies of TC, AMP, and AMOX were carried out using PKS-CAS-CS composite to determine their adsorption tendencies. The TC, AMP, and AMOX stock solutions were prepared by dissolving 1 gram of TC, AMP, and AMOX in 1000 mL of distilled water to achieve 1 g/L stock solutions of the antibiotics. The composite (1 g) developed based on the experimental design was added to 100 mL of varying concentrations (20-100 mg/L) of the working solution of TC, AMP, and AMOX mixtures as mixed pollutants. The concentrations of the mixed pharmaceuticals before and after adsorption were quantified with a UV-visible spectrophotometer at a maximum wavelength of 525, 623, and 46 nm for TC, AMP, and AMOX, respectively. Subsequently, the adsorption capacity and the percentage removal were estimated using equations 1 and 2, respectively.

where, C₀ and C_e (mg/L) are the liquid-phase pharmaceutical concentrations at initial and equilibrium, respectively, M (g) is the mass of the adsorbent, and V is the volume (L) of the aqueous.

2.5. Adsorption Isotherm Studies

Adsorption isotherms describe the equilibrium relationships between sorbent and adsorbate at a constant temperature. The adsorption isotherms models have one or more parameters evaluated based on the relationships between the adsorption capacity and concentration adsorbed at equilibrium. The different adsorption models adopted in this study are highlighted in Table 3.

3. Result and Discussion

3.1. Model Summary of the Adsorption and Removal Efficiency of Tetracycline, Ampicillin, and Amoxicillin by Biocomposite Adsorbent

The mixture and simple centroid were used as the study category for the experimental design in the adsorption and removal efficiency of TC, AMP, and AMOX. The factors considered were the percentage of each precursor (i.e., PKS, CAS, and CS) in a composite, while the responses were adsorption capacity and removal efficiency. Special quadratic as well as quadratic and special cubic models were selected for the adsorption of AMP and AMOX, respectively, based on the 13 experimental runs generated. Run 13 (55% PKS, 20% CAS, and 25% CS) recorded the maximum adsorption capacities of 8.66 mg/g, 9.12 mg/g, and 7.11 mg/g, equivalent to 86.61, 91.19, and 71.13% of removal efficiencies for TC, AMP, and AMOX, respectively (Table 4). Run 13 was made of the composite biosorbent, with the highest percentage attributed to PKS. It is of no surprise that the run with the highest PKS exhibited the highest removal efficiency, and a previous study conducted by Aremu et al (18) significantly removed phenol from wastewater (85 64%) using activated carbon from PKS (608 °C, 0.5 M KOH at 60 minutes). All the runs have a relatively good capacity for removing TC and AMP, with a removal efficiency of > 80%, while the maximum removal efficiency for AMOX was 71.1%, which was as low as 7.13%, indicating the good adsorptive capacity of the biocomposite. Boukhelkhal et al (22) reported a removal efficiency of 84% for AMOX at 25 °C with a pH of 7 for a five-minute contact time and 0.24 g/L initial AMOX concentration. The efficiency of CS-activated carbon in removing ibuprofen was reported by Bello et al (23), showing an adsorption capacity of 76.92 mg/g. The higher removal efficiencies exhibited by these materials indicated the potential of the biocomposite for the effective removal of pharmaceutical pollutants.

3.2. Analysis of Variance

The ANOVA substantiated the adequacy of the developed quadratic regression models. A very low probability value of the F-test and values of Prob > F less than 0.05 within the ranges of 0.05 and 0.10 generally indicate that the terms of the model are significant, while values greater than 0.10 denotes the insignificant level (24). The ANOVA for the adsorption capacity of TC displays that the suggested model withan F value of 24.75 and P value of 0.0119 is significant (Table 5). The interaction terms (AB and BC) are nominal model terms in the regression equation. Hence, the ANOVA revealed that the composite of PKS-CAS and CAS-CS in the PKS-CAS-CS biocomposite does not have a significant effect on the adsorption of TC. In contrast, the PKS-CS composite had a significant effect on the adsorption of TC. The Model F values of 3.89 obtained for the adsorption of AMP by biocomposite PKS-CAS-CS implies that the model is relatively significant at Prob > F ranges (0.0642) between 0.05 and 0.10 (Table 5), with 6.42% chance of occurrence due to noise. The model term AB is the only significant interaction term, and this indicates the high propensity of the PKS-CAS mixture to affect the adsorption of TC significantly, unlike PKS-CS and CAS-CS mixtures. The model F value of 21.93 and P value of 0.0443 suggested that the model is statistically significant in the adsorption of AMOX by the biocomposite PKS-CAS-CS. All the model terms except BC were significant. Similar trends were observed by the ANOVA for the removal efficiency of TC, AMP, and AMOX onto the PKS-CAS-CS biocomposite (Table 6). The significance level for the TC and AMP removal efficiencies has Prob > F greater than 0.05, implying an inclination toward insignificant, though within acceptable limits. In addition, the removal efficiency of AMOX onto the PKS-CAS-CS biocomposite displays a high level of significance statistically for its model and model terms.

3.3. Model Equation

The model equation for the adsorption capacity and removal efficiencies of TC, AMP, and AMOX are presented in Equations 18-20 and 21-23. The coded factors equation can be used to predict the response for given levels of each factor. By default, the high levels of the mixture components are coded as + 1, and the low levels are coded as 0. The coded equation helps identify the relative impact of the factors by comparing the factor coefficients. The positive signs in the model equation equally convey a beneficial effect of the factor for increased responses, while negative signs indicate opposition to increased responses (25).

3.4. Diagnostic Studies on the Analysis of TC, AMP, and AMOX

The model’s suitability for removing TC, AMP, and AMOX was checked through diagnostic plots (Fig. 1a-c). The plots should lie closely along a straight line to show that the regression model prediction is accurate and that the residual values are negligible (24). The parity plot of predicted versus actual (Fig. 2a-c) shows that the predicted responses by the model equations agree with the observed responses, as fitted points lie closely along a straight line (24). The experimental and predicted values for removing TC, AMP, and AMOX agree and are well-correlated. Moreover, the plot of residuals versus the experimental run for TC, AMP, and AMOX (Fig. 3a-c) exhibits that the residuals lie within -14.089 to 14.089, -4.983 to + 4.983, and -140.054 to + 140.054 intervals, respectively. Additionally, no data were outside the range, demonstrating that the fitted model to the response surface was consistent with all the data, which confirms no error in recording the data (26).

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Fig. 1.

Normal Plot of Residual for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 1.

Normal Plot of Residual for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

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Fig. 2.

Predicted vs Actual Plot for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 2.

Predicted vs Actual Plot for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

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Fig. 3.

Residual vs Run Plot for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 3.

Residual vs Run Plot for the Adsorption Capacity of PKS-CAS-CS Biocomposite for the Removal of TC, AMP, and AMOX. Note. PKS: Palm kernel shell; CAS: Chrysophyllum albidium shell; CS: Coconut shell; TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

3.5. Model Graph

The contour (Fig. 4a-c) and 3-D graphs (Fig. 5a-c) illustrate the effect of the solid/solvent ratio on the adsorption capacity of TC, AMP, and AMOX using a maximum weight of 55.00%, 55.00%, and 50.00% for PKS, CS, and CAS, respectively. The red region indicates where the adsorption is maximum (hot zone), graduating through yellow and green to blue zones, where the adsorption is minimal (cold zone). The removal efficiency of the PKS-CAS-CS biocomposite is demonstrated by the contour graph (Fig. 6a-c) and 3-D graph (Fig. 7a-c). The removal efficiency of AMOX was lowest at PKS (55% wt) and 25 wt% for CAS and CS, respectively, as indicated by the blue region. Similarly, regarding the shape of the adsorption of AMP, the contour and 3-D graph exhibit the exact representation. However, the removal efficiency of TC was significantly influenced by the high percentage of PKS (55%wt), as depicted in the contour graph.

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Fig. 4.

The Contour Plot for the Adsorption Capacity of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 4.

The Contour Plot for the Adsorption Capacity of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

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Fig. 5.

The 3D Model Plot for the Adsorption Capacity of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 5.

The 3D Model Plot for the Adsorption Capacity of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

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Fig. 6.

The Contour Plot for the Removal Efficiency of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 6.

The Contour Plot for the Removal Efficiency of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

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Fig. 7.

The 3D model Plot for the Removal Efficiency of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 7.

The 3D model Plot for the Removal Efficiency of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

3.6. Effect of Contact Time on Adsorption Capacity

The effect of contact time on the adsorption of TC, AMP, and AMOX with bio-composites of PKS, CAS, and CS was carried out at varying time ranges (10-120 minutes) with 55 mg/L of simulated wastewater. As Fig. 8 indicates, the contact time significantly affected the adsorption process and agitation speed of 120 rpm and room temperature of 298 K. The adsorbate uptake increased with the increase in contact time (27). However, at about 30 minutes, the adsorption capacity of the biosorbent for the removal of the three pharmaceuticals remained constant, indicating that the adsorption site might have been saturated. The maximum adsorption capacity for removing AMP, TC, and AMOX was found to be 5.5 mg/g, 4.8 mg/g, and 4 mg/g, respectively.

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Fig. 8.

Effect of Contact Time on the Adsorption of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 8.

Effect of Contact Time on the Adsorption of TC, AMP, and AMOX. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

3.7. Adsorption Isotherm Effect on Concentration

3.7.1. Langmuir-2 Model

The plot evaluated the Langmuir parameters for the adsorption of TC, AMP, and AMOX unto the biocomposite (Fig. 9a). The Q_m (mg/g) and K_L (L/mg) are the Langmuir constants, and their values are summarized in Table 7. The R² obtained for the removal rate of TC, AMP, and AMOX by biocomposite is 1.0000, 0.7728, and 0.9878, respectively (Table 6), indicating the suitability of the biocomposite for the removal of the pharmaceuticals. However, it fitted best for the removal of TC, indicating monolayer adsorption. The R² of this study was compared well with that of previous studies (28-31). However, negative values of Q_M and K_L indicate inappropriateness.

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Fig. 9.

Linearized Isotherm Models for the TC, AMOX, and AMP. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

Fig. 9.

Linearized Isotherm Models for the TC, AMOX, and AMP. Note. TC: Tetracycline; AMP: Ampicillin; AMOX: Amoxicillin

3.7.2. Freundlich Model

The isotherm constants (K_F and n) are calculated from the slope and intercept of the linear plot (Fig. 9b). The adsorption intensity K_F of the biocomposite for removing TC, AMP, and AMOX were 2.5363, 30.47, and 0.1774 (L/mg), respectively (Table 7), suggesting that the biocomposite for the removal of AMP has the highest K_F. The Freundlich isotherm showed the model’s suitability for removing TC, AMP, and AMOX with R² of 0.9997, 0.7502, and 0.9898, respectively. The numerical value, n, is an important index to determine the favorability of the adsorption of dichlorvos. It is generally stated that the values of n in the range 2–10 represent ‘good heterogeneity’, 1–2 indicate ‘moderately good’, and less than 1 represents ‘poor’ adsorption characteristics. However, only the value of ‘n’ obtained for the removal of TC by this study can be rated as good.

3.7.3. Temkin Model

This isotherm contains a factor that explicitly considers the adsorbent–adsorbate interactions. The plot of qe against lnCe can be found in Fig. 9c. The Temkin isotherm equilibrium-binding constant (A) (L/mg) for the biocomposite on TC, AMP, and AMOX are 1.34 × 10⁷⁹ L/mg, 2.43 × 10^-73 L/mg, and 8.22 × 10³³ L/mg, respectively. Moreover, the constant β, the heat of adsorption, was found to be highest in the adsorptive removal of AMP using biocomposite. Compared to their studies, the Temkin isotherm model fitted best with the adsorption TC (R² = 0.9962).

3.7.4. DubininRadushkevich Model

The porosity, free energy, Ɛ, and adsorption mechanism are determined from the Dubinin-Radushkevich isotherm plot. The linear relationship between the plot of Inqe against Ɛ² generated the ß and Inq_m as the slope and intercept of the plot, respectively (Fig. 9h). The estimated q_m parameters are 16.7634, 12.2008, and 14.7715 mg/g for TC, AMP, and AMOX, respectively (Table 8). The calculated values of the related adsorption energy (ß) for the adsorption TC, AMP, and AMOX were 2 × 10^-6, 7 × 10^-7, and 1 × 10^-5 mol² kJ^-2. The ß for the adsorption of AMOX was close to that in the study by Jannat Abadi (32), where Fe-doped zeolite was used to remove TC. Furthermore, the R² of the Dubinin Radushkevich (Dubinin R.) model for the removal of TC, AMP, and AMOX by composite were 0.9931, 0.7755, and 0.9994, respectively.

3.7.5. Harkin-Jura Model

This model considers the possibility of multilayer adsorption on the surface of absorbents having heterogeneous pore distribution (34). The plot of

3.7.6. Kiselev Model

This model, known as the localized monomolecular layer model, is only valid for surface coverage 𝜃 > 0.68 (35). The plot of

3.7.7. Hill-DeBoer Model

Hill-DeBoer isotherm model delineates a phenomenon with mobile adsorption and lateral interaction among adsorbed molecules (38). The plot of

3.7.8. Halsey Model

The Halsey model plot was obtained by the plot of lnq_e against lnC_e (Fig. 8g). It evaluates multilayer adsorption at a relatively large distance from the surface. The n_H values of TC, AMP, and AMOX removal by biocomposite were -0.7656, -1.6923, and -0.7967, respectively (Table 9). Moreover, the estimated K_H parameters were 1.4981, 4.4101, and 0.4718 for TC, AMP, and AMOX removal by biocomposite. Additionally, the model fit is best for biocomposite used for removing TC (R² = 0.9997).

3.7.9. Fowler Guggenheim Model

This isotherm model is established because the heat of adsorption varies linearly with loading. The plot of

3.7.10. Jovanovich Model

The Langmuir isotherm model was involved allowing the mechanical interaction. The slope K_f and intercept q_max were obtained from the linear plot of the model lnqe against Ce, as depicted in Fig. 5j and Table 9. The R² obtained from the Jovanovich plot for TC and AMOX adsorption was high (0.9995 and 0.9798) but slightly less than Langmuir isotherm. However, the R² obtained from the Jovanovich plot AMP adsorption was low (0.7367), indicating a lateral interaction (19).

3.7.11.Elovich Isotherm Model

The Elovich model was based on multilayer adsorption, and adsorption increased exponentially with the adsorption site (39). Elovich constants q_m and K_e, representing maximum adsorption capacity and adsorption constant, respectively, were evaluated from the slope and intercept of the plot of ln (q_e/_Ce) versus q_e (Fig. 9k). The maximum adsorption capacity of biocomposite in the removal of AMOX was the highest (36.10 mg/g); hence, Elovich model was not suitable for the adsorption of AMP with an R² of 0.1537 but was suitable for the adsorption of TC and AMOX whose R² are 1.0000 and 0.8379, respectively.

3.7.12. Flory-Huggins Model

The Flory-Huggins isotherm model was used to examine the degree of surface coverage characteristics of the TC, AMP, and AMOX on the surface of the biocomposite. The plot of

Table 10 presents the summary of the arrangements of the selected isotherm models based on the R². It can be deduced that the order of isotherm models for TC adsorption (in descending order) is as follows: Langmuir and Elovich > Freundlich and Halsey > Hill-DeBoer > Jovanovich > Flory Huggins > Kiselev > Temkin > Fowler Guggenheim > Dubinin R. > Harkin-Jura. For AMP adsorption, the isotherm models include (in descending order) Hill-DeBoer > Kiselev > Fowler Guggenheim > Dubinin R. > Freundlich and Halsey > Jovanovich > Langmuir > Harkin-Jura > Temkin > Elovich > Flory Huggins. Finally, for AMOX adsorption, the suitability of the isotherm models are as follows (in descending order): Dubinin R. > Freundlich and Halsey > Langmuir > Jovanovich > Harkin-Jura > Hill-DeBoer > Flory Huggins > Elovich > Temkin > Kiselev > Fowler Guggenheim.

4. Conclusion

This study revealed the effectiveness of a biocomposite made from PKS, CAS, and CS for removing TC, AMP, and AMOX from aqueous solutions. The study successfully used the mixture and simple centroid methods to produce the composite biosorbent, achieving maximum removal efficiencies of TC (86.61%), AMP (91.19%), and AMOX (71.13%) under optimal conditions of 55% PKS, 20% CAS, and 25% CS, respectively. Special quadratic and cubic models were generated for the adsorption of AMP and AMOX, respectively, while a special cubic model was generated for TC. The ANOVA results showed that the interaction between mixture CAS-CS in the bio-composite PKS-CAS-CS do not significantly affect the adsorption of TC, AMP, and AMOX, as their P values were higher than 0.05. The biocomposite PKS-CAS-CS demonstrated high adsorption capacities for TC, AMP, and AMOX, with values of 4.8 mg/g, 5.5 mg/g, and 4 mg/g, respectively, after a contact time of 120 minutes. Moreover, the adsorption capacity of the biosorbent on AMP was highest and became constant after approximately 30 minutes of contact time. Furthermore, the adsorption behavior of TC was well described by the Langmuir and Elovich isotherm models (with R² = 1.000), while the Dubinin R. and Hill-DeBoer models best described the equilibrium data for the adsorption of AMOX and AMP, respectively. Finally, this study found that biocomposite PKS-CAS-CS exhibits an excellent potential for removing TC, AMP, and AMOX from aqueous solutions.

Authors’ Contribution

Conceptualization: Abass O. Alade; Tinuade J. Afolabi.

Data curation: Ogundipe, S.Opawale; Ayobami O. Ajani.

Formal Analysis: Abass O. Alade; Idris O. Okeowo.

Funding acquisition: Tinuade J. Afolabi; Ogundipe S. Opawale.

Investigation: Ogondipe S. Opawale.

Methodology: Abass O. Alade; Adetoro R. Olaitan.

Project administration: Abass O. Alade; Latinwo G. Kayode.

Resources: BWERG, Laboratory, LAUTECH, Ogbomoso, Nigeria.

Software: Abass O. Alade; Ayobami O. Ajani.

Supervision: Abass O. Alade; Latinwo G. Kayode.

Validation: Abass o Alade; Idris O. Okeowo.

Visualization: Tinuade J. Afolabi; Latinwo G. Kayode.

Writing – original draft: Ogundipe S. Opeoluwa.

Writing – review & editing: Abass O. Alade; Idris O. Okewow

Competing Interests

The authors declare that they have no conflict of interests.

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