Chemical treatment of sugarcane bagasse and its influence on glyphosate adsorption

Tratamento químico de bagaço de cana-de-açúcar e sua influência na adsorção de glifosato

ABSTRACT

Due to the production rates of sugarcane, nowadays, the sugarcane bagasse stemming in the sugar and alcohol industry is the agro-industrial waste produced in greater volume throughout in Brazil. In 2019, about 192 million tons of this waste were generated. The use of this waste has been the aim of researches around the world, with emphasis on applications that aim to meet the prerogatives of the concept of circular economy. Within this scenario, sugarcane bagasse (SB) was treated in an alkaline medium, forming an adsorbent material, SB_NaOH. The effects of chemical treatment were evaluated for surface properties and for glyphosate removal in an aqueous medium. The adsorptive phenomenon was studied through isotherm tests. The results obtained were fitted to classical models of Langmuir, Freundlich and Dubinin-Radushkevich. The characterization indicated that the chemical treatment promoted an important change in the surface of the residue, increasing the surface area. SB and SB_NAOH had a feasible behavior as adsorbent and good performance in the removal of the herbicide, presenting values greater than 65% of under all working conditions. The theoretical adsorption saturation governed by Dubinin-Radushkevich (q_S) was in the order of 8.988 mg/g (R²=0.988) for SB at 120 minutes of contact and maximum adsorption capacity by Langmuir (Q_max) was 13.720 mg/g (R²=0.984) for SB_NaOH at 40 minutes of contact. The process was governed by the exchange or sharing of electrons. The adsorbate is distributed heterogeneously on the SB surface, justifying the presence of active sites with greater ionic strength, and homogeneously on the SB_NaOH surface (monolayer). In general, the treated sugarcane bagasse, coming from an agro-industrial residue, proved to be an alternative and promising biosorbent for the removal of glyphosate from aqueous systems, thus generating a new application of this residue.

Keywords
Biosorbent; Agro-industrial waste; Adsorption; Herbicide; Alkaline treatment

RESUMO

Em virtude dos índices de produção da cana-de-açúcar, o bagaço proveniente do processamento da cana na indústria sucroalcooleira é hoje o resíduo agroindustrial produzido em maior volume no Brasil. Em 2019 foram gerados cerca de 192 milhões de toneladas deste resíduo. A utilização deste resíduo tem sido alvo de pesquisas em todo o mundo, com destaque às aplicações que visam atender as prerrogativas do conceito de economia circular. Dentro desse cenário, o bagaço de cana-de açúcar (SB) foi tratado em meio alcalino, formando um material adsorvente, SB_NaOH. Os efeitos do tratamento químico foram avaliados quanto a propriedades de superfície e quanto a remoção do herbicida glifosato em meio aquoso. O fenômeno adsortivo foi estudado por meio de ensaios de isotermas. Os resultados obtidos foram ajustados aos modelos clássicos de Langmuir, Freundlich e Dubinin-Radushkevich, onde cada material adsorvente se encaixou em um modelo diferente. A caracterização indicou que o tratamento químico promoveu alteração importante na superfície do resíduo, ampliando a área superficial. SB e o SB_NaOH tiveram um comportamento favorável como adsorvente e boa performance na remoção do herbicida, apresentando valores maiores que 65% de em todas as condições de trabalho. A saturação teórica de adsorção regida por Dubinin-Radushkevich (q_S) foi na ordem de 8,988 mg/g (R²=0,988) para o SB aos 120 minutos de contato e capacidade máxima encontrada por Langmuir (Q_máx) foi de 13,720 mg/g (R²=0,984) para o SB_NaOH aos 40 minutos de contato. O processo foi governado por troca ou partilha de elétrons. O adsorvato se distribui de forma heterogênea na superfície SB, justificando a presença sítios ativos com maior força iônica, e homogeneamente sobre a superfície (monocamada) de SB_NaOH. Em geral, o bagaço de cana tratado, provindo de um resíduo agroindustrial, se mostrou um biosorvente alternativo e promissor para remoção de glifosato de sistemas aquosos, gerando assim uma nova aplicação deste resíduo.

Palavras-chave
Biosorvente; Resíduos agroindustriais; Adsorção; Herbicida; Tratamento alcalino

1. INTRODUCTION

The world population has been growing in an alarming number. According to the United Nations (UN) in 2024 the total number of people will be superior to 8 billion, and in 2050, more than 9 billion; those numbers show an increase of 13.16% from 2012 to 2024 and 34.90% from 2012 to 2050 [¹]. With the population growth, the demand for food, has been increasing and consequently the increase of world agricultural production. The intensive utilization of pesticides, fertilizers and genetic development of seeds, among other factors contributed to increase the world agricultural production [²]. Among the compounds that are more used in the agricultural field can highlight the herbicides, because eliminate plants that will compete with planted crops for nutrients [³]. Glyphosate (N-(phosphonomethyl)glycine) is the most widely used herbicide on earth with properties of a non-selective, systemic and emerging herbicide which its most important function is to control the growth of weeds and grasses [⁴].

Its application in large areas of cultivation and possible excessive use makes the glyphosate appear more between researches. Although it is considered non-toxic in the last few years it is preoccupying the whole world because of its direct and indirect possible effects on health [⁵]. The effect to the human body from this herbicide had been demonstrated in a temporary study (2001 to 2015) in adults who live in the northeast of Germany which showed the concentrations of glyphosate on its limit and beyond quantification limit in these people´s urine [⁶]. MARTÍNEZ et al. [⁷] reported alterations in neurotransmitters in mice brain after exposure to glyphosate. Meanwhile in zebrafish the glyphosate caused alteration in morphological and behavioral parameters [⁸]. Furthermore, the contamination in the air, soil and water for excessive use of pesticides become a constant concern in last years [⁹].

Due to high mobility of water bodies, it becomes the main concern since even when the herbicide is applied to the soil in large quantities, the contaminating residues are leached into groundwater sources [¹⁰]. This possibility of contaminants leaching makes the water available to the human, animal and plant population even more scarce. Unfortunately, about 1.2 billion people in the world do not have safe, potable and affordable water for their use, due their own activities including extensive use of pesticides, herbicides and, fertilizers [¹¹].

Once this contaminant reaches water bodies removal and remediation pathways such as coagulation [¹²], membrane filtration [¹³] and advanced oxidative processes (AOPs) [¹⁴, ¹⁵], are being studied. Among these, the adsorption process seems to be the most promising removal pathways of this contaminant [¹⁶, ¹⁷]. Because of the large amount produced, being non-toxic and low cost, agricultural residues such as fruit [¹⁸, ¹⁹], sawdust [²⁰], rice husks [²¹], coconut fibers [²², ²³] and sugarcane bagasse [²⁴- ²⁶], show as an alternative to this adsorption process.

Recently, the bagasse from the processing of the sugar-alcohol industry is the agricultural residue produced in a large volume in Brazil because of the high production of sugarcane (Saccharum officinarum) in the country. In 2019/2020 season were produced 642.7 tons of million of sugarcane [²⁷]. The quantities of sugarcane bagasse (SB) from this activity corresponds around 30% of the total cane crushed in the industry, generating large amount of residues [²⁸]. Being a lignocellulosic material in the form of biomass plant the sugarcane bagasse is constituted specially of cellulose (C₅H₁₀O₅), hemicellulose (C₅H₈O₄) and lignin (C₇H₁₀O₃) [²⁹, ³⁰]. Cellulose is rich in hydroxyl which allows the molecule to go through countless of chemical modifications making it interesting to the production of new materials and with different applications [³¹].

In function of the quantity produced, physical and chemical characteristics, such as environment and low cost the sugarcane bagasse has been studied in several areas including animal nutrition [³²], construction [³³] and biocomposites [³⁴]. Its versatility allows to be used as a biosorbent in the removal of water contaminants including dyes [³⁵, ³⁶], metal ions [³⁷], medicines [³⁸] and pesticides [³⁹]. Furthermore, researchers about biochar production from waste has demonstrated the removal of caffeine [⁴⁰], oxytetracycline [⁴¹] and copper [⁴²] an easier adsorption even though assigned process and consequently obtaining costs in the adsorbent. CUBA et al. [⁴³] used sugarcane bagasse in the biochar production to remove glyphosate demonstrating that the use of sugarcane bagasse as raw material to produce charcoal chemically activated shows that it is favorable to the formulation removal based on glyphosate.

Based on the above considerations, its notorious the relevance of waste used from clean source in the adsorption process for the water decontamination. Because of the low number of studies in relations to adsorption of pesticides in the sugarcane bagasse its potential to generate new materials and the exacerbated in the use of glyphosate in agriculture. The present study aims use the sugarcane bagasse treated and untreated as adsorbent material to glyphosate removal.

MATERIALS AND METHODS

Commercial active Roundup® Original DI herbicide glyphosate (N-(phosphonomethyl) glycine) was used for this study obtained in the local market. The sugarcane bagasse was donated from Usina Alto Alegre S/A sugar-alcohol industry located in Santo Inácio-Paraná- Brazil. Sodium hydroxide (99% purity; NaOH; Synth), Ninhydrin (99% purity; C₉H₆O₄; Chemical Dynamics) and sodium molybdate (99% purity; Na₂MoO₄.2H₂O; Synth). All chemicals were used as received.

2.1 Sugarcane bagasse fibers processing and treatment

For the removal of impurities in the sugarcane bagasse it was washed in running water during 48 hours and later on washed in deionized water. The fibers were dried in an oven at 60 °C for 72 h until the mass stabilized. Finally, the fibers were micronized and sieved to obtain particles between 0.15 and 0.11 mm (100 and 140 mesh). This process resulted in the sugarcane bagasse (SB).

The chemical treatment of the sugarcane bagasse fibers was carried out with the main purpose of removing the lignin and increasing cellulose access. For this procedure it used sodium hydroxide solution, 10% w/v (NaOH) and 50 g of sugarcane bagasse according to the methodology described by SANCHEZ et al. [⁴⁴]. Briefly, the waste was immersed in alkaline solution under agitation for 24 hours in room temperature (25ºC±2ºC). After this time, the fibers were removed from the solution and washed with deionized water until its pH neutralization. The resulting of the bagasse was dried in the oven for 5 hours at 100 ° C. The treated bagasse is called SB_NaOH.

2.2 Characterizatio

The determination of the point of zero charge (pH_pzc) was based on GIACOMNI et al. [⁴⁵], which it kept in contact 0.1 g of adsorbent with 10 mL of the aqueous solutions of 100 mg L^-1 of glyphosate with 11 different initial pH conditions (1 to 11). The pH_pzc of the samples were obtained when calculating the average between the final points of pH tended the same value.

The specific surface area was determined by Brunauer-Emmett-Teller (BET) analyses, using ASAP 2020 (196 ºC - 0 ºC), and pore volume and diameter were calculated using the Barrett-Johner-Halenda method (BJH). The morphology of fibers was determined using Scanning Electron Microscopy (SEM), the images were obtained in a Carls Zeiss microscope EVO-LS 15 model.

2.3 Herbicide Solution and Analysis

Using the methodology proposed by TZASKOS et al.[⁴⁶] calibration curve was prepared from a stock solution of 100 mg L^-1 of glyphosate. A volume of 1.5 mL of glyphosate solution with aliquots ranging from 0.5 to 10 mg L^-1 were transferred to glass vials and 1.5 mL of 5% ninhydrin and 1.5 mL of 5% of sodium molybdate were added to each of the vials. The vials were sealed and kept in a water bath in a temperature of 85-95° C for 12 minutes. Then the samples were cooled to room temperature (25ºC±2ºC) and were quantitatively transferred to volumetric flasks and added 8 mL of MilliQ water. Then the reading was performed by Spectrophotometer-1800, SHIMADZU spectrophotometer at 570 nm.

From this data was constructed a calibration curve with the absorbance as a function of glyphosate concentration in the range from 0.5 to 10 mg L^-1. For the baseline of the instrument 1,5 mL of ninhydrin and sodium molybdate solution was used, to a total volume of 4,5 mL. The coefficient od determination (R-squared) was 0.99589.

2.4 Adsorption tests

The pH study of adsorption tests was performed in which the value between the pH range analyzed those results in a larger glyphosate removal. To evaluate this effect the pH solution was adjusted in nine different conditions (2.0 to 10.0) with hydrochloric acid solution and/or NaOH at 0.5 M.

The kinetics adsorption studies were performed through the contact of 0.1g of the adsorbent to 10 mL of contaminated solution (glyphosate concentration of 100 mg L^-1) added in glass vials and agitated by a mechanical stirrer at room temperature (25ºC±2ºC) and a gap of 10 min to 24 hours and pH 5 and 9 to the SB and SB_NaOH, respectively. After the adsorption time the adsorbents were separated from the aqueous solutions by centrifugation at 4000 rpm for 30 min and so the supernatant was collected. Sequentially, the remain amount of glyphosate was analyzed with the quoted procedure before (item 2.3). All experiments were conducted in triplicates.

The amount of glyphosate adsorbed at equilibrium (q_e) was calculated by Equation (1).

$${\mathrm{q}}_{\mathrm{e}}=\frac{({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{f}})\mathrm{V}}{\mathrm{m}}$$ (1)

Where: q_e (mg g^-1) is the adsorption capacity at the equilibrium; C₀ (mg L^-1) corresponding the initial concentration of glyphosate in the solution, C_f (mg L^-1) the concentration of glyphosate at equilibrium, V (L) is the volume of the glyphosate solution and m (g) is the mass of the sugarcane bagasse.

2.5 Adsorption isotherms

For the adsorption of isotherm studies were utilized fixed amounts of adsorbents were used, 0.1 g for 10 mL of contaminated solution. The concentrations range were 5 - 10 - 20 - 30 - 40 - 50 - 60 - 80 and 100 mg L^-1, time of 2 hours at pH 6 to SB and 40 min at pH 9 to SB_NaOH. The glyphosate adsorption capacity (q_e) was calculated by Equation 1 and the removal percentage calculated by Equation 2.

$$\mathrm{\%}\text{Removal}=\left[\frac{{\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{F}}}{{\mathrm{C}}_0}\right]\ast 100$$ (2)

In order to describe the interactive behavior between the glyphosate and sugarcane bagasse, were calculated the adsorption balance through nonlinear models by LANGMUIR, FREUNDLICH [⁴⁷] and DUBININ-RADUSHKEVICH [⁴⁸], according with the Equation (3), (4) and (5), respectively.

$$q_e=Q_{max}\ast K_l\ast C_e/[1+(K_l\ast C_e)]$$ (3)

$${\mathrm{q}}_{\mathrm{e}}={\mathrm{K}}_{\mathrm{f}}\cdot {\mathrm{C}}_{\mathrm{e}}^{1/\mathrm{n}}$$ (4)

$${\mathrm{q}}_{\mathrm{e}}=\left({\mathrm{q}}_{\mathrm{s}}\right)\cdot \exp (-K_{\mathit{a}\mathit{d}}{\epsilon }^2)$$ (5)

Where: q_e (mg g-¹); is the amount of glyphosate adsorbed at equilibrium on the sugarcane bagasse; q_max (g.mg^-1) is the amount of glyphosate adsorbed at saturation; K_l (L g^-1) is the Langmuir adsorption equilibrium that represents surface affinity; C_e (mg L^-1) is the concentration of glyphosate in the liquid phase at equilibrium; K_f (mg g^-1); n is an empirical parameter (dimensionless) of Freundlich model, where n provides an indication whether the isotherm is favorable or unfavorable. For D-R isotherm, q_s indicate the theoretical isotherm saturation capacity (mg/g), K_ad is the constant related to the adsorption energy (mol² kJ^-2), and ε is the Dubinin–Radushkevich isotherm constant.

3. RESULTS AND DISCUSSION

The chemical treatment of the sugarcane bagasse surface with alkaline solution of sodium hydroxide it was possible the majority remove of lignin and the increased exposure to cellulose in consequent increase of roughness and surface area of material. This was observed by PAIVA et al. [³⁴] when those treated sugarcane bagasse with alkaline solution for composites production. The treatment of sugarcane bagasse with sodium hydroxide caused swelling in the fibers, increasing the interior surface of the cellulose causing the decrease of crystallinity that is necessary for the lignin breakdown [⁴⁹] explain the significant increase of the surface area and pore volume of the fibers treated as shown in Table 1.

Table 1
BET and BJH surface parameters of raw sugarcane bagasse (SB) and treated (SB_NaOH).

Samples	Surface Area (m² g-1)	Pore Volume (cm³ g-1)	Pore Size (Ᾰ)
SB	0.114	0.0018	620.3297
SBNaOH	0.411	0.0021	205.0075

It can be observed that a variation in the results of the surface area SB (0.114 m² g^-1) in the present study and one reported by MOUBARIK & NABIL [⁵⁰] (0.487 m² g^-1). This variation between the value of literature and this work can be considered not significant once these fibers properties can slightly vary because of the production factors, such as: planting conditions, seasonality factors, irrigation volumes like the way the plant is harvested.

The samples morphology was analyzed by SEM. The Figure 1 shows SB (a - b) and SB_NaOH (c-d). The SB images shows an ordered uniform and smooth structure which is associated with the presence of amorphous constituents such as lignin and hemicellulose, as well as wax and extracts as reported by LI et al. [⁵¹]. While in the SB_NaOH images the fibrils were exposed due to the effect of lignin removal that causes the fibrillation process indicating the disorganization in the cellulose structure, confirming the increase of roughness and structure surface area (Table 1) result corroborated by AGUIAR and LUCENA [⁵²]. However, the alkaline treatment promotes the release of new active sites thus allowing a better interaction between the bagasse and the contaminant.

Figure 1
Scanning electron microscopy images of SB (a) 100 X; b) 700 X; and SB_NaOH (c) 100 X; (d) 700 X.

Using the plot of final pH vs initial pH for the SB and SB_NaOH, it is possible evaluate the stabilization trend at a given pH, regardless of the initial conditions, which we call pH_PZC. The investigation in the adsorption efficiency of glyphosate in different pH`s such as the determination of the point of zero charge (pH_PZC) the adsorbents is justified because the adsorption process is dependent on the pH which affects the surface charge ionization level and adsorbate species [⁴⁵]. According Figure 2 the point of zero charge (pH_PZC) was obtained at pH 6.36 and pH 9.12, for SB and SB_NaOH, respectively.

Figure 2
pH at the point of zero charge (pH_pzc) of SB and SB_NaOH.

The adsorption study of the pH indicates what value between the analyzed pH range which results in greater glyphosate removal. According to pH_PZC, for SB_NaOH the optimum adsorption pH would be higher than for SB adsorbent reaching more active sites for adsorption. As observed in Figure 3 the pH value which showed a greater SB removal was the pH 5 approximately 67% while for SB_NaOH was the pH 9 with 86%.

Figure 3
Glyphosate removal percentage as a function of effect pH on the adsorption and dissociation onto SB and SB_NAOH.

Glyphosate belongs to the phosphonated amino acids group and like the precursor glycine can be separated in two charges being one positive in the amino group and one negative in the phosphonate group [⁵³]. In a pH < 2.6 the glyphosate shows a positive liquid charge, in a pH = 2.6 the glyphosate is neutral and the negative charges increase with pH > 2.6 [⁵⁴]. MAYAKADUWA et al. [⁵³] and ESSANDOH et al. [⁵⁵] reported that when the pH_pzc is lower than the pH of the solution the adsorbent surface will be negatively charged while when the pH_PZC is higher than the pH of the solution the adsorbent surface tends to be positively charged.

For the SB the pH_PZC is greater than the pH solution and the glyphosate molecule in the values of pH 5 (Figure 3) has a prevalence of negative charges, value similar to that used by CUBA et al. [⁴³] therefore in this case the removal occurs with the interaction of positive biosorbent charges and negative charges of glyphosate phosphonate group. For SB_NaOH the pH_PZC value is equal to the pH solution indicating the adsorbent matrix surface has the same amount of positive and negative charges being this way the adsorption occurs by a ligand exchange between the sugarcane bagasse hydroxyl treated with sodium hydroxide and glyphosate phosphonic portion of P-O- group similar reported by PICCOLO et al. [⁵⁶].

The percentual kinetic study of glyphosate removal in function to time was performed taking in consideration the pH values. Analyzing Figure 4 it is established that the kinetics process was fast for both adsorbents in 40 minutes happens 81.4% of removal to SB_NaOH while for the SB has showed a percentage of removal of 77.2% in the first two hours and the maximum removal of 77.9% in 24 hours.

Figure 4
% Glyphosate removal in function of adsorption time on SB and SB_NAOH (concentration of of 100 mg L^-1).

Observing the data can be noted a reduction in the glyphosate removal percentage after obtaining the maximum samples removal. Such fact can be explained because the bagasse has initially various empty places which were progressively filled until an equilibrium point was reached. When the amount of adsorption glyphosate increased like forces of repulsion between adsorbed molecules made more difficult the adsorption on the rest sites, reducing consequently the adsorption rate making it possible the desorption phenomenon that can occur in the biosorbent surface [⁵⁴].

The results in the application of nonlinear models of Langmuir, Freundlich and Dubinin-Radushkevich in the obtained experimental data are shown in Figure 5 (A and B), that shows glyphosate adsorbed at equilibrium (qe) as function of concentration of glyphosate in the liquid phase at equilibrium (Ce). The values of the calculated parameters are shown in Table 2.

Figure 5
Experimental and predicted adsorption isotherms for glyphosate for the Langmuir, Freundlich and Dubinin-Radushkevich non-linear models for (A) SB and (B) SB_NAOH.

Table 2
Freundlich and Langmuir isotherm parameters for glyphosate removal using SB and SB_NaOH.

	Langmuir				Freundlich				Dubinin- Radushkevich
Adsorbent	Qmax (mg/g)	KL (L/mg)	RL	R²	n	1/n	KF (mg/g)	R²	qs (mg/g)	Kad (mol2/kJ2)	R²
SB	7.628	0.011	0.759	0.981	13.259	0.075	8.353	0.982	8.988	11.013	0.988
SBNaOH	13.720	0.018	0.767	0.984	9.391	0.107	11.174	0.975	9.266	10.683	0.973

It is important to note that all isotherm models applied in that work had satisfactory behavior for both adsorbent materials, with similar adjustments for tested models when consider R². However, even with similar coefficient of determination, each type of adsorbent present better fits for different model.

The sugarcane bagasse adsorbent (SB) was adjusted for both models, the high R² values (Langmuir and Freundlich) and the n value (Freundlich) which was showed in Table 2 is greater than 1 indicating that the adsorption is favorable a result confirmed by K_L and the 1/N value is 0.075. NASCIMENTO et al. [⁴⁷] explained the as higher the n value is lower the 1/n value will be implying in a greater interaction between the glyphosate and the sugarcane bagasse. However, the Dubinin-Raduchkevich (D-R) fitted slightly better for those fibers. The D–R isotherm model was developed to account for the effect of the porous structure assuming that the adsorption process was related to micropore volume on the adsorbent walls [⁵⁷]. Which is in accordance with the SEM discussion, where the SB has amorphous part in its structure.

When analyzing the coefficients of determination (R²), the treated sugarcane bagasse (SB_NaOH) showed better fit in Langmuir isotherm, where the herbicide molecules are adsorbed in monolayer. That result corroborate with the experiments of ABREU et al. [⁵⁸] with sugarcane biochar for the adsorption of Cadmium (Cd), and CARVALHO et al. [⁵⁹] who studied orange peel biochar for tetracycline removal. Analyzing the SB_NaOH for the Langmuir model was noticed that the maximum adsorbed amount in the experiment (Table 2) was 13.720 mg.g^-1 while the R_L factor (separation factor at 100 mg.L^-1) was 0.767 mgL^-1 indicating that adsorption was favorable (0 <R_L <1) that is the adsorbate prefer the solid phase than the liquid [⁴⁷]. The fit in Langmuir model proposed that adsorption occurs by covering the monolayer of glyphosate molecules above surface of SB_NaOH that is each site is responsible by adsorption of only one molecule cannot to occurs additional adsorption [⁶⁰], further assuming that the adsorption takes with active sites of the adsorbent with equal affinity for the adsorbate in which interferences in the adsorption of neighboring sites are disregarded [⁵⁹].

4. CONCLUSIONS

The use of sugarcane bagasse (SB) and chemically treated sugarcane (SB_NaOH) showed as favorable to the glyphosate removal in the studied conditions being with pH 5 for SB and pH 9 for SB_NaOH at room temperature. SB adsorbent showed removal efficiency of 77% (q_S 8.988 mg g^-1) occurred in 2 hours with an adsorption plateau, fitting to all tested models (Langmuir, Freundlich and Dubinin-Radushkevich) with showed a similar coefficient of determination. However, the Dubinin-Radushkevich fitted better for those fibers due their amorphous and porous structure of lignin and hemicellulose compounds.

The SB_NaOH showed a similar behavior, with small difference between the R². This adsorbent present fast adsorption with 81% of removal in 40 min and maximum capacity of adsorption of 13.720 mg g^-1 (Q_max). In this case it occurred adjust for the Langmuir model, therefore the adsorption occurs by covering the monolayers of glyphosate molecules over the surface bagasse.

All factors involved in the study showed that the alkaline treatment in sugarcane bagasse and final glyphosate adsorption fulfill the proposed objective providing biosorbent with capacity of maximum removal higher than untreated material as well a smaller taken time for adsorption.

As shown in previous literature - mentioned in this work - the alkaline treatment for natural fibers has been shown to be very efficient and viable for different applications. In this case it was no different, the treatment proved to be efficient in improving the adsorbent material for herbicide removal. As it is a cheap alkaline, easy to handle, and with small amount of waste, this type of treatment has been feasible in terms of cost/benefit.

Therefore, presenting a possibility alkaline treatment to increase efficiency in the lignocellulosic fibers such as aqueous solutions decontamination agents. Hence, the perspectives for this material and its future application in the industry are very favorable, however more evaluations such as the effect of temperature and recyclability must be carried out.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the financial support from “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior” (CAPES - Brazil) - Finance Code 001 and “Conselho Nacional de Desenvolvimento Científico e Tecnológico” (CNPq). The authors also thank “LabMMEV- FCT/UNESP” by microscopy images.

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Publication Dates

• Publication in this collection
  13 May 2022
• Date of issue
  2022

History

• Received
  11 Feb 2021
• Accepted
  19 Sept 2021