Use of low-cost adsorbent derived from the brazilian cerrado biome to remove pollutants in effluent

The biochar of the Pequi peel represents a sustainable alternative in the process of treating effluents through adsorption system. This study investigates the adsorption capacity in a fixed bed column of the activated biochar from pequi peel (ABPP) to remove the components. The biochar was obtained by pyrolysis, which was activated with zinc Chloride ZnCl2. Through the Thomas model, it was found that the concentration of Paracetamol of 5 mg L obtained 3.21 mg g of drug adsorption, which was higher than the adsorption obtained with the concentrations of 10 mg L (3.02 mg g) and 20 mg L (1.22 mg g). Methylene blue was tested with a concentration of 3 mg L, adsorbing 8.07 mg g. The data fit the Thomas model with an R2 higher than 0.90. The capacity of ABPP to adsorb methylene blue and Paracetamol was satisfactory, with adsorbing significant.


Introduction
Over the years, the contamination of water resources through to the inadequate disposal of pollutants has brought global concerns, mainly due to the environmental and public health impacts Cvitanovic & Hobday, (2018); Moino et al., (2017). Sustainable environmental management has an objective of the United Nations agenda 2030, for reuse of waste to technological innovation and, besides, to the solution of environmental problems Lee et al. (2016).
The high concentration of theses pollutants in wastewater, demonstrated the commonly used on a large scale, showing the growth of the pharmaceutical industry due to the wide accessibility to medicines allied to the offer of medical treatments (Bisognin et al., 2018;Ribas et al., 2021).
Paracetamol (N -acetyl-4-aminophenol), it is an analgesic and antipyretic normally used and can be easily identified in aquatic environments. The order of 58-90% of the ingested Paracetamol are not metabolized, and are expelled by the human body (Sellaoui et al., 2017). From the point of view of sustainability, the recovery of Paracetamol in wastewater contributes to the recycling of essential non-renewable resources and to the protection of natural water against pollution by drugs (Cao et al., 2020).
Trace levels (ng L-1 to μg L-1) of drugs, has great resistance to biological and physical-chemical degradation , pointing the weakness in the wastewater treatment system (Gurke et al., 2015).
Another pollutant that is identified in effluents is methylene blue (3,7-bis-dimethylaminophenothiazin-5-a chloride), a cationic dye that is used mainly in the textile industry for coloringcotton, paper, hair dyes and others. The wastewater from the process of textile industry has about 8-20% of dye, with 3-5% being chemical substances pour out in large quantities in water bodies. The investigation the removal of dye in effluents is essential, due to its strong adsorption on solid supports and toxicity.
When the water waste is untreated, the dye interferes with the photosynthetic activity of the aquatic environment and the transparency of the water, inducing changes in water ecosystem Jorge et al., 2021;Pin et al., 2021).
The use of activated carbon in the adsorption process is efficient (99.8%) for removing these pollutants, due to the adsorption power of the biochar where captures and traps the contaminants (Marcelino et al., 2020;Martins et al., 2020).
Biochar are carbon-abundant materials, produced under high and low temperature in the absence of oxygen by the pyrolysis process (Bhuvaneshwari et al., 2019). Renewable biomasses have been widely researched as a raw material for obtaining biochar (Borba et al., 2019;Dong et al., 2020;Gwenzi et al., 2020;Pozo et al., 2021;Patra et al., 2021;Olu-Owolabi et al., 2021) and as a filter for pollutants.
In the search for sustainable alternatives, the pequi peel (Caryocar brasilienses) came as an alternative for obtaining activated carbon. However, most of the times the pequi peel are discarded, generating tons of residues (Moura et al., 2013;Borges et al., 2020). Thus, pequi may represent a relevant source of income in the Brazilian cerrado (Basílio et al., 2020;Miranda et al., 2020).

Methodology
According to Peres et al., (2018) the methodology of this work was quantitative, as numerical data were collected, processed and boosted, generating results. All tests in this study were performed in the laboratory.

Biomass Preparation
The biomass used was fresh pequi peel (Caryocar brasiliense). All residues used in the tests were collected in public areas in Palmas -TO in September/2020. Pequi fruits were pulped and the peels were dried at 60 °C in an oven for 24 hours in the Innovation and Innovation and use of waste and energy sustainability laboratory (LARSEN) at the Federal Institute of Tocantins, Palmas -TO.

Crushing
In order to obtain homogeneity of the biomass to facilitate the analytical tests, the samples were crushed in a knife milland were sieved (180 -850 μm) and stored in airtight glass.

Briquette Production
Briquettes were made using fresh biomass, oven dried and milled. Was added 70 ml of distilled water in 300 g of biomass for hydration occurred for 30 minutes. Then, the hydrated biomass was pressed into a 20 cm long and 32 mm diameter pipe. The finished briquettes were dried in an oven at 50 °C for 24 hours. The productivity of the briquettes was 4 units for each batch.

Pyrolysis Process
Pyrolysis occurred using a tubular fixed-bed quartz reactor, 10 cm in external diameter and 100 cm in length. The briquette (20 cm long and 20 mm in diameter) of the pequi peel was inserted into the reactor in batch mode. Was used water vapor as carrier gas. At the end of the reactor, a condensing system composed of a Friedrich-type condenser, a vacuum flask, two tubes and a 20 L water tank for cooling the condenser was coupled. With the passage of the vapor it was possible to separate the biogas from the liquid products (bio-oil and acid extract), which are retained in the vacuum flask.
The heating of the reactor was through a reclining oven. To monitor the temperature, a thermocouple was connected to the reactor. The temperature was 500 °C, with a heating rate of 20 °C and the reaction time was 30 minutes. At the end of the process, the biochar was collected, crushed and sieved (180-850 μm).

Surface Area Analysis by Brunauer, Emmett and Teller -BET method
The surface area system and porosimetry (ASAP 2010 micro-merit model) established the N2-BET surface area and the pore size arrangement. The diameter range used as standard was 0.35 to 300 nm for the pores and 0.01 to 3000 m²g-1 in the surface area range, the treatment temperature was 30 to 350 °C.

Biochar Activation
The activation process followed the methodology proposed by Costa et al., (2015) The solution was prepared by adding zinc chloride -ZnCl2 (Merck) with a concentration of 10% m/v, in the proportion 1:5 (m/v). The container with the solution was covered with parafilm for 24 hours. Then, the samples were washed with distilled water and dried in an oven at 110 ± 5 °C for 12 hours.
The dry biochar was inserted in a cordierite crucible, closed with rockwool and cordierite plate, and again taken to the muffle to be pyrolyzed at 600 ± 5 °C, for 2 hours. Subsequently, the hydrochloric acid solution -HCl (Merck), at 2 mol L-1 was used to remove and unclog the pores. To finish the process, the biochar was again dried in an oven at 110 ± 5 °C for 24 hours, thus obtaining the ABPP.

Adsorption Tests
In this study, two adsorption systems were carried out: testing the adsorption of methylene blue dye and of Paracetamol and adding two grams of activated biochar.

Fixed bed column adsorption
The fixed bed column adsorption system consists of the circulation of the effluent to be treated, where the effluent control of the concentration is performed to determine the breakthrough curve (Ortiz et al., 2019).
The fixed bed adsorption study in this work was carried out in a system consisting of a tank containing the solution with the pollutants (Methylene blue and Paracetamol), a peristaltic pump for the flow control, a column with effluent with the pollutants and a filter coupled to this column containing the ABPP. The effluent contained in the tank was taken to the fixed bed column by the pump. In the column, the effluent was treated in a downward flow using a filter with biochar, and the flow control of the effluent that passed through the filter was done manually by a tap.

Methylene blue adsorption
The adsorption of the effluent was carried out in a downward filter, using ABPP. The continuous flow test was carried out, and the dye solution contained a concentration of 3 mg L-1 and pH 6.6.
The filtration system consisted of: lower tank of 50 L, upper tank of 10 L with drain system and filter systems in series of sand and biochar. The dye was transported to the upper tank using a submerged pump attached to the lower tank. To maintain the volume of the liquid and minimize variations in the flow of the liquid during filtration, a drain system was used.
The transport of liquids in the upper tank was carried out by three pipes: feeding from the lower tank, drain to the lower tank and filter feeding, it was done by gravity. The dimensions of the filters were: total height of the pipe 40 cm, height of the biochar and sand in the pipe, 11 cm, diameter of the pipe 2.0 cm. In each batch of tests, about 3g of ABPP was inserted into the filter.

Adsorption of Paracetamol
The Paracetamol test was performed on a fixed bed column, with continuous flow, using the pollutant solution in concentrations of 5, 10 and 20 mg L-1 with the following values of pH 7.2, 7.4 and 7.1 respectively. The filtration system consists of a tank of 10 L in volume and 1 m in height, containing a biochar filter and sand, using 3 grams of ABPP. The filter was filled up by gravity.
The pollutant adsorption was measured using a spectrophotometer (DR6000 UV/VIS), at wavelength of 250 nm, with a calibration curve.

Thomas model
The Thomas model (Thomas, 1944) is applied to express the performance of the adsorption process in a fixed bed column, being indicated fo favorable and/or unfavorable conditions of adsorption. It is common to apply this model to determine the maximum adsorption capacity of the adsorbent in continuous systems. With the Thomas model (Eq. 1) it is possible to determine the adsorption . Where takes into account the physical properties of the adsorbent and adsorbate, in addition, the temperature and pressure of the systems must be constant and the external resistance to mass transfer and axial and radical dispersion are considered negligible in the column (Moino et al., 2017). For the work tests, Thomas's formula was linearized. The data were expressed in: ln of C0/C versus volume (V). Thus, equation 1 is transformed into Eq. 2. Research, Society and Development, v. 10, n. 13, e58101321154, 2021 (CC BY 4.

Characterization of biochar from pequi peel
In our previous studies, Brito et al., (2020), the activated biochar of the pequi peel was characterized and the results are shown in Table 1. Through Table 1, we can observe the characterization of the Pequi bark. One of the axes of this research is the production of biochar, and we must consider: Fixed carbon, Carbon, Higher heating value, BET surface area (m²/g) and Size micropores (cm³ g-1) which demonstrate the quality of the biochar.
The low moisture content found was a satisfactory result for the adsorption process. Since high moisture content influences on the quality of the biochar and consequently on application as an adsorbent, reducing the efficiency of pyrolysis and decomposing oxygenated compounds. Furthermore, the moisture ratio is inversely proportional to HHV, the lower the moisture the better the HHV and the greater the adsorption capacity of the biochar (Pedroza et al., 2014).
In the adsorption system, the pH interferes with the distribution of chemical species and electrical loads. The pH effect determines how surface charges of the adsorbent interact with the treated effluent solution. It is important to know that, the pH value depends on the composition and surface characteristics of the biomass, depending on the pH range, where the electrical loads on the surface of the adsorbent are zero, the so-called zero electrical load point . The acid pH of ABPP is 4.71 when interacting with the heated solutions of the pollutants methylene blue (3 -6.6 mg L-1) and Paracetamol (5 -7.2 mg L-1; 10 -7.4 mg L-1; and 20 -7.1 mg L-1) which have a neutral features, increase the adsorption process, as the attraction of negative charges present in ABPP and positive charges in aqueous solutions contribute to the attraction process between adsorbent and adsorbate.
The biomass fraction does not have volatile material, called fixed carbon, is the most resistant fraction that remains in the biochar after the pyrolytic process (Veiga et al., 2017). The low H/C and O/C ratios demonstrate the presence of aromatic structures and carbon stability, contributing to better adsorbent efficiency (Gascó et al., 2018).
The surface area and pore volume are relevant characteristics in the adsorption process. As they are involved in the transport of molecules and nutrients, if the surface area are larger, greater the material's ability to adsorb pollutants. On the other hand, micropores, increase the hydrodynamics and aeration of the adsorbent/pollutant ratio (Ferraro et al., 2021).

The breakthrough curves of Methylene Blue and Paracetamol
To demonstrate the behavior of the pollutant, breakthrough curve tests were performed (Figure 1.). Research, Society and Development, v. 10, n. 13, e58101321154, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21154 8 The curupture curve demonstrates the relationship of final concentration (C) and concentration (C0) with respect to time. The so-called breakdown occurs when the C / C0 ratio reaches 1, the longer it takes, the better the efficiency of the coal in removing pollutants.
Regarding the breakthrough curve, it is important to note that it demonstrates how the movement of the transfer mass occurs in the bed, so the breakthrough time is the time for the concentration of the effluent to reach 10% of the initial concentration. [ (Gabelman A, 2017)]. According to Figure 1a, the increase in the C/C0 concentration of methylene blue, shows the time decreases. That the breakthrough time is faster as the concentration is high. This phenomenon occurs because it has more adsorbate available in the solution when the concentration is higher, saturating the pores of the adsorbents in a shorter time. This same behavior was portrayed by Andrade et al., (2017)  Regarding the equilibrium time, results of this research 750 min (5 mg L -1 ), 720 (10 mg L -1 ), 810 min (20 mg L -1 ), were superior to some studies (Nourmoradi et al., 2018;, demonstrating that it can be a good aspect, since the longer it takes the biochar to reach the equilibrium point, the longer it will be adsorbing, due to the removal of the pollutant.  Biochar efficiency is related to the time it takes to saturate. Thus, the longer the biochar is operating with high removal rates, the more efficient it will be in removing pollutants.

Biochar's efficiency in removing pollutants
In the first 3.3 hours of operation, at average flow rate of 1.7 mL min -1 , the filter achieved 100% detention. Then the flow rate was increased and maintained at 5 mL min -1 , in this phase there was a decay of efficiency due to the saturation of the biochar. The lowest rate of removal from the system was 12.5% with 26 hours of operation. Regarding the system with effluent of 5 mg L -1 , the filter showed 90% detention in the first 30 min of operation. The detention remained above 70% with an average flow rate of 2 mL min -1 . After 8.5 hours of operation, the decay of efficiency was 55%, occurs constantly due to the proximity of the saturation of the biochar. In this batch, the lowest efficiency was 9% at 12 hours with an average flow rate of 2 mL min -1 .
In the 10 mg L -1 system, the best detention was 88%, which was maintained in the first 100 min of operation with an average flow rate of 1.4 mL min -1 . Then the detention decreases constantly, up to 4.8% less than that of 12.5 hours of operation with an average flow rate of 1.4 mL min -1 . Research, Society andDevelopment, v. 10, n. 13, e58101321154, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21154 10 During the operation of the system with a concentration of 20 mg L -1 , the maximum detection of 67.8% was less than the filters tested previously. The average flow rate 2.2 mL min -1 of this system was higher than the others, reducing the removal efficiency. A detention rate greater than 60% was constant during the first 120 min of operation of the system, then the removal decreased, reaching 2.17% at 7 hours, with an average flow rate of 2.2 mL min -1 . Rodrigues et al., (2019), when researching the efficiency of the green coconut endocarp biochar in removing caffeine in a system with 30 mg L -1 , obtained only 17% of efficiency, that is, detention lower than those identified in this research.
In their study of adsorption of Paracetamol with commercial activated biochar, Haro et al., (2021), obtained 95% removal for 120 min with a concentration of 5 g L -1 , a result close to that obtained in the present study. In their investigation on the potential of adsorption of the grape stalk biochar on Paracetamol (20 mg L -1 ), Villaescusa et al., (2011) obtained a removal of 30%, a percentage lower than that identified in this work when comparing the concentration of the pollutant.
The best detention occurred in the system with the lower concentration of 5 mg L -1 with 90% removal efficiency, a similar result to that found by Gupta and Nain (2019). This occurs because of the solute-adsorbent interactions, which at lower concentrations are stronger than the higher concentrations. This behavior is observed in discontinuous systems due to the balance between the adsorbate retained in the adsorbent and the solute in solution .

Adsorption rate of biochar
The literature (Table 2) is a tricky point, due to the variables chosen both for the synthesis of materials and for the removal tests, which differ from one study to another. Research, Society andDevelopment, v. 10, n. 13, e58101321154, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21154 Table 2 shows a comparison of the adsorption capacity of the biochar of this study with the literature. Other biochars from similar biomasses are compared to the results of this research. Table 2 presents data from the literature on adsorption of methylene blue and paracetamol in different biomasses and concentrations. It is possible to see that the ABPP obtained high adsorption compared to the other authors. Lima et al., (2018) investigated the application of Timbaúvas bark biochar to adsorb methylene blue using a concentration of 3 mg L -1 and obtained an adsorption (1.2 mg g -1 ) lower than this study (4.77 mg g -1 ). The Peel Pineapple and Timbaúva Bark biochar obtained lower adsorption values at higher concentrations of methylene blue than the used in this study.
It is important to highlight that Paracetamol has high hydrophilicity, which hinders its retention with the adsorbent Ferchichi & Dhaouadi (2016), demonstrating that it is not easily removed by the tested biochar. The adsorption capacity of Pineapple peel in the case of Paracetamol is close to the literature. The best condition obtained in this research was with a concentration of 5 mg L -1 , adsorbing 3.08 mg g -1 . Some works, García-Mateos et al., (2015), Ferreira et al., (2018), Lima et al., (2019), demonstrated higher adsorption rates when compared to the present study. The molecular structure of Paracetamol (C8H9NO2) has an aromatic ring and double bonds; if the drug is not well diluted and well homogenized, there is the possibility of electrostatic attraction between the double bond O and OH, which may form Paracetamol agglomerate, which will increase the size of the molecule, making it difficult for the biochar to adsorbate. Nascimento et al., (2020) said that high concentrations of solute affect the efficiency of removal of the pollutant by biochar.
Another characteristic in this study is the low content of adsorption of 2.81 mg g -1 in the concentration of 20 mg L -1 .
This low removal of Paracetamol when compared to the other concentrations can be justified by the preferential routes taken by the pollutant in the filter during the adsorption process. This means that the effluent was probably treated by only one region of the filter, limiting its potential for adsorption of ABPP .
The direction of the fixed bed column in which the adsorption tests were carried out in this study was downward, this contributed to the establish the preferential paths. The operation of the column in a fixed bed, when carried out in a downward flow, can cause the compactation of the bed, resulting to system loss and the creating preferential paths, reducing the efficiency of the biochar in the treatment of the effluent from the adsorption process (Schmal M, 2014).

Thomas Model
The Thomas model assumes that in the fixed bed adsorption system the flow is continuous, and the adsorption follows the Langmuir isotherm, disregarding the radial and/or axial dispersion and admits second order reversible kinetics (Thomas HC, 1944). Thomas' model demonstrates how the data from adsorption systems fit the model. The closer to 1 the value of R², the better the fit of the data.
The determination coefficient (R²) was used as a parameter to verify which of the concentrations best adapted to the Thomas model (Figure3). According to Nascimento et al., (2020) the R² is the most used parameter to identify the efficiency of the adjustment of the theoretical model referring to the data system (adsorption system). Concentrations of 10 and 20 mgL -1 of Paracetamol obtained R² closer to 1, that is to say that the data of these systems adapted to the Thomas Model more efficiently than the others. Franco et al., (2018), when studying the use of commercial biochar for the removal of Paracetamol, using the Thomas model, obtained R² of 0.83, a value well below that obtained in this research. Figure 3 shows the Thomas model. Figures 3c and 3d shows the adsorption systems that best adapted the modelling of the Thomas model, being higher R² values than the other concentrations.

Conclusion
Activated biochar of pequi peel was applied in a fixed bed adsorption system, in two pollutants that establish largescale impacts on the environment, mainly in water bodies. Regarding Paracetamol, the effluent tested at a concentration of 5 mg L -1 obtained 90% removal of the drug and 3.08 mg g -1 of adsorption, presenting itself as the best option. Regarding methylene blue, 100% dye removal and 4.47 mg g -1 of adsorption were obtained. The R² values in all systems were greater Research, Society andDevelopment, v. 10, n. 13, e58101321154, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21154 13 than 0.95, demonstration the efficiency of the data modelling (Thomas model), the 10 and 20 mg L -1 solutions of Paracetamol were the ones that presented the best fit for the model.
The use of this biomass prevents the waste from being inadequate discarded resulting environmental impacts. The utilization through the biochar managed to adsorb significant amounts of drug and dye present in the water.
The possibility of applying pequi peel, in segments of effluent treatment and biorefinery, has great potential for economic return to extractivists. In future research, research on acidic substances in the biochar activation process can be verified in order to improve the efficiency of pollutant removal. In addition to Methylene Blue and Paracetamol, other drugs from the group of antibiotics and analgesics can be verified in the biochar adsorption process from this biomass