Abstract
The decolorization of reactive yellow 145 from wastewater in batch mode of operation using groundnut shell-based biochar was studied in the present research. The adsorption process was studied by investigating the effects of different adsorption variables such as temperature, initial dye concentration, pH, and biochar dosage. The results showed that biochar dosage had a substantial impact on dye absorption potential. The equilibrium biochar dosage was determined to be 1 g/L, with an absorption capacity of 7.33 mg/g. The effect of pH was examined by varying between 2.0 and 5.0, and equilibrium pH was obtained at pH 2.0. The effect of temperature was examined by varying temperature ranges from 30 to 45°C, and the optimum condition was identified as 35°C. The characteristics of biochar were studied using analytical instruments, and results concluded that dye sorption onto biochar resulted in variation of biochar. Desorption studies were carried out to evaluate the biochar potential by examining various elutants and altering the solid to liquid ratio. Groundnut shell-generated biochar was reported to remediate dye-bearing Remazol wastewater with a removal effectiveness of about 62% based on the experimental data.
1. Introduction
Water consumption has increased dramatically due to the growth of the global population and industrialization. Several pollutants from industries are released in large quantities into rivers and streams, causing water quality to deteriorate and the aquatic ecology to be disturbed [1]. In recent years, water pollution was considered as one of the global challenges that have increased vigorously. This water pollution is caused due to pollutants that are emerging from the industries during the manufacturing and processing of raw materials. For instance, tannery industries, distillery industries, brewery industries, dairy industries, and slaughterhouses are consuming an enormous amount of water daily for industrial activities. The utilization of this water for processing resulted from an increase in toxic pollutants in the water, and it is discharged to the environment without proper treatment. There are several rules and regulations proposed at the national and international levels to control water pollution in recent years. But still, water pollutant level was not decreased, and this may be the nonavailability of proper low-cost treatment methods. Colouring is one of the key pollutants that causes extreme surface pollution, which is due to the usage of dyes in the majority of industries. Dyes differ from one another and are often categorized as synthetic dyes and natural dyes [2]. The synthetic dyes are obtained from chemical methods. Dyes commonly released by industries were a major contributor to the degradation of water quality [3]. The techniques and methods available in modern days are not sufficient to treat these large volumes of dye-bearing wastewater [4]. In India, sewage treatment capacity is less than the volume of wastewater generated in major cities [5]. Dye-containing effluent from industry is discharged directly into surrounding water sources without treatment. This excessive dye usage often results in a large amount of dye waste. The majority of the dye-contaminated effluents are carcinogenic and nonbiodegradable [6]. When dye-bearing effluent is discharged into freshwater, it has serious effects on public health.
Dyes can be harmful to one’s health, causing respiratory problems, allergies, and even kidney and liver cancer [7]. Therefore, it is necessary to eliminate these toxic materials from wastewater. Ion exchange, adsorption, oxidation, ozonation, and membrane filtering are some of the ways of removing dyes from wastewaters [8]. In addition to this, there is the biological process called bioremediation, which involves the treatment of dye with biological materials. In the biological method of treatment, biomaterials collected from nature were transformed into biochar under specific conditions such as temperature for successful dye remediation [9]. A carbon-rich compound called biochar is prepared by the thermal decomposition of organic molecules in the absence of oxygen. This method is called pyrolysis. Since it is a carbon-rich material, its efficiency is high in treating dye-bearing wastewater. This method has become very attractive in industrial wastewater remediation as they are eco-friendly [10]. Biochar has a variety of properties, including many pores, pore size, and functional groups. Because of these properties, biochar is an effective substance for the decolorization of hazardous contaminants in wastewater. Remazol dye, when combined with various reactive groups, produces azo-based chromophores [11]. Around 50% of Remazol dyes may be lost in the water used for washing during fiber dyeing [12]. The typical activated sludge treatment system is only capable of removing 10% of total Remazol dyes in wastewater [13]. Hence, new and practical techniques for the effective remediation of dye-bearing wastewaters are required. The proposed objective of the current investigation is to decolorize the reactive yellow 145 from the aqueous solution using biosorbent. Biochar was prepared from agricultural waste biomass of groundnut shells. This research will result in a concept called waste to energy. India is an agricultural country with a variety of crops grown every year. Globally, India stands second in the overall production of groundnut with an average production of 68 lakh tonnes of groundnut. One of the major disadvantages of this groundnut is during processing, it will result in the generation of a huge quantity of waste biomass in the form of groundnut shell. Biochar production from this waste biomass will result in a concept called waste to energy.
2. Materials and Methods
2.1. Dye and Other Chemicals
In this study, the reactive yellow 145 (RY145) was used (Figure 1), which has an empirical formula of C28H20ClN9Na4O16S5, a molecular weight of 1026.25 g/mol, and a wavelength of 597 nm. All the chemicals and the dye used were purchased from Sigma-Aldrich (India).
2.2. Agrowastes and Biochar Preparation
Agrowastes produced from groundnut shells were used in the current study. All raw materials were collected from local areas (Rajam, Andhra Pradesh, India). The raw materials were segregated and cleaned in deionized water and were naturally dried for 24 hours. This sun-dried raw material was ground into a fine powder and followed by sieving to obtain uniform particles of size 75 mm. A particular amount of raw material (sun-dried) was used and covered with aluminum foil and heated at 400°C in an electrical muffle furnace (make: ANTSLD) for 120 minutes. Because there is no oxygen in the muffle furnace, the sample undergoes pyrolysis, which converts it to biochar. The furnace was allowed to cool to normal operating conditions once the pyrolysis was completed, and the crucible was removed from the furnace [14].
2.3. Batch Experiments
These studies were conducted to attain the greatest dye sorption capacity of the biochar. A fixed amount of biochar (control: 1 g/L) was taken in a conical flask of 250 mL which contains 100 mL dye at a well-known concentration (control: 5 mg/L). These samples are then placed in the orbital shaker, which is set to run at 200 rpm for 6 hours. The suspension was then carefully transferred into vials and centrifuged for 25 minutes at 2600 rpm. Following the completion of the centrifuge, the samples were carefully removed without creating any disturbance. The top layer of liquid is then transferred to another set of vials for spectrometer readings. The dye concentration in the collected supernatant was analyzed at a wavelength of 597 nm in a spectrophotometer (Shimadzu UV-1800)[15].
2.3.1. Influence of Biochar Dose on RY145 Removal
The biochar dosage was varied between 0.5, 1, 2, 4, 6, 8, and 10 g/L. These trials were conducted at a constant pH (2.0), temperature (350°C), and initial concentration (15 ppm).
2.3.2. Influence of Equilibrium pH on RY145 Removal
The pH was varied from 2.0 to 5.0. The trials were performed at fixed biochar dosage (1 g/L), temperature (35°C), and initial concentration (15 ppm).
2.3.3. Influence of Initial RY145 Concentration
Isotherm experiments were conducted to determine the maximum possible dye uptake of biochar. The dye concentrations are varied as 5, 10, 15, 25, 50, and 100 ppm. The trials were performed at fixed pH (2.0), temperature (35°C), and biochar dosage (1 g/L).
2.3.4. Influence of Temperature on RY145 Removal
The temperature values were varied from 30 to 45°C. The experiments were conducted at fixed biochar dosage (1 g/L), initial concentration (15 ppm), and solution pH (2.0).
2.4. Biochar Characterization
Analytical methods were used to analyze the characteristics of the biochar. A thermogravimetric analyzer (TG-DSC/NETZSCHSTA 449 F3 Jupiter) was utilized to determine the material’s thermal stability. The Scanning Electron Microscope (FEIQuantaFEG200F) was used to analyze the biochar surface which was highly significant in the molecular adsorption of dye using the pores present on the surface. Fourier Transform Infrared Spectroscopy (Bruker-FTIR/ATR) was utilized to evaluate functional groups because functional groups in biochar lead to maximum sorption of dye molecules.
2.5. Desorption Studies
The potential of biochar in successive adsorption and desorption was studied by conduction batch desorption experiments. Elutants, namely sodium hydroxide, sodium carbonate, ammonium hydroxide, hydrochloric acid, methanol, and EDTA were used. A solid-to-liquid (S/L) ratio was also investigated to analyze the optimum use of elutants. Furthermore, regeneration experiments were conducted to conclude the number of cycles that a sorbent may be efficiently used for adsorption[16].
3. Results and Discussion
3.1. Biochar Characterization
The effect of temperature on the materials’ thermal stability using a thermogravimetric analyzer was investigated. The thermal stability of a material is important in the production of biochar[17]. The results concluded that an increase in temperature reduced the weight of the biomaterials. It was observed that a total weight loss of around 74.63% was lost at a temperature of 699°C. The thermal decomposition of the groundnut shell was divided into three zones. The first decomposition occurred between 0 and 100°C and resulted in a total weight loss of 5.65% due to the presence of moisture content. Between 100 and 350°C, the second active disintegration zone occurred, resulting in a total weight loss of 41.29%. It was clear that the maximum decomposition occurred in the second stage is due to the partial degradation presence of cellulose, lignin, and hemicellulose content of the groundnut shell, and total moisture content had been escaped [18]. The final decomposition stage occurred between 350 and 500°C, with a weight loss of 30.33% and a subsequent increase in temperature resulting in mass sample content. As a result, a peak curve was achieved at a temperature of 451.5°C and it is close to the pyrolysis temperature of 450°C that was chosen for biochar production.
Scanning electron micrographs for the raw groundnut shell biochar before and after adsorption of reactive dye are shown in Figure 2. It was clear from the observations that the raw biochar had numerous pores and enhanced binding sites. These biochar properties may favor dye molecule adsorption on the surface of biochar [19]. Figure 2 illustrated that the biochar surface becomes smooth after adsorption, indicating sorption of dye molecule by biochar.
The FTIR spectra of the raw biochar and dye-adsorbed biochar are summarized in Table 1. From Table 1, it was clear that the biochar has complex characteristics. This complex nature increases the dye molecules’ adsorption among different functional groups [20]. From the results, it is concluded that biochar is composed of primary alcohols, alkanes, and alkyl groups. It is also observed that after the adsorption of the dye molecules, there are major shifts in the FTIR spectra indicating that dyes and functional groups were bonded together.
3.2. Effect of Biochar Dosage on RY145 Removal
The dosage of biochar was varied as 0.5, 1, 2, 4, 6, 8, and 10 g/L. During these experiments, pH was kept constant at 2.0, the temperature was kept constant at 35°C, and the initial concentration of the dye was kept constant at 15 ppm, respectively. Figure 3 presents the sorption uptake of biochar towards RY145. The absorption capacity of biochar was found to decrease as the dosage was increased. By enhancing the dosage of biochar from 0.5 to 10 g/L, it was observed that the uptake capacity of RY145 by biochar decreased from 9.60 to 0.93 mg/g. The high absorption capacity is acquired at a low dosage due to fewer binding sites compared to excess dye concentration. The functional groups of biochar were utilized as a result of this condition, resulting in high uptake [21]. From Figure 3, it was found that % dye removal increases with the surge in the concentration of biochar. The removal efficiency of biochar towards RY145 increased from 32 to 62%. Higher sorption absorption was observed at higher dosages, which may be due to the enormous availability of surface area of biochar[22]. Taking into account all of the factors, the biochar dosage of 1 g/L was considered optimum.
3.3. Effect of Equilibrium pH on RY145 Removal
The pH was altered as 2.0, 2.5, 3, 3.5, 4, 4.5, 5.0.During these experiments biochar dosage (1 g/L), temperature (35°C), and initial RY145) concentration (15 ppm) respectively were maintained. Figure 4 presents the impact of pH on RY145 removal. The pH of the equilibrium solution is important in determining the sorbent’s sorption capacity during sorption[23]. The results showed that both uptake capacity and % removal efficiency declined with a surge in solution pH. At pH 2.0 and 5.0, the uptake capacity was found 7.33 mg/g and 5.43 mg/g, the removal efficiency was found at 48.87% and 36.20% respectively. Electrostatic interactions between anions of biochar and dye resulted in maximum dye sorption. At low pH, the excess H+ ions and the surface possess a positive charge [24]. The dyes are negatively charged ions that react with the positively charged surface of the sorbent [25]. Considering all the parameters, the pH was optimized as 2.0 and used in all batch trials.
3.4. Effect of Temperature on RY145 Removal
The temperature was taken as 30°C, 35°C, 40°C, and 45°C. During these studies, the dosage of biochar was kept constant at 1 g/l, pH was kept constant at 2.0, and the initial concentration of the dye was kept constant at 15 ppm, respectively. The uptake of biochar increases with temperature and subsequently decreases, as shown in Figure 5. The biochar’s uptake capacity towards RY145 increased from 6.63 mg/g at 30°C to 7.33 mg/g at 35°C and decreased to 2.32 mg/g at 45°C, respectively. The biochar uptake increases and then declines with temperature, as seen in Figure 5. The efficiency of groundnut shell-derived biochar towards RY145 increased from 44.23% at 30°C to 48.87% at 35°C and decreased to 15.45% at 45°C, respectively. From the results, it is concluded that initial adsorption capacity increases with the increase in temperature and a further increase in temperature decreased the adsorption capacity, and this indicates that initially adsorption was due to endothermic upto 35°C, and it becomes exothermic reaction after 35°C. Considering all the parameters, the temperature was optimized as 35°C and used in all batch trials [26].
3.5. Effect of Initial Concentration on RY145 Removal
The concentration of the dye was varied as 5 to 100 mg/L. During these studies, the pH was kept constant at 2.0 and temperature was kept constant at 35°C. Figure 6 shows that the dye sorption potential of biochar derived from coconut shells increases as the dye concentration increases. Higher dye concentration resulted in uptake capacity saturation, which resulted in no change in uptake capacity. For example, with an initial RY145 concentration of 5 mg/L, an absorption capacity of 2.50 mg/g was found, whereas an initial RY145 concentration of 100 mg/L results in an absorption capacity of 53.80 mg/g. It was also observed with an increase in initial RY145 concentration from 5 to 100 mg/L; the percentage removal efficiency of RY145 was enhanced from 50 to 53.80%. The removal efficiency was increased at an elevated initial RY145 concentration and it may due to the availability of sufficient binding sites to remediate dye molecules [27]. As a result of the research, it was determined that an initial RY145 concentration of 5 mg/L provided the best removal efficiency.
3.6. Desorption Studies
The desorption efficiency of various elutants is represented in Figure 7. It was determined from Figure 7(a) that sodium hydroxide had a maximum desorption efficiency of 98.4%. This could be because the presence of more OH- ions favored the removal of dye molecules from the biochar, as reactive dyes are composed of more positive ions. It is most important to conduct a solid-to-liquid (S/L) ratio to optimize the volume of the elutant used for the desorption studies. From Figure 7(b), it was concluded that the S/L ratio of 5 is optimum. S/L ratio of 5 indicates that the volume of the elutant required for the desorption studied is five times lesser than the volume of the solute required for the adsorption. Regeneration studies were also carried out to assess the biochar’s potential in successive adsorption and desorption. Figure 7(c) shows that for three consecutive sorption-elution cycles, a maximum desorption efficiency of 98.1% was obtained. So, based on the desorption tests, sodium hydroxide with an S/L ratio of 5 was used for three sorption-elution cycles in a row.
(a)
(b)
(c)
4. Conclusion
It was concluded that biochar can be used to effectively remediate reactive yellow 145 (RY145) from dye-bearing wastewater. The biochar was found to have extremely high uptakes of the dye tested. Through batch experiments, the optimum sorbent dosage, pH, and temperature were determined as 1 g/L, pH 2.0, and 35°C, respectively. The biochar derived from the groundnut shell had the highest sorption uptake for RY145, with a maximum sorption uptake of 53.80 mg/g. Thus, through this study, effective sorbents were proposed to remediate different Remazol dyes from aqueous and wastewater solutions. Biochar, as a low-cost and ecologically friendly substance, has the potential to replace expensive activated carbon in the treatment of dye-bearing wastewaters.
Data Availability
The data used to support the findings of this study are included in the article.
Disclosure
This study was performed as a part of the employment of Samara University, Ethiopia.
Conflicts of Interest
The authors declare that they have no conflicts of interest regarding the publication of this study.
Acknowledgments
The authors appreciate the support from Samara University, Ethiopia. The authors thank GMR Institute of Technology, Rajam, Andhra Pradesh, for the technical assistance to complete this experimental work.