Abstract
A huge volume of industrial wastewater laden with toxic heavy metals, including cadmium, lead, nickel and copper, is discharged into the environment without treatment. Pressmud, a byproduct of sugar industry, could serve as an efficient, low-cost and environment friendly amendment for the biosorptive removal of lead (Pb) from wastewater. This study aimed to assess the biosorption efficiency of pressmud in removing Pb from water. Primarily, it evaluated the biosorption potential of pressmud for Pb, and compared it with other amendments such as, citrus waste, rice straw, biochar and activated carbon. Subsequently, the biosorption of Pb by the pressmud was measured at different temperatures (20–45 °C), pH (5–10) and biosorbent doses (2–10 g L−1). The kinetics of Pb biosorption onto pressmud were studied by pseudo-first-order (PFO), pseudo-second-order (PSO) and Elovich models. The equilibrium isotherms were studied for a range of Pb concentrations (25–500 mg L−1) using Freundlich, Langmuir and Sips models. Moreover, the pressmud was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET). The pressmud exhibited a biosorption capacity of 5.30 mg g−1 for Pb, while surpassing other biosorbents. The biosorption capacity of rice straw, biochar, and activated carbon for Pb was 4.44, 1.94, and 0.49 mg g⁻¹, respectively. The highest biosorption capacity of pressmud was observed with contact time of 4 h, biosorbent dose of 8 g L−1, temperature of 37 °C, pH 7 and Pb concentration of 500 mg L−1. The biosorption of Pb onto pressmud followed the PFO reaction with R2RMSE and SSE of 0.981, 0.0333 and 0.0067, respectively. Langmuir model best described the adsorption behavior of Pb and predicted the maximum biosorption capacity of 43.7 mg g−1. FTIR, SEM and BET depicted that the adsorption of Pb by pressmud could be attributed to the presence of various functional groups, highly porous nature and a large surface area. Thus, pressmud could be used as a highly effective biosorbent for removal of Pb from industrial wastewater prior to its discharge into the environment.
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Introduction
The increasing level of heavy metal contamination in fresh water sources has become a major threat to environment. Among heavy metals, lead (Pb) in industrial wastewater poses significant health risks due to its high toxicity, non-biodegradability and persistent nature1,2,3. About 2301 × 10⁶ m³ of wastewater from various industries is generated annually in Pakistan4. Unfortunately, the country lacks adequate facilities to treat this substantial volume of wastewater containing heavy metals. Due to escalating water scarcity, farmers are compelled to use industrial wastewater for crop irrigation. According to the guidelines of the World Health Organization, the safe limit for Pb in wastewater used for agricultural purposes is 10 µg L−15. The soil contamination with heavy metals have been found to reduce the crop yields6,7. They tend to contaminate the food chain through bioaccumulation in the edible parts of crops, leading to severe adverse health effects in humans. The Pb accumulates in bones and deteriorates peripheral and central nervous system8. Infants, children and pregnant women are the most vulnerable to the harmful effects of Pb9. In light of the adulteration of food chain, a sustainable approach to remove these metals from wastewater is urgently needed10.
Traditional methods such as chemical precipitation, coagulation, complexation, ion exchange, solvent extraction, foam flotation, electro-deposition, cementation, and membrane operations for metal remediation are limited by their high costs. Among these methods, biosorption using organic and inorganic materials is still considered a sustainable option due to its affordability, operational simplicity and flexibility11,12,13. Previously, different organic materials including coriander seed powder, Schleichera oleosa bark, rice straw, peanut husk powder, maize cob, saw dust, mucilaginous seeds of Cydonia oblonga and biochar have been used to remove Pb from water13,14,15,16,17,18,19,20. Pressmud (PM) is a byproduct of the sugar industry produced in large quantities in the country9. PM is a spongy, amorphous and brownish to dark brown material21. Over 1.28 million tons of PM are generated annually in Pakistan22. The most common use of PM is burning it in brick kilns, which pollutes the environment. The high cation exchange capacity (CEC) of PM can play a vital role in the biosorption of heavy metals from wastewater. The presence of several functional groups in PM may facilitate the binding of heavy metals. However, the potential of PM for biosorption of Pb from water remains unexplored. The comparative studies assessing the biosorption efficiency of PM for Pb against other plant-based biosorbents have not been conducted. The research on kinetic models and adsorption isotherms for PM in relation to Pb is lacking.
Thus, this study aimed to compare the biosorption of Pb from water by PM and other plant-based biosorbents. The optimal environmental conditions for Pb biosorption, along with adsorption isotherms and kinetic models, were evaluated. The PM biomass was characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) techniques.
Materials and methods
Chemicals
The chemicals used in this study, including ammonium acetate (C₂H₇NO), boric acid (H3BO3), hydrochloric acid (HCl), dipotassium hydrogen phosphate (K2HPO4), nitric acid (HNO3), lead nitrate [Pb(NO3)2], potassium dihydrogen phosphate (KH2PO4), potassium chloride (KCl), potassium bromide (KBr), perchloric acid (HClO4), potassium hydroxide (KOH), sodium hydroxide (NaOH), sodium chloride (NaCl), sodium acetate (CH3COONa) and sodium molybdate dihydrate (Na2MoO4·2H2O) were purchased from Sigma-Aldrich, USA. The purity of these chemicals is listed in Table S1.
Preparation of solutions of pb and biosorbents for batch studies
The stock solution (1000 mg L−1) of Pb was prepared in distilled water and kept in a refrigerator at 4 °C to inhibit microbial growth and to ensure stability of Pb in solution. Pb(NO3)2 salt was used to prepare stock solutions of Pb (1000 mg L−1), respectively. The required metal concentrations for various batch studies were achieved by diluting the necessary volume of stock solutions with distilled water. The pH of solutions of Pb was adjusted to 7 with sodium hydroxide (1 N) and/or hydrochloric acid (0.1 M) solutions while using a calibrated pH meter.
Different biosorbents including rice straw, citrus waste, biochar, activated carbon and PM were oven-dried at 70 °C in a hot-air oven. These materials were ground to a fine powder using a Wiley Mill (CZ13, JANKE & KUNKEL, Germany). Subsequently materials were sieved through a 1 mm sieve to get a particle size of up to 1 mm.
Measurement of pb biosorption potential of PM and plant-based biosorbents
The efficacy of biosorbents (rice straw, citrus waste, biochar, activated carbon and PM) to remove Pb from water was evaluated using three replicates. Fifty mL of Pb solution (with a concentration of 50 mg L−1) was taken in 100 mL conical flasks. Each biosorbent was added into the metal solution at a dose rate of 8 g L−1. The conical flasks were kept on a shaker at 150 rpm at 37 ± 2 °C. After 24 h, the mixture was filtered using Whatman No. 42 filter paper to obtain a clear supernatant. Then the supernatant was analyzed on atomic absorption spectrometer (AAS) to determine the concentration of Pb.
The biosorption capacity was calculated using the formula given below23;
Q represents the adsorption capacity (mg g−1), C₀ is the initial Pb concentration (mg L−1), Ce is the Pb concentration after 24 h (mg L−1), v refers to the total volume of the Pb solution (L) and m indicates the amount of biosorbent (g).
Adsorption kinetic models
To determine the equilibrium time for the adsorptive removal of Pb, 50 mL (with a concentration of 50 mg L−1) of metal solution was taken in 100 mL conical flasks in triplicate. The 8 g L−1 dose of PM was used. After adding PM, the flasks were kept in a refrigerated shaking incubator at 150 rpm and 37 ± 2 °C. The biosorption capacity was calculated at intervals of 0, 2, 4, 6, 8, 10, 12- and 24-hours using Eq. 1.
The adsorption kinetics of Pb was analyzed using pseudo-first-order (PFO), pseudo-second-order (PSO) and Elovich kinetic models by plotting adsorption capacity against time (t)24.
The nonlinear PFO equation is given below23;
In this equation, Qt represents the biosorption capacity (mg g−1) at a given time t, Qe denotes the adsorption capacity (mg g−1) at equilibrium and k1(min−1) is the rate constant.
The nonlinear PSO equation is given bellow23;
Where k2 (kg g−1 min−1) is the rate constant for the PSO equation.
The non-linear elovich equation is shown below25;
Where u and v are constants during the experiment, with u representing the initial rate (mg g−1 min−1) and v being the desorption constant (g mg−1).
Goodness-of-fit measure
The sum of square error (SSE) and the root mean squared errors (RMSE) were calculated by Eq. (5) and Eq. (6)26,27;
where the subscripts ‘‘exp” and ‘‘calc” are the experimental and calculated values of qe, respectively and n is the number of measurements.
The coefficient of determination (R2) was calculated by Eq. (7)28;
Evaluation of the biosorption capacity of PM under varying temperatures, pH and biosorbent doses
The effect of incubation temperature (20, 28, 30, 37 and 45 °C) on biosorption capacity of PM for Pb was evaluated while keeping the other parameters constant (pH 7, adsorbent dose 8 g L−1, shaking speed 150 rpm, metal concentration 50 mg L−1 and time 4 h). Based on the results of this study, the highest biosorption capacity was observed at 37 °C, which led to the selection of 37ºC for further studies. The effect of pH (5, 6, 7, 8, 9, and 10) of Pb containing wastewater on biosorption capacity of PM for Pb was evaluated while keeping the other parameters constant (temperature 37 °C, adsorbent dose 8 g L−1, shaking speed 150 rpm, metal concentration 50 mg L−1 and time 4 h). In the subsequent batch experiment, the influence of different biosorbent doses (2, 4, 6, 8, and 10 g L−1) on the adsorptive removal of Pb was examined, while maintaining other parameters constant (pH 7, temperature 37 °C, shaking speed 150 rpm, metal concentration 50 mg L−1 and time 4 h). The Pb biosorption was calculated using Eq. (1). All biosorption batch studies were performed in triplicates.
Adsorption isotherms models
The biosorption capacity of PM for various concentrations of Pb (25–500 mg L−1) was evaluated under optimal conditions (Contact time of 4 h, temperature of 37 °C and pH of 7, adsorbent dose of 8 g L−1). Each experimental treatment was conducted in triplicate. The adsorption performance at equilibrium was analyzed by fitting the experimental data to the widely used Langmuir, Freundlich and Sips isotherm models.
The Langmuir equation is expressed in the following nonlinear form23;
Where Qe represents the biosorption capacity of the metals at equilibrium (mg g−1), KL is the Langmuir constant (m³ g−1), qm, L denotes the maximum adsorption capacity (mg g−1) and Ce refers to the equilibrium metal concentration (mg L−1).
The nonlinear form of the Freundlich equation can be expressed as follows29;
Where Qe represents the adsorption capacity at equilibrium (mg g−1), 1/n and KF are the empirical constants of the Freundlich isotherm, and Ce denotes the equilibrium concentration (mg L−1)23.
The Sips isotherm model equation can be written as follows30;
Where qms represents the maximum biosorption capacity (g kg−1) according to the Sips equation, Ks is the Sips isotherm constant (m3 g−1)1/ns, and 1/ns is the Sips isotherm exponent.
To check the R2RMSE and SSE were calculated as described in Eqs. 5, 6 and 7 to determine the goodness-of-fit of the models.
Characterization of PM biosorbent
The CEC of PM was determined following protocol31. Briefly, 1 g of PM was taken into a 50-mL Falcon tube, 33 mL of 1 N CH3COONa were added, shaken for 5 min at 120 rpm, centrifuged and supernatant was discarded. This process was repeated four times. Afterward, 33 mL of 95% ethanol were added to PM sample, shaken at 120 rpm, centrifuged and supernatant was discarded. This rinsing with ethanol was repeated three more times. The adsorbed sodium (Na+) from the sample was extracted three times with 33 mL 1 N C₂H₇NO₂ solution and extract was analyzed for Na+ concentration using a flame photometer (PFP-7, Jenway, UK). The CEC was calculated from the Na+ concentration in the extract. The specific surface area was determined using BET technique, while the total pore volume (TPV) was computed at relative pressure P/P0 (Fig. S1). The pore diameter (PD) was estimated using a t-plot and a density functional theory (DFT) model23. FTIR spectroscopy was performed on PM using a Spectrum Two FTIR spectrometer (Perkin–Elmer, USA) to identify the functional groups. The data were collected over the wavenumber range of 400–4000 cm−1 with a resolution of 4 cm−1. Spectrum 10 software was used to process the data32. XRD was used to know the amorphous or crystalline nature of dried PM. The diffractometer used was a Philips X’Pert-MPD operating at a current power of 40 kV and 40 mA, scanning within a range of 10–80° (2θ). Defects were identified by utilizing the LabRamHR Raman Spectrophotometer (French JY Co., France) equipped with a 514 nm laser and scanning from 400 to 3400 cm−1. SEM (GeminiSEM 500, Carl Zeiss, Germany) with energy dispersive spectroscopy (EDS) was used to document surface morphologies and chemical composition of PM.
Statistical analysis
The data regarding biosorption of Pb by biosorbent type, biosorbent dose, pH and incubation temperature were analyzed for analysis of variance (ANOVA) using Statistix 10 statistical software33. The least significant difference test was applied to compare the treatment means at 5% probability level. Non-linear regression was used to estimate kinetics and adsorption parameters by SigmaPlot 15 software.
Results
Biosorption capacity of different biosorbents for pb
The data on the biosorption (mg g−1) of Pb from contaminated water by five biosorbents—pressmud, rice straw, citrus waste, biochar, and activated carbon are presented in Fig. 1. A significant variation in the biosorption capacity (Qe) of the different biosorbents was observed. The citrus waste exhibited biosorption capacity of 5.96 mg g−1 for Pb, while the biosorption capacities of PM was 5.30 mg g−1. In contrast, rice straw, biochar and activated carbon exhibited biosorption capacities of 4.44, 1.94, and 0.49 mg g−1 for Pb, respectively. The biosorption capacity followed this order: citrus waste > PM > rice straw > biochar > activated carbon. Notably, both biochar and activated carbon demonstrated very low biosorption capacities for Pb.
Biosorption capacity of different biosorbants for Pb. Bar showing different alphabets are significantly different at p ≤ 0.05. Error bars indicate standard deviation (n:3).
Effect of contact time on the adsorption of Pb onto PM and the adsorption kinetic models
With the increase in contact time for interaction between metals and PM, the biosorption capacity of PM for Pb initially increased and reached to equilibrium after 4 h (Fig. 2). The adsorption process occurred in two stages: a rapid initial phase, followed by a slower secondary phase. The relationship between adsorption and time was analyzed using PFO, PSO, and Elovich kinetic models to evaluate the adsorption kinetics of Pb (Fig. 3a). The values of R2RMSE and SSE for the PFO adsorption kinetics models were 0.98, 0.03 and 0.01, respectively, for the PSO values were R2 0.97, RMSE 0.09 and SSE 0.05 and for Elovich kinetic model values were R2 0.94, RMSE 0.17 and SSE 0.17 (Table 1).
Biosorption capacity of pressmud for Pb at different time intervals. Bar showing different alphabets are significantly different at p ≤ 0.05. Error bars indicate standard deviation (n:3).
(a) Non-linear adsorption kinetics for Pb. (b) Non-linear adsorption isotherm models for Pb.
Biosorption capacity of PM for pb under varying temperatures, pH levels and biosorbent doses
The effect of incubation temperature (20–45 °C) on the biosorption capacity of PM for Pb (50 mg L−1 each) is presented in Fig. 4a. It was observed that as the temperature increased from 20 °C to 37 °C, the biosorption capacity of PM also increased. Pb biosorption increased from 5.69 mg g−1 at 20 °C to 6.20 mg g−1 at 37 °C. However, temperatures above 37 °C resulted in a decline in the biosorption capacity. Furthermore, variation in pH (5–10) also resulted in significant change in biosorption capacity of PM for Pb (Fig. 4b). As the pH increased from 5 to 7, the biosorption capacity of PM increased, with a peak biosorption of 6.19 mg g−1 at pH 7. Further increases in pH beyond these values led to a decrease in biosorption capacity.
The adsorbent dose is a critical parameter in batch adsorption studies. The influence of different biosorbent doses (2, 4, 6 8, and 10 g L−1) on biosorption at equilibrium time, optimal temperature and pH is shown in Fig. 4c. The biosorption capacity of PM for Pb increased with the adsorbent dose, reaching a maximum at 6.21 mg g−1. Based on the highest removal rates, 8 g L−1 dose rate was selected as the optimal doses for further studies.
Biosorption capacity of pressmud for Pb different (a) temperatures (b) pH levels and (c) adsorbent doses. Bar showing different alphabets are significantly different at p ≤ 0.05. Error bars indicate standard deviation (n:3).
Effect of initial pb concentration and adsorption isotherms
The influence of Pb concentrations (25, 50, 75, 100, 150, 200, 300, 400 and 500 mg L−1 each) on the biosorption capacity of PM is shown in Fig. 5. The results indicate that as the concentrations of Pb increased, the adsorption capacity of PM progressively increased. The maximum biosorption capacities of 38.7 mg g−1 was recorded at the highest concentration of 500 mg L−1. The adsorption isotherm analysis indicated that the Langmuir model was the most suitable for Pb (Fig. 3b; Table 2). The comparison of R2, RMSE and SSE values depicted that Langmuir model was the best fit model while predicting the maximum biosorption capacity among the studied models. Moreover, the values of maximum biosorption capacities obtained from this model were close to the values obtained from the experimental data. The highest adsorption capacities predicted by Langmuir model and experimental data were 43.7 and 38.7 mg g−1, respectively.
Biosorption capacity of PM for lead at different metal concentrations.
Characteristics of PM biosorbent
The PM exhibited a high CEC of 68 meq 100 g−1. The specific surface area (SSA) of the PM was 7.716 m2 g−1., TPV was 0. 0.0247 cm3g−1 and APD was 22.81 nm (Table 3). The FTIR spectrum of PM is given in Fig. 6a, which revealed the presence of several key functional groups. A broad band between 3000 and 3800 cm−1 suggested the presence of both free and hydrogen-bonded OH groups on the PM surface. The stretching at 2980 cm−1 corresponded to silanol (Si–OH) groups, while the stretching of OH groups bound to methyl radicals produced signals between 2850 cm−1 and 2980 cm−1. Peaks around 1503 cm−1 were attributed to –CH₂ and –CH₃ groups, with additional peaks at 1308 cm−1 indicative of –CH₃ groups. Weak and broad peaks around 1750 cm−1 corresponded to stretching from –CO and –C–OH groups, likely from aldehydes and ketones. Transmittance near 980 cm−1 suggested the presence of lactones, while peaks around 828 cm−1 indicated Si–H groups. The X-ray diffraction patterns of pressmud are presented in Fig. 6b. The prominent peaks were observed at 26.418° (d-spacing: 3.3711 Å), 27.701° (d-spacing: 2178 Å), 28.150° (d-spacing: 3.1675 Å), 29.240° (d-spacing: 3.0518 Å), 30.716° (d-spacing: 2.9085 Å), 40.339° (d-spacing: 2.2341 Å), 50.026° (d-spacing: 1.8218 Å), and 68.181° (d-spacing: 1.3743 Å). The SEM-EDS analysis of the PM sample at 1000x magnification revealed a porous surface structure (Fig. 7a). The elemental composition, as identified by EDS, showed the presence of oxygen, silicon, carbon, potassium, iron, aluminum, magnesium, calcium, sodium, sulfur and chloride (Fig. 7b).
Analysis of different characteristics of pressmud (a) Fourier-transform infrared spectroscopy and (b) X-ray diffraction.
Analysis of different characteristics of pressmud (a) Scanning electron microscope image and (b) elemental analysis of a selected area.
Discussion
The treatment of wastewater is a major global challenge, and scientists are striving to protect the environment and, ultimately, the food chain. This study explores the potential of PM as a biosorbent for the removal of Pb from wastewater. The biosorption capacity of PM for Pb was determined to be 5.30 mg g−1, exceeding those of rice straw, biochar and activated carbon. Previous research has confirmed that PM exhibits a higher biosorption capacity compared to many other plant-based biosorbents34,35,36. The biosorption of Pb is attributed to PM’s large SSA and high CEC. The large SSA provides additional binding sites for Pb35while the high CEC enhances PM’s ability to remove metal ions, further increasing its effectiveness as a biosorbent37.
Biosorption depends on the interaction time between the adsorbent and adsorbate. Therefore, the kinetics of Pb uptake by biological materials were evaluated using kinetic models. The results showed that biosorption occurred rapidly at first, achieving more than half of the saturation level within the first 2 h. Subsequently, the biosorption rate slowed, eventually reaching equilibrium after approximately 4 h (Fig. 2). This slowdown can be attributed to the saturation of available adsorption sites on the PM surface38. The results of the kinetic models analysis indicated that the PFO provided the best fit for Pb adsorption based on R2RMSE and SEE values. The PFO kinetic model predicts the physical adsorption of Pb onto PM, where the adsorption rate is directly proportional to the availability of active sites on the adsorbent39. Consistent with our results, previous studies also identified the PFO model as the best fit for the adsorption kinetics of Pb40,41,42.
Temperature is an important factor that can affect the metal biosorption on the biological materials43,44. The adsorption of Pb on PM was influenced by temperature: the adsorption increased as the temperature increased to an optimum value of 37 °C, and decreased beyond it. This enhancement in adsorption up to 37 °C is likely due to increased surface activity and the kinetic energy of metal ions, which strengthened the interaction between adsorbate and adsorbent45,46,47. However, further increase in temperature might had damaged the binding sites and weakened the metal ion bonds with functional groups on the PM surface48,49. The pH also plays a vital role in biosorption44,50. The biosorption of Pb increased with the increase in pH, reaching the maximum value at the pH values of 7. At lower pH, the competition between H⁺ ions and metal ions for binding sites is stronger, while higher pH causes metal ion precipitation due to increased hydroxyl anion concentrations46. Furthermore, the removal of Pb increased with increasing PM dosage, from 2 to 10 g L−1, which could be due to the more availability of the binding sites51.
Biosorption isotherms represent the relationship between the amount of a substance adsorbed per unit mass of biosorbent and the concentration of that substance in the solution46. Adsorption isotherm parameters offer important understandings into surface properties, adsorbent affinity, and adsorption mechanisms, making accurate correlation of equilibrium curves essential for optimizing adsorption system conditions. As the initial concentrations of Pb increased from 25 to 500 mg L−1, a gradual rise in the adsorption capacity of PM was observed. This can be attributed to the enhanced contact between metal ions and the PM at higher metal concentrations35. A comparative analysis of maximum adsorption capacities for Pb using various biosorbents from previous studies is presented in Table 4. The experimental data were fitted to the Langmuir, Freundlich, and Sips isotherms, with parameters obtained through non-linear equation fitting. The Langmuir model provided the best fit for Pb adsorption, while predicting the maximum biosorption capacity (43.7 mg g−1) with R² value of 0.97. The Langmuir model describes adsorption on a homogeneous monolayer surface, where each site accommodates only one adsorbate molecule, and all sites possess equal energy. In this model, interactions between adsorbed species are assumed to be negligible52,53. Furthermore, the maximum biosorption capacity predicted by the isotherm models was found to be closely aligned with the values obtained from the experimental data. According to the Langmuir isotherm model, the predicted maximum adsorption capacity of PM for Pb was 43.7 mg g−1. The predicted adsorption capacities of PM for Pb is higher than those reported in previous studies54,55. They identified the Langmuir isotherm as the best fit for Pb biosorption, with R² values of 0.99 using both apple residue and Lysinibacillus fusiformis KMNTT-10 biomass.
Pressmud consists of cellulose, hemicellulose and lignin56. These components play a crucial role in understanding FTIR analysis results for materials of this nature. The FTIR spectra showed the presence of different functional groups for the adsorption of Pb (Fig. 6a). The FTIR peaks observed in PM around 3716 cm−1 are likely linked to free and hydrogen-bonded OH groups. Peaks at 2980 and 2850 cm−1 are associated with the stretching of OH bonds in hydroxyl groups, primarily related to methyl groups (CH₃)57,58. The first peak at 3716 cm−1 in biosorbents is likely attributed to OH stretching vibrations associated with cellulose, lignin and absorbed water. The peaks observed around 1750 and 1503 cm−1 can be attributed to the asymmetric and symmetric stretching vibrations of the carboxylate group (-COO)56,59,60. The peak at 980 cm−1 is likely attributed to the stretching vibration of CO in polysaccharides, associated with silica groups (Si-O-C or Si-O-Si bonds)57,61. It may also correspond to the stretching vibrations of -SO3 in hemicelluloses, as well as O-H bonds in alcohols (both primary and secondary) and aliphatic ether groups62. The peaks observed at 828 cm−1 may indicate the presence of C-H and Si-H groups61. The Powder XRD spectrum of PM demonstrated that the biomass exhibits an amorphous structure (Fig. 6b). The main peaks identified were 26.418°, 27.701°, 28.150°, 29.240°, 30.716°, 40.339° 50.026° and 68.181°. Previously research reported XRD spectrum of PM with key peaks at 26.505°, 28.135°, 29.235°, 40.155°, 50.025° and 66.195°7. The BET analysis of PM revealed SSA, TPV and APD values of 7.716 m² g−1, 0.0247 cm³ g−1 and 22.81 nm, respectively. These characteristics, including its significant porosity and large surface area, suggest that PM is an effective biosorbent for Pb adsorption. SEM analysis revealed that the surface of PM is irregular and porous, providing a substantial interface for the biosorption process.
Conclusion
Pressmud proves to be an effective biosorbent for the removal of Pb from wastewater. The biosorption capacity of pressmud exceeded that of other materials, including rice straw, biochar and activated carbon. The optimal conditions for Pb removal was achieved with a biosorbent dose of 8 g L−1, a temperature of 37 °C, pH 7 and Pb concentration of 500 mg L−1. The biosorption followed pseudo-first-order kinetics and was well described by the Langmuir model, with a maximum capacity of 43.7 mg g−1. Characterization analyses indicated that high surface area and porous structure of pressmud facilitated the effective removal of Pb. Thus, pressmud offers a sustainable solution for treating heavy metal-laden wastewater. Future research should focus on scaling up pressmud-based biosorption for industrial applications and assessing its performance in real wastewater conditions.
Data availability
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.
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Acknowledgements
Authors are thankful to Soil and Environmental Sciences Division, Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan for providing space for the experimentation. We thank Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi Arabia (KFU251778), for supporting this research work. The authors would also like to extend their sincere appreciation to the research support by the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (grants no. 451−03−66/2024−03/200032).
Funding
This work was supported by Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi Arabia (KFU251778).
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Basit Haider: Data curation, Investigation, Methodology, Project administration, Formal data analysis, Writing-Original Draft. Muhammad Imran: Conceptualization, Supervision, editing original draft. Asif Naeem: Writing- Reviewing and Editing. Hossam S. El-Beltagi: Writing- Reviewing and Editing. Hadeeqa Arshad: Methodology, Writing- Reviewing and Editing. Azhar Hussain: Writing- Reviewing and Editing. Usman Zulfiqar: Software, Writing- Reviewing and Editing. Nazih Y. Rebouh: Writing- Reviewing and Editing. PV Vara Prasad: Writing- Reviewing and Editing. Ivica Djalovic: Conceptualization, Writing- Reviewing and Editing.
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Haider, B., Imran, M., Naeem, A. et al. Adsorptive removal of lead from wastewater using pressmud with evaluation of kinetics and adsorption isotherms. Sci Rep 15, 22823 (2025). https://doi.org/10.1038/s41598-025-05169-9
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DOI: https://doi.org/10.1038/s41598-025-05169-9
