Adsorptive removal of lead from wastewater using pressmud with evaluation of kinetics and adsorption isotherms

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.