Recycling of Sewage Sludge: Synthesis and Application of Sludge-Based Activated Carbon in the Efficient Removal of Cadmium (II) and Lead (II) from Wastewater

The limited supply of drinking water has aroused people's curiosity in recent decades. Adsorption is a popular method for removing hazardous substances from wastewater, especially heavy metals, as it is cheap, highly efficient and easy to use. In this work, a new sludge-based activated carbon adsorbent (SBAC1 / SBAC2) was developed to remove hazardous metals such as cadmium (Cd+2) and lead (Pb+2) from an aqueous solution. The chemical structure and surface morphology of the produced SBAC1 and SBAC2 were investigated using a range of analytical tools such as CHNS, BET, FT-IR, XRD, XRF, SEM, TEM, N2 adsorption/desorption isothermal and zeta potential. BET surface areas were examined and SBAC2 was found to have a larger BET surface area (498.386 m2/g) than SBAC1 (336.339 m2/g). SBAC2 had a lower VBJH (1.5026 cm3 g-1) than SBAC1 (1.59873 cm3 g-1), but a higher VT (0.3748 cm3 g-1) than SBAC1 (0.2688 cm3 g-1), while the average pore size was 10-100 nm for SBAC1 and 45-50 nm for SBAC2. The ideal conditions investigated for the removal of Pb+2 and Cd+2 were 10 mg SBAC1 / SBAC2, Pb+2 / Cd+2 at an starting concentration of 30 mg/L, a temperature of 40 and 50 °C, pH = 6, 8 and contact times of 10 and 15 minutes for Pb+2 and Cd+2, respectively. SBAC1 and SBAC2 eliminated approximately 99.99% of Cd+2 and Pb+2 out the water under all conditions tested. The results of the adsorption of Cd+2 and Pb+2 were in good agreement with the pseudo-second-order equation (R2 = 1.00). Under the experimental conditions, the Cd+2 and Pb+2 adsorption equilibrium data were effectively linked to the Langmuir and Freundlich equations for SBAC1 and SBAC2, respectively. Langmuir model calculated the adsorption capacities of SBAC1 and SBAC2 for Cd+2 (309.24 and 329.62 mg/g) and for Pb+2 (318.46 and 339.61 mg/g), respectively. The regeneration showed high recyclability for the fabricated SBAC1 and SBAC2 during five consecutive reuse cycles. As a result, the produced SBAC1 and SBAC2 are attractive adsorbent for the elimination of heavy metals from various environmental and industrial wastewater samples.