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

Abstract

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 (thickened samples SBAC1 and un-thickened samples 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). While the average pore size was 10-100 nm for SBAC1 and 45-50 nm for SBAC2. 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. The regeneration showed a high recyclability for the fabricated SBAC1 and SBAC2 during five consecutive reuse cycles. As a result, the produced SBAC1 and SBAC2 are attractive adsorbents for the elimination of heavy metals from various environmental and industrial wastewater samples.

Keywords: adsorption; isotherms; low-cost adsorbents; wastewater and heavy metals.

Figure 1

FTIR spectra of (a) thickened sewage sludge, (b) SBAC1, (c) SBAC1 after absorption Cd⁺², and (d) SBAC1 after absorption Pb⁺².

Figure 2

FT-IR spectra of (a) unthickened sewage sludge, (b) SBAC2, (c) SBAC2 after absorption Cd⁺², and (d) SBAC2 after absorption Pb⁺².

Figure 3

N₂ adsorption and desorption isotherms of (a) SBAC1 and (b) SBAC2 samples.

Figure 4

XRD spectra of produced activated carbons SBAC1 and SBAC2.

Figure 5

SEM micrographs of produced activated carbons SBAC1 (a,b), SBAC2 (d,e), and TEM image (c) SBAC1 and (f) SBAC2.

Figure 6

Effect of dosage of SBAC1 and SBAC2 on the adsorption of Cd⁺² and Pb⁺²; metal ion concentration = 30 mg/L; contact time = 10 min; pH = 7.

Figure 7

Effect of metal ion concentration on the adsorption by SBAC1 and SBAC2. Adsorbent mass 10 mg; contact time = 10 min; pH = 7 for Cd⁺² and Pb⁺².

Figure 8

Effect of solution pH on the adsorption of Cd²⁺ and Pb²⁺ by SBAC1 and SBAC2. Adsorbent mass 10 mg, [M]²⁺ = 30 mg/L; contact time = 10 min.

Figure 9

Effect of contact time on the adsorption of Cd⁺² and Pb⁺², from aqueous solution by SBAC1 and SBAC2 at pH of 7, 10 ppm activated carbon, and a metal ion concentration of 30 ppm.

Figure 10

Adsorption kinetics of Cd⁺² and Pb⁺² adsorption on SBAC1 and SBAC2, Ci = 30 mg/L, T = 40 °C, and pH =7.00.

Figure 11

Adsorption isotherms of (a) Cd⁺² and (b) Pb⁺² on both activated carbons SBAC1 and SBAC2 at carbon mass 100 mg, solution pH = 7, and T = 25 °C.

Figure 12

The removal efficiency of Cd⁺² and Pb⁺² onto intact and regenerated SBAC1 and SBAC2 adsorbent during eight adsorption/desorption cycles.