Removal of lead from aqueous solution using modified dewatered sewage sludge as adsorbent

Abstract

The increasing demand for clean water also increases sewage and its sludge by-products. Current challenges of disposing and treating sewage sludge necessitates the development and modification of the material into valuables. The composition and structure of sewage sludge give it the potential to be used as an adsorbent for heavy metal ions removal. This study investigated the performance of three different types of dewatered sludge-based adsorbents prepared with varying methods of activation, consisting of CS (carbonized sludge at 600 oC), CS-NaOH (CS activated with NaOH), and CS-KOH (CS activated with KOH) to remove lead (Pb) from aqueous solution. Adsorption experiments were carried out using synthetic Pb wastewater in a batch system. Several experimental parameters were evaluated, including adsorbent types, contact time, adsorbent dose, pollutant concentration, pH, and competing adsorbates. Adsorption data were analysed using isotherms and kinetics model equations and were found to fit Langmuir and pseudo-second-order models, which suggests that the adsorptive behaviour of CS-NaOH is monolayer chemical sorption and depends on the active surface sites. The study revealed that the highest Pb removal, achieving a 100% removal efficiency, was observed with CS-NaOH adsorbent dose of 1 g/L, initial Pb (II) concentration of 10 mg/L, and a contact time of 120 minutes at pH 6. The presence of cadmium (Cd) and methyl orange (MO) in synthetic wastewater inhibited Pb(II) adsorption efficiency using CS-NaOH, which indicates potential competition between adsorbates. In conclusion, CS-NaOH was revealed as a promising adsorbent for lead removal from water.