Replacing Potassium Hydroxide with Carbide Lime Waste in Preparing Sludge-Based Activated Carbon for Methylene Blue Removal from Aqueous Solutions

Domestic wastewater treatment plants produce large amounts of waste sludge. Sludge can be used to produce activated carbon using potassium hydroxide (KOH) as an activating agent. However, KOH is expensive (relative to the cost of waste carbide lime), making the conversion of waste into valuable products unsustainable. This study explored the utilization of a solid waste by-product, carbide lime waste, as a replacement for KOH to produce sludge-based activated carbon (SBAC). The effects of activation conditions on the characteristics of SBAC were investigated and its performance for methylene blue (MB) removal from a solution was assessed. Post-production analyses using scanning electron microscopy and Fourier-transform infrared spectroscopy indicated that the SBAC produced had a porous surface rich in hydroxyl, aromatic, and alkyl functional groups. Among the tested cases of SBAC prepared using carbide lime, the highest removal of MB (240 mg/g) was achieved for the SBAC prepared at 700 °C with a 1:1 impregnation ratio when activated for 60 min and post-treated with 5M hydrochloric acid. The equilibrium adsorption of MB on SBAC was nonlinear. A strong correlation was found between the pore volume and adsorption capacity of the SBAC produced. The findings of this study suggest that the use of carbide lime waste for SBAC production is a viable alternative to an analytical-grade KOH activator.