Environmental Impacts and Adsorption Isotherms of Coconut Shell Activated Carbon: Effect of Acid Activation, Water, and Fuel

Activated biomass has gained interest as an alternative to coal-based activated carbon (AC). This work investigates the environmental impact (EI) of coconut shell (CS)-derived AC as a substitute for non-renewable coal-based AC. The AC was produced in-house using tandem acid activation and pyrolysis, employing two activation pathways: sulfuric acid (H2SO4) and phosphoric acid (H3PO4). This study further investigates the impact of activation routes, fuel types, and water sources on environmental outcomes. This evaluation focuses on six key impacts: climate change, fossil depletion, freshwater ecotoxicity, freshwater eutrophication, land use, and energy net. The H2SO4 activation pathway is more favorable in terms of EI due to its lower net energy requirement (27.2 MJ) and reduced carbon emissions (1.2 kg CO2 eq.). However, it requires 4.7 kg of AC to adsorb 1 kg of dye, whereas the H3PO4 pathway requires only 4.3 kg. Therefore, while the H3PO4 pathway may be preferred for applications needing higher adsorption capacities, the H2SO4 pathway offers a more environmentally benign option, highlighting the trade-offs in selecting an activation method for AC production. Additionally, this study highlights that CS-derived AC offers substantial energy savings of 78%, alongside a 75% reduction in carbon emissions and an 80% decrease in fossil depletion compared to coal-based AC. Overall, the synthesized AC shows promise as a sustainable alternative to coal-based counterparts.