Silver ions and silver nanoparticles removal by coffee derived biochar using a continuous fixed-bed adsorption column

Abstract

Even low concentration monovalent silver (Ag+) and silver nanoparticles (Ag NPs) are emerging environmental threats, seeking an eco-friendly and cost-effective continuous treatment process to mitigate their pollution. In this study, an attempt has been made to investigate the potential of spent coffee grounds (SCGs) biochar in a fixed-bed column, to remove silver ions and silver nanoparticles from wastewater. A series (adsorption and desorption) of fixed-bed column experiments were performed under different operating conditions to determine the breakthrough curves (BTCs) and understand the effect of initial concentration (50–100 mg/L), the quantity of biochar (0.5–1 g), and the form of silver Ag+ and Ag NPs on biochar removal capacity. Thomas and Yoon-Nelson models were applied to simulate different column parameters, such as breakthrough time, saturation time, the volume of treated effluent, and percentage of removal. These simulated results could assist in the scale-up of the process for an actual industrial operation. Experimental data showed good agreement with both Thomas and Yoon-Nelson models, where the simulated values were closely matched with the experimental values. Biochar was collected after the adsorption and characterised to confirm the morphology, crystal structure, and ionic state of silver. The saturated column was regenerated by 0.05 M HNO3 as eluent and used at least 3 times with 15% capacity loss compared to initial performance, which demonstrated the viability and effectiveness of the biochar adsorption process.