Optimization of process variables to prepare activated carbon from Noug (Guizotia abyssinica cass.) stalk using response surface methodology

Abstract

Even though adsorption is considered the simple, effective, and efficient method for the treatment of wastewater, accessibility of low-cost and locally available activated carbon remains the challenge. In response to this, recently significant amounts of agricultural byproducts have been investigated to prepare low-cost porous carbon, but there is still a problem related to cost and availability. So, Noug stalk, chosen because of its abundance and low cost as an agricultural byproduct in Ethiopia, was chemically activated with phosphoric acid to produce a low-cost porous carbon. The production of Noug stalk activated carbon (NSAC) is optimized using response surface methodology. A central composite design was used to investigate the effect of three process parameters, namely carbonization temperature (450–650 °C), activation time (90–150 min), and impregnation ratio (w/w) (1–3), on the BET surface area and yield of porous carbon. The analysis of variance (ANOVA) result shows that all three process parameters showed a significant effect on the surface area of porous carbon, while only carbonization temperature showed a significant effect on the yield of porous carbon. The best conditions for NSAC preparation were a carbonization temperature of 537.50 °C, an activation time of 127 min, and an impregnation ratio of 1.95, resulting in a BET surface area and yield of 473.45 m2 g−1 and 53.78%, respectively. The expected and observed values of the model for the outcome variable were highly comparable. Several analytical techniques, including proximal analysis, Fourier transform infrared spectroscopy, and N2 adsorption-desorption, were used to characterize the NSAC. The results demonstrated that the prepared NSAC has a highly porous structure comparable to porous carbon obtained from other biomass feedstocks. This implies it would be used as a potential low-cost alternative for wastewater treatment using the adsorption process.