Adsorptive removal of cationic methylene blue and anionic Congo red dyes using wet-torrefied microalgal biochar: Equilibrium, kinetic and mechanism modeling

• Main Authors: Yu, Kai Ling, Lee, Xin Jiat, Ong, Hwai Chyuan, Chen, Wei-Hsin, Chang, Jo-Shu, Lin, Chih-Sheng, Show, Pau Loke, Ling, Tau Chuan
• Format: Article
• Published: Elsevier 2021
• Subjects: GE Environmental Sciences; QH Natural history
• Online Access: http://eprints.um.edu.my/33949/
• Institution: Universiti Malaya

This study aims to investigate the adsorption behavior of cationic and anionic dyes of methylene blue (MB) and Congo red (CR) onto wet-torrefied Chlorella sp. microalgal biochar respectively, as an approach to generate a waste-derived and low-cost adsorbent. The wet-torrefied microalgal biochar possessed microporous properties with pore diameter less than 2 nm. The optimum adsorbent dosage of wet-torrefied microalgal biochar for MB and CR dyes removal were determined at 1 g/L and 2 g/L, respectively, with their natural pHs as the optimum adsorption pHs. The determined equilibrium contact times for MB and CR were 120 h and 4 h, respectively. Based on the equilibrium modeling, the results revealed that Langmuir isotherm showed the best model fit, based on the highest R-2 coefficient, for both the adsorption processes of MB and CR using the wet-torrefied microalgal biochar, indicating that the monolayer adsorption was the dominant process. From the modeling, the maximum adsorption capacities for MB and CR were 113.00 mg/g and 164.35 mg/g, respectively. The kinetic modeling indicated the adsorption rate and mechanism of the dyes adsorption processes, which could be crucial for future modeling and application of wet-torrefied microalgal biochar. From the results, it suggests that the valorization of microalgae by utilizing wet-torrefied microalgal biochar as the effective adsorbent for the removal of toxic dyes with an approach of microalgal biorefinery and value-added application to the environment is feasible. (C) 2020 Elsevier Ltd. All rights reserved.