Kinetic and thermodynamic investigations of sewage sludge biochar in removal of Remazol Brilliant Blue R dye from aqueous solution and evaluation of residual dyes cytotoxicity

Abstract

Biochar derived from sewage sludge has emerged as an alternative for sustainable utilization as a soil amendment. However, the use of sewage sludge biochar (SSB) has been less explored in the field of wastewater treatment. Therefore, the purpose of this study was to investigate the efficiency of biochar prepared from sewage sludge at 450 °C (SSB-450), as an adsorbent for the removal of Remazol Brilliant Blue R (RBBR) from an aqueous solution. Brunauer–Emmett–Teller (BET), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize SSB-450, with maximum RBBR removal efficiency. The removal of RBBR from aqueous solution by SSB-450 was investigated in batch mode at varying adsorbent dose, contact time, initial RBBR dye concentration temperature and pH. The BET analysis showed the type IV isotherm that indicates the mesoporous structure of SSB-450. The total pore volume and BET specific surface area of SSB-450 particles were found to be 3.936 cm −3 /g and 12.447 m 2 /g, respectively. The RBBR dye adsorption ( q e ) at equilibrium by SSB-450 was found to increase from 8.56 to 80.6 mg g −1 with an increase in initial dye concentration from 10 to 100 mg L −1 . The maximum monolayer adsorption capacity (qmax) was 126.59 mg/g of SSB-450, determined by the Langmuir adsorption model. At various RBBR dye concentrations (10 to 100 mg/g), the range of the separation factor ( R L ) was 0.98–0.9, which indicates the favourable adsorption of RBBR dye onto the surface of SSB-450. Besides, Evans blue and triphenyl tetrazolium chloride (TTC) staining of Allium cepa L. roots germinated with dye solutions revealed that biochar treated residual RBBR was non-cytotoxic. • Sewage sludge biochar prepared at 450 °C (SSB-450) efficiently removed RBBR. • Type IV isotherm indicated the mesoporous structure of SSB-450. • Linear Langmuir model fitted well with equilibrium adsorption data. • Pseudo-second-order kinetics model best described adsorption of RBBR. • RBBR adsorption by SSB-450 was spontaneous and endothermic.