Elimination of indigo carmine in water by Pinus patula biochar: adsorption process optimization, kinetics and isotherms

The textile industry causes major pollution to water bodies due to the discharge of dye-containing wastewater, such as indigo carmine (IC). Biochar has been used to treat organic pollutants like dyes because of its pore structure and surface area, as well as the functional groups contained, low cost, and sustainability of this material. In this study, biochar derived from Pinus patula wood pellets was used to assess its efficiency in the elimination of IC in water. Under optimal conditions of pH, biochar dose, and particle size (3, 13.5g/L, and 300-450µm, respectively), a 99% removal of a 25mg/L solution of IC was achieved. Furthermore, studies on dissolved organic carbon (DOC) revealed that Pinus patula biochar contributed to a 73.8% reduction in the organic matter present in water. The IC adsorptive process was described by the pseudo-second order kinetic and the Freundlich isotherm models. Chemical and physical adsorption mechanisms were associated with the uptake of IC by Pinus patula biochar. Hydrogen bonding, electrostatic attraction, π-π interactions, and pore-filling were regarded as the possible mechanisms involved in the adsorption system. Pinus patula wood pellets biochar was shown to be an efficient adsorbent to remove dyes from water.