Sugarcane bagasse and straw as low-cost lignocellulosic sorbents for the removal of dyes and metal ions from water

Sugarcane bagasse (stalk) and straw (leaves), an agricultural waste, which had been subjected to either an organosolv or organosolv-oxidative pretreatment were used for the removal of methylene blue dye or heavy metals (Fe(III) and Cu(II)) from model aqueous solutions. The sorption of methylene blue was investigated as a function of pH, dye concentration, and contact time. The sorption of metal ions was studied as a function of concentration. Classical Langmuir and Freundlich adsorption models were used to analyze the sorption process. It was shown that adsorption isotherms fitted better into Freundlich isotherm model, which assumes a multilayer adsorption on a heterogeneous surface. The morphological, textural, and structural characteristics such as bulk and true densities, particle size distributions, porosity, and thermal decomposition features of the biosorbents were determined to understand better the mechanism of sorption of various pollutants. The results showed significant differences in the chemical compositions and physical properties of the initial and modified biomass samples, especially for the cellulosic biosorbents prepared with organosolv-oxidative pretreatment. For the removal of dyes, the development of a pore structure as a result of the pretreatment seemed to play an important role, while the sorption of metals was strongly dependent on the chemical composition of the biosorbent. The highest adsorption capacity for methylene blue and for Fe(III) and Cu(II) was obtained for a lignocellulosic sorbent from sugarcane straw prepared by organosolv pretreatment. The results obtained confirm a great potential use of agricultural waste from sugarcane industry in wastewater treatment. Graphic abstract