Sorption properties of lignocellulosic waste from sugarcane processing

Abstract

Background. Adsorption is considered to be one of the most acceptable methods of removing toxicants from aquatic environments. In recent years, the interest of scientists in biosorption with the use of living (microorganisms) and non-living (plant materials) biomass has increased. Such lignocellulosic materials, as wood and crops consisting of cellulose, hemicellulose, lignin and other components in small quantities, exhibit sorption properties due to their multicomponent composition and the presence of various active functional groups on their surface.
Sugarcane (stem residue obtained after juice extraction) and straw (leaves) are by-products that can be considered as a promising sorbent for water purification.
The aim is to determine the chemical composition of sugarcane bagasse and straw and to study their structural-sorption properties for synthetic dye and heavy metal ions.
Materials and methods. Thebagasse and straw of sugarcane, grinded to the size of 0.5–1 mm, were used as sorbent.
The structure of the starting materials was investigated using Fourier transform infrared spectroscopy (FTIS), the morphology of the samples – by scanning electron microscopy, the specific surface area – by nitrogen adsorption/desorption at –272 °C using a NOVA 2200 analyzer, the amount of sorption pores – by the adsorption of benzene vapor in the desiccator.
The sorption of synthetic organic dye methylene blue and Fe³⁺ and Cu²⁺ ions was studied using relevant model solutions under certain conditions. The starting and equilibrium concentrations of methylene blue and Fe³⁺were determined by spectrophotometric method at a wavelength of 664 nm and 510 nm respectively, and Cu²⁺ ions – by iodometric method.
Results. The results of investigation of the chemical composition of sugarcane bagasse and straw indicate that the main components are structural components, namely holocellulose (cellulose and hemicelluloses) and lignin. Both materials contain approximately the same amount of polysaccharides and aromatic components. However, the content of mineral and extractive substances is slightly higher in the straw.
Microphotographs show a complex morphology of the surface of both materials, which contains macro- and micro pores. Despite the smaller specific surface area, sugarcane bagasse has a larger volume of adsorption pores, which is associated with a higher content of polysaccharide component, which is able to swell in an organic solvent environment.
The maximum sorption of methylene blue is achieved at pH 6–7. The sorption capacity of bass and straw on methylene blue is 27.7 and 30.0 mg/g, respectively. The larger sorption capacity corresponds to the material with a larger specific surface area. The absorption rate of the dye on the studied materials is maximum during the first 20 min. The subsequent decrease in the concentration of methylene blue occurs more slowly until the equilibrium value is reached, which is reached within 300 min from the beginning of sorption.
The maximum sorption capacity for Fe³⁺ and Cu²⁺ ions corresponds to the straw and is 9 and 14 mg/g, respectively, and is slightly inferior to other plant waste representatives.
Conclusion. The sorption properties of sugar cane processing wastes – sugarcane bagasse and straw in relation to methylene blue depend on the specific surface of the materials, i. e. on the availability of active sorption centers. Both materials have good sorption capacity for cationic dye at pH 6 and above and are not inferior to other agricultural secondary wastes – sunflower seeds and corn cobs.
The highest sorption capacity for methylene blue and Fe³⁺ and Cu²⁺ ions corresponds to sugar cane straw.
The results indicate a great potential for both types of sugar cane processing waste as bio sorbents for the treatment of wastewater from organic dyes.