Fermented cocoa bean shell by-product as an enhanced adsorbent for dye of the textile industry

Abstract

This work proposes a biotechnological alternative to remove methylene blue (MB) dye contaminants generated during textile industry operations. The use of biological adsorbents is crucial for dye removal due to their renewability, wide availability, and low cost. Cocoa bean shell (CBS), an agricultural by-product, was fermented using the fungus Penicillium roqueforti ATCC 10110 (FCBS) to enhance its adsorption properties for the MB dye in aqueous solutions. Physicochemical characterization and Fourier-transform infrared spectroscopy analysis demonstrated the degradation of cellulose, hemicellulose, and lignin, along with a higher presence of OH–, NH, and NH₂ radicals in FCBS. Thermogravimetric analysis supported these findings, indicating increased hygroscopicity and lower weight loss rates associated with the degradation of lignocellulosic material. Scanning electron microscopy revealed alterations in the biomass’ topographical surface, which was fully colonized by the fungus. Brunauer–Emmett–Teller analysis showed a 6.27-fold increase in surface area, a 28.45-fold increase in pore volume, and a 3.54-fold increase in average pore size in FCBS due to fermentation. Adsorption kinetics at 25 °C indicated equilibrium with an adsorbed dye/adsorbent ratio of 11.8 mg/g after 120 min, with enhanced adsorption observed with increasing temperature and pH (optimal between 6 and 8). Kinetic models suggested more efficient chemisorption for FCBS compared to CBS, as adsorption primarily occurred within the biomass pores for FCBS, while for CBS, it was limited to the surface. The developed adsorbent facilitated the removal of 95% of MB after 60 min. After three cycles of reusability and regeneration, FCBS adsorbed 77% more dye than CBS. These results demonstrate that FCBS is a cost-effective biotechnological adsorbent for the removal of dyeing agents from textile industry effluents. Future research should explore its application in real-world textile industry wastewater treatment. Furthermore, it is highlighted that Penicillium roqueforti ATCC 10110 has been shown to be a multi-enzyme producer, capable of degrading lignin, cellulose, and hemicellulose, which is essential for the adsorption process and dye removal.