Production and characterization of fermented solid derived from cocoa waste for lead adsorption in water

Environmental pollution from toxic metals and waste generation have become major global concerns, driven by industrial and agricultural growth. To produce the adsorbent, the fungus Aspergillus niger ATCC 1004 was inoculated into cocoa pod husk bran. The samples were labeled as fermented solid (FS) and non-fermented solid (NFS) and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, point of zero charge, and surface area analysis via N₂adsorption using the Brunauer–Emmett–Teller method. A univariate design was carried out to optimize the pH conditions, adsorbent mass, and stirring time. The results showed that fermentation had a positive impact on adsorption, as the fungus broke down lignocellulosic compounds, making the FS surface more porous and adding functional groups crucial for effective adsorption, particularly oxygen groups that interact with Pb²⁺, enhancing adsorption efficiency and increasing the solid's crystallinity and thermal stability. FS achieved a 90% adsorption efficiency for Pb²⁺, compared to 76% for NFS. Therefore, fermenting cocoa pod husks significantly enhances the material's adsorption capacity, making it a promising adsorbent for removing lead ions from aqueous solutions.