A lignocellulosic waste oiltea shell (OTS) was evaluated as an inexpensive sorbent to remove methylene blue (MB) from aqueous solution. Fungal treatment of OTS increased the MB adsorption by modifying the physicochemical properties of OTS and simultaneously produced laccase as a beneficial co-product. Without fungal treatment, the maximum amount of adsorption (qm) of MB by OTS was 64.4 mg/g, whereas the treatment with fungus Pycnoporus sp. and Trametes versicolor increased qm up to 72.5 mg/g and 85.7 mg/g, respectively. This is because of the improved surface area and pore sizes as well as altered chemical compositions. The equilibrium sorption data for OTS both with and without treatment fitted to the Langmuir model, and the sorption rate data well fitted to the pseudo second-order kinetic model. The changes in free energy (ΔG°) and separation factor (RL) indicated that the sorption was spontaneous and favorable. Scanning electron microscopy and Fourier transform infrared spectroscopy showed the changes in the surface morphology and functional groups of OTS after fungal treatment. The agro-waste OTS could be utilized as a low-cost adsorbent for efficient dye removal, and fungal treatment can serve as a mild and clean technique to increase the adsorptive capacity of OTS.

The present study investigated the adsorptive and enzymatic removal of aniline blue dye (AB) from aqueous solution using waxy riceprocessing waste (RW), peanut shell (PS), microbial waste of Aspergillus niger (MW) as low cost adsorbents, and laccase (Lac) as a biocatalyst. Commercial activated carbon (AC) was also employed to compare the adsorption performance with the three adsorbents. Dye removal was examined under various parameters in batch experiments. It was found that dye removal by RW and Lac was 89–94% noticeably better than that by MW and PS (20–70%). In any cases, AC produced the highest dye removal among the tested materials. The kinetics, isotherms, and thermodynamics were then analyzed to elucidate the adsorption process by the four adsorbents. The pseudo-second order kinetic was superior to the pseudo first order kinetic model in describing adsorption for all adsorbents. The Langmuir model fitted the adsorption process very well, indicating monolayer coverage of dyes on a solid surface. A thermodynamic analysis of enthalpy (ΔH°), entropy (ΔS°), and Gibbs free energy (ΔG°) classified the adsorption as a nonspontaneous and endothermic process. The results reveal diverse natural materials (e.g., processing waste RW) as novel substitutes for traditional activated carbon, as well as laccase as a green catalyst for the treatment of dye wastewater.

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