Use of Cassava Residue for the Removal of Congo Red from Aqueous Solution by a Novel Process Incorporating Adsorption and In Vivo Decolorization

Abstract

To investigate the removal of Congo red (CR) from an aqueous solution using cassava residue, a novel process incorporating adsorption and in vivo decolorization was proposed. The conditions and characteristics of CR adsorption on cassava residue were investigated by batch adsorption experiments. Langmuir and pseudo-second order models were found to fit well with the data of equilibrium adsorption and kinetics adsorption, respectively. The adsorption was affected considerably by the adsorbent (cassava residue) dosage and CR concentration. The maximum adsorptive capacity was 59.2 mg/g (mCR/mcassava residue), calculated by the Langmuir model. Then, CR-loaded cassava residue was further decolorized via an in vivo process by Trametes sp. SYBC-L4. The laccase produced by Trametes sp. SYBC-L4 effectively decolorized CR, which was revealed by native polyacrylamide gel electrophoresis. The moisture content affected the performance of in vivo decolorization considerably. Decolorization of 81.6 ± 2.4% was achieved under the conditions of pH 5.5, temperature 30 °C, and moisture content of 60% after 16 days of cultivation. Moreover, analyses of Fourier transform infrared spectroscopy and scanning electron microscopy indicated that the carbonyl (C=O), hydroxyl (-OH), and amino (-NH) groups in cassava residue were the potential adsorption sites for interaction with CR and that the structure of cassava residue was modified in the process of in vivo decolorization.