Synthesis and characterization of biocers as high-performance biosorbents for dye removal process

Abstract

The immobilization of the biological species such as prokaryotic and eukaryotic cell systems (e.g. bacteria, animal and plant cells, and fungi) and cell-derived subunits (e.g. proteins and enzymes) within inorganic oxide matrices as a class of nanocomposite materials especially through sol-gel technique attracts increasing interests for biocatalysis, bioremediation and structured material templates applications. These interests are justified due to the unique approach to explore the richness of the biological structures for technical uses. In this study, Biocers (biologically modified ceramics) of Trametes versicolor (TV) embedded in silica matrices was synthesized according to the sol-gel method using tetraethyl orthosilicate (TEOS) as a precursor. The synthesized materials namely free silica (SS), hybrid silica with PVA (hSS), TV Biocers (TVB), hybrid TV Biocers with PVA (hTVB), acclimatized TV Biocers (TVB/AC) and PVA-hybrid acclimatized TV Biocers (hTVB/AC) were characterized using scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption measurement and laccase enzyme catalytic activity assay. The performance of the TV Biocers as biosorbents was evaluated using dyes as model emerging organic micropollutants carried out in batch (i.e. shake flask) and continuous (packed-bed) systems. It was observed that the dye removal performance, ? (mmol/g) of the TV Biocers for methylene blue (MB) and malachite green (MG) respectively was 7.400 and 5.569 mmol/g which was 18 and 128 % higher than the SS and free TV cells. These results demonstrated that the TV Biocers can offer better dye removal performance through a combination of adsorption and biodegradation processes. The optimization experiment was carried out using MG due to its higher removal performance (adsorption and biodegradation) than MB. The dye removal performance by hTVB was found maximum when operated at pH 6, temperature of 30 oC, 150 rpm of agitation speed, and a biocers/dye ratio of 30 % (w/v) with MG at concentration of 0.5mM. The hTVB was also able to remove MB, methyl orange, and reactive red. The acclimatized TV Biocers (i.e. TVB/AC and hTVB/AC) was studied for dye removal performance in batch and packed-bed process. The highest dye removal by the hTVB/AC was at concentration of 0.2 mM, temperature of 30 oC, and pH 7 for batch process and fastest at concentration of 0.05 mM, bed height of 1 cm and flow rate of 3.0 mL/min for continuous process. The biosorption thermodynamics and kinetics as well as biodegradation kinetic studies were conducted for all biocers (i.e. SS, hSS, TVB, hTVB, TVB/AC and hTVB/AC) for both batch and continuous processes. High correlation coefficients favour Langmuir isotherm and Elovich model for batch and continuous process for biosorption. Meanwhile, the biodegradation fitted the Haldane model well for batch and continuous process. This is the first reported study on the immobilization of the TV cells in silica matrices for removal of emerging organic micropollutants.