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Desorption of synthetic dye methylene blue from dye-adsorbed lignocellulosic biosorbent using organic solvents

Adsorption is the method most often used for the removal of dyes from industrial effluents. However, due to the high-cost of conventional adsorbents, a wide range of lignocellulosic waste materials are being extensively investigated as a possible novel adsorbents. Many of them proved to be very effective. Dye-loaded lignocellulosic material cannot be directly discarded to the environment, so one of the alternatives is to ferment it using fungi that are capable of degrading the dye. For the purpose of future analyses of fermented dye-loaded lignocellulosic material, i.e. the quantification of the dye degradation extent, a series of organic solvents were used to extract the methylene blue (MB) adsorbed onto brewers’ spent grain (BSG). Both unfermented and fermented (solid-state fermentation using T. versicolor) dye-adsorbed BSG samples were tested. The individual solvents used in this study included nonpolar slovents (benzene, toluene, chloroform, dichloromethane and xylene), polar aprotic solvents (tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide), and polar protic solvents (ethanol, methanol, amyl alcohol and water). Furthermore, a two-component solvent system (methanol : water 1 : 1) and three-component solvent system (methanol : chloroform : water 1 : 1 : 1) were also used. To stress the importance of the principles of green chemistry, ultrasonic-assisted extraction of MB from BSG with deep eutectic solvents (DES), choline chloride/hydrogen bond donor (ChCl/HBD) was also explored. The results showed that the highest desorption of MB from BSG was achieved using polar protic solvents, out of which methanol was the best. The lowest desorption was achieved using non-polar solvents. The results of the MB extraction from BSG using deep eutectic solvents indicated that some of the tested eutectic solvents could be used as an “green” alternative to organic solvents. However, they were far less efficient than the polar protic solvents.

eutectic solvents, extraction, polar protic solvents, methylene blue

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