A solid agricultural waste, coffee husk, was applied as an adsorbent for reactive dye-polluted wastewater treatment. Coffee husk biochar was pyrolyzed at 450 °C and then chemically activated using 50% ZnCl2 solution. The surface of activated coffee husk biochar was modified using a cationic surfactant, Cetyltrimethylammonium bromide (CTAB), to create CTAB-modified coffee husk biochar (MCH), to improve reactive adsorption of anionic dyes from synthetic wastewater. The selected reactive dyes were reactive yellow 145 (RDY145), reactive red 195 (RDR195), and reactive blue 222 (RDB222). The adsorption kinetics fit well using a pseudo-second order model for all three dyes. The adsorption isotherms matched well with the Langmuir model .The removal efficiency of RDY145 (83.7%) was the highest, followed by RDR195 (71.1%) and RDB222 (59.6%). The amount of RDY145 adsorbed by MCH was about 9-fold that adsorbed by conventional activated carbon. Additionally, the solution pH had no effect on reactive dye removal efficiency using MCH.
Nonionic surfactants have been utilized to improve the enzymatic hydrolysis of lignocellulosic materials. However, the role of surfactant adsorption affecting enzymatic hydrolysis has not been elaborated well. In this work, nonionic surfactants differing in their molecular structures, namely the polyoxyethylene sorbitan monooleate (Tween 80), the secondary alcohol ethoxylate (Tergitol 15-S-9), and the branched alcohol ethoxylate (Tergitol TMN-6), were studied for their effects on the enzymatic hydrolysis of palm fruit bunch (PFB). The PFB was pretreated with a 10% w/v sodium hydroxide solution and then hydrolyzed using the cellulase enzyme from Trichoderma reesei (ATCC 26921) at 50 °C and pH 5. The optimal conditions providing similar yields of reducing sugar required Tween 80 and Tergitol TMN-6 at 0.25% w/v, while Tergitol 15-S-9 was required at 0.1% w/v. All the surfactants improved the enzymatic conversion efficiency and reduced unproductive binding of the enzyme to lignin. In addition, the adsorption isotherm of cellulase was fit well by the Freundlich isotherm, while adsorption of the three nonionic surfactants agreed well with the Langmuir isotherm. Adsorption capacities of the three nonionic surfactants were consistent with their enhancement efficiencies in hydrolysis. The critical micelle concentration was observed as a key property of nonionic surfactant for adsorption capacity.
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