The eradication of reactive black 5 dye liquid wastes using Azolla filiculoides aquatic fern as a good and an economical biosorption agent

Abstract

Azolla filiculoides (AF) biomass has been tested for its performance as a biosorbent agent toward removing reactive black 5 (RB5) dyes from polluted water. The morphology and structure of the AF was characterized using several advanced techniques. To understand the mechanism of the RB5 biosorption by AF, isotherm, kinetic, and thermodynamic analyses were performed. In addition, the biosorption capacity of AF was tested under various environmental conditions such as solution pH (3–11), biosorbent dosage (0.5–8.0 g/L), contact time (up to 150 min), initial pollutant concentration (25–200 mg/L), and solution temperature (273–333 K). The results demonstrated that the biosorption process of RB5 dye onto AF was quite rapid as the biosorption equilibrium status was attained within 60 min of reaction initiation. A negative effect on the removal efficiencies was noted with increase in the pH values from 3 to 11, while the removal efficiency increase by double with the AF dose increase from 0.5 to 2.0 g/L. The kinetic study revealed that the biosorption trend conformed to the kinetic reaction of the pseudo-second-order. The determined parameters of the thermodynamic studies demonstrated the endothermic and spontaneous of the biosorption nature. Complete compatibility of the biosorption isotherm process with the Langmuir model, with regards to this model the maximum biosorption capacity reached to 41.73 mg/g under the optimized conditions (pH = 3, biosorbent dose = 4 g/L, initial concentration = 25 mg/L, and room temperature). The biosorption process occurred through both physical interactions and chemical reactions between the pollutant molecules and the biosorbent reaction sites. Our study thus revealed that AF biomass is a cheap and excellent agent with potential for application in the abatement of RB5 dye concentration in wastewater with acidic pH.