Characterization and utilization of industrial microbial waste as novel adsorbent to remove single and mixed dyes from water

Abstract

Industrial microbial waste (IMW) from amylase production using Aspergillus niger was characterized and utilized as novel adsorbent to remove two model cationic dyes (crystal violet, CV; methylene blue, MB) in their single and binary system. IMW was composed of organic Aspergillus niger biomass and inorganic perlite and diatomite, and thereby was regarded as a composite sorbent which was also characterized using FTIR, SEM, and XPS. The sorptive properties of IMW were studied in batch experiments by varying initial dye concentration, contact time, temperature, sorbent dosage, and NaCl concentration. The adsorption of CV and MB exhibited very similar trends in both single and binary dye solutions. Isotherms, kinetics, and thermodynamics were used to describe the sorption processes. The Langmuir model provided a good fit of the experimental data with the maximum monolayer adsorption (qm) of 175.4 mg/g and 92.6 mg/g for CVs and MBs, respectively in the single dye system. In the mixed dye solutions, the qm for CVm and MBm was reduced to 74.6 mg/g and 52.9 mg/g, respectively. Second-order kinetic model (R2 > 0.999) better explained the adsorption for the two dyes in single or mixed forms, suggesting chemical sorption nature of the process. The adsorption was dominated primarily by membrane diffusion and found to be endothermic and spontaneous. The IMW can thus be repurposed as a novel and promising cleaning agent for removal of organic pollutants from miscellaneous wastewaters.