A comparative study on selective biosorption in aqueous mixtures of dyes with different ionic characters by Chlorella sp. biomass

In this study, the adsorption percentages of Chlorella Sp. biomass towards five ionic dyes and their relevant combinations in aqueous media were studied as a model system for wastewater remediation compared to a proper type of activated carbon. Since wastewater effluents often contain a large variety of ionic micropollutants, there are an ongoing need to determine biosorption potential against various structures of single chemical contaminants. To have a more realistic model and understanding of biosorption to remove aqueous chemical contamination, combinations of aqueous contaminants are herein proposed to be monitored. Five molecules with distinct ionic and structural characteristics, namely a cationic dye Methylene Blue, anionic dyes Isolan Dark Blue and Eriochrome Black T, a zwitterionic dye Methyl Orange, and a larger molecular weight zwitterionic dye Congo Red constituted the targeted set of model adsorbates. Cationic molecules demonstrate a higher tendency to be adsorbed onto Chlorella Sp. than anionic and zwitterionic dyes. Therefore, the cationic dye was selected to investigate its potential to facilitate better biosorption of the selected anionic and zwitterionic dyes, through the possible generation of additional positive charges on the adsorbent surface of microalgae biomass. Single dyes and selected mixtures of them were employed to determine the removal percentages of Chlorella Sp., by monitoring dye removal through observation of decreasing concentrations using UV absorption spectroscopy, under different aqueous conditions. Reliable measurements of concentration changes in the case of dye mixtures based on light absorption from multiple wavelengths were established.