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Various studies were reported for the evaluation of the adsorption performance of kaolin clay using single dye types. This paper aimed to evaluate the comparative adsorption capacity of prepared adsorbents from Ethiopian kaolin for different dye types (Basic Yellow 28 (BY 28), Congo Red (CR), and Reactive Red 120 (RR 120)). Because different dye classes may have a significant impact on the removal efficiency by the prepared adsorbent. Moreover, we intended to investigate the interaction effect of adsorbent-sorbate in the adsorption phenomenon for the three different class dyes. The adsorbents from kaolin clay were prepared via mechanical treatment, beneficiation, and calcination (700 °C). The effect of operating parameters (pH, adsorbent dose, contact time, dye concentration, and adsorption temperature) was evaluated. before and after adsorption of the adsorbents were characterized using FTIR spectroscopy. Furthermore, adsorption isotherm, kinetic models, and the thermodynamic processes in the adsorption phenomenon were computed. The percentage removal efficiency of dyes was recorded as 92.08%, 88.63%, and 73.33% for BY 28, CR, and RR 120 dyes, respectively at the experimental condition: adsorbent dosage = 1 g/100 mL, solution pH = 9 (BY 28), and pH = 3 (CR, and RR 120), contact time = 60 min, initial dyes concentrations = 20 mg/L, and temperature = 30 °C. The adsorption of adsorbates onto kaolin adsorbents was well fitted with pseudo-second-order kinetics and Langmuir isotherm models. The thermodynamic parameters indicate that the adsorption process is spontaneous and exothermic for all dyes. The comparative percentage removal of, with the same operational parameters and kaolin adsorbent, was recorded as BY 28 > CR > RR120 resulting from their surface charge and molecular size/structure dyes properties. We confirm that the adsorption at each operational parameter and peak intensity of FTIR spectra, before and after adsorption, revealed that the different dye types have varied removal efficiency onto the prepared kaolin adsorbent. This is due to that being dominantly influenced by the electrostatic interaction and steric effects at the surface of the sorbent and sorbate characteristics. We deduced that the kaolin clay used as an adsorbent is highly dependent on the dye types and their featured characteristics.

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives are common pollutants that require effective remediation techniques. PAH biodegradation using bacterial and fungal enzymes has gained popularity because it effectively removes these contaminants. Ligninolytic enzymes (LEs), such as laccase (Lac), lignin peroxidase (LiP), manganese peroxidase (MnP), and versatile peroxidases (VPs), have been studied for their role in PAHs biodegradation. These enzymes, produced by different living organisms, have demonstrated significant potential in degrading complex PAH structures, contributing to cleaner and more sustainable remediation techniques. This review evaluates the biodegradation capacity of PAHs using different strains and/or their LEs and provides an in-depth analysis of their mechanisms and removal efficiencies. In addition, the fundamental catalytic mechanisms governing the biodegradation of PAHs and factors that must be optimized to promote effective breakdown and detoxification are highlighted. This review also highlights recent biosensor developments that provide enhanced sensitivity and specificity for PAH detection. Although some LE-producing strains are efficient in completely biodegrading certain PAH types, further research is needed to explore the complete biodegradation of PAHs with higher molecular structures using genetically modified strains or their LEs. Despite progress, challenges remain in optimizing enzyme activity and integrating biosensors into large-scale use. Future research should focus on enhancing stability and improving field deployment for better environmental monitoring.