Biosorption of metronidazole using Spirulina platensis microalgae: process modeling, kinetic, thermodynamic, and isotherm studies

Abstract

Metronidazole is well-known antibiotic which, globally, ranks high in popular usage. Therefore, traces of residues of this antibiotic were identified in aquatic bodies. A photosynthetic cyanobacterium, of the microalgae category, S. platensis, has been found to be efficient in the removal of this antibiotic. This study was performed to evaluate the efficiency of S. platensis in the removal of metronidazole from aqueous environments. To set up the optimum conditions for facilitating metronidazole removal, BBD model was employed. The experiment included the following parameters: the initial metronidazole level (10–80 mg/L), pH (4–10), contact time (10–60 min), and biomass dose (0.1–0.5 g/L). From the findings it was evident that S. platensis was able to remove 88.15% of the metronidazole under the following conditions: contact time 38.05 min, metronidazole level 35 mg/L, pH 7.71 and a biomass dose 0.3 g/L. The quadratic model revealed that metronidazole concentration was the chief variable that influenced its removal rate. MNZ removal rate was observed to follow the pseudo-second-order model and the Freundlich model. From the thermodynamic data it appeared that the process of metronidazole biosorption was spontaneous, exothermic and physical. The results of this study revealed that S. platensis could be used as an inexpensive and efficient biosorbent to remove the metronidazole from aqueous solutions.