Parameters screening and kinetic study of amoxicillin biodegradation by Aspergillus tamarii

Amoxicillin (AMX) is a semisynthetic β-lactam antibiotic classified known as aminopenicillin due to an extra amine group. It is commonly used against bacterial infections in both humans and animals. However, AMX is abused and is consumed in large amounts globally. A significant amount of amoxicillin residue in water bodies is difficult to remove and will negatively affect the environment by increasing the bacterial resistance towards amoxicillin. This will simultaneously harm the aquatic ecosystem in the environment due to the genotoxic effect of AMX residues. Other existing methods are costly, may have fouling problems, are too complex in real field operations and consume a high amount of energy causing the technology inaccessible to developing countries. Biodegradation is a studied method which is low risk, low cost, environmentally friendly and easy to control. The fungus, Aspergillus tamarii was observed in a previous study to exhibit degradation ability against AMX in submerged fermentation. This study screened the significant parameters: initial pH, agitation speed, incubation time, and inoculum level using the fractional factorial with a 24-1 design, with the percentage amoxicillin biodegradation (AMX%) as a response. It was discovered that the main effects including incubation time, initial pH, agitation speed and inoculum size were found to be significant (p < 0.05) to the biodegradation process. Using the significant parameters obtained, the process achieved maximal biodegradation of 81.18 ± 2.5% (mean±SD). Using the parameters obtained, this study also evaluates the fermentation profiles and kinetics of A. tamarii with the presence and absence of AMX in shake flasks. Results showed that AMX presence had minimal impact on A. tamarii’s growth, glucose consumption and protein production. Kinetic models demonstrated strong agreement between simulated and experimental data. Further experiments were conducted in a stirred tank reactor (STR) at 250, 500 and 770 rpm impeller speeds to investigate its large scale potential. Among the tested speeds, 770 rpm showed the highest efficiency, yielding the lowest residual glucose concentration (3.94 g/L) and the highest protein production (0.071 g/L). AMX degradation data fitted well with the second-order polynomial regression model, with high R2 values at 250 rpm (0.98) and 770 rpm (0.94). In conclusion, the significant conditions were successfully screened, and the process was enhanced using fractional factorial design (FFD) with live fungal biomass for amoxicillin biodegradation. A. tamarii exhibits potential degradation abilities against pollutants like AMX, as the antibiotic did not affect its metabolism according to the kinetic studies. Upscaling processes is complicated, thus requiring stringent control of operational parameters to ensure efficient and predictable biodegradation.