Biosynthesis of silver nanoparticles using Macrococcus caseolyticus strain AgD isolated from crude oil-contaminated water samples and their application in remediation of crude oil contamination in the Niger Delta aquatic environment

This study was carried out to synthesize bacterial silver nanoparticles (AgNPs) using Macrococcus caseolyticus strain AgD for remediation of crude oil contamination in aquatic environment. Characterization was done to ascertain the size, crystallinity, morphology and elemental composition of the bacterial AgNP, which was used for the removal of Total Petroleum Hydrocarbons (TPH) in the water samples. Response surface methodology (RSM) was used for design and optimization of the TPH response. The results indicated that TPH in some water samples were above permissible limits given by the World Health Organization. The results of 16S rDNA sequencing showed that the isolate is related to Macrococcus caseolyticus. The optical properties of AgNPs showed a peak at 425 nm while the XRD patterns revealed crystallinity with average crystallite size of 25.25204 ± 5.89 nm. The RSM showed a good fit for 2FI regression model for the AgNP as elucidated by the coefficient of determination with R² value of 0.9295. Run 1 (contact time 22.5 mins, stirring speed 1625 rpm, dosage 0.275 g, temperature 55 °C) obtained the highest TPH removal of 94.26 %, which was higher than the predicted (93.15 %) using the bacterial strain. The maximum predicted TPH removal was however 94.02 % at optimum factors of contact time (22.5 mins /100 mL), stirring speed (1620 rpm/100 mL), dosage (0.3206 g) and temperature (67.5 °C). The study showed that the bacterial strain was useful in the synthesis of AgNPs to enhance the efficient removal of contaminants in water samples, and that the model developed (2FI) using RSM technique was useful in predicting optimal TPH removal.