Naphthalene concentration dynamics in an aqueous medium in the presence of Bacillus megaterium

The study examined the concentration dynamics of naphthalene, with its initial concentrations of 1, 2, and 3 g/L in synthetic wastewater. The initial number of Bacillus megaterium MK64-1 cells in the medium amounted to 1.7×10 7 CFU/mL. On day 14 of the experiment, the concentration of naphthalene decreased to hundredths of a gram, while the microbial count increased to 10 9 CFU/mL (at the initial naphthalene concentrations of 1 and 2 g/L) and 10 11 CFU/mL (at the initial naphthalene concentration of 3 g/L). After 14 days, the medium pH decreased by an average of 0.7 units (from 8.56 to 7.86) in both test and control media, with the addition of a microbial suspension. During this time, the redox potential of the medium increased by an average of 70 mV in the test media. Quite a strong direct correlation (p < 0.05) was found between the initial concentration and the amount of pollutant degraded by bacteria. The determination of dehydrogenase activity in Bacillus megaterium by means of two methods (with 2,3,5-triphenyltetrazolium chloride and methylene blue), as well as microbial sensitivity to hydrocarbon concentrations of 1, 2, and 3 g/L via the disk-diffusion method, showed no toxic effect of the analyzed pollutant concentrations on bacteria under the experimental conditions. The obtained results indicate the ability of Bacillus megaterium strain MK64-1 to biodegrade naphthalene.