Assessment of the Half Maximal Effective Concentration of Growth Inhibition for Heavy Metals on Bacteria Present in Sequencing Batch Reactors

Among the chemical pollutants present in wastewater, heavy metals are persistent compounds the toxicity of which on biological wastewater processes, humans, and the environment has been proven in various studies. In this study, the half maximal effective concentration (EC50) of growth inhibition of cadmium, lead, and mercury was assessed on dominant bacterial species present in sequencing batch reactors (SBR).
Biomass sample was obtained from the biological unit of the SBR established in Moorchekhort Industrial Settlement, Isfahan, Iran. After cultivation and isolation of the dominant bacterial species, their DNA was sequenced through polymerase chain reaction (PCR) technique and the bacteria species were determined. After exposure of these bacteria to different concentrations of mercury, cadmium, and lead, their EC50 was determined using resazurin bioassay.
Findings: Aeromonas, Pseudomonas, Bacillus, and Enterobacter were registered as the 4 dominant bacterial species in the SBR. A great difference was observed in the sensitivity of these 4 bacteria to the heavy metals. Pseudomonas was the most sensitive bacteria to cadmium and lead, while Aeromonas was the most sensitive specie to lead.
It can be concluded that Aeromonas and Pseudomonas are suitable bioindicators for toxicity assessment of wastewater and effluents contaminated with heavy metals.