The impact of toxicity of metals on the activity of ureolytic mixed culture during the precipitation of calcium

In this article, the inhibitory impact of metals on substrate utilization and microbial carbonate precipitation (MCP) by ureolytic mixed cultures (UMC) was investigated with glucose and mineral medium under batch conditions. The IC50 (toxicant concentration eliciting 50% inhibitory effect) values were determined from the BOD values of samples. Inhibition, expressed as the value of 50% inhibitory effect (IC50), was evaluated by the decrease in substrate removal using BOD tests. The effect of toxicity of metals on substrate degradation, IC50 values, was found to increase in the following order: Cd(II) > Cu(II) > Pb(II) > Cr(VI) > Ni(II) > Zn(II). Nitrification a possible phenomenon in the biocatalytic process was observed in several samples and this inhibited the precipitation of soluble calcium. During the removal of calcium from industrial calcium-rich wastewater, toxicity of metal at higher metal concentrations and possibility of nitrification at higher sludge ages should be considered.