Effects of chromium (VI) on the activities of ureolytic mixed culture

BACKGROUND: Ureolytic microbial carbonate precipitation (MCP) is a novel process for removing excess calcium from industrial effluents. This process is based on the hydrolization of urea to provide a suitable medium for the precipitation of Ca as CaCO3. RESULT: A toxicity identification evaluation was conducted on synthetic wastewater simulating wastewater from paper recycling to determine the inhibition or toxicity of chromium(VI) ions on the activities of a ureolytic mixed culture (UMC) with respect to the removal rate of COD and removal of Ca2+ in batch reactors. The 50% inhibiting concentration (IC50) and the 25% inhibiting concentration (IC25) values of Cr(VI) on UMC were determined as 40 and 18 mg L-1, respectively, for an exposure time of 1 day. The inhibitory effects of Cr(VI) were lower on UMC after longer exposure times of 3,4 and 5 days. COD removal rate, ammonium production and Ca removal of samples with 512 mg Cr(VI) L-1 were significantly inhibited. CONCLUSION: The present study has shown that the effects of different metallic species, organic toxicants and other environmental factors should be taken into account when removing problematic Ca and other possible elements from the environment using UMC. (C) 2008 Society of Chemical Industry