Efficacy of ureolytic Enterobacter cloacae EMB19 mediated calcite precipitation in remediation of Zn (II)

Abstract

In this study, urease mediated calcite precipitation technique was used for remediation of Zn (II). A urease positive Enterobacter cloacae EMB19 was used to produce calcite impregnated with Zn ions. In co-presence of Ca (II), Zn (II) concentrations of 10 and 20 mg L⁻¹ were completely remediated by the bacterium from the media at 72 and 96 h of incubation, respectively. Co-precipitation of Ca (II) and Zn (II) to form calcite–Zn precipitate is one of the major mechanisms of Zn remediation in the present study. Role of urease in calcite–Zn precipitation was substantiated by using urease/carbonate and ammonium enriched cell free culture supernatant (CFS) obtained after sufficient microbial growth. Using CFS, 68% removal of initial 50 mg L⁻¹ Zn (II) was detected. Energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction pattern (XRD) of the precipitate supports calcite mediated remediation of Zn. Remediation of multiple metals viz. Cd, Zn, Cu was also analyzed using CFS laden with urease. The preparation showed 40% Cd, 23% Zn, and 8% Cu reduction from the solution containing initial 25 mg L⁻¹ of each metal. Overall, it can be concluded that, the E. cloacae mediated calcite precipitation technique could effectively be used for alleviation of Zn (II) and other heavy metals from the contaminated environment.

Keywords:

• Calcite
• urease
• metals
• zinc
• bioremediation
• Enterobacter cloacae EMB19

Acknowledgments

The financial support provided by Science and Engineering Research Board (SERB)-Department of Science & Technology (DST), Govt. of India in the form of National Postdoctoral Fellowship (FILE NO. PDF/2015/000234) to AB is gratefully acknowledged.