Advances in Environmental Research, Vol. 3, No. 4 (2014) 283-292 DOI: http://dx.doi.org/10.12989/aer.2014.3.4.283 283 Copyright © 2014 Techno-Press, Ltd. http://www.techno-press.org/?journal=aer&subpage=7 ISSN: 2234-1722 (Print), 2234-1730 (Online) Optimization of Cu, Hg and Cd removal by Enterobacter cloacae by ferric ammonium citrate precipitation Rashmi R. Singh, Devayani R. Tipre and Shailesh R. Dave  Department of Microbiology and Biotechnology, School of Sciences, Gujarat University, Ahmedabad 380 009. Gujarat, India (Received January 17, 2014, Revised May 30, 2014, Accepted August 01, 2014) Abstract. Iron precipitating organisms play a significant role in the formation of ferric hydroxide precipitate, which acts as strong adsorbent for toxic metal. In this respect four different iron precipitating cultures were isolated from Hutti gold mine surface winze water sample on citrate agar medium. The best isolate was screened out for metal removal study on the basis of fast visual iron precipitation. The selected isolate was identified as Enterobacter sp. based on routine biochemical tests and Biolog GN microplate results and as Enterobacter cloacae subsp. dissolvens by 16S rRNA gene sequence analysis (GenBank accession number EU429448). Influence of medium composition, medium initial pH, the influence of inoculum size, effect of various media and ferric ammonium citrate concentration were studied on metal removal in shake flask experiments. Under the optimized conditions studied, E. cloacae showed 94 ± 2, 95 ± 2 and 70 ± 2% of cadmium, copper and mercury removal from a simulated waste in shake flask studies. In lab scale column reactor more than 85% of copper and mercury removal was achieved. Keywords: biosorption; iron precipitation; Enterobacter cloacae; copper; mercury; cadmium 1. Introduction Today indiscriminate and uncontrolled discharge of metal contaminated industrial effluents into the environment has become an issue of major concern (Hakeem and Bhatnagar 2010). Rapid industrialization and urbanization have resulted in elevated levels of toxic heavy metals entering the biosphere (Safavi et al. 2011). Heavy metals like copper, cadmium, mercury, chromium, iron, cobalt, nickel, and lead are detrimental to human health and ecosystem stability (Rajasimman and Murugaiyan 2010). The permissible limit for copper, cadmium and mercury in drinking water as per World Health Organization guidelines is 1.0, 0.005 and 0.001 mg/L respectively (Kumar and Puri 2012). Copper, finds its way to the water stream from electroplating, mining, electrical, electronics, printing, photography and metal finishing industries (Shetty and Rajkumar 2009). Ingesting of heavy metals can cause headaches, dizziness, nausea, vomiting, diarrhoea, hypertension, emphysema, damage to vital organs and can even cause death (Tilaki and Ali 2003, Mortazavi et al. 2005, Rajeshkumar and Kartic 2011, Sinha and Khare 2012). Methods, such as chemical precipitation, oxidation or reduction, electrochemical treatment, Corresponding author, Professor, E-mail: shaileshrdave@yahoo.co.in