Biosorption of chromium and nickel by heavy metal resistant fungal and bacterial isolates
Introduction
Chromium and nickel are released into the environment by a large number of processes such as electroplating, leather tanning, wood preservation, pulp processing, steel manufacturing, etc., and the concentration levels of chromium and nickel in the environment widely varies. These two metals are of major concern because of their larger usages in developing countries and their nondegradability nature. Hexavalent chromium is highly soluble in water and carcinogenic to human. Ni(II) is more toxic and carcinogenic metal when compared with Ni(IV). Due to their toxic effects on living systems stringent limits have been stipulated for the discharge of chromium and nickel into the environment. According to ISI: Bureau of Indian Standard (BIS) the industrial effluent permissible discharge level of Cr(VI) and Ni(II) into inland water is 0.1 and 3.0 mg L−1, respectively.
Conventional physicochemical methods such as electrochemical treatment, ion exchange, precipitation, reverse osmosis, evaporation, and sorption [1], [2] for heavy metal removal from waste streams are not cost effective [3] and hence biological approach has been considered as an alternative remediation for heavy metal contamination. Recently microbial systems like fungus, bacteria and algae have been successfully used as adsorbing agents for removal of heavy metals [4], [5], [6], [7]. Microbial populations in metal polluted environments adapt to toxic concentrations of heavy metals and become metal resistant [8]. Different species of Aspergillus, Pseudomonas, Sporophyticus, Bacillus, Phanerochaete, etc., have been reported as efficient chromium and nickel reducers [9], [10]. The response of microorganisms towards toxic heavy metals is of importance in view of their interest in the reclamation of polluted sites. In the present investigation, the ability of isolated fungal and bacterial strains towards remediation of chromium and nickel was evaluated by characterizing the bioaccumulation of these metals. Effect of temperature, pH, and tolerance to the heavy metals by the isolated organisms were carried out.
Section snippets
Sampling
Soil samples were collected from a 30-year-old small scale electroplating industry at Sipcot, Vellore district, Tamil Nadu, India that uses chromium and nickel for metal plating. In the soil sample collected, the chromium and nickel concentration were approximately between 100 and 50 mg L−1, respectively. Other reported literature values for contamination in soil are chromium: 4700 mg kg−1 and nickel: 5100 mg kg−1 [11]. The collected samples were stored at −80 °C before analysis.
Isolation of metal-resistant microorganisms
Chromium and Nickel
Optimal pH and temperature for heavy metals removal by the isolated species
In the pH range studied (3–11 for 100 mg L−1 of chromium and 50 mg L−1 of nickel), maximum removal of Cr(VI) (92%) and Ni(II) (90%) were observed around pH 5 in the case of Aspergillus sp. (Fig. 1, Fig. 2). Micrococcus sp. reported a maximum removal for Cr(VI) (90%) and Ni(II) (55%) at pH 7.0 (Fig. 3, Fig. 4). With increase in pH from two to four almost no bioaccumulation occurred in the case of both the metals for the isolated Aspergillus and Micrococcus sp. Above pH 5, the percent removal for
Conclusion
In this study, Chromium- and Nickel-resistant microorganisms were isolated from heavy metal contaminated environments, and the applicability of their heavy metal removal from industrial wastewater was evaluated at a laboratory scale. The optimum conditions for both the growth and heavy metal removal were determined for each isolate. The optimal pH for fungal isolates was lower (5–5.2) than that for bacterial isolates. The observed effect(s) of pH on bioaccumulation was attributable mainly to
References (29)
- et al.
Activated carbon prepared from biomass as adsorbent: elimination of Ni(II) from aqueous solution
Bioresour. Technol.
(2002) - et al.
Removal of heavy metals from industrial wastewaters by adsorption onto activated carbon prepared from an agricultural solid waste
Bioresour. Technol
(2001) - et al.
Algal–bacterial processes for the treatment of hazardous contaminants: a review
Water Res.
(2006) - et al.
Heavy metals removal by the microalga Scenedesmus incrassatulus in continuous cultures
Biores. Technol.
(2004) - et al.
Heavy metal removal from aqueous solution by fungus Mucor rouxii
Water Res.
(2003) - et al.
Effect of microbial activity on the mobility of chromium in soils
Waste Manag.
(2002) - et al.
Removal of hexavalent chromium using distillery sludge
Biores. Technol.
(2003) - et al.
Adsorption of Ni(SO4) on Malaysian rubber–wood ash
Biores. Technol.
(2000) - et al.
Comparative studies on the microbial adsorption of heavy metals
Adv. Environ. Res.
(2003) - et al.
Removal of metal ions from aqueous solution by polysaccharide produced from Bacillus firmus
Water Res.
(2003)