Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag

doi:10.1016/j.jhazmat.2009.01.030

Journal of Hazardous Materials

Volume 167, Issues 1–3, 15 August 2009, Pages 516-522

https://doi.org/10.1016/j.jhazmat.2009.01.030 Get rights and content

Abstract

Hexavalent chromium (Cr) is a toxic element causing serious environmental threat. Recently, more and more attention is paid to the bio-remediation of Cr (VI) in the contaminated soils. Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag at a steel-alloy factory in Hunan Province, China, was investigated in the present study. The results showed that when sufficient nutrients were amended into the contaminated soils, total Cr (VI) concentration declined from the initial value of 462.8 to 10 mg kg⁻¹ at 10 days and the removal rate was 97.8%. Water soluble Cr (VI) decreased from the initial concentration of 383.8 to 1.7 mg kg⁻¹. Exchangeable Cr (VI) and carbonates-bound Cr (VI) were removed by 92.6% and 82.4%, respectively. Meanwhile, four Cr (VI) resistant bacterial strains were isolated from the soil under the chromium-containing slag. Only one strain showed a high ability for Cr (VI) reduction in liquid culture. This strain was identified as Pannonibacter phragmitetus sp. by gene sequencing of 16S rRNA. X-ray photoelectron spectroscope (XPS) analysis indicated that Cr (VI) was reduced into trivalent chromium. The results suggest that indigenous bacterial strains have potential application for Cr (VI) remediation in the soils contaminated by chromium-containing slag.

Introduction

Chromium (Cr (VI)) contamination in soils mainly results from the discharge of chromium-containing waste and waste-water from ore refining, production of steel and alloys, metal plating, tannery, wood preservation, and pigmentation. In soil environment, the most stable oxidation states of chromium are Cr (III) and Cr (VI). Cr (VI) is toxic and carcinogenic to humans via inhalation for long exposures [1], [2]. Furthermore, Cr (VI) in soils can be leached into surface water or groundwater because of its high solubility and mobility. Concentrations of Cr (VI) as low as 0.5 mg L⁻¹ in solution and 5 mg kg⁻¹ in soils can be toxic to plants [3]. Hence, Cr (VI) is a significant risk to human health when it released into the soil environment.

Conventional technologies for Cr (VI) remediation in soils are physico-chemical extraction, land filling, stabilization/solidification, soil washing, flushing and excavation. However, most of these methods require high energy and large quantities of chemical re-agents [4], which could result in occurrence of secondary pollution. Thus, these technologies are not completely applied on a large scale. Recently, biological treatments arouse great interest in Cr (VI) remediation of contaminated sites because it is an economical and environmentally friendly way as compared to the conventional technologies. The bio-remediation strategy is to convert Cr (VI) into less toxic and less mobile Cr (III). Consequently, Cr (III) is immobilized in the soil matrix.

Many microbes were reported to reduce Cr (VI) under aerobic and anaerobic conditions [5], [6], [7], [8], [9]. Bio-reduction of Cr (VI) can be directly achieved as a result of microbial metabolism [10] or indirectly achieved by a bacterial metabolite such as H₂S [11], [12], [13]. Various bacteria were reported to remedy Cr (VI) contamination in soils. For instance, Jeyasingh and Philip [4] isolated a bacterial strain from a highly contaminated site and found the strain could reduce 5.6 mg g⁻¹ Cr (VI) within 20 days in soil reactors. Desjardin et al. [14] found that Cr (VI) in soils was reduced by Streptomyces thermocarboxydus isolated from the contaminated soil. Bader et al. [15] studied Cr (VI) reduction in soil by microbial community under aerobic conditions and found that Cr (VI) was reduced by as much as 33% within 21 days. Virtually, most of the previous researches on biological reduction of Cr (VI) were conducted in batch reactors using pure cultures. The strains from contaminated sites were enriched and used as exogenous inoculums to remedy Cr (VI) contamination in the autoclaved soils. However, exogenous strains will inevitably lead to ecology risk in soil environmental due to the competition between exogenous strains and indigenous microorganisms. Since Cr (VI)-reducing microbial populations may widely distribute in soils, we can effectively utilize indigenous microorganisms to remedy contaminated soils. Furthermore, most of researches focus on the removal of water soluble Cr (VI). The information on the reduction of other Cr (VI) forms in soils is scanty.

In the present study, Cr (VI) biological reduction by indigenous microorganisms was investigated in contaminated soils by chromium-containing slag. In addition, the remediation of water soluble Cr (VI) and other Cr (VI) forms including exchangeable Cr (VI), carbonates-bonded Cr (VI), Fe and Mn oxides-bonded Cr (VI), organic matter-bonded Cr (VI) and residual Cr (VI) are also studied. The predominant strains that can reduce Cr (VI) were isolated and identified.

Section snippets

Soil sampling

Soil samples were collected from the top soil horizon (0-20 cm) of the sites under the chromium-containing slag heap at a steel-alloy factory in Hunan Province (27°75′N; 112°50′E) in central southern part of China. The samples were collected in spring, 2007. Ten kilograms of soil were taken, thoroughly mixed, air-dried and then passed through a 0.26 mm polyethylene sieve. The soil was classified as ferralic cambisol according to FAO/UNESCO soil classification system and the physical and chemical

Cr (VI) remediation in the contaminated soils by indigenous microorganisms

In the contaminated soils under the chromium-containing slag heap in a steel-alloy factory, the average total Cr (VI) and water soluble Cr (VI) were 462.8 and 383.8 mg kg⁻¹, respectively. As shown in Fig. 1, total Cr (VI) concentration in original soils (non-autoclaved) without culture medium addition did not have significant change. Furthermore, nutrient medium addition in the autoclaved soil did not result in changes of total Cr (VI) concentration (data was not shown), indicating that abiotic

Conclusions

In the present study, indigenous bacteria consortium proved to be able to efficiently remediate Cr (VI) in the soils contaminated by chromium-containing slag. These indigenous bacteria not only effectively removed water soluble Cr (VI), but also removed exchangeable Cr (VI) and carbonates-bonded Cr (VI) within 10 days. Four indigenous bacteria strains were isolated from the Cr-contaminated soil. Only one strain had a high ability to reduce Cr (VI) and this isolate was identified as

Acknowledgements

The authors acknowledge the financial support by the National High-Tech Research and Development Program of China (2006AA06Z374, 2007AA021304) and the Key Program of Science and Technology in Hunan Province (2008SK2007).

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Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag

Abstract

Introduction

Section snippets

Soil sampling

Cr (VI) remediation in the contaminated soils by indigenous microorganisms

Conclusions

Acknowledgements

Int. Biodeter. Biodegr.

Free Radic. Biol. Med.

J. Hazard. Mater.

Chemosphere

Soil Biol. Biochem.

Chemosphere

Environ. Pollut.

Geochim. Cosmochim. Acta.

Chemosphere

Waste Manage.

Process. Biochem.

Corros. Sci.

Corros. Sci.

Chemosphere

Process. Biochem.

Biore. Technol.

Microbiol. Res.