Abstract
Hexavalent Chromium (Cr(VI)) has long been known to be highly mobile and toxic when compared with the other stable oxidation state, Cr(III). Cr(VI)-soluble environmental pollutants have been detected in soils and water bodies receiving industrial and agricultural waste. The reduction of Cr(VI) by microbial organisms is considered to be an environmentally compatible, less expensive and sustainable remediation alternative when compared to conventional treatment methods, such as chemical neutralization and chemical precipitation of Cr. This study aims to isolate and identify the composition of the microbial consortium culture isolated from waste activated sludge and digested sludge from a local wastewater treatment plant receiving high loads of Cr(VI) from an abandoned chrome foundry in Brits (North Waste Province, South Africa). Furthermore, the Cr(VI) reduction capability and efficiency by the isolated bacteria were investigated under a range of operational conditions, i.e., pH, temperature and Cr(VI) loading. The culture showed great efficiency in reduction capability, with 100% removal in less than 4 h at a nominal loading concentration of 50 mg Cr(VI)/L. The culture showed resilience by achieving total removal at concentrations as high as 400 mg Cr(VI)/L. The consortia exhibited considerable Cr(VI) removal efficiency in the pH range from 2 to 11, with 100% removal being achieved at a pH value of 7 at a 37 ± 1 °C incubation temperature. The time course reduction data fitted well on both first and second-order exponential rate equation yielding first-order rate constants in the range 0.615 to 0.011 h−1 and second order rate constants 0.0532 to 5 × 10−5 L·mg−1·h−1 for Cr(VI) concentration of 50–400 mg/L. This study demonstrated the bacterial consortium from municipal wastewater sludge has a high tolerance and reduction ability over a wide range of experimental conditions. Thus, show promise that bacteria could be used for hexavalent chromium remediate in contaminated sites.
Highlights
Chromium (Cr) and its compounds have been extensively used in many industrial processes, such as metal finishing, metal electroplating, steelworks manufacturing, wood preservation, leather tanning, textile dyeing, and synthesis of pigments [1,2]
This work aims to isolate and investigate the Cr(VI) reduction by consortium bacterium from a sludge coming from a municipal wastewater treatment of Brits, South Africa, that receives high periodic loads of hexavalent chromium from a chrome foundry nearby
The second-order rate constant was in the range of 0.0532–5 × 10−5 L−1·mg−1·h, and decreased with increasing initial concentration
Summary
Chromium (Cr) and its compounds have been extensively used in many industrial processes, such as metal finishing, metal electroplating, steelworks manufacturing, wood preservation, leather tanning, textile dyeing, and synthesis of pigments [1,2]. As a result of the wide anthropogenic use of Cr, large quantities of Cr containing wastes have been produced, and the lack of effective disposal methods of Cr effluents has led to the contamination of surface and groundwater environments, soils and aquatic sediments [3]. Another major concern is that these high Cr(VI) effluents end up in municipal sewer lines and build up in the sludge because only a small quantity is discharged with the wastewater final effluent [4]. Reduction of Cr(VI) to the relatively nonhazardous Cr(III) is an effective strategy to mitigate the risks for human health and the environment
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