The Influence of Biochar and Black Carbon on Reduction and Bioavailability of Chromate in Soils

University of South Australia, Australia.
Journal of Environmental Quality (Impact Factor: 2.65). 07/2012; DOI: 10.2134/jeq2011.0145


The widespread use of chromium (Cr) has a deleterious impact on the environment. A number of pathways, both biotic and abiotic in character, determine the fate and speciation of Cr in soils. Chromium exists in two predominant species in the environment, trivalent [(Cr(III)] and hexavalent [Cr(VI)]. Of these two forms, Cr(III) is non-toxic and is strongly bound to soil particles, while Cr(VI) is more toxic, soluble and readily leaches into groundwater. The toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. The objective of this study was to examine the effect of organic carbon sources on the reduction, microbial respiration and phytoavailability of Cr(VI) in soils. Organic carbon sources such as black carbon and biochar were tested for their potential in reducing Cr(VI) in acidic and alkaline contaminated soils. An alkaline soil was selected to monitor the phytotoxicity of Cr(VI) in sunflower plant. Our results showed that using black carbon resulted in greater reduction of Cr(VI) in soils compared to biochar. This is attributed to the differences in dissolved organic carbon (DOC) and functional groups that provide electrons for the reduction of Cr(VI). When increasing levels of Cr were added to soils, both microbial respiration and plant growth decreased. The application of black carbon was more effective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). The net benefit of black carbon emerged as an increase in plant biomass and a decrease in Cr concentration in plant tissue. Consequently, it was concluded that black carbon is a potential reducing amendment in mitigating Cr(VI) toxicity in soil and plants.

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Available from: Girish Choppala, Jul 18, 2015
    • "The addition of BC did increase the microbial activity of soil, as measured by increased respiration but we didn't examine reducers. Choppala et al. (2012) found addition of BC increased the microbial respiration by 2 times, which may be due to the greater abundance of carbon as an energy source for microbes. BC application to soil significantly increased CO 2 evolution through increases in soil microbial activity, which may be attributed to the addition of labile C and increase in soil pH (Farrell et al., 2013). "
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    ABSTRACT: Heavy metals such as chromium (Cr) and arsenic (As) occur in ionic form in soil, with chromate [Cr(VI)] and arsenate As(V) being the most pre-dominant forms. The application of biochar to Cr(VI) and As(V) spiked and field contaminated soils was evaluated on the reduction processes [(Cr(VI) to Cr(III)] and [As(V) to As(III))], and subsequent mobility and bioavailability of both As(V) and Cr(VI). The assays used in this study included leaching, soil microbial activity and XPS techniques. The reduction rate of As(V) was lower than that of Cr(VI) with and without biochar addition, however, supplementation with biochar enhanced the reduction process of As(V). Leaching experiments indicated Cr(VI) was more mobile than As(V). Addition of biochar reversed the effect by reducing the mobility of Cr and increasing that of As. The presence of Cr and As in both spiked and contaminated soils reduced microbial activity, but with the addition of biochar to these soils, the microbial activity increased in the Cr(VI) contaminated soils, while it was further decreased with As(V) contaminated soils. The addition of biochar was effective in mitigating Cr toxicity by reducing Cr(VI) to Cr(III). In contrast, the conversion process of As(V) to As(III) hastened by biochar was not favourable, as As(III) is more toxic in soils. Overall, the presence of functional groups on biochar promotes reduction by providing the electrons required for reduction processes to occur as determined by XPS data.
    Chemosphere 09/2015; 144:374-381. DOI:10.1016/j.chemosphere.2015.08.043 · 3.34 Impact Factor
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    • "Estimation of Cr(VI) half-life was calculated based on the first-order decay rate equation as described by Choppala et al. (2012). In this equation, the net rate of change in residual Cr(VI) at any instant time will be equal to the decay rate (V dec ), which is expressed by the following first-order differential equation: "
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    ABSTRACT: This study was aimed to examine the efficiency of a novel bacterial consortium on the reduction of toxic hexavalent chromium [Cr(VI)] to non-toxic trivalent Cr [Cr(III)]. Six Cr(VI)-resistant bacteria (IS1-IS6) were isolated from a tannery waste disposal site at Mount Barker, South Australia, of which three viz., IS1, IS2 and IS3 were selected based on Cr(VI) reduction ability in minimal salt medium. The isolates were identified as Bacillus endophyticus (IS1), Microbacterium paraoxydans (IS2) and Bacillus simplex (IS3) by 16S rRNA gene sequencing. All three isolates were able to tolerate chromium (Cr(VI), 300–400 mg L−1), arsenic (As(V), 1,000 mg L−1), copper (Cu(II), 300–400 mg L−1) and lead (Pb(II), 1,000 mg L−1). The isolates were evaluated both as an individual and as a consortia for Cr(VI) reduction in minimal salt medium and storm water, both spiked with 100 mg Cr(VI) L−1. In both cases, the rate of Cr(VI) reduction was found to be significantly higher in the bacterial consortium inoculation (t ½ = 8.45 for minimal salt medium; 6.02 h for storm water), compared to inoculation with individual isolates (t ½ = 53.3–115.5 h for minimal salt medium; 8.77–9.76 h for storm water). The rate of Cr(VI) reduction in both minimal salt medium and storm water was found to be higher in bacterial consortium inoculation (IS1 + IS2 + IS3) than in individual isolate inoculation. This experiment demonstrated that bacterial consortium prepared by using B. endophyticus, M. paraoxydans and B. simplex was more effective in Cr(VI) detoxification than application of individual bacterium. This experiment also proved that a bacterial consortium was more effective in Cr(VI) detoxification than the application of individual bacterial strain.
    Water Air and Soil Pollution 11/2013; 224(12). DOI:10.1007/s11270-013-1716-9 · 1.55 Impact Factor
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    • "The resulting charred residues were washed with 1 M HCl and later washed with 1:1 1 M HCl and 1 M HF to remove any silica and other inorganic materials. Following several cycles of thorough washing with distilled water until the pH of the BC remained constant, the BC samples were dried in a hot air oven at 60 °C for 48 h and stored in an air tight glass container (Choppala et al. 2012). Chicken manurederived biochar (CM) and green waste-derived biochar (GW) were produced at a treatment temperature of 550 °C in a pyrolysis plant by Pacific Pyrolysis at Somersby, New South Wales (www.pacificpyrolysis. "
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    ABSTRACT: Biochar has great potential as a soil amendment to immobilize heavy metals, thereby reducing their bioavail-ability. In this study, biochars derived from chicken manure and green waste were compared with commercial activated carbon (AC) and laboratory produced black carbon (BC) for the sorption of Pb and Cd. Sorption kinetics and equilibrium sorption isotherms for Pb and Cd were obtained for the char materials and the data were fitted to kinetic and sorption isotherm models.. Chicken manure-derived biochar (CM) showed the highest sorption capacity for both Pb and Cd, and the Pb sorption by biochars was higher than the Cd sorption because of the precipitation of Pb with various ions released from the biochars such as carbonate, phosphate, and sulfate. The sorption data for both Pb and Cd were better represented by the pseudo-second order kinetic model than the pseudo-first order kinetic model, which indicates chemical sorption between biochar and metals. For the isotherm studies, char materials was mixed with various amount of Pb or Cd solutions and the remaining metal concentration was measured. The equilibrium sorp-tion data followed a Langmuir isotherm with a maximum sorption capacity of 6.8–11 and 1.7–8.0 mg/g by biochars for Pb and Cd, respectively. Furthermore, CM immobilized Pb and Cd up to 93.5 and 88.4 %, respec-tively, while BC was not effective in the immobilization of Pb in soil. Overall, the sorption experiments in solution and the immobilization experiment in soil showed that biochars are more effective than AC in the sorption of Pb and Cd, and that they have the potential to be used as a soil amendment to remediate metal-contaminated soil.
    Water Air and Soil Pollution 11/2013; 224(12). DOI:10.1007/s11270-013-1711-1 · 1.55 Impact Factor
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