Reduction of chromium (VI) by the indirect action of Thiobacillus thioparus

Abstract

The microbial reduction of chromium(VI) to chromium(III) has been one of the most widely studied forms of metal bioremediation. Recently, we have found that Thiobacillus ferrooxidans and Thiobacillus thiooxidans, growing on elemental sulphur, can indirectly promote chromium(VI) reduction by producing reducing agents such as sulphite and thiosulphate, which abiotically reduce chromium(VI). Those species of Thiobacillus are acidophilic bacteria which grow optimally at pH values lower than 4. However, most of those reducing agents are stabilised at higher pH values. Thus, the present paper reports on the ability to reduce chromium(VI) using another specie of Thiobacilli, Thiobacillus thioparus, which is able to grow at pH close to 7.0. T. thioparus cultures were carried out in a fermentation vessel containing medium and sulphur as the sole energy source and maintained at 30ºC and 400 rpm. The pH was adjusted to 6.0, 7.0 or 8.0 and maintained with the automatic addition of KOH. Our results show high chromium (VI) reduction values (close to 100% at the end of bacterial growth) at the three pH values. The results of these experiments are very promising for development of a microbiological process to be used in the detoxification of chromium(VI)-polluted effluents

Screening of plant growth promoting traits in heavy metals resistant bacteria: Prospects in phytoremediation

“…For example, chromate may act as terminal electron acceptor for gaining energy [32]. Reduction of Cr (VI) might be due to the chemical compounds like cysteine, sulphite, glutathione and thiosulfates might reduce Cr (VI) into Cr (III) [33]. The enzymatic activities of bacteria might also be one of the possible reasons for reduction of Cr (VI) by soluble and membrane-bound reductases that exist in several of aerobic, facultative and anaerobic bacteria [34].…”

Adsorption of chromium ion (VI) by acid activated carbon

“…The tolerance limit for the discharge of Cr(VI) into inland surface water is 0.1 mg/L and in potable water is 0.05 mg/L (EPA, 1990). A wide range of physical and chemical processes are available for the removal of Cr(VI) from waste water such as electro-chemical precipitation, ultrafiltration, ion exchange, electro-dialysis, reverse osmosis, chemical precipitation, and adsorption (Jung and Shiau, 2000, Yan and Viraraghavan, 2001, Balel and Kumiawan, 2004, Donati et al, 2003. The major drawbacks with these processes are high cost, toxic sludge generation or incomplete metal removal.…”

Fabrication of Metal‐Nanoparticle‐Modified Semiconducting Copper– and Silver–TCNQ Materials as Substrates for the Reduction of Chromium(VI) Using Thiosulfate Ions at Ambient Temperature

“…It has been reported that organic molecules, such as formic acid (HCOOH), can act as a strong reducing agent for the catalytic reduction of Cr VI to Cr III at Pt‐ and Pd‐based nanoparticle catalysts 9. Additionally, thiosulfate ions have also been demonstrated as reductants, albeit relatively ineffectively with conversion times of up to several days 8f. 10 Importantly, however, thiosulfate salts are a National Sanitation Foundation (NSF, a WHO collaborator) approved water treatment chemical and, unlike other reductants such as formic acid, they avoid the potential problem of decreasing the pH of the reaction solution, which can inhibit the precipitation of Cr III 10.…”