A new approach to the remediation of heavy metal liquid wastes via off-gases produced byKlebsiella pneumoniae M426

Abstract

When the off-gas from an aerobic culture of Klebsiella pneumoniae M426 grown in the absence of added heavy metals was passed through a solution of Hg(2+), Cd(2+), Pb(2+), or Cu(2+) a yellow-white (Hg), white (Cd, Pb), or blue (Cu) precipitate was formed. Metal removal from solution was >97% within 2 h at initial concentrations of (as metal): Hg, 8.5; Cd, 12.6; Pb, 7.8; Cu, 9.5 mg/mL. Mercury was removed from solution at pH 2 and in up to 1 M NaCl. Energy dispersive X-ray microanalysis (EDX) of the precipitates showed them to comprise metal, sulfur and carbon in the case of Hg, Cd, and Pb, and, in the case of Cd and Pb, also oxygen. The pH of the solution increased by 1-2 units at an initial pH of 7 and by 4-5 units at an initial pH of 2. In the case of cadmium and lead, the presence of crystalline metal carbonates and hydroxides was confirmed by X-ray powder diffraction (XRD) analysis and additional peaks were seen which could not be assigned to known compounds in the diffraction file database. In the case of copper, hydroxides, and a form of copper sulfate, were found. In the case of mercury the XRD patterns could not be assigned to any known compound, except for HgCl in the solution at the acidic initial pH. The absence of sharp peaks in the pattern for the Hg-precipitate was indicative of poorly crystalline, nanocrystalline or amorphous material. The unknown mercury compound, since it contained non-carbonate carbon, was suggested to be derived from a volatile organothiol in the gases evolved from the culture. Analysis of the culture head gas by GC-MS showed the presence of dimethyldisulfide as a likely precipitant. No sulfur compound was found using XRD analysis in the case of cadmium and lead, although EDX analysis suggested this as a major component and the lack of XRD pattern is evidence for a non-crystalline metal-organothiol. The exact chemistry of the new materials remains to be elucidated but metal precipitation via a biogenic organothiol is a potentially effective approach to the remediation of aggressive metal wastes.

Isolation and Characterization of Environmental Bacteria Capable of Extracellular Biosorption of Mercury

“…Precipitation of HgS by bacteria releasing H 2 S has been proposed as a method for mercury removal (4,(17)(18). Mercury precipitation can also result from the production of volatile organosulfur compounds, yielding precipitates containing mercury together with sulfur and carbon (17). Since the release of dimethyl disulfide has been reported previously for a Serratia marcescens strain (40), a precipitate containing Hg, S, and C can be proposed here for S. marcescens HG19.…”

“…Precipitation of mercury with sulfide or organosulfur compounds is a detoxification mechanism described as a mercury tolerance mechanism rather than an effective resistance process (4,21). Precipitation of HgS by bacteria releasing H 2 S has been proposed as a method for mercury removal (4,(17)(18). Mercury precipitation can also result from the production of volatile organosulfur compounds, yielding precipitates containing mercury together with sulfur and carbon (17).…”

Palladium and gold removal and recovery from precious metal solutions and electronic scrap leachates by Desulfovibrio desulfuricans

“…3Cii) was treated with biogas from a culture of K. pneumoniae as described previously (Essa et al 2005(Essa et al , 2006 or, in some experiments, using biogas made in the same way from E. coli. Organothiols from the breakdown of sulphur-amino acids (Essa et al 2005(Essa et al , 2006 together with an alkalinisation of the medium attributable to production of ammonia or volatile amines by the culture (Essa et al 2006) were shown previously to mediate the removal of copper from solution as a mixture of hydroxide and sulphate (Essa et al 2006). Accordingly, copper was precipitated from the Pd-depleted solution as a blue-green precipitate (Fig.…”

“…H 2 was sparged for 30 min and precipitation was followed over 45 min and left to go to completion over 24 h under gravity. The precious metal-depleted solutions were then treated using biogas from broth-grown cultures of Klebsiella pneumoniae or, in some tests, E. coli, as described previously (Essa et al 2005(Essa et al , 2006. Residual metals were analysed commercially as described above.…”

“…With the objective to develop an integrated chemical and bio-technology for the recycling of printed circuit board scrap (Henderson 2004), the purpose of this study was to evaluate the extent to which native and palladised biomass of D. desulfuricans could be applied to the recovery of Au and Pd in the presence of an excess of Cu, a ubiquitous non-precious metallic component of electronic scrap. In addition, a new bioprecipitation technology utilising bacterial culture off-gas (Essa et al 2005(Essa et al , 2006 was evaluated for copper recovery from the precious metal-depleted solution.…”