Formation of silver halos by Sphingomonas paucimobilis MX8 and its bioleaching of silver from computer keyboard printed circuit boards.

Silver (Ag) is currently obtained from primary and secondary sources through hydrometallurgical and pyrometallurgical processes. However, these processes consume high amounts of energy and are environmentally unfriendly. The search for bacteria tolerant with a high leaching capacity for to Ag is therefore a necessary requirement as part of the development of bioleaching technologies with reduced impact on the environment and lower energy expenditure. In this sense, the objective of this research was to evaluate the tolerance of Sphingomonas paucimobilis MX8 to Ag added to nutrient agar, and to determine whether this tolerance could favor the bioleaching of Ag present on the printed circuit boards (PCBs) of computer keyboards. The bacteria Sphingomonas paucimobilis MX8 was cultured in Petri dishes with nutrient agar and four different concentrations of AgNO3 (200, 400, 600, and 800 mg L-1) at 28 °C for 10 days. For the bioleaching experiment, the bacteria were grown in a mineral medium with computer keyboard PCBs for 30 days at room temperature (17 to 22 °C) and centrifugation at 150 rpm. The results indicate that Sphingomonas paucimobilis MX8 is tolerant to Ag and forms a silvery halo around its growth in the presence of this metal. Furthermore, Sphingomonas paucimobilis MX8 was able to bioleach 12% of the Ag found in computer keyboard PCBs. The results obtained could help generate more environmentally friendly silver bioleaching processes in which the silver bioleaching capacity of this bacterium is increased.

Microbial Bioleaching of Ag, Au and Cu from Printed Circuit Boards of Mobile Phones.

Electronic waste (E-Waste) is consumed at high speed in the world. These residues contain metals that increase their price each year, generating new research on the ability of microorganisms to recover the metals from these wastes. Therefore, this work evaluated the biologic lixiviation of Cu, Ag and Au from printed circuit boards (PCB) of mobile phones by three strains of Aspergillus niger, Candida orthopsilosis, Sphingomonas sp. and their respective consortia, in addition to leaching with citric acid. The microorganisms were cultured in mineral media with 0.5 g of PCB, and the treatments with 1M citric acid were added the same amount of PCB. All treatments were incubated for 35 days at room temperature. The results showed that Sphingomonas sp. MXB8 and the consortium of C. orthopsilosis MXL20 and A. niger MXPE6 can increase their dry biomass by 147% and 126%, respectively, in the presence of PCB. In the bioleaching of metals, the inoculation of A. niger MXPE6, the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 and Sphingomonas sp. MXB8 leached 54%, 44.2% and 35.8% of Ag. The consortium of A. niger MX5 and A. niger MXPE6 showed a leaching of 0.53% of Au. A. niger MX5 leaching 2.8% Cu. Citric acid increased Cu leaching by 280% compared to treatments inoculated with microorganisms. Although further research is required, A. niger MXPE6 and the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 could be an alternative to recover Ag from PCB of mobile phones.

Induced accumulation of Au, Ag and Cu in Brassica napus grown in a mine tailings with the inoculation of Aspergillus niger and the application of two chemical compounds.

This study evaluated the ability of Brassica napus for extracting gold (Au), silver (Ag) and copper (Cu) from a mine tailings, with the inoculation of two Aspergillus niger strains, and the application of ammonium thiocyanate (NH4SCN) or ammonium thiosulfate [(NH4)2S2O3]. After seven weeks of growth inoculated or non-inoculated plants were applied with 1 or 2 g kg-1 of either NH4SCN or (NH4)2S2O3, respectively. Eight days after the application of the chemical compounds, plants were harvested for determining the total dry biomass, and the content of Au, Ag, and Cu in plant organs. Application of (NH4)2S2O3 or NH4SCN resulted in enhanced Au-accumulation in stems (447% and 507%, respectively), while either (NH4)2S2O3+Aspergillus, or NH4SCN increased the Au-accumulation in roots (198.5% and 404%, respectively) when compared to the control. Treatments with (NH4)2S2O3 or (NH4)2S2O3+Aspergillus significantly increased (P ≤ 0.001) the accumulation of Ag in leaves (677% and 1376%, respectively), while NH4SCN + Aspergillus, and (NH4)2S2O3 enhanced the accumulation in stems (7153% and 6717.5%). The Ag-accumulation in roots was stimulated by NH4SCN+ Aspergillus, and (NH4)2S2O3+ Aspergillus (132.5% and 178%, respectively), when compared to the control. The combination of NH4SCN+Aspergillus significantly enhanced the Cu-accumulation in leaves (228%); whereas NH4SCN+ Aspergillus, or (NH4)2S2O3+ Aspergillus resulted in greater accumulation of Cu in stems (1233.5% and 1580%, respectively) than the control. Results suggest that either NH4SCN or (NH4)2S2O3 (with or without Aspergillus) improved the accumulation of Au and Ag by B. napus. Accumulation of Au and Ag in plant organs overpassed the hyperaccumulation criterion (> 1 mg kg-1 of plant biomass); whereas Cu-accumulation in stems and roots also overpassed such criterion (> 1000 mg kg-1) by applying either NH4SCN or (NH4)2S2O3 + A. niger.

Lead phytoextraction from printed circuit computer boards by Lolium perenne L. and Medicago sativa L.

This work assessed the ability of Lolium perenne and Medicago sativa for extracting lead (Pb) from particulate printed circuit computer boards (PCB) mixed in sand with the following concentrations: 0.5, 1.0 and 1.5 g of PCB, and including a control treatment without PCB. The PCB were obtained from computers, and grinded in two particle sizes: 0.0594 mm (PCB1) and 0.0706 mm (PCB2). The PCB particle sizes at their corresponding concentrations were applied to L. perenne and M. sativa by using three experimental assays. In assay II, PCB2 affected the biomass production for both plants. For assay III, the PCB1 increased the biomass of M. sativa (236.5%) and L. perenne (142.2%) when applying either 0.5 or 1.0 g, respectively. In regards to phytoextraction, assay I showed the highest Pb-extraction by roots of L. perenne (4.7%) when exposed to 1.5 g of PCB1. At assay I, L. perenne showed a Pb-bioconcentration factor higher than 1.0 when growing at 0.5 g of PCB1, and when HNO3 was used as digestion solution; moreover, in assay III both plants showed a Pb-translocation factor higher than 1.0. Therefore, Lolium perenne and Medicago sativa are able to recover Pb from electronic wastes (PCB).

Lipid extraction from the biomass of Trichoderma koningiopsis MX1 produced in a non-stirring culture for potential biodiesel production.

Oleaginous microorganisms such as microalgae, yeasts, bacteria and filamentous fungi are alternative sources of vegetal or animal fats for biodiesel production. This research evaluated the lipid production by the biomass Trichoderma koningiopsis MX1 with a non-stirring culture at room temperature, and fungal lipids were extracted through three techniques for biodiesel generation purposes. The three modified lipid extraction techniques yielded 18.4, 10.3 and 17.1 % of fungal lipids. The trans-esterification of lipids indicated that the controlling components for biodiesel were palmitic (40.8 %) and linoleic acids (ranging from 37.6 % to 41.2 %). Results show that fungal cultural conditions and the lipid extraction technique are determinants for producing biodiesel from fungal lipids. Therefore, the modification of some of these conditions could increase their efficiency and viability.

Bioleaching of gold, copper and nickel from waste cellular phone PCBs and computer goldfinger motherboards by two Aspergillus nigerstrains.

In an effort to develop alternate techniques to recover metals from waste electrical and electronic equipment (WEEE), this research evaluated the bioleaching efficiency of gold (Au), copper (Cu) and nickel (Ni) by two strains of Aspergillus niger in the presence of gold-plated finger integrated circuits found in computer motherboards (GFICMs) and cellular phone printed circuit boards (PCBs). These three metals were analyzed for their commercial value and their diverse applications in the industry. Au-bioleaching ranged from 42 to 1% for Aspergillus niger strain MXPE6; with the combination of Aspergillus niger MXPE6 + Aspergillus niger MX7, the Au-bioleaching was 87 and 28% for PCBs and GFICMs, respectively. In contrast, the bioleaching of Cu by Aspergillus niger MXPE6 was 24 and 5%; using the combination of both strains, the values were 0.2 and 29% for PCBs and GFICMs, respectively. Fungal Ni-leaching was only found for PCBs, but with no significant differences among treatments. Improvement of the metal recovery efficiency by means of fungal metabolism is also discussed.

Bioleaching of gold, copper and nickel from waste cellular phone PCBs and computer goldfinger motherboards by two Aspergillus nigerstrains

In an effort to develop alternate techniques to recover metals from waste electrical and electronic equipment (WEEE), this research evaluated the bioleaching efficiency of gold (Au), copper (Cu) and nickel (Ni) by two strains of Aspergillus niger in the presence of gold-plated finger integrated circuits found in computer motherboards (GFICMs) and cellular phone printed circuit boards (PCBs). These three metals were analyzed for their commercial value and their diverse applications in the industry. Au-bioleaching ranged from 42 to 1% for Aspergillus niger strain MXPE6; with the combination of Aspergillus niger MXPE6 + Aspergillus niger MX7, the Au-bioleaching was 87 and 28% for PCBs and GFICMs, respectively. In contrast, the bioleaching of Cu by Aspergillus niger MXPE6 was 24 and 5%; using the combination of both strains, the values were 0.2 and 29% for PCBs and GFICMs, respectively. Fungal Ni-leaching was only found for PCBs, but with no significant differences among treatments. Improvement of the metal recovery efficiency by means of fungal metabolism is also discussed.

Tolerance and growth of 11 Trichoderma strains to crude oil, naphthalene, phenanthrene and benzo[a]pyrene.

Petroleum hydrocarbons (PHs) are major organic contaminants in soils, whose degradation process is mediated by microorganisms such as the filamentous fungi Cunninghamella elegans and Phanerochaete chrysosporium. However, little is known about the tolerance and the degradation capability of Trichoderma species when exposed to PH. This research evaluated the tolerance and growth of 11 Trichoderma strains to crude oil (COil), naphthalene (NAPH), phenanthrene (PHE) and benzo[a]pyrene (B[a]P) by using in vitro systems. Petri dishes containing solid mineral minimum medium were separately contaminated with COil, with seven doses of either NAPH or PHE (250, 500, 750, 1000, 2000, and 3000 mg L(-1)), and with six doses of B[a]P (10, 25, 50, 75, and 100 mg L(-1)). Non-contaminated plates were used as controls. Trichoderma strains were exposed to all the contaminants by triplicate, and the growth of each fungal colony was daily recorded. No significant differences were observed among Trichoderma strains when they were exposed to COil in which the maximum fungal growth was reached at 96 h. In contrast, Trichoderma strains showed variations to tolerate and grow under different doses of either NAPH, PHE or B[a]P. Increasing NAPH doses resulted on significant greater fungal growth inhibition than PHE doses. The exposure to B[a]P did not inhibited growth of some Trichoderma strains.