Recent progress in biohydrometallurgy and microbial characterisation

Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisatio

Kinetics and modelling of thiosulphate biotransformations by haloalkaliphilic Thioalkalivibrio versutus

Biotransformation of thiosulphate by Thioalkalivibrio versutus was studied under haloalkaline conditions (pH 10, 0.66–1.2 M Na +) using batch assays and modelling tools for possible sulphur recovery from haloalkaline industrial streams. The thiosulphate was fully biotransformed to sulphate or to sulphate and elemental sulphur at initial S 2O 3 2−-S concentrations of 25–550 mM within 10 days. The highest biotransformation rate of 2.66 mM [S 2O 3 2−-S] h −1 was obtained at initial S 2O 3 2−-S concentration of 550 mM with half saturation constant (K s) of 54.5 mM [S 2O 3 2−-S]. At initial concentrations below 100 mM S 2O 3 2−-S, the main product was sulphate whilst at above 100 mM also elemental sulphur was produced with up to 29% efficiency. The model approach developed incorporated S 2O 3 2− biotransformation to SO 4 2− and S 0. The kinetic modelling results were compatible (R 2 &gt; 0.90) with the experimental data. The maximum growth rate (µ m) was 0.048 h −1 (0.47 mM C 5H 7NO 2 h −1) and the maximum growth yield 0.18 mM C 5H 7NO 2/mM S 2O 3 2−-S (20 g cell/mol S 2O 3 2−-S). The high rate thiosulphate biotransformation and elemental sulphur recovery results together with the developed kinetic model can be used for bioprocess design and operation. The potential industrial applications would aim at sustainable resource recovery from industrial haloalkaline and sulphurous process and/or effluent streams.</p

High rate autotrophic denitrification in fluidized-bed biofilm reactors

High rate, high efficiency thiosulfate-driven autotrophic denitrification and denitritation with Thiobacillus denitrificans dominated biofilms were achieved in fluidized-bed reactors (FBRs) operated at 20.0 ± 2.0 and 30.0 ± 0.2 C. Complete nitrate removal was obtained even at nitrate loading rate and hydraulic retention time (HRT) of 600 mg L1 h1 and 10 min, respectively. Further decrease of HRT to 5 min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5 min. Effluent pH remained at 5.8 during denitrification. When nitrite was supplemented as the electron acceptor, denitritation effectively proceeded with the highest nitrite loading rate of 228 mg L1 h1. Similar denitrification and denitritation performances were obtained at 20.0 ± 2.0 and 30.0 ± 0.2 C. Batch assays conducted at temperature range from 1 to 46 C, however, showed a significant impact of temperature on autotrophic denitrification. Ratkowsky model was used to estimate the minimum, optimal and maximum growth temperatures of T. denitrificans dominated culture that were below 1, 26.6 and 50.8 C, respectively

Storing of exoelectrogenic anolyte for efficient microbial fuel cell recovery

<p>Starting up a microbial fuel cell (MFC) requires often a long-term culture enrichment period, which is a challenge after process upsets. The purpose of this study was to develop low-cost storage for MFC enrichment culture to enable prompt process recovery after upsets. Anolyte of an operating xylose-fed MFC was stored at different temperatures and for different time periods. Storing the anolyte for 1 week or 1 month at +4°C did not significantly affect power production, but the lag time for power production was increased from 2 days to 3 or 5 days, respectively. One month storing at –20°C increased the lag time to 7 days. The average power density in these MFCs varied between 1.2 and 1.7 W/m³. The share of dead cells (measured by live/dead staining) increased with storing time. After 6-month storage, the power production was insignificant. However, xylose removal remained similar in all cultures (99–100%) while volatile fatty acids production varied. The results indicate that fermentative organisms tolerated the long storage better than the exoelectrogens. As storing at +4°C is less energy intensive compared to freezing, anolyte storage at +4°C for a maximum of 1 month is recommended as start-up seed for MFC after process failure to enable efficient process recovery.</p