Selection and Application of Sulfide Oxidizing Microorganisms Able to Withstand Thiols in Gas Biodesulfurization Systems.

After the first commercial applications of a new biological process for the removal of hydrogen sulfide (H2S) from low pressure biogas, the need arose to broaden the operating window to also enable the removal of organosulfur compounds from high pressure sour gases. In this study we have selected microorganisms from a full-scale biodesulfurization system that are capable of withstanding the presence of thiols. This full-scale unit has been in stable operation for more than 10 years. We investigated the microbial community by using high-throughput sequencing of 16S rRNA gene amplicons which showed that methanethiol gave a competitive advantage to bacteria belonging to the genera Thioalkalibacter (Halothiobacillaceae family) and Alkalilimnicola (Ectothiorhosdospiraceae family). The sulfide-oxidizing potential of the acclimatized population was investigated under elevated thiol loading rates (4.5-9.1 mM d-1), consisting of a mix of methanethiol, ethanethiol, and propanethiol. With this biomass, it was possible to achieve a stable bioreactor operation at which 80% of the supplied H2S (61 mM d-1) was biologically oxidized to elemental sulfur. The remainder was chemically produced thiosulfate. Moreover, we found that a conventionally applied method for controlling the oxygen supply to the bioreactor, that is, by maintaining a redox potential set-point value, appeared to be ineffective in the presence of thiols.

Isolation and characterization of an obligately chemolithoautotrophic Halothiobacillus strain capable of growth on thiocyanate as an energy source.

Molecular and microbiological analysis of a laboratory bioreactor biomass oxidizing thiocyanate at autotrophic conditions and at 1 M NaCl showed a domination of a single chemolithoautotrophic sulfur-oxidizing bacterium (SOB) capable of using thiocyanate as an energy source. The bacterium was isolated in pure cultures and identified as a member of the Halothiobacillus halophilus/hydrothermalis clade. This clade includes moderately halophilic chemolithoautotrophic SOB from marine and hypersaline habitats for which the ability to utilize thiocyanate as an electron donor has not been previously demonstrated. Halothiobacillus sp. strain SCN-R1 grew with thiocyanate as the sole energy and nitrogen source oxidizing it to sulfate and ammonium via the cyanate pathway. The pH range for thiocyanate oxidation was within a neutral region between 7 and 8 and the range of salinity was from 0.2 to 1.5 M NaCl, with an optimum at 0.5 M. Despite the close phylogenetic relatedness, none of the tested type strains and other isolates from the H. halophilus/hydrothermalis group exhibited thiocyanate-oxidizing capacity.

Application of bacteria involved in the biological sulfur cycle for paper mill effluent purification.

In anaerobic wastewater treatment, the occurrence of biological sulfate reduction results in the formation of unwanted hydrogen sulfide, which is odorous, corrosive and toxic. In this paper, the role and application of bacteria in anaerobic and aerobic sulfur transformations are described and exemplified for the treatment of a paper mill wastewater. The sulfate containing wastewater first passes an anaerobic UASB reactor for bulk COD removal which is accompanied by the formation of biogas and hydrogen sulfide. In an aeration pond, the residual CODorganic and the formed dissolved hydrogen sulfide are removed. The biogas, consisting of CH4 (80-90 vol.%), CO2 (10-20 vol.%) and H2S (0.8-1.2 vol.%), is desulfurised prior to its combustion in a power generator thereby using a new biological process for H2S removal. This process will be described in more detail in this paper. Biomass from the anaerobic bioreactor has a compact granular structure and contains a diverse microbial community. Therefore, other anaerobic bioreactors throughout the world are inoculated with biomass from this UASB reactor. The sludge was also successfully used in investigation on sulfate reduction with carbon monoxide as the electron donor and the conversion of methanethiol. This shows the biotechnological potential of this complex reactor biomass.

Prediction of volumetric productivity of an outdoor photobioreactor.

Volumetric productivity of Monodus subterraneus cultivated in an outdoor pilot-plant bubble column was predicted with a mathematical model. Two border cases to model the photobioreactor were chosen. Firstly, a model with no light integration in which it is assumed that microalgae can adapt immediately to local light conditions. Secondly, full light integration implicating that microalga can convert all absorbed light with a photosynthetic yield based on average light intensity. Because temperature and light conditions in our photobioreactor changed during the day, photosynthetic yields at any combination of temperature and light intensity were needed. These were determined in repeated-batch lab-scale experiments with an experimental design. The model was evaluated in an outdoor bubble column at different natural light conditions and different temperatures. Volumetric productivities in the bubble column were predicted and compared with experimental volumetric productivities. The light integration model over-estimated productivity, while the model in which we assumed no light integration under-estimated productivity. Light integration occurred partly (47%) during the period investigated. The average observed biomass yield on light was 0.60 g.mol(-1). The model of partly light integration predicted an average biomass yield on light of 0.57 g.mol(-1) and predicted that productivity could have been increased by 19% if culture temperature would have been maintained at 24 degrees C.