Biofiltration of hydrogen sulfide by Sulfolobus metallicus at high temperatures

A comprehensive review of flue gas bio-mitigation: chemolithotrophic interactions with flue gas in bio-reactors as a sustainable possibility for technological advancements

Flue gas mitigation technologies aim to reduce the environmental impact of flue gas emissions, particularly from industrial processes and power plants. One approach to mitigate flue gas emissions involves bio-mitigation, which utilizes microorganisms to convert harmful gases into less harmful or inert substances. The review thus explores the bio-mitigation efficiency of chemolithotrophic interactions with flue gas and their potential application in bio-reactors. Chemolithotrophs are microorganisms that can derive energy from inorganic compounds, such as carbon dioxide (CO2), nitrogen oxides (NOx), and sulfur dioxide (SO2), present in the flue gas. These microorganisms utilize specialized enzymatic pathways to oxidize these compounds and produce energy. By harnessing the metabolic capabilities of chemolithotrophs, flue gas emissions can be transformed into value-added products. Bio-reactors provide controlled environments for the growth and activity of chemolithotrophic microorganisms. Depending on the specific application, these can be designed as suspended or immobilized reactor systems. The choice of bio-reactor configuration depends on process efficiency, scalability, and ease of operation. Factors influencing the bio-mitigation efficiency of chemolithotrophic interactions include the concentration and composition of the flue gas, operating conditions (such as temperature, pH, and nutrient availability), and reactor design. Chemolithotrophic interactions with flue gas in bio-reactors offer a potentially efficient approach to mitigating flue gas emissions. Continued research and development in this field are necessary to optimize reactor design, microbial consortia, and operating conditions. Advances in understanding the metabolism and physiology of chemolithotrophic microorganisms will contribute to developing robust and scalable bio-mitigation technologies for flue gas emissions.

Biooxidation of hydrogen sulfide to sulfur by moderate thermophilic acidophilic bacteria

The copper industry utilizes significant amounts of sulfuric acid in its processes, generating sulfate as waste. While sulfate-reducing bacteria can remove sulfate, it produces hydrogen sulfide (H2S) as a byproduct. This study examined the capability of a consortium consisting of Sulfobacillus thermosulfidooxidans and Sulfobacillus acidophilus to partially oxidize H2S to S° at a temperature of 45 °C. A fixed-bed bioreactor, with glass rings as support material and sodium thiosulfate as a model electron donor, was inoculated with the consortium. Formation of biofilms was crucial to maintain the bioreactor's steady state, despite high flow rates. Afterward, the electron donor was changed to H2S. When the bioreactor was operated continuously and with high aeration, H2S was fully oxidized to SO42-. However, under conditions of low aeration and at a concentration of 0.26 g/L of H2S, the consortium was able to oxidize H2S to S° with a 13% yield. S° was discovered attached to the glass rings and jarosite. The results indicate that the consortium could oxidize H2S to S° with a 13% yield under low aeration and at a concentration of 0.26 g/L of H2S. The findings highlight the capability of a Sulfobacillus consortium to convert H2S into S°, providing a potential solution for addressing environmental and safety issues associated with sulfate waste generated by the mining industry.

Biotechnology of extremely thermophilic archaea

Although the extremely thermophilic archaea (Topt ≥ 70°C) may be the most primitive extant forms of life, they have been studied to a limited extent relative to mesophilic microorganisms. Many of these organisms have unique biochemical and physiological characteristics with important biotechnological implications. These include methanogens that generate methane, fermentative anaerobes that produce hydrogen gas with high efficiency, and acidophiles that can mobilize base, precious and strategic metals from mineral ores. Extremely thermophilic archaea have also been a valuable source of thermoactive, thermostable biocatalysts, but their use as cellular systems has been limited because of the general lack of facile genetics tools. This situation has changed recently, however, thereby providing an important avenue for understanding their metabolic and physiological details and also opening up opportunities for metabolic engineering efforts. Along these lines, extremely thermophilic archaea have recently been engineered to produce a variety of alcohols and industrial chemicals, in some cases incorporating CO2 into the final product. There are barriers and challenges to these organisms reaching their full potential as industrial microorganisms but, if these can be overcome, a new dimension for biotechnology will be forthcoming that strategically exploits biology at high temperatures.

Physiological, metabolic and biotechnological features of extremely thermophilic microorganisms

The current upper thermal limit for life as we know it is approximately 120°C. Microorganisms that grow optimally at temperatures of 75°C and above are usually referred to as 'extreme thermophiles' and include both bacteria and archaea. For over a century, there has been great scientific curiosity in the basic tenets that support life in thermal biotopes on earth and potentially on other solar bodies. Extreme thermophiles can be aerobes, anaerobes, autotrophs, heterotrophs, or chemolithotrophs, and are found in diverse environments including shallow marine fissures, deep sea hydrothermal vents, terrestrial hot springs-basically, anywhere there is hot water. Initial efforts to study extreme thermophiles faced challenges with their isolation from difficult to access locales, problems with their cultivation in laboratories, and lack of molecular tools. Fortunately, because of their relatively small genomes, many extreme thermophiles were among the first organisms to be sequenced, thereby opening up the application of systems biology-based methods to probe their unique physiological, metabolic and biotechnological features. The bacterial genera Caldicellulosiruptor, Thermotoga and Thermus, and the archaea belonging to the orders Thermococcales and Sulfolobales, are among the most studied extreme thermophiles to date. The recent emergence of genetic tools for many of these organisms provides the opportunity to move beyond basic discovery and manipulation to biotechnologically relevant applications of metabolic engineering. WIREs Syst Biol Med 2017, 9:e1377. doi: 10.1002/wsbm.1377 For further resources related to this article, please visit the WIREs website.

Operational aspects of SO2 removal and microbial population in an integrated-bioreactor with two bioreaction zones

An integrated-bioreactor, which consisted of a suspended zone and an immobilized zone, was applied to treat gases containing SO₂. The removal of SO₂ in suspended zone differed slightly from that in immobilized zone. The influences of operational aspects such as SO₂ load, temperature, and pH on integrated-bioreactor performance and bacterial community composition were investigated. The synergistic action of the two zones led to effective reduction of SO₂, and the total removal efficiencies with the inlet concentration of 91-117 mg/m³, were over 85 % in steady state. Paenibacillus sp. and Lysinibacillus sp. dominated both zones as desulfurization bacteria. Results of polymerase chain reaction-denaturing gradient gel electrophoresis followed by clone library analysis indicated that temporal shifts in bacterial community composition in both zones developed differently. Differences in the concentration of introduced SO₂ and supported mode of microorganisms for survival, confirmed that bacterial community composition and abundance significantly differed among individual zones.

Performance of a new suspended filler biofilter for removal of nitrogen oxides under thermophilic conditions and microbial community analysis

A suspended biofilter, as a new bioreactor, was constructed for the removal of nitrogen oxides (NOX) from simulated flue gas under thermophilic conditions. The suspended biofilter could be quickly started up by inoculating the thermophilic denitrifying bacterium Chelatococcus daeguensis TAD1. The NO concentration in the inlet stream ranged from 200mg/m(3) to 2000mg/m(3) during the operation, and inlet loading ranged from 8.2-164g/(m(3)·h). The whole operation period was divided into four phases according to the EBRT. The EBRT of phases I, II, III and IV were 88s (9-43d), 44s (44-61d), 66s (62-79d) and 132s (80-97d), respectively. An average NO removal efficiency of 90% was achieved during the whole operation period, and the elimination capacity increased linearly with the increase in NO inlet loading and the maximum elimination capacity reached 146.9g/(m(3)·h). No clogging was observed, although there was a high biomass concentration in the biofilter bed. The remarkable performance in terms of NO removal could be attributed to the rich bacterial communities. The microbial community structure in the biofilm was investigated by high throughput sequencing analysis (16S rRNA MiSeq sequencing). The experimental results showed that the microbial community structure of the biofilm was very rich in diversity, with the most abundant bacterial class of the Alphaproteobacteria, which accounted for 36.5% of the total bacteria, followed by Gammaproteobacteria (30.7%) and Clostridia (27.5%). It was worthwhile to mention that the dominant species in the suspended biofilter biofilm were all common denitrifying bacteria including Rhizobiales (inoculated microbe), Rhodospirillales, Enterobacteriales and Pseudomonadales, which accounted for 19.4%, 17%, 21.6% and 7%, respectively. The inoculated strain TAD1 belonged to Alphaproteobacteria class. Because high-throughput 16S rRNA gene paired-end sequencing has improved resolution of bacterial community analysis, 16S rRNA gene sequencing of these bacteria could provide more functional and phylogenetic information about the bacterial communities.

Thermophilic biofilter for SO2 removal: performance and microbial characteristics

A bench-scale thermophilic biofilter was applied to remove SO2 at 60°C in the present study. The SO2 concentration in the inlet stream ranged from 100mg/m(3) to 200mg/m(3). An average SO2 removal efficiency of 93.10% was achieved after developing acclimated organisms that can degrade SO2. The thermophilic biofilter effectively reduced SO2, with a maximum elimination capacity of 50.67g/m(3)/h at a loading rate of 51.44g/m(3)/h. Removal efficiency of the thermophilic biofilter was largely influenced by the water containing rate of the packing materials. The SO2 transfer in the biofilter included adsorption by the packing materials, dissolution in liquid, and microbial degradation. The main product of SO2 degradation was SO4(2-). The temporal shifts in the bacterial community that formed in the biofilter were determined through polymerase chain reaction-denaturing gradient gel electrophoresis and DNA sequence analysis. These shifts revealed a correlation between biofilter performance and bacterial community structure.