Syngas as Electron Donor for Sulfate and Thiosulfate Reducing Haloalkaliphilic Microorganisms in a Gas-Lift Bioreactor

Abstract

Biodesulfurization processes remove toxic and corrosive hydrogen sulfide from gas streams (e.g., natural gas, biogas, or syngas). To improve the efficiency of these processes under haloalkaline conditions, a sulfate and thiosulfate reduction step can be included. The use of H2/CO mixtures (as in syngas) instead of pure H2 was tested to investigate the potential cost reduction of the electron donor required. Syngas is produced in the gas-reforming process and consists mainly of H2, carbon monoxide (CO), and carbon dioxide (CO2). Purification of syngas to obtain pure H2 implies higher costs because of additional post-treatment. Therefore, the use of syngas has merit in the biodesulfurization process. Initially, CO inhibited hydrogen-dependent sulfate reduction. However, after 30 days the biomass was adapted and both H2 and CO were used as electron donors. First, formate was produced, followed by sulfate and thiosulfate reduction, and later in the reactor run acetate and methane were detected. Sulfide production rates with sulfate and thiosulfate after adaptation were comparable with previously described rates with only hydrogen. The addition of CO marginally affected the microbial community in which Tindallia sp. was dominant. Over time, acetate production increased and acetogenesis became the dominant process in the bioreactor. Around 50% of H2/CO was converted to acetate. Acetate supported biomass growth and higher biomass concentrations were reached compared to bioreactors without CO feed. Finally, CO addition resulted in the formation of small, compact microbial aggregates. This suggests that CO or syngas can be used to stimulate aggregation in haloalkaline biodesulfurization systems.

Hydrogen Sulfide and Carbon Monoxide Tolerance in Bacteria

“…[ 63 ], and in some sulfate reducing bacteria, including the thermophilic archaeon Archaeoglobus fulgidus in which CO is an electron donor for sulfate reduction. The CO tolerance of these strains is considered a beneficial alternative to biodesulfurisation processes [ 64 , 65 , 66 ].…”

“…Transcriptomics studies of CO-oxidizing bacteria in the presence of CO gas were done for A. fulgidus, Parageobacillus thermoglucosidasius , Calderihabitans maritimus and C. pertinax . The general trend was the upregulation of CODH encoding genes, and in P. thermoglucosidasius a transcriptional pattern related with transition from aerobic to anaerobic growth was observed [ 56 , 65 , 66 , 67 ].…”

Extremofiles 2.0

“…This, for several reasons, some, fundamental and related with the search for the limits of life [ 2 ], and others, more pragmatic and focused on the biotechnological potential of extremophiles, has sparked a marked growth of interest in the ecology of extreme environments [ 3 ]. The 2019–2020 version of Extremofiles 2.0, a Special Issue of Microorganisms devoted to extremophiles, has gathered eleven papers dealing with different aspects of microorganisms that thrive in extreme environments: five on halophiles [ 4 , 5 , 6 , 7 , 8 ], three on acidophiles [ 9 , 10 , 11 ], one on thermophiles [ 12 ], one on psycrophiles [ 13 ] and one on metal resistant microorganisms [ 14 ].…”

“…Finally, Plugge et al characterized the efficiency of a gas-lift bioreactor in which H 2 /CO mixtures instead of pure H 2 were used. The addition of CO marginally affected the microbial community; over time acetate production increased and acetogenesis became the dominant process [ 8 ].…”