Abstract
Bacterial communities’ composition, activity and robustness determines the effectiveness of biofiltration units for the desulfurization of biogas. It is therefore important to get a better understanding of the bacterial communities that coexist in biofiltration units under different operational conditions for the removal of H2S, the main reduced sulfur compound to eliminate in biogas. This review presents the main characteristics of sulfur-oxidizing chemotrophic bacteria that are the base of the biological transformation of H2S to innocuous products in biofilters. A survey of the existing biofiltration technologies in relation to H2S elimination is then presented followed by a review of the microbial ecology studies performed to date on biotrickling filter units for the treatment of H2S in biogas under aerobic and anoxic conditions.
Highlights
Biogas is a promising renewable energy source that could contribute to regional economic growth due to its indigenous local-based production together with reduced greenhouse gas emissions [1]
The drawbacks of conventional biofilters, especially under long-term operation, are (a) the accumulation of biomass and S0 which may lead to bed clogging episodes causing preferential flow in the biofilter bed and pressure drop with the consequent reduction of the available mass transfer area; (b) acidification of the packing material due to the generation of SO42− which leads to the formation of H2SO4, especially at the inlet area where the H2S concentration and oxidation rate are higher, which may decrease the pH to values
The bacteria were not identified, the authors report that the bacterial diversity was reduced during the progressive adaptation from NO3− to NO2−, the denaturing gradient gel electrophoresis (DGGE) banding patterns were similar, indicating that the same bacterial community was involved in sulfur-driven autotrophic denitrification with both electron acceptors
Summary
Biogas is a promising renewable energy source that could contribute to regional economic growth due to its indigenous local-based production together with reduced greenhouse gas emissions [1]. The molecular techniques that have been used to characterize bacterial communities in biofilters are briefly presented followed by a review on the current knowledge on microbial communities in biofiltration units used for biogas desulfurization under aerobic and classical applications of biofiltration technologies for odor control in wastewater treatment plants (WWTPs) or other industrial processes. NO3− is sequentially reduced to NO2−, nitric oxide (NO), nitrous oxide (N2O) and nitrogen gas (N2), depending on the bacterial species and environmental conditions (refer to Section 3) [32] This process is known as sulfur-oxidizing autotrophic denitrification. It has been shown that, in Calyptogena, key enzymes from five different sulfur oxidation pathways are expressed under three different environmental conditions (aerobic and semioxic) indicating that all pathways may function simultaneously to support intracellular endosymbiotic life [35] This may be an advantage in an environment where the H2S concentration rapidly fluctuates. AN/AE AN/AE sqr, fcc, sox without soxCD, dsr, apr tet, tqo, sqr, sdo, tst, hdr, sox without soxCD * fcc, sox without soxCD, hdr, dsr &
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