ena-STUDY-UCC-19-05-2018-01:10:44:708-352
M'thermobacter and ex situ biogas upgrading
Ex situ biomethanation is a cost-effective modification of anaerobic digestion, in which hydrogenotrophic methanogens are provided excess hydrogen (H2) and carbon dioxide (CO2) in the absence of a solid biogas feedstock, placing both the process and metabolic emphasis on near-total conversion of CO2 and H2 to biomethane. The concept can be applied ex situ as 'biological upgrading' to biogas from anaerobic digestion, and is usually carried out at thermophilic temperatures (>50°C) in order to accelerate methanogenesis. The ex situ methanogenic community responsible for this upgrading is currently poorly characterised but is expected to feature abundant methanogens specialising in fixation of CO2 and H2 to CH4. Given the lack of a digestion feedstock, the importance of bacteria in an upgrading community is less clear. In this study, the methanogenic and microbial communities involved in thermophilic ex situ upgrading of a 1 CO2 : 4 H2 mix were characterised during disruption and restoration of biogas production due to a process shift to higher temperatures (55°C to 65°C). Although DGGE, 16S clone library and 16S pyrosequencing approaches showed Methanothermobacter to be the dominant methanogen throughout operation, no relationship was evident between decreased upgrading function and Methanothermobacter abundance. Instead, it is possible that biogas production was restored through addition of organic and/or inorganic substrate in a re-inoculation event. This implies a role for the ex situ bacterial community, the majority of which (>50% reads) belong to uncharacterised Firmicutes taxa, in particular the MBA03 group.
Ex situ biomethanation is a cost-effective modification of anaerobic digestion, in which hydrogenotrophic methanogens are provided excess hydrogen (H2) and carbon dioxide (CO2) in the absence of a solid biogas feedstock, placing both the process and metabolic emphasis on near-total conversion of CO2 and H2 to biomethane. The concept can be applied ex situ as 'biological upgrading' to biogas from anaerobic digestion, and is usually carried out at thermophilic temperatures (>50°C) in order to accelerate methanogenesis. The ex situ methanogenic community responsible for this upgrading is currently poorly characterised but is expected to feature abundant methanogens specialising in fixation of CO2 and H2 to CH4. Given the lack of a digestion feedstock, the importance of bacteria in an upgrading community is less clear. In this study, the methanogenic and microbial communities involved in thermophilic ex situ upgrading of a 1 CO2 : 4 H2 mix were characterised during disruption and restoration of biogas production due to a process shift to higher temperatures (55°C to 65°C). Although DGGE, 16S clone library and 16S pyrosequencing approaches showed Methanothermobacter to be the dominant methanogen throughout operation, no relationship was evident between decreased upgrading function and Methanothermobacter abundance. Instead, it is possible that biogas production was restored through addition of organic and/or inorganic substrate in a re-inoculation event. This implies a role for the ex situ bacterial community, the majority of which (>50% reads) belong to uncharacterised Firmicutes taxa, in particular the MBA03 group.