Trisha DUPNOCK
PIRE PhD student
Duke University in Dr. Marc Deshusses Group
High performance biomethanation of CO2 to CH4 using a biotrickling filter and Hydrogenotrophic methanogens
Summary:
This research reports the novel development of a biotrickling filter (BTF) to upgrade biogas, which is achieved by adding H2 to reduce CO2. A bench-scale bioreactor was packed with polyurethane foam (PUF) and inoculated with hydrogenotrophic methanogens (HMs) enriched from swine waste. H2 and CO2 were fed to the bioreactor at a ratio of 80:20 based on the biological reaction stoichiometry. Maximum CH4 production capacity (PC) rates recorded were as high as 38 m3 CH4 m-3reactor d-1, which is over an order of magnitude faster than previous BTF studies and nearly 5 times faster than bioreactors with gas sparging through hollow fiber membranes. These fast rates allowed for a quick retention time of 11 min, compared to previous studies which required gas contact times of over an hour. The high rates were attributed to the efficient mass transfer and high density of methanogens in the biotrickling filter. The recorded removal efficiencies for H2 and CO2 during this optimal period were 83% and 96%, respectively.
This study also uniquely considered the biofilm composition with respect to system optimization. CTC/DAPI staining revealed that 67% of cells were live near the gas entrance port, while only 8.3% were live at the exit. Furthermore, DNA sequencing showed that only 27% of the live biomass was comprised of Euryarchareota. These results showed that the use of a consortium incoculm, despite external enrichment, provided a low relative abundance of HM within the reactor biomass.
Recent work involved with monitoring the dissolved hydrogen concentrations in the bioreactor under various operational configurations has provided valuable insight into the system’s mass transfer capabilities. Factors such as increased bed velocity, hydrogen mass transfer from the gas to non-wetted biofilm phases, and the amount of dissolved hydrogen entering the bioreactor have an impact on the methane production capacity. Fully understanding these effects should help advance the technology in terms of overcoming current mass transfer barriers.
