Abstract:
Carbon capture and utilization (CCU) has received a lot of attention to reduce
CO2 emissions. Anaerobic digestion (AD) employs hydrogenotrophic methanogen
(HHM) for converting CO2 to CH4. Several studies have used zero-valent iron (ZVI) as
an electron donor to accelerate the AD for CO2 to CH4 conversion. In this study,
HCOOH/HCOONa were used as a substrate for HM enrichment in a fed-batch reactor
that was operated for 209 days with an organic loading rate (OLR) of 1.31 g COD/L-d. The average COD conversion efficiency of 93.62% and Methanobacteriales had the
highest increase. Following that, HM-enriched sludge was used to convert CO2 to CH4 using ZVI powder as an electron donor in three continuous flow reactors (CFRs) with
different mixing modes (continuous stirring, 15 min every I h, and 15 min every 3 h).
Due to mixing is important parameter affect mass transfer and microbial community for
extracellular polymeric substances (EPS) formation for adhesion between cell-cell and
cell- ZVI surface. Three CFRs were operated for 100 days, continuous feeding 99.99%
CO2, ZVI concentration of 105.04 g/L, and hydraulic retention time (HRT) of 15 days.
CFR B has the highest average methane production rate of 7.40 x 10 L CH4/Lreactor'd
and has the highest gene copy numbers of microbials attached on ZVI surface per dried
weight of ZVI in all species, Methanobacteriales as dominant methanogens in 1.26 x
10 copy number/g ZVI. As a result, the mixing mode in CFR affects the amount of
HM attached to the ZVI surface.