ABSTRACT
During in situ biomethanation, microbial communities can convert complex Organic Matter (OM) and H2 into CH4. OM biodegradation was compared between Anaerobic Digestion (AD) and in situ biomethanation, in semi-continuous processes, using two inocula from the digester (D) and the post-digester (PoD) of an AD plant. The impact of H2 on OM degradation was assessed using a fractionation method. Operational parameters included 20 days of hydraulic retention time and 1.5 gVS.L-1.d-1 of organic loading rate. During in situ biomethanation, 485 NmL of H2 were injected for each feeding (3 times a week). Maximum organic COD removal was 0.6 gCOD in AD control and at least 1.6 gCOD for in situ biomethanation. Therefore, COD removal was 2.5 times higher with H2 injections. These results bring out the potential of H2 injections during AD, not only for CO2 consumption but also for better OM degradation.
ABSTRACT
The performance of hydrogen consumption by various inocula derived from mesophilic anaerobic digestion plants was evaluated under ex situ biomethanation. A panel of 11 mesophilic inocula was operated at a concentration of 15 gVS.L-1 at a temperature of 35 °C in batch system with two successive injections of H2:CO2 (4:1 mol:mol). Hydrogen consumption and methane production rates were monitored from 44 h to 72 h. Hydrogen consumption kinetics varies significantly based on the inoculum origin, with no accumulation of volatile fatty acids. Microbial community analyses revealed that microbial indicators such as the increase in Methanosarcina sp. abundance and the increase of the Archaea/Bacteria ratio were associated to high initial hydrogen consumption rates. The improvement in the hydrogen consumption rate between the two injections was correlated with the enrichment in hydrogenotrophic methanogens. This work provides new insights into the early response of microbial communities to hydrogen injection and on the microbial structures that may favor their adaptation to the biomethanation process.
