Reversibility of hydrolysis inhibition at high hydrogen partial pressure in dry anaerobic digestion processes fed with wheat straw and inoculated with anaerobic granular sludge. (15th February 2019) - Cazier, Elisabeth A.
Highlights: Methanogenesis high PH2 inhibition was reversed after CO2 addition. Duration of H2 inhibition had only a transitory effect on AD performances. H2 accumulation had a residual inhibitory effect on acetate degradation kinetics. Adding H2 led to an increase of Clostridiales and a decrease of Bacteroidiales. Hydrogenotrophic methanogens decreased with the time spent at high PH2 . Abstract: In dry anaerobic digestion (AD), methanogenic performances are lowered by high solid contents. Low performances are often caused by a decrease of the gas-liquid transfer kinetics leading to local accumulation of inhibitory by-products. Hydrogen was previously identified as an inhibitor of hydrolytic and acetogenic microbial activities in dry AD. CO2 is also generated but its impact on the microbial activity remains unknown. In this study, the reversibility of dry AD inhibition at high H2 partial pressure ( PH 2 of 1 bar) was investigated by adding CO2 (400 mbars) after 11 and 18 days of methanogenesis inhibition, in an AD process operated at 25% TS, using wheat straw as substrate and inoculated with anaerobic granular sludge. As soon as CO2 was added, the methanogenic activity rapidly recovered within 3 days, from 0.41 ± 0.1 to 3.77 ± 0.8 and then 2.25 ± 0.3, likely through the hydrogenotrophic pathway followed by the acetoclastic pathway, respectively. This result was confirmed by the high abundance of Methanomicrobiales (83%) and the emergence of Methanosarcinales sp (up to 17%) within the methanogenic community. Furthermore, the recovery kinetics were impacted by the duration of the inhibition period suggesting a different impact of the high PH 2 on hydrogenotrophic and acetoclastic methanogens.