Dynamics of propionic acid degradation in a two-phase anaerobic system

• Propionic acid was produced and accumulated in the acidogenic reactor.
• 0.02% Desulfacinum and 0.08% Desulfobulbus were present in the acidogenic reactor.
• Propionic acid was degraded in the methanogenic reactor.
• 2.68% Smithella and 0.35% Syntrophobacter were present in the methanogenic reactor.
• ATP may be an optional indicator for process stability.

This paper reports on propionic acid (HPr) degradation in a laboratory scale two-phase anaerobic system, where HPr was accumulated in the acidogenic reactor and degraded in the methanogenic reactor. Batch tests using biomass from the two-phase anaerobic system showed HPr degradation was rarely detectable in the acidogenic reactor when HPr concentration ranged from 639 to 4531 mg HPr L−1 and at pH 4.50 to 6.50. Biomass from the methanogenic reactor could, however, successfully degrade HPr at its initial concentration of up to 4585 mg HPr L−1 at pH 6.40–7.30. ATP results showed that differences in the degradation ability of HPr by the acidogenic and methanogenic biomass may be related with their respective different biomass activities. Results from pyrosequencing showed that the predominant propionic acid oxidizing bacteria (POB) in the methanogenic reactor were Smithella (2.68%) and Syntrophobacter (0.35%); while poor degradation of HPr in the acidogenic reactor may be associated with the low abundance of POB (0.02% Desulfacinum and 0.08% Desulfobulbus). This might have been induced by the long-term unfavorable environment for POB growth in the acidogenic reactor.