Bioaugmentation of Anaerobic Sludge with Syntrophomonas zehnderi as a Prospect for Enhanced Methane Production from Oleate

Bioaugmentation of anaerobic sludge with long-chain fatty acids (LCFA)-degrading bacteria can be a feasible strategy to enhance methane production from LCFA. This hypothesis was studied in batch assays with Syntrophomonas zehnderi as bioaugmenting strain. This bacterium is able to degrade a wide range of saturated and unsaturated LCFA, and its presence has been reported in several oleate-fed bioreactors. Bioaugmentation assays were performed in the presence and absence of the solid microcarrier sepiolite, and with oleate (unsaturated C18:1 LCFA, 1 mM) as substrate. S. zehnderi addition enhanced methane production from oleate, leading to high methane yields in the bioaugmented assays, i.e. 895% and 721% in the absence and presence of sepiolite, respectively. Comparing bioaugmented assays, a two times faster methane production was observed in the presence of sepiolite, where maximum cumulative methane production was attained after 15 days of incubation. Also, acetate accumulation was prevented by the microcarrier, probably due to a decrease of acetoclastic methanogens inhibition by oleate. Bioaugmentation of anaerobic bioreactors with S. zehnderi or other syntrophic LCFA-degraders can be potentially useful for faster reactor start-up or recovery of LCFA-inhibited processes.