New strategies for optimal methane production from long chain fatty acids

Abstract

High methane production can be expected from biodegradation of long chain fatty acids (LCFA) in anaerobic bioreactors; however, in practice, this process is limited by LCFA accumulation onto the sludge. To optimize methane production from LCFA-rich wastewater, two novel strategies were tested: (i) bioreactor start-up based on the alternation of continuous-feeding phases with batch-degradation phases, and (ii) bioreactor bioaugmentation with the LCFAdegrading bacterium Syntrophomonas zehnderi. Using the first strategy, and after five alternation cycles, continuous bioreactor operation at an organic loading rate (OLR) up to 21 kgCOD.m-3.day-1 (50% as oleate) was successfully applied, with an average methane yield of 72%. A specialized microbial community, exhibiting high LCFA-tolerance and high methanogenic activity, was developed. Methanobacterium- and Methanosaeta-like microorganisms prevailed in this system. Syntrophic activity was also shown to be an important factor for the efficient conversion of LCFA to methane. Anaerobic sludge amended with S. zehnderi and incubated in the presence of a solid microcarrier (sepiolite) achieved 1.7x higher methane yields and 4x higher methane production rates than the correspondent non-bioaugmented controls. This effect was more pronounced in bioaugmented assays amended with sepiolite+Fe(OH)3. This work opens new perspectives for efficient treatment of LCFA-rich wastewater combined with high methane recovery.