Potential enhancement of syntrophic metabolism with two carrier materials for biofilm formation during anaerobic digestion of tomato liquid fraction

AIMS: This study evaluated the influence of two carrier materials, a nylon pad (NP) and a nylon-silicon carbide pad (NSCP), on fixed-bed reactor (FBR) and microbiomes performances during the anaerobic digestion of tomato liquid fraction. METHODS AND RESULTS: FBR performance was evaluated during start-up, biofilm formation, and biodegradability tests, applying principal components analysis (PCA) to correlate biological, physicochemical, and operating variables. PCA results showed two positive interactions, the first one between facultatively-syntrophic fermenters and CO2-reducing methanogens in both carriers, increasing chemical oxygen demand (COD) removal and methane yield through interspecies formate/H2 transfer. The second interaction was associated with Geobacter daltonii and Methanosarcina spelaei in NSCP, suggesting a direct interspecies electron transfer (DIET) to acetotrophic methanogens. CONCLUSIONS: Biodegradability tests revealed positive microbial interactions to enhance COD removal and methane yield via sugars→butyrate→acetate→methane pathway in both pads. The use of NP and NSCP carrier materials enhanced syntrophisms, impacting FBR performance. In NSCP syntrophic relationships were associated with the acetotrophic pathway that was increased by a DIET; while in NP a competitive exclusion mechanism where the fermenter Trichococcus alkaliphilus successfully competed against obligately-syntrophic acetogens for sugars and fatty acids was observed.