Biology subjects

Jagoutz, O.

Publications and source records attributed to Jagoutz, O..

2 recordsLinked to original sources

bioRxiv2026

Minimizing methane emissions during the degradation of sewage sludge in a sulfate-rich bioreactor

Simultaneous removal of organic waste and industrial gypsum was assessed in continuous flow-through bioreactors that treat sulfate-rich sewage sludge. Metabolic fluxes, the composition of microbial communities, and profiles of organic matter in the presence of different organic loads were tracked over [~]190 days. The addition of a pre-enriched microbial community enhanced the rates of sulfate reduction during the establishment of the sludge blanket, but microbial diversity in established reactors depended primarily on organic loading. Organic removal rates were comparable to those in standard anaerobic digesters, but methane production accounted for [~]1% of electron flow compared to >70% in traditional systems. Stoichiometric analyses revealed that molar COD: sulfate ratios below [~]1 favored complete oxidation of acetate by sulfate-reducing bacteria (SRB) and those above [~]2.1 permitted either complete or incomplete oxidation, allowing sulfate reduction and methanogenesis to co-occur. Sequencing of the 16S rRNA confirmed these trends by revealing that the faster-growing SRB that do not oxidize acetate were more abundant at higher organic loads and during the establishment of the sludge blanket, whereas complete oxidizers became more abundant when the molar COD: sulfate ratio was [≤]3.2. In reactors that had been seeded with the pre-enriched communities, acetate-oxidizing SRB became prevalent over the incomplete oxidizers 25-50 days earlier. These results enable targeted design and control of microbial processes and bioreactors that remove waste organics and gypsum while producing less methane due to the competition for acetate between methanogenic archaea and SRB that oxidize acetate.

microbiology↗

bioRxiv2026

Organic availability and microbial competition for acetate suppress methane emissions during the conversion of gypsum in sewage sludge

Conventional anaerobic digestion emits methane from organic waste. Here, we investigate a sulfate-based alternative that suppresses methane production and generates alkaline solutions that may sequester carbon by carbonate precipitation. Although methanogenesis is known to occur when reduced organic carbon is replete and sulfate is limiting, it remains unclear whether methane emissions during microbial conversion of waste gypsum are primarily driven by community composition or organic availability. By comparing fluxes of electrons from organic matter toward sulfate or methane in microbial communities grown on different organic loads, we show that community composition, microbial growth, and organic availability collectively determine sulfide and methane fluxes. Lower organic loads increase the importance of syntrophic interactions with fermenters and competition between sulfate reducing bacteria and methanogens due to scarcity of substrates. Microbes present in the original sewage sludge reduce less sulfate, produce more methane, and generate less alkalinity compared to the communities enriched by multiple cycles of growth in the presence of sulfate and sewage sludge. The inoculation of communities enriched at low organic loadings in the presence of sulfate decreases the production of methane by enabling the growth of sulfate reducing bacteria from the order Desulfobacterales that can oxidize acetate to CO2 and compete with methanogens for acetate. The use of such enrichments in sludge treatment systems can stimulate the removal of organic substrates and waste gypsum, while suppressing methane production, over timescales comparable to those in the current sludge treatment systems that do not contain sulfate.

microbiology↗