Phase separation as a strategy to prevent sulfide-related drawbacks in methanogenesis: performance and energetic aspects

The establishment of sulfate (SO42−) reduction during methanogenesis may considerably hinder the efficient energetic exploitation of methane, once removing sulfide from biogas is obligate and can be costly. In addition, sulfide generation can negatively impact the performance of methanogens by triggering substrate competition and sulfide inhibition. This study investigated the impacts of removing SO42− during fermentation on the performance of a second-stage methanogenic continuous reactor (R2), comparing the results with those obtained in a single-stage system (R1) fed with SO42−-rich wastewater (SO42− of up to 400 mg L−1, COD/SO42− of 3.12–12.50). The organic load (OL) was progressively increased to 5.0 g COD d−1 in both reactors, showing completely discrepant performances. Sulfate-reducing bacteria outperformed methanogens in the consumption for organic matter during the start-up phase (OL = 2.5 g COD d−1) in R1, directing up to 73