Direct interspecies electron transfer stimulated in anaerobic structured-bed reactors under very low inoculum content

This study investigated the influence of granular activated carbon as a conductive bed in a fixed-film reactors fed with synthetic carbohydrate solution and stressed under low inoculum content. The reactor R1 was altered with nylon while reactor R2 was altered with GAC. Both reactors underwent a startup step with three recirculation stages followed by a continuous feed step with two load increase stages. During the startup stage, the GAC was able to reverse stress metabolites in R2, reaching higher CH4 production yield at the end of the third feeding cycle. In continuous step, the R2 showed methanogenic conversion around 18% higher than R1. Microbiological analysis identified that the metabolic stress initially defined for both reactors stimulated the development of a higher content of DIETers in the presence of GAC, reflecting the robustness of the reactor R2. Metabolic stress had a selective effect on organisms in the inoculum, stimulating different microbiomes between the reactor's bed and bottom. GAC stimulates the development of DIETers microbiomes, being essential for the performance of advanced syntrophic mechanisms for methanogenesis.