Enrichment of Methanosaetaceae on carbon felt and biochar during anaerobic digestion of a potassium-rich molasses stream

Biorefineries allow the production of value-added chemicals, yet this also causes the formation of considerable amounts of wastewater that require suitable treatment. These biorefinery wastewaters often contain a high salinity, which inhibits methanogenesis. In this research, molasses were used to mimic these waste streams to evaluate their treatability by anaerobic digestion. Two different carrier materials, i.e., carbon felt and biochar, with similar surface properties were evaluated for their potential to stabilize anaerobic digestion of these wastewaters via active enrichment of the methanogenic community. Initial stable methane production values between 620 and 640 mL CH4 L-1 day(-1) were reported in each treatment. At the end of the experiment, methane production decreased with more than 50 %, while VFA increased to values up to 20 g COD L-1, indicating severe process failure, due to the high potassium concentration in these wastewaters, irrespective of the presence of carrier material. However, an increased relative abundance of Methanosaetaceae both on the biochar and carbon felt was observed. In conclusion, this research demonstrated that carbon felt and biochar are both suitable carrier materials for selective enrichment of Methanosaetaceae, yet this did not lead to stable anaerobic digestion of a potassium-rich molasses waste stream. The increased relative abundance of Methanosaetaceae on both carrier materials can, nonetheless, be considered valuable in terms of alternative applications and warrants further research.

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