Methanogenic Fermentation of Formate by an Upflow Anaerobic Sludge Blanket (UASB) Reactor under Thermophilic Conditions

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Abstract
The performance of a thermophilic (65 °C) upflow anaerobic sludge blanket (UASB) reactor was investigated using wastewater consisting of formate as a main carbon source for a period of 126 days. The removal efficiencies on the basis of influent TOC vs. effluent DOC were above 90% at loading rates of 10–23 kg TOC m−3 d−1. No granulation of the biomass retained in the reactor was observed throughout the experimental period, and the sludge concentration was found to be exceptionally low (around 3000 mg VSS l−1 throughout the reactor column at the termination of the experiment). The methanogenic activity of the biomass for formate was calculated to be 9.0 kg CH4-COD kg VSS−1 d−1 according to the results of methane production from the reactor and the biomass volume. This high methanogenic activity led to the relatively high performance of the reactor despite the low sludge concentration. Microscopic examinations indicated that the biomass mostly comprised cylindrical, and slightly curved rod-shaped bacterium, which was presumably Methanobacterium thermoformicicum.

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