Start-up of a thermophilic methanol-fed UASB reactor: change in sludge characteristics

Experiments were performed to study the change in sludge characteristics and sludge granulation during the start-up of a thermophilic methanol-fed upflow anaerobic sludge bed (UASB) reactor. The laboratory scale reactor, was inoculated with thermophilic granular sludge and operated at 55°C over 130 days at organic loading rates (OLR) varying from 2.7 to 47 gCOD.L⁻¹.d⁻¹. Physical characterisation was performed for both the seed and the cultivated sludge. Results demonstrated that a good quality, well settleable granular sludge was cultivated and retained in the reactor, allowing an OLR of 47 gCOD.L⁻¹.d⁻¹ with 93% of methanol removal, where 79% was converted into methane. Using a community analysis of the cultivated consortia, high numbers of rod-shaped hydrogenotrophic methanogens were enumerated. Biomass washout coincided with a high specific gas load, but was not detrimental to the system in the conditions tested.