START-UP OF A THERMOPHILIC UPFLOW ANAEROBIC SLUDGE BED (UASB) REACTOR WITH MESOPHILIC GRANULAR SLUDGE

Fast start-up of thermophilic upflow anaerobic sludge bed (UASB) reactors was achieved at process temperatures of 46, 55 and 64-degrees-C, using mesophilic granular sludge as inoculum and fatty acid mixtures as feed. The start-up was brought about by increasing the temperature of mesophilic UASB reactors in a single step, which initially led to a sharp drop in the methane production rate. Thereafter, stable thermophilic methanogenesis was achieved within a period of 1 or 2 weeks depending on the temperature of operation. Mesophilic granules functioned initially as effective carrier material for thermophilic organisms. However, long-term operation led to disintegration of the granules, resulting in wash-out of thermophilic biomass. The temperature optima for acetotrophic methanogenic activity of the sludges cultivated at 46, 55 and 64-degrees-C, were similar, but differed significantly from the temperature optimum of the mesophilic inoculum. All the sludges examined were dominated by Methanothrix-like rods. These could be distinguished by antigenic fingerprinting into two subpopulations, one predominant at 36-degrees-C and the other predominant at 46-degrees-C and above.