DEVELOPMENT OF THERMOPHILIC METHANOGENIC SLUDGE IN COMPARTMENTALIZED UPFLOW REACTORS

The characteristics and development of thermophilic anaerobic sludge i n upflow staged sludge bed (USSB) reactors were studied. The compartme ntalized reactors were inoculated with partially crushed mesophilic gr anular sludge and then fed with either a mixture of volatile fatty aci ds (VFA) or a mixture of sucrose and VFA. The staged degradation of th e soluble substrate in the various compartments led to a clear segrega tion of specific types of biomass along the height of the reactor, par ticularly in reactors fed with the sucrose-VFA mixture. Both the biolo gical as well as the physical properties of the cultivated sludge were affected by the fraction of nonacidified substrate, The sludge in the first compartment of the reactor treating the sucrose-VFA mixture was whitish and fluffy, most likely resulting from the development of aci difying bacteria, Sludge granules which developed in the top part of t his reactor possessed the highest acetogenic and methanogenic activity and the highest granule strength as well. The experiments also reveal ed that the conversion of the sucrose-VFA mixture into methane gradual ly deteriorated at prolonged operation at high organic loading rates ( 50 to 100 g COD . L(-1). day(-1)). Stable long-term performance of a r eactor can only be achieved by preserving the sludge segregation along the height of the reactor. in the reactor fed solely with the VFA mix ture little formation of granular sludge occurred. In this reactor, la rge differences in sludge characteristics were also observed along the reactor height. Li+-tracer experiments indicated that the hydraulic r egime in the USSB reactor is best characterized by a series of at leas t five completely mixed reactors. The formation of granular sludge was found to influence the liquid flow pattern. (C) 1996 John Wiley & Son s, Inc.