Layered structure of bacterial aggregates produced in an upflow anaerobic sludge bed and filter reactor

Abstract

The ultrastructure of bacterial granules that were maintained in an upflow anaerobic sludge bed and filter reactor was examined. The reactor was fed a sucrose medium, and it was operated at 35°C. Scanning and transmission electron microscopy revealed that the granular aggregates were three-layered structures. The exterior layer of the granule contained a very heterogeneous population that included rods, cocci, and filaments of various sizes. The middle layer consisted of a slightly less heterogeneous population than the exterior layer. A more ordered arrangement, made up predominantly of bacterial rods, was evident in this second layer. The third layer formed the internal core of the granules. It consisted of large numbers of Methanothrix-like cells. Large cavities, indicative of vigorous gas production, were evident in the third layer. On the basis of these ultrastructural results, a model that presents a possible explanation of granule development is offered.

Effect of influent COD/SO42− ratios on mesophilic anaerobic reactor biomass populations: physico-chemical and microbiological properties

“…Hybridization of the reactor sludge from R1 with the EUB338 and ARC915 probes showed a layered architecture with an outer layer harbouring mainly Eubacterial cells and an inner layer dominated by Archaeal species. Similar layered structures were reported by MacLeod et al (1990), Harmsen (1996), Sekiguchi et al (1999) and Liu et al (2002) for anaerobic sludges granules degrading glucose, sucrose, starch and brewery wastewater.…”

Abrasion of suspended biofilm pellets in airlift reactors: Importance of shape, structure, and particle concentrations

“…This type of measurement will also be complicated by density gradients. Layered structures are frequently observed in UASB reactors (Bochem et al, 1982;Fang et al, 1995;MacLeod et al, 1990;Quarmby and Forster, 1995;Uemura and Harada, 1995) and have also been found in aggregates from an anaerobic gaslift reactor (Beeftink, 1987;Beeftink and Staugaard, 1986). The thickness of the outer layer is commonly related to the penetration depth of a limiting nutrient, in airlift reactors probably oxygen.…”

“…Irregular shapes of suspended biofilm pellets and granules are quite common. They often resemble spheres, ellipsoids, or disks; sometimes they are needlelike, knobby, or com-pletely irregular (Alphenaar, 1994;Csikor et al, 1994;Diekman et al, 1990;Gjaltema et al, 1995;MacLeod et al, 1990;Peereboom and Vereijken, 1994;Quarmby and Forster, 1995;Ro and Neethling, 1994;Tijhuis et al, 1996). The advantage of a bioparticle not being spherical is clear:…”

Molecular monitoring of microbial diversity in expanded granular sludge bed (EGSB) reactors treating oleic acid

“…Besides microbial organization, good settling properties are also pointed as an advantage of biomass aggregation [37]. However, for lipid/LCFA containing wastewaters, granule stability is very problematic and disintegration is often observed [6,24,41].…”