Microbiological investigations into granular sludge from two anaerobic digesters differing in design and industrial effluent purified.

Abstract

Due to a combination of selection criteria, sludges from upflow anaerobic digesters treating industrial waste waters consist primarily of well-settling, dense agglomerates called granules. Quantification of the component mixed microbial populations of these granules has been severely restricted by the inability of researchers to disrupt them without concomitantly destroying numerous cells. In situ quantification using light and electron microscopy is complicated by the high cell numbers and bacterial diversity; the small cell size; and the destructive nature of electron microscopy preparative techniques preventing the viewing of more than a small percentage of the population at a time. For these reasons, in this investigation, standardization of qualitative electron microscopic techniques was performed prior to their application to granules. Isolation and electron and light microscopic techniques were applied to granules from a fullscale clarigester treating effluent from a maize-processing factory. In addition, a method using montaged transmission electron micrographs (TEMs) taken along a granule radius, and image analysis, was developed for bacterial quantification within granules. This method, together with antibody probe quantification, was applied to granules from an upflow anaerobic sludge blanket (UASB) digester treating a brewery effluent. The clarigester granules contained a metabolically and morphologically diverse population of which many members were not isolated or identified. By contrast, the UASB digester granules consisted primarily of morphotypes resembling Methanothrix, Methanobacterium and Desulfobulbus, in order of predominance. However, only about one-third of the population reacted with antibody probes specific to strains of bacterial species expected to occur within these granules. According to the antibody probe library used, the Methanobacterium-like cells observed in TEMs were probably Methanobrevibacter arboriphilus. From this study it is apparent that different anaerobic digester designs, operational parameters, and the chemical composition of the waste water purified, are factors which influence the formation and maintenance of granules differing with respect to their microbial populations. Until the difficulties associated with quantification are overcome, the processes governing granule formation and/or population selection will remain obscure.