Factual analysis of granule flotation in brewery wastewater treatment plants by the fluorescence in situ hybridization method.

The factors that change the microbial distribution and consequently the flotation of brewery granules were investigated using laboratory-scale upflow anaerobic sludge blanket (UASB) reactors and the fluorescence in situ hybridization (FISH) method. The startup operations of laboratory-scale UASB reactors fed with acetate-based synthetic wastewater, in which the loading rate was maintained at 0.1 gCOD/gVSS/d (Run 1) and increased in a stepwise manner from 0.1 gCOD/gVSS/d to 1.0 gCOD/gVSS/d (Run 2), generated methanogen colonies near the granule surface, while the overloading operation at 1.0 gCOD/gVSS/d from the startup (Run 3) resulted in the formation of methanogen colonies deep in the granules. In each run, a proportion of the granules floated when overloaded at 2.0 gCOD/gVSS/d and circulation was stopped. The ratio of floating granules increased as the methanogen-growing region increased. On the other hand, the Bacteria layer on the granule surface, which is also considered as a possible cause of granule flotation, was not formed by the inflow of other organic acids such as propionate and lactate. Glucose caused formation of a 5-microm-thick surface Bacteria layer, but the granules were still resistant to flotation. Interfusing of air under glucose feeding caused the formation of a Bacteria layer over 50 microm thick leading to granule flotation.

Microbial analyses by fluorescence in situ hybridization of well-settled granular sludge in brewery wastewater treatment plants.

The characteristics of granular sludge from full-scale upflow anaerobic sludge blanket reactors used for the treatment of brewery wastewater were investigated. Fluorescence in situ hybridization (FISH) analyses of settled granules from a reactor that had been treating brewery wastewater stably at COD removal rates of over 90% for more than 6 months showed that a methanogen of the genus Methanosaeta was predominant near the granule surface and that Bacteria were not abundant. The center of the granules was composed of dead or resting cells, or both, which were used as a support for active archaeal and bacterial cells near the surface. Periodic analysis of granules from full-scale plants showed that granules containing methanogens deep within them tended to float. Granules with a Bacteria layer on the surface also tended to float. On the basis of these findings, well-settled granules are considered to have methanogens that develop near the granule surface so that the gases generated during methane fermentation are readily released.