An examination of the structure of UASB granules

Sonication, staining and the analysis of extracellular polymers (ECP) were used to examine the structure of granules from pilot-scale and laboratory-scale anaerobic upflow sludge blanket reactors. The pilot-scale unit was part of the SERC Anaerobic Facility which was treating the liquors from the manufacture of instant coffee. The laboratory-scale reactors used a chemically defined substrate. The results showed that, although the strength of the granules from the pilot-plant, as measured by the effect of sonication, varied with time, the variations could not be related to the microbial composition of the granules. However, it was found that the granules tended to become weaker as the organic load increased and the ECP from weak granules had a lower polysaccharide content. The effect of inhibitory agents (pyrogallol and coffee oil) on granule structure was also examined. These studies showed that the effect was to reduce the strength of the granules.