MICROBIAL STRUCTURE AND ACTIVITY OF UASB GRANULES TREATING DIFFERENT WASTEWATERS

The microstructure of three types of UASB granules respectively treati ng sucrose, glutamate and brewery wastewaters in mesophilic conditions were analyzed by light, scanning electron and transmission electron m icoscopies, along with the specific methanogenic activity (SMA) of the granules. Results showed that the granule's microstructure was depend ent on the nature of the substrate. Those degrading soluble carbohydra tes exhibited a layered structure, while those degrading glutamate exh ibited a rather uniform structure. Such a difference was explained bas ed on the substrate's rates of acidogenesis and diffusion. A model of the typical layered structure was proposed. In addition, the acetoclas tic Methanothrix was found as the key structural element ill all the g ranules, suggesting that it plays an important role in granulation. Th ree types of syntrophic microcolonies were found to be abundant ill gr anules degrading soluble carbohydrates: two were juxtapositioned syntr ophic microcolonies, each was composed of hydrogen-producing acetogens and hydrogen-consuming methanogens, while the third was a cluster-typ e of syntrophic association between two microcolonies. The SMA data us ing individual VFA as substrate provided supporting evidence to the ob servations of the bacterial compositions in the granules.