Influence of the microbial content of different precursory nuclei on the anaerobic granulation dynamics

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Abstract
Anaerobic granule nuclei enriched in either acidogens (AF), syntrophic consortia (SN), Methanosaega spp. (MT) and Methanosarcina spp. (MN) were developed in four upfiow bed filter reactors fed with sucrose, an ethanol/acetate mixture, acetate and methanol, respectively. The four developed granule nuclei presented different settling velocities: 3.2, 8.7, 10.5 and 11.3 m/h for the AF flocs, the MS-, the SN- and the MT-nuclei, respectively. The ash content represented 60%, 40%, 30% and 16% of dry weight for the MT-, MS-, SN-enriched nuclei, and AF floes, respectively. Acidogenic floes contained high amount of extracellular polymeric substances. The influence of these four different nuclei on the time course of complex granule development was investigated by shifting the feed carbon of all of the four reactors to sucrose. Granulation proceeded rapidly both on syntrophic and Methanosaeta nuclei. The largest granules (Sauter diameter of 2.36 mm), however, were obtained within the shortest period in the reactor started with syntrophic nuclei. These nuclei presented also the best colonization by fermentative bacteria as shown by the evolution of their glucotrophjc activities, Less satisfying granulation was obtained on Methanosarcina nuclei. In contrast, granulation was significantly retarded when acidogens were used as precursors. From these results it appears that syntropbs and Methanosaeta spp. play the principal role in anaerobic granulation process.

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