Characterization of different microbial nuclei as potential precursors of anaerobic granulation

Abstract

Anaerobic granule nuclei enriched in either acidogens, syntrophic consortia, Methanosaeta spp. or Methanosarcina spp. were developed in four upflow bed filter reactors fed with sucrose, an ethanol/acetate mixture, acetate and methanol, respectively. The enrichment process was evaluated by scanning electron microscopy and by the change in trophic specific activities. The four developed granule nuclei presented different settling velocities: 3.2, 8.7, 10.5 and 11.3 m h−1 for the acidogenic floes, the Methanosarcina-, the syntrophic consortia and the Methanosaeta-enriched nuclei, respectively. These velocities were related to the size and the ash content of the various aggregates. Acidogenic floes were relatively small in size ( < 0.6 mm in diameter), compared to the other granule nuclei (up to 1.2 mm in diameter). The ash content represented 60%, 40%, 30% and 16% for Methanosaeta-, Methanosarcina-enriched nuclei, syntrophic consortia and acidogenic floes, respectively. Methanosaeta-enriched nuclei contained high amounts of Ca2+ (140 mg per g SS) compared to the other ones (1–8 mg per g SS). Acidogenic floes contained high amount of extracellular polymeric substances compared to the other types of nuclei.