STRUCTURE AND METHANOGENIC ACTIVITY OF GRANULES FROM AN ASBR TREATINGDILUTE WASTE-WATER AT LOW-TEMPERATURES

The microstructure of ASBR granules treating synthetic substrate consi sting of non-fat-dry-milk at temperatures of 5, 15 and 25 degrees C wa s analyzed by scanning and transmission electron microscopy. The speci fic methanogenic activity of the granules was tested at 35 degrees C u sing acetate and mixtures of acetate and propionate as substrates. Res ults revealed no significant variation in microbial structure for the different temperature conditions. Granules at 15 and 25 degrees C exhi bited uniform structure, predominantly Methanothrix-like microorganism s, while granules at 5 degrees C indicated the existence of a layered structure. This reinforces the hypothesis that layering is largely sub strate specific, but also suggests that temperature may have a role. A ctivity tests revealed that even after long periods of operation at ps ychrophilic temperatures, mesophilic bacteria are active and have the ability to rapidly degrade acetate and mixtures of acetate and propion ate. (C) 1997 IAWQ. Published by Elsevier Science Ltd.