1999 Volume 22 Issue 2 Pages 152-159
Abundance and spacial distribution of nitrifying bacteria in aerobic biofilm consortia were investigated by using fluorescent in situ hybridization (FISH) with 16SrRNA-targeted oligonucleotide probes. The biofilms were developed in a novel reactor named downflow hanging sponge-cubes (DHS), which was employed as a cost-effective aerobic post-treatment unit after an UASB anaerobic pre-treatment unit receiving municipal sewage. Microscopic direct counting of nitrifying bacteria detected by the FISH technique was carried out to disintegrated biofilm samples, which were obtained by squeezing the sponge-cubes at different reactor height locations. The cell enumeration suggested that the DHS biomass contained 1.4×109-1.2×108 cells·ml-1 cube of Nitrosomonas and 1.8×108-0.15×108 cells·ml-1-cube of Nitrobacter, giving the presence ratio to total cells (detected by DAPI-staining) at 1.4% and 0.18%, respectively. Cell concentrations of both nitrifying bacteria were well correlated with ammonia-oxidizing and nitrite-oxidizing activities evaluated by batch tests. Application of the FISH technique to thinsectioned intact biofilm revealed that both Nitrosomonas and Nitrobacter were rather present in the interior space of sponge-cubes, as attached onto sponge materials. A relatively small amount of Nitrosomonas was observed only until 50μm-depth outer layer of the thick biofilm formed on the surface of sponge-cubes.
