Molecular and modeling analyses of the structure and function of nitrifying activated sludge

Activated sludge community structure was assessed directly by oligonucleoti de probes for seven treatment plants in France and two treatment plants in The Netherlands. Routine operating data also were obtained for these plants . Mathematical modeling was employed to translate the operating data into p arameters that reflect community function and structure, These model-transl ated measures were compared to the direct probing measures of community str ucture. Extraction of RNA and subsequent slot-blot hybridization with probe s Nso1225 (for active ammonium oxidizers) and Eub338 (for all active bacter ia) confirmed that the ratio of active nitrifiers to active heterotrophs wa s mainly explained by the ratio of TKN:BODL removed and that probe Nso1225 provided a quantitative measure of ammonium oxidizers easily distinguishabl e from background. Fluorescent in situ hybridization (FISH) followed simila r trends. The ratio of active nitrifiers to total VSS depended on the TKN/B ODL removal ratio and the sludge age. Finally, the ng rRNA/mg VSS hybridize d by probe Eub338 was strongly and inversely correlated to the sludge age a nd suggests that specific rRNA contents of about 11,000 ng rRNA/mg VSSactiv e for heterotrophic bacteria and 14,000 ng rRNA/mg VSS,,ti,, for ammonium o xidizers can be used to estimate active VSS from probing results targeted t o rRNA. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserve d.