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As part of the EU-sponsored MACOBS (Monitoring and Control of Bulking Sludge through Molecular Probe Assays) project, the size and the composition of the filamentous population in 73 industrial activated sludge plants, were investigated. The inventory included plants in Denmark, Germany, Italy and The Netherlands. Large filamentous populations were present in about 60% of the plants, which means that bulking of activated sludge, which is no longer a serious problem in modern domestic nutrient removal plants, still occurs frequently in industrial treatment plants. The filamentous micro-organisms present were identified/described by "traditional" methods, based on their morphological features and several staining techniques, and by the application of molecular probes (FISH: Fluorescent In Situ Hybridisation). Nine species specific probes were available when the project started, nine new probes have been developed during the project. Fifty nine different filamentous species were observed in the samples, including ca. 40 species that have not been described so far. The unknown species are denoted as Type Ind-1, 2, 3, etc. Probes are now available for the identification of about 17 species. Further research aimed at developing additional probes will be necessary in order to establish which species distinguished provisionally are identical, viz. morphotypes of the same filamentous organism.

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The diversity of filamentous bacteria present in industrial wastewater treatment plants was analysed by a combination of classical and molecular-biological approaches. Many unknown filamentous bacteria were observed in about 80 screened activated sludge samples from different industries with sometimes severe bulking sludge problems. A special focus was paid to filaments which resembled "Nostocoida limicola", a filamentous bacterium which was found to be present in many WWTPs. These filamentous bacteria are hardly cultivable and only one strain was obtained and maintained in co-culture with a yeast. The 16S rRNA sequences of several other "Nostocoida limicola"-like filamentous bacteria from different sludge samples were obtained by micromanipulation and different molecular-biological methods. The sequences were phylogenetically analyzed and specific molecular probes were developed and applied. The results clearly demonstrate that "Nostocoida limicola"-like filaments from industrial WWTPs are different from all other "Nostocoida limicola" types investigated so far. Our strains are affiliated to the alpha-subclass of Proteobacteria.

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Fluorescent In Situ Hybridisation (FISH) was used to monitor the presence of filamentous microorganisms in industrial wastewater treatment plants (WWTPs). Monitoring with a restricted set of FISH probes in WWTPs from potato industry showed growth and decline of Thiothrix populations that could be linked to operational procedures. In a follow up project new FISH probes were developed for filamentous bacteria in industrial WWTPs and 70 WWTPs were analysed for presence of these filaments. Several newly described species of filamentous bacteria appear to be common and dominant in industrial WWTPs. Monitoring of a WWTP from textile industry showed growth and decline of one of these organisms when operational conditions in the plant were varied. The present paper demonstrates that bulking sludge in industrial wastewater treatment plants can effectively be monitored using a combination of standard chemical analyses and the FISH technique.

Waste streams from industrial processes such as metal smelting or mining contain high concentrations of sulfate and metals with low pH. Dissimilatory sulfate reduction carried out by sulfate-reducing bacteria (SRB) at low pH can combine sulfate reduction with metal-sulfide precipitation and thus open possibilities for selective metal recovery. This study investigates the microbial diversity and population changes of a single-stage sulfidogenic gas-lift bioreactor treating synthetic zinc-rich waste water at pH 5.5 by denaturing gradient gel electrophoresis of 16S rRNA gene fragments and quantitative polymerase chain reaction. The results indicate the presence of a diverse range of phylogenetic groups with the predominant microbial populations belonging to the Desulfovibrionaceae from delta-Proteobacteria. Desulfovibrio desulfuricans-like populations were the most abundant among the SRB during the three stable phases of varying sulfide and zinc concentrations and increased from 13% to 54% of the total bacterial populations over time. The second largest group was Desulfovibrio marrakechensis-like SRB that increased from 1% to about 10% with decreasing sulfide concentrations. Desulfovibrio aminophilus-like populations were the only SRB to decrease in numbers with decreasing sulfide concentrations. However, their population was <1% of the total bacterial population in the reactor at all analyzed time points. The number of dissimilatory sulfate reductase (DsrA) gene copies per number of SRB cells decreased from 3.5 to 2 DsrA copies when the sulfide concentration was reduced, suggesting that the cells' sulfate-reducing capacity was also lowered. This study has identified the species present in a single-stage sulfidogenic bioreactor treating zinc-rich wastewater at low pH and provides insights into the microbial ecology of this biotechnological process.