The treatment of ammonium rich wastewater, like sludge digester effluent, can be significantly improved when new biotechnological processes are introduced. In this paper, the combination of a partial nitrification process (SHARON®) and anoxic ammonium oxidation (Anammox®) process for the treatment of ammonia rich influents is evaluated. Herein the combined process has been studied with sludge recycle liquor from the WWTP Rotterdam-Dokhaven. The SHARON process was operated stably for more than 2 years in a 10 l CSTR under continuous aeration with a HRT of 1 day. The ammonia in the sludge liquor was converted by 53% to nitrite only. During the test period no formation of nitrate was observed. The effluent of the SHARON process was ideally suited as influent for the Anammox reactor. The Anammox process was operated as a granular sludge SBR-process. More than 80% of the ammonia was converted into dinitrogen gas at a load of 1.2 kgN/m3 per day. Planctomycete-like bacteria dominated the mixed community of the Anammox reactor, and only a small percentage of the population consisted of aerobic ammonium-oxidizing bacteria. This showed that the ammonium-oxidizers in the effluent of the SHARON process did not accumulate in the SBR. The test period showed that the combined SHARON-Anammox system can work stably over long periods and the process is ready for full-scale implementation.

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are competing microbial nitrate-reduction processes. The occurrence of DNRA has been shown to be effected qualitatively by various parameters in the environment. A more quantitative understanding can be obtained using enrichment cultures in a laboratory reactor, yet no successful DNRA enrichment culture has been described. We showed that a stable DNRA-dominated enrichment culture can be obtained in a chemostat system. The enrichment was based on the hypothesis that nitrate limitation is the dominant factor in selecting for DNRA. First, a conventional denitrifying culture was enriched from activated sludge, with acetate and nitrate as substrates. Next, the acetate concentration in the medium was increased to obtain nitrate-limiting conditions. As a result, conversions shifted from denitrification to DNRA. In this selection of a DNRA culture, two important factors were the nitrate limitation and a relatively low dilution rate (0.026 h − 1 ). The culture was a highly enriched population of Deltaproteobacteria most closely related to Geobacter lovleyi, based on 16S rRNA gene sequencing (97% similarity). We established a stable and reproducible cultivation method for the enrichment of DNRA bacteria in a continuously operated reactor system. This enrichment method allows to further investigate the DNRA process and address the factors for competition between DNRA and denitrification, or other N-conversion pathways.

Here we describe the diversity and activity of sulfate-reducing bacteria (SRB) in sulfidogenic bioreactors by using the simultaneous analysis of PCR products obtained from DNA and RNA of the 16S rRNA and dissimilatory sulfite reductase (dsrAB) genes. We subsequently analyzed the amplified gene fragments by using denaturing gradient gel electrophoresis (DGGE). We observed fewer bands in the RNA-based DGGE profiles than in the DNA-based profiles, indicating marked differences in the populations present and in those that were metabolically active at the time of sampling. Comparative sequence analyses of the bands obtained from rRNA and dsrB DGGE profiles were congruent, revealing the same SRB populations. Bioreactors that received either ethanol or isopropanol as an energy source showed the presence of SRB affiliated with Desulfobulbus rhabdoformis and/or Desulfovibrio sulfodismutans, as well as SRB related to the acetate-oxidizing Desulfobacca acetoxidans. The reactor that received wastewater containing a diverse mixture of organic compounds showed the presence of nutritionally versatile SRB affiliated with Desulfosarcina variabilis and another acetate-oxidizing SRB, affiliated with Desulfoarculus baarsii. In addition to DGGE analysis, we performed whole-cell hybridization with fluorescently labeled oligonucleotide probes to estimate the relative abundances of the dominant sulfate-reducing bacterial populations. Desulfobacca acetoxidans-like populations were most dominant (50 to 60%) relative to the total SRB communities, followed by Desulfovibrio-like populations (30 to 40%), and Desulfobulbus-like populations (15 to 20%). This study is the first to identify metabolically active SRB in sulfidogenic bioreactors by using the functional gene dsrAB as a molecular marker. The same approach can also be used to infer the ecological role of coexisting SRB in other habitats.

In order to meet increasingly stringent European discharge standards, new applications and control strategies for the sustainable removal of ammonia from wastewater have to be implemented. In this paper we discuss a nitrogen removal system based on the processes of partial nitrification and anoxic ammonia oxidation (anammox). The anammox process offers great opportunities to remove ammonia in fully autotrophic systems with biomass retention. No organic carbon is needed in such nitrogen removal system, since ammonia is used as electron donor for nitrite reduction. The nitrite can be produced from ammonia in oxygen-limited biofilm systems or in continuous processes without biomass retention. For successful implementation of the combined processes, accurate biosensors for measuring ammonia and nitrite concentrations, insight in the complex microbial communities involved, and new control strategies have to be developed and evaluated.

Molecular analysis of bacteria enriched under in situ-like conditions and mechanically isolated by micromanipulation showed that a hitherto-uncultivated microaerophilic bacterium thriving in oxygen-sulfide counter-gradients (R. Thar and M. Kühl, Appl. Environ. Microbiol. 68:6310-6320, 2000) is affiliated with the ε-subdivision of the Proteobacteria. The affiliation was confirmed by the use of whole-cell hybridization with newly designed specific oligonucleotide probes. The bacterium belongs to a new genus and received the provisional name “Candidatus Thioturbo danicus.”