Identifying causes for N2O accumulation in a lab-scale sequencing batch reactor performing simultaneous nitrification, denitrification and phosphorus removal

The recently described process of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) has a great potential to save capital and operating costs for wastewater treatment plants. However, the presence of glycogen-accumulating organisms (GAOs) and the accumulation of nitrous oxide (N2O) can severely compromise the advantages of this process. In this study, these two issues were investigated using a lab-scale sequencing batch reactor performing SNDPR over a 5-month period. The reactor was highly enriched in polyphosphate-accumulating organisms (PAOs) and GAOs representing around 70% of the total microbial community. PAOs were the dominant population at all times and their abundance increased, while GAOs population decreased over the study period. Anoxic batch tests demonstrated that GAOs rather than denitrifying PAOs were responsible for denitrification. NO accumulated from denitrification and more than half of the nitrogen supplied in a reactor cycle was released into the atmosphere as NO. After mixing SNDPR sludge with other denitrifying sludge, N2O present in the bulk liquid was reduced immediately if external carbon was added. We therefore suggest that the N2O accumulation observed in the SNDPR reactor is an artefact of the low microbial diversity facilitated by the use of synthetic wastewater with only a single carbon source. (C) 2005 Elsevier B.V. All rights reserved.

Putative glycogen-accumulating organisms belonging to the Alphaproteobacteria identified through rRNA-based stable isotope probing

Deterioration of enhanced biological phosphorus removal (EBPR) has been linked to the proliferation of glycogen-accumulating organisms (GAOs), but few organisms possessing the GAO metabolic phenotype have been identified. An unidentified GAO was highly enriched in a laboratory-scale bioreactor and attempts to identify this organism using conventional 16S rRNA gene cloning had failed. Therefore, rRNA-based stable isotope probing followed by full-cycle rRNA analysis was used to specifically identify the putative GAOs based on their characteristic metabolic phenotype. The study obtained sequences from a group of Alphaproteobacteria not previously shown to possess the GAO phenotype, but 90% identical by 16S rRNA gene analysis to a phylogenetic clade containing cloned sequences from putative GAOs and the isolate Defluvicoccus vanus. Fluorescence in situ hybridization (FISH) probes (DF988 and DF1020) were designed to target the new group and post-FISH chemical staining demonstrated anaerobic-aerobic cycling of polyhydroxyalkanoates, as per the GAO phenotype. The successful use of probes DF988 and DF1020 required the use of unlabelled helper probes which increased probe signal intensity up to 6.6-fold, thus highlighting the utility of helper probes in FISH. The new group constituted 33% of all Bacteria in the lab-scale bioreactor from which they were identified and were also abundant (51 and 55% of Bacteria) in two other similar bioreactors in which phosphorus removal had deteriorated. Unlike the previously identified Defluvicoccus-related organisms, the group identified in this study were also found in two full-scale treatment plants performing EBPR, suggesting that this group may be industrially relevant.

Spatial patterns of aerobic and anaerobic mineralization rates and oxygen penetration dynamics in coral reef sediments

Oxygen consumption rates (OCR), aerobic mineralization and sulfate reduction rates (SRR) were studied in the permeable carbonate reef sediments of Heron Reef, Australia. We selected 4 stations with different hydrodynamic regimes for this study. In situ oxygen penetration into the sediments was measured with an autonomous microsensor profiler. Areal OCR were quantified from the measured oxygen penetration depth and volumetric OCR. Oxygen penetration and dynamics (median penetration depths at the 4 stations ranged between 0.3 and 2.2 cm), OCR (median 57 to 196 mmol C m(-2) d(-1)), aerobic mineralization (median 24 to 176 mmol C m(-2) d(-1)) and SRR (median 9 to 42 mmol C m(-2) d(-1)) were highly variable between sites. The supply of oxygen by pore water advection was a major cause for high mineralization rates by stimulating aerobic mineralization at all sites. However, estimated bottom water filtration rates could not explain the differences in volumetric OCR and SRR between the 4 stations. This suggests that local mineralization rates are additionally controlled by factors other than current driven pore water advection, e.g. by the distribution of the benthic fauna or by local differences in labile organic carbon supply from sources such as benthic photosynthesis. Carbon mineralization rates were among the highest reported for coral reef sediments, stressing the role of these sediments in the functioning of the reef ecosystem.

Candidatus "Anammoxoglobus propionicus" a new propionate oxidizing species of anaerobic ammonium oxidizing bacteria

The bacteria that mediate the anaerobic oxidation of ammonium (anammox) are detected worldwide in natural and man-made ecosystems, and contribute up to 50% to the loss of inorganic nitrogen in the oceans. Two different anammox species rarely live in a single habitat, suggesting that each species has a defined but yet unknown niche. Here we describe a new anaerobic ammonium oxidizing bacterium with a defined niche: the co-oxidation of propionate and ammonium. The new anammox species was enriched in a laboratory scale bioreactor in the presence of ammonium and propionate. Interestingly, this particular anammox species could out-compete other anammox bacteria and heterotrophic denitrifiers for the oxidation of propionate in the presence of ammonium, nitrite and nitrate. We provisionally named the new species Candidatus "Anammoxoglobus propionicus".