Daan Beheydt

Characterization of an autotrophic nitrogen-removing biofilm from a highly loaded lab-scale rotating biological contactor.

ABSTRACT In this study, a lab-scale rotating biological contactor (RBC) treating a synthetic NH4+ wastewater devoid of organic carbon and showing high N losses was examined for several important physiological and microbial characteristics. The RBC biofilm removed 89% ± 5% of the influent N at the highest surface load of approximately 8.3 g of N m−2 day−1, with N2 as the main end product. In batch tests, the RBC biomass showed good aerobic and anoxic ammonium oxidation (147.8 ± 7.6 and 76.5 ± 6.4 mg of NH4+-N g of volatile suspended solids [VSS]−1 day−1, respectively) and almost no nitrite oxidation (< 1 mg of N g of VSS−1 day−1). The diversity of aerobic ammonia-oxidizing bacteria (AAOB) and planctomycetes in the biofilm was characterized by cloning and sequencing of PCR-amplified partial 16S rRNA genes. Phylogenetic analysis of the clones revealed that the AAOB community was fairly homogeneous and was dominated by Nitrosomonas-like species. Close relatives of the known anaerobic ammonia-oxidizing bacterium (AnAOB) Kuenenia stuttgartiensis dominated the planctomycete community and were most probably responsible for anoxic ammonium oxidation in the RBC. Use of a less specific planctomycete primer set, not amplifying the AnAOB, showed a high diversity among other planctomycetes, with representatives of all known groups present in the biofilm. The spatial organization of the biofilm was characterized using fluorescence in situ hybridization (FISH) with confocal scanning laser microscopy (CSLM). The latter showed that AAOB occurred side by side with putative AnAOB (cells hybridizing with probe PLA46 and AMX820/KST1275) throughout the biofilm, while other planctomycetes hybridizing with probe PLA886 (not detecting the known AnAOB) were present as very conspicuous spherical structures. This study reveals that long-term operation of a lab-scale RBC on a synthetic NH4+ wastewater devoid of organic carbon yields a stable biofilm in which two bacterial groups, thought to be jointly responsible for the high autotrophic N removal, occur side by side throughout the biofilm.

Nitrous oxide emissions from soils: "from the bottle to the model

Abstract Since the early 1990s, we have been carrying out experiments on N2O production, emission and sorption from a variety of soils and ecosystems. These laboratory studies revealed insights on the complex process of N2O formation in soils under contrasting conditions. Within Belgium, we also carried out numerous field experiments to measure in situ N2O emissions, using the closed chamber technique. The latter allowed us to suggest a region-specific N2O-N emission factor (2.66% of the applied N) for direct soil emissions and to assess the spatial and temporal variability of N2O emissions. Recently, we have been using these N2O field emission data to validate an adapted version of the DNDC process-based model to predict direct N2O emissions from agricultural soils of the Flemish region. Ultimately, it is our aim to develop, based on this validated DNDC model, scenario analyses of future direct N2O emissions from agricultural soils.