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Project description:For the application of biofilm processes, a better understanding of nitrous oxide (N2O) formation within the biofilm is essential for design and operation of biofilm reactors with minimized N2O emissions. In this work, a previously established N2O model incorporating both ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine (NH2OH) oxidation pathways is applied in two structurally different biofilm systems to assess the effects of co- and counter-diffusion on N2O production. It is demonstrated that the diffusion of NH2OH and oxygen within both types of biofilms would form an anoxic layer with the presence of NH2OH and nitrite ( ), which would result in a high N2O production via AOB denitrification pathway. As a result, AOB denitrification pathway is dominant over NH2OH oxidation pathway within the co- and counter-diffusion biofilms. In comparison, the co-diffusion biofilm may generate substantially higher N2O than the counter-diffusion biofilm due to the higher accumulation of NH2OH in co-diffusion biofilm, especially under the condition of high-strength ammonium influent (500 mg N/L), thick biofilm depth (300 μm) and moderate oxygen loading (~1-~4 m(3)/d). The effect of co- and counter-diffusion on N2O production from the AOB biofilm is minimal when treating low-strength nitrogenous wastewater.
| S-EPMC4926105 | biostudies-literature
Project description:Ecophysiological interactions between the community members (i.e., nitrifiers and heterotrophic bacteria) in a carbon-limited autotrophic nitrifying biofilm fed only NH(4)(+) as an energy source were investigated by using a full-cycle 16S rRNA approach followed by microautoradiography (MAR)-fluorescence in situ hybridization (FISH). Phylogenetic differentiation (identification) of heterotrophic bacteria was performed by 16S rRNA gene sequence analysis, and FISH probes were designed to determine the community structure and the spatial organization (i.e., niche differentiation) in the biofilm. FISH analysis showed that this autotrophic nitrifying biofilm was composed of 50% nitrifying bacteria (ammonia-oxidizing bacteria [AOB] and nitrite-oxidizing bacteria [NOB]) and 50% heterotrophic bacteria, and the distribution was as follows: members of the alpha subclass of the class Proteobacteria (alpha-Proteobacteria), 23%; gamma-Proteobacteria, 13%; green nonsulfur bacteria (GNSB), 9%; Cytophaga-Flavobacterium-Bacteroides (CFB) division, 2%; and unidentified (organisms that could not be hybridized with any probe except EUB338), 3%. These results indicated that a pair of nitrifiers (AOB and NOB) supported a heterotrophic bacterium via production of soluble microbial products (SMP). MAR-FISH revealed that the heterotrophic bacterial community was composed of bacteria that were phylogenetically and metabolically diverse and to some extent metabolically redundant, which ensured the stability of the ecosystem as a biofilm. alpha- and gamma-Proteobacteria dominated the utilization of [(14)C]acetic acid and (14)C-amino acids in this biofilm. Despite their low abundance (ca. 2%) in the biofilm community, members of the CFB cluster accounted for the largest fraction (ca. 64%) of the bacterial community consuming N-acetyl-D-[1-(14)C]glucosamine (NAG). The GNSB accounted for 9% of the (14)C-amino acid-consuming bacteria and 27% of the [(14)C]NAG-consuming bacteria but did not utilize [(14)C]acetic acid. Bacteria classified in the unidentified group accounted for 6% of the total heterotrophic bacteria and could utilize all organic substrates, including NAG. This showed that there was an efficient food web (carbon metabolism) in the autotrophic nitrifying biofilm community, which ensured maximum utilization of SMP produced by nitrifiers and prevented buildup of metabolites or waste materials of nitrifiers to significant levels.
| S-EPMC368389 | biostudies-literature
Project description:Microbial biofilms are ubiquitous in aquatic environments where they provide important ecosystem functions. A key property believed to influence the community structure and function of biofilms is thickness. However, since biofilm thickness is inextricably linked to external factors such as water flow, temperature, development age and nutrient conditions, its importance is difficult to quantify. Here, we designed an experimental system in a wastewater treatment plant whereby nitrifying biofilms with different thicknesses (50 or 400 µm) were grown in a single reactor, and thus subjected to identical external conditions. The 50 and 400 µm biofilm communities were significantly different. This beta-diversity between biofilms of different thickness was primarily caused by deterministic factors. Turnover (species replacement) contributed more than nestedness (species loss) to the beta-diversity, i.e. the 50 µm communities were not simply a subset of the 400 µm communities. Moreover, the two communities differed in the composition of nitrogen-transforming bacteria and in nitrogen transformation rates. The study illustrates that biofilm thickness alone is a key driver for community composition and ecosystem function, which has implications for biotechnological applications and for our general understanding of biofilm ecology.
| S-EPMC6434030 | biostudies-literature
Project description:The amount of oxygen released by Phragmites roots and the community structure and in situ activity of nitrifying bacteria in the root biofilms were analyzed by the combined use of 16S rRNA gene-cloning analysis, quantitative PCR (qPCR) assay and microelectrodes. Axial and radial O? microprofiles were obtained for individual roots of Phragmites in a horizontal flow reactor fed with artificial medium continuously. Axial O? profiles revealed that O? was released at a rate of 0.21 ?mol O? cm?² (root surface area) h?¹ only in the apical region (up to ca. 40 mm from the root apex), where there was a high abundance (10? to 10? copies g?¹ biomass) of Nitrosomonas-like AOB and Nitrospira-like NOB. This abundance, however, sharply declined to the detection limit at positions more basal than 80 mm. Phylogenetic analysis based on 16S rRNA gene identified strains related to Nitrosomonas oligotropha and Nitrosomonas cryotolerans as the predominant AOB and strains related to Nitrospira marina and Nitrospira moscoviensis as the predominant NOB in the root biofilms. Based on radial O? microprofiles, the oxic region only extended about 0.5 mm into the surrounding sediment due to a high rate of O? consumption in the rhizosphere. The net NH?? and O? consumption rates in the apical region were higher than those determined at the oxic sediment surface in which the abundance of AOB and NOB was one order of magnitude lower than in the rhizosphere. These results clearly indicated that Phragmites root biofilms played an important role in nitrification in the waterlogged anoxic sediment.
| S-EPMC4036055 | biostudies-literature
Project description:In nitrifying biofilms, the organic carbon to ammonia nitrogen (C/N) supply ratio can influence resource competition between heterotrophic and nitrifying bacteria for oxygen and space. We investigated the impact of acute and chronic changes in carbon supply on inter-guild competition in two moving bed biofilm reactors (MBBR), operated with (R1) and without (R0) external organic carbon supply. The microbial and nitrifying community composition of the reactors differed significantly. Interestingly, acute increases in the dissolved organic carbon inhibited nitrification in R1 ten times more than in R0. A sustained increase in the carbon supply decreased nitrification efficiency and increased denitrification activity to a greater extent in R1, and also increased the proportion of potential denitrifiers in both bioreactors. The findings suggest that autotrophic biofilms subjected to increases in carbon supply show higher nitrification and lower denitrification activity than carbon-fed biofilms. This has significant implications for the design of nitrifying bioreactors. Specifically, efficient removal of organic matter before the nitrification unit can improve the robustness of the bioreactor to varying influent quality. Thus, maintaining a low C/N ratio is important in nitrifying biofilters when acute carbon stress is expected or when anoxic activity (e.g. denitrification or H2S production) is undesirable, such as in recirculating aquaculture systems (RAS).
| S-EPMC7189377 | biostudies-literature
Project description:Nitrifying biofilms deprived of organic carbon show higher functional resilience to increases in carbon supply
| PRJEB37773 | ENA
Project description:Effects of salinity changes on freshwater and low-salinity nitrifying biofilter media
| PRJNA926625 | ENA