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Category: Environmental Microbiology
Nitrification in Wastewater Treatment, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817145/9781555814816_Chap16-1.gif /docserver/preview/fulltext/10.1128/9781555817145/9781555814816_Chap16-2.gifAbstract:
Microbial nitrification is a necessary step in removing nitrogen from wastewaters via biological denitrification and is becoming more important due to strict regulations on nitrogen discharge. However, microbial nitrification is recognized as being difficult to maintain in practical wastewater treatment plants (WWTPs) owing to the lower kinetics, yields, and sensitivity of nitrifying bacteria to physical, chemical, and environmental disturbances as mentioned, even though nitrification has been studied more than any other specific biochemical reactions occurring in wastewater treatment to date. Influent NO2 -, chromium, and nickel influenced the AOB community structure, while correlations between other metals analyzed in this study and the AOB community structure were insignificant. As an oxidation process, nitrification significantly consumes oxygen, and dissolved oxygen (DO) concentration is a key factor for maintaining nitrification stably as well as pH. In an activated sludge process, 3% salt inhibited both the maximum utilization rate and the saturation constant, suggesting uncompetitive inhibition. Nitrification in wastewater treatment systems has been studied extensively. Despite their importance, knowledge about the identity and ecology of nitrifying bacteria carrying out nitrification in WWTPs has been scarce. Thus, biological nitrogen removal processes have been regarded as “a black box” in practice because the lack of fundamental microbiological understanding hampers knowledge-driven process design and operation.
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Typical process flow sheets for biological nitrogen removal. (A) A portion of the wastewater can be bypassed to the anoxic tank (denitrifying tank). (B) Bardenpho process.
(A) Photomicrograph of an activated sludge floc. (B and C) Confocal laser-scanning microscope images of an activated sludge floc showing the in situ spatial organization of bacteria and AOB. FISH was performed using a fluorescein isothiocyanate-labeled EUB338-mixed probe and a tetramethylrhodamine 5-isothiocyanate-labeled Nso190 probe. The probe Nso190-stained AOB appear to be yellow because of binding of both probes, and bacterial cells are green.
Typical concentration profiles of O2, NH4 +, and NO3 – in an activated sludge floc at 45 µM O2. The shaded area indicates the floc. The center of the floc is at a depth of 0 µm. (From Satoh et al. [2003a ], with permission from Biotechnology and Bioengineering.)
The consumption rates of NH4 + and inorganic nitrogen (Ni) defined as the sum of NH4 +, NO2 –, and NO3 – as determined by the batch experiments at various O2 concentrations in the bulk liquid. Rates shown are mean values, and error bars indicate standard deviations. (From Satoh et al. [2003a ], with permission from Biotechnology and Bioengineering.)
Steady-state concentration profiles of O2 and NH4 + in the autotrophic nitrifying biofilm incubated in the media at C/N = 0 (A), C/N = 1 (B), and C/N = 3.4 (C), respectively. The modeled profiles are indicated by solid lines. The spatial distributions of NH4 + oxidation rates are indicated by stippled area. Surface is at a depth of 0 µm. (From Okabe et al. [2004b], with permission from Biotechnology and Bioengineering.)
Spatial distributions of surface fractions of AOB in biofilms cultured in the media at C/N = 0, 1, and 2, respectively. The biofilm surfaces are indicated by the dotted lines.
(A) Spatial distribution of average microbial cluster sizes of AOB hybridized with probe Nso190 in different biofilms cultured at C/N = 0 and 1. (B) Cross-section of biofilm cultured at C/N = 0.
(A) Steady-state concentration profiles of O2, NH4 +, NO2 –, and NO3 – in a biofilm cultured at C/N = 2. (B) Spatial distribution of the estimated volumetric consumption and production rates of NH4 +, NO2 –, and NO3 –. The biofilm surface is at a depth of 0 µm.
Proposed ecophysiological interactions between nitrifiers and heterotrophic bacteria in a carbon-limited autotrophic nitrifying biofilm fed with only NH4 + as energy source.
(A) Two-dimensional (2-d) IbM model description of actions occurring at the individual scale. (B) Spatial scales in the 2-d model of nitrifying granules. (a) Representative biomass granule comprised in a square computational domain; (b) the square grid elements discretizing the space, each containing several biomass particles; (c) individual biomass particles, of different possible biomass types. All biomass particles within a single grid element experience the same substrate concentrations. The biomass concentrations within a grid element are calculated from the mass of all individual biomass particles within the element volume ( Xavier et al., 2005 , Matsumoto et al., 2010 ).
Detailed insight into the spatial localization of HetU (a), HetB (b), and HetO (c) provided by a two-dimensional IbM simulation, at day 100. White dotted line shows the granule surface ( Matsumoto et al., 2010 ).
Spatial distributions of bacteria along the radius of a nitrifying granule as detected by FISH. The abundance ratio of each bacterium was quantified in 50-µm-thick shells starting at the granule surface (left). Abundance data presented are averages of six replicate measurements. The total bacterial volumetric occupancy in the granule is derived from fluorescence of EUB338 mix-tagged cells (open circles along the R-axis). The α-Proteobacteria constitute the bacterial group that hybridized with probe ALF1b, excluding the genus Nitrobacter that hybridized with probe NIT3. (The figure was reconstructed from the data of Matsumoto et al. [2010 ].)
Comparison of the steady-state solute concentrations in the biofilm calculated in two-dimensional (2-d) IbM model simulations, with the experimental microelectrode data (open circles, triangles and squares for O2, NH4 +, NO3 –, NO2 –). The model results are at day 100. To obtain the comparable profiles along the radius, the 2-d concentration distributions were averaged in concentric shells with different radii. (The figure was reconstructed from the data of Matsumoto et al. [2010 ].)
Stoichiometric parameters for microbial reactions