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      Effect of substrate availability on nitrous oxide production by deammonification processes under anoxic conditions

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      Microbial Biotechnology

      Blackwell Publishing Ltd

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          Summary

          Due to its high global warming potential, nitrous oxide (N 2O) emissions from wastewater treatment processes have recently received a high degree of attention. Nevertheless, there is still a lack of information regarding the microbiological processes leading to N 2O production. In this study, two lab‐scale sequencing batch reactors were operated with deammonification biomass to investigate the role of denitrification and the influence of substrate availability regarding N 2O formation during the anoxic phase of deammonification. Three different operational phases were established: within the first phase conversion by anammox was favoured and after a transition phase, denitrification activity was promoted. Low nitrous oxide production was observed during stable operation aiming for anammox conversion. Pulsed inflow of the wastewater containing ammonium (NH 4 +) and nitrite (NO 2 ) led to increased N 2O production rates. Within the period of denitrification as dominating nitrogen conversion process, the nitrous oxide concentration level was higher during continuous inflow conditions, but the reaction to pulsed inflow was less pronounced. The results indicated that denitrification was responsible for N 2O formation from the deammonification biomass. Operational settings to achieve suppression of denitrification processes to a large extend were deducted from the results of the experiments.

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          Most cited references 27

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          Nitrous oxide emission during wastewater treatment.

          Nitrous oxide (N(2)O), a potent greenhouse gas, can be emitted during wastewater treatment, significantly contributing to the greenhouse gas footprint. Measurements at lab-scale and full-scale wastewater treatment plants (WWTPs) have demonstrated that N(2)O can be emitted in substantial amounts during nitrogen removal in WWTPs, however, a large variation in reported emission values exists. Analysis of literature data enabled the identification of the most important operational parameters leading to N(2)O emission in WWTPs: (i) low dissolved oxygen concentration in the nitrification and denitrification stages, (ii) increased nitrite concentrations in both nitrification and denitrification stages, and (iii) low COD/N ratio in the denitrification stage. From the literature it remains unclear whether nitrifying or denitrifying microorganisms are the main source of N(2)O emissions. Operational strategies to prevent N(2)O emission from WWTPs are discussed and areas in which further research is urgently required are identified.
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            Biochemistry and molecular biology of anammox bacteria.

            Anaerobic ammonium-oxidizing (anammox) bacteria are one of the latest additions to the biogeochemical nitrogen cycle. These bacteria derive their energy for growth from the conversion of ammonium and nitrite into dinitrogen gas in the complete absence of oxygen. These slowly growing microorganisms belong to the order Brocadiales and are affiliated to the Planctomycetes. Anammox bacteria are characterized by a compartmentalized cell architecture featuring a central cell compartment, the "anammoxosome". Thus far unique "ladderane" lipid molecules have been identified as part of their membrane systems surrounding the different cellular compartments. Nitrogen formation seems to involve the intermediary formation of hydrazine, a very reactive and toxic compound. The genome of the anammox bacterium Kuenenia stuttgartiensis was assembled from a complex microbial community grown in a sequencing batch reactor (74% enriched in this bacterium) using a metagenomics approach. The assembled genome allowed the in silico reconstruction of the anammox metabolism and identification of genes most likely involved in the process. The present anammox pathway is the only one consistent with the available experimental data, thermodynamically and biochemically feasible, and consistent with Ockham's razor: it invokes minimum biochemical novelty and requires the fewest number of biochemical reactions. The worldwide presence of anammox bacteria has now been established in many oxygen-limited marine and freshwater systems, including oceans, seas, estuaries, marshes, rivers and large lakes. In the marine environment over 50% of the N(2) gas released may be produced by anammox bacteria. Application of the anammox process offers an attractive alternative to current wastewater treatment systems for the removal of ammonia-nitrogen. Currently, at least five full scale reactor systems are operational.
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              Anammox bacteria disguised as denitrifiers: nitrate reduction to dinitrogen gas via nitrite and ammonium.

              Anaerobic ammonium-oxidizing (anammox) bacteria oxidize ammonium with nitrite and produce N(2). They reside in many natural ecosystems and contribute significantly to the cycling of marine nitrogen. Anammox bacteria generally live under ammonium limitation, and it was assumed that in nature anammox bacteria depend on other biochemical processes for ammonium. In this study we investigated the possibility of dissimilatory nitrate reduction to ammonium by anammox bacteria. Physically purified Kuenenia stuttgartiensis cells reduced (15)NO(3) (-) to (15)NH(4) (+) via (15)NO(2) (-) as the intermediate. This was followed by the anaerobic oxidation of the produced ammonium and nitrite. The overall end-product of this metabolism of anammox bacteria was (15)N(15)N dinitrogen gas. The nitrate reduction to nitrite proceeds at a rate of 0.3 +/- 0.02 fmol cell(-1) day(-1) (10% of the 'normal' anammox rate). A calcium-dependent cytochrome c protein with a high (305 mumol min(-1) mg protein(-1)) rate of nitrite reduction to ammonium was partially purified. We present evidence that dissimilatory nitrate reduction to ammonium occurs in Benguela upwelling system at the same site where anammox bacteria were previously detected. This indicates that anammox bacteria could be mediating dissimilatory nitrate reduction to ammonium in natural ecosystems.
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                Author and article information

                Journal
                Microb Biotechnol
                Microb Biotechnol
                MBT
                Microbial Biotechnology
                Blackwell Publishing Ltd (Oxford, UK )
                1751-7915
                1751-7915
                May 2012
                16 April 2012
                : 5
                : 3
                : 415-424
                Affiliations
                Institute for Sanitary Engineering and Waste Management (ISAH), Leibniz Universitaet Hannover, Welfengarten 1, 30167 Hannover, Germany
                Author notes
                *E‐mail schneider@ 123456isah.uni‐hannover.de ; Tel. (+49)(0)511 762 2478; Fax (+49) (0)511 762 2881.
                Article
                10.1111/j.1751-7915.2011.00328.x
                3821684
                22296600
                Copyright © 2012 The Authors. Microbial Biotechnology © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd
                Categories
                Research Articles

                Biotechnology

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