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Related Concept Videos

Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

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Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme...
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2° Amines to N-Nitrosamines: Reaction with NaNO201:20

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Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
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Metabolism of Chemolithotrophs01:15

Metabolism of Chemolithotrophs

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Chemolithotrophs are microorganisms that obtain energy by oxidizing inorganic molecules such as hydrogen gas (H₂), ammonia (NH₃), reduced sulfur compounds (H₂S, S²⁻), and ferrous iron (Fe²⁺). Unlike heterotrophic organisms that rely on organic carbon, chemolithotrophs transfer electrons from these inorganic donors to the electron transport chain (ETC), generating a proton motive force (PMF) that drives ATP synthesis through oxidative phosphorylation.
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1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview01:26

1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview

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Nitrous acid and nitric acids are two types of acids containing nitrogen, among which nitrous acid is weaker than nitric acid. Nitrous acid with a pKa value of 3.37 ionizes in water to give a nitrite ion and the hydronium ion.
The nitrous acid is unstable. Hence, it is formed in situ from a solution of sodium nitrite and cold aqueous acids such as hydrochloric or sulfuric acid. In an acidic solution, the –OH group of nitrous acid undergoes protonation to give oxonium ion, followed by...
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Overview of Nitrogen Metabolism01:20

Overview of Nitrogen Metabolism

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Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
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Nitriles undergo acid-catalyzed hydrolysis or base-catalyzed hydrolysis to form a carboxylic acid. These reactions proceed via an amide intermediate.
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Achieving Stable Partial Nitritation in an Acidic Nitrifying Bioreactor.

Jiyun Li1, Kangning Xu2, Tingsheng Liu1

  • 1School of Environment, Tsinghua University, Beijing 100084, China.

Environmental Science & Technology
|December 3, 2019
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Summary

This study shows that acidic conditions can achieve partial nitritation for nitrogen removal. Acid-tolerant ammonia-oxidizing bacteria (AOB) create free nitrous acid (FNA) to inhibit nitrite-oxidizing bacteria (NOB).

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Area of Science:

  • Environmental Science
  • Microbiology
  • Biotechnology

Background:

  • Partial nitritation is crucial for two-stage autotrophic nitrogen removal systems.
  • Conventional systems often struggle with nitrite-oxidizing bacteria (NOB) inhibition.
  • Acidic conditions present an alternative for controlling NOB activity.

Purpose of the Study:

  • To demonstrate a novel approach for partial nitritation in an acidic bioreactor.
  • To investigate the self-sustainability of free nitrous acid (FNA) production by acid-tolerant ammonia-oxidizing bacteria (AOB).
  • To evaluate the efficiency and microbial community dynamics under acidic partial nitritation.

Main Methods:

  • Operation of a lab-scale acidic bioreactor at pH 5-6 with high dissolved oxygen and long sludge retention time.
  • Influent nitrogen concentration of approximately 200 mg/L.
  • 16S rRNA amplicon sequencing for microbial community analysis and kinetic characterization of AOB.

Main Results:

  • Stable nitrite accumulation (>95% ratio of NO2-/(NO2- + NO3-)) achieved over 200 days.
  • Free nitrous acid (FNA) levels up to 2 mg HNO2-N/L successfully inhibited NOB.
  • Nitrosospira identified as the dominant AOB, with Nitrosomonas and Nitrospira disappearing; Nitrosospira showed high substrate affinity and tolerance to FNA.

Conclusions:

  • Acidic partial nitritation is a viable and potentially cost-effective strategy for nitrogen removal.
  • Acid-tolerant AOB can self-sustain FNA to inhibit NOB, simplifying the process.
  • Further research is needed to manage hazardous nitric oxide (NO) gas emissions from acidic nitrifying bioreactors.