Research Article: Abundance and diversity of nitrogen-removing microorganisms in the UASB-anammox reactor

Date Published: April 22, 2019

Publisher: Public Library of Science

Author(s): Rui Chen, Junqin Yao, Nuerla Ailijiang, Ruisang Liu, Lei Fang, Yinguang Chen, Sartaj Ahmad Bhat.

http://doi.org/10.1371/journal.pone.0215615

Abstract

Anaerobic ammonium oxidation is considered to be the most economical and low-energy biological nitrogen removal process. So far, anammox bacteria have not yet been purified from cultures. Some nitrogen-removing microorganisms cooperate to perform the anammox process. The objective of this research was to analyze the abundance and diversity of nitrogen-removing microorganisms in an anammox reactor started up with bulking sludge at room temperature. In this study, the ammonia-oxidizing archaea phylum Crenarchaeota was enriched from 9.2 to 53.0%. Nitrosomonas, Nitrosococcus, and Nitrosospira, which are ammonia-oxidizing bacteria, increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, which are anammox bacteria, were detected in the seeding sludge, accounting for 77.1, 11.5, and 10.6%. After cultivation, the dominant genus changed to Ca. Kuenenia, accounting for 82.0%. Nitrospirae, nitrite oxidation bacteria, decreased from 2.2 to 0.1%, while denitrifying genera decreased from 12.9 to 2.1%. The results of this study contribute to the understanding of nitrogen-removing microorganisms in an anammox reactor, thereby facilitating the improvement of such reactors. However, the physiological and metabolic functions of the ammonia-oxidizing archaea community in the anammox reactor need to be investigated in further studies.

Partial Text

The discovery of the anaerobic ammonium oxidation (anammox) process, a chemolithoautotrophic microbial process, took place in a denitrifying fluidized bed reactor in the early 1990s [1]. Under anaerobic conditions, the anammox reaction can directly convert ammonium to nitrogen gas using nitrite as an electron acceptor [2]. Stoichiometric ratios are considered to be an indicator of anammox processes [3]. According to previous studies, the corresponding molar ratios of the anammox process for NH4+ consumption, NO2- consumption and NO3- production are 1.00:1.32: 0.26, respectively [2]. Anammox is also an economical and effective method for nitrogen removal, since it was first discovered, compared to the traditional nitrification-denitrification method [1].

In this study, the diversity, richness, and evenness of AOA were significantly increased, while the unclassified AOA genus Crenarchaeota was enriched and increased from 9.2 to 53.0%, most likely because it adapted to the oxygen-poor environment. The AOB genera Nitrosomonas, Nitrosococcus, and Nitrosospira were enriched and increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Three anammox bacterial genera, Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, were detected. After cultivation, Ca. Kuenenia was enriched from 11.5 to 82.0% and became the dominant anammox bacterial genus, while Ca. Brocadia decreased from 77.1 to 18.0% and Ca. Scalindua disappeared completely. The NOB genus Nitrospira decreased from 2.2 to 0.1%, while denitrifying bacteria decreased from 12.9 to 2.1%.

 

Source:

http://doi.org/10.1371/journal.pone.0215615

 

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