Nitrospira in wastewater treatment: applications, opportunities and research gaps

Nitrification is an intermediary reaction common to various processes applied to treat nitrogen-containing wastewaters. The genus Nitrospira is the most diverse among nitrifying microorganisms and of significant importance in nitrification in natural and engineered environments. These microorganisms are versatile, and niche differentiation has been observed even at the same lineage level. In general, bacteria of the genus Nitrospira can adapt to a wide range of conditions such as substrate concentrations, dissolved oxygen, and temperature. However, environmental and operating factors governing the presence and abundance of these organisms in different habitats are still not completely understood. Nitrite-oxidizing bacteria and complete ammonia oxidizers (comammox) of the genus Nitrospira are the nitrifying organisms frequently predominant in wastewater treatment plants. Nitrospira may also be associated with opportunities for wastewater treatment such as bioprocesses that consume less energy for aeration and produce a smaller volume of pollutant gases during nitrification. Nevertheless, the genus Nitrospira has not yet been completely characterized, and very few isolates have been obtained, making it difficult to investigate their unique metabolism for wastewater treatment. Therefore, to fill knowledge gaps and improve the understanding of the ecophysiology and importance of Nitrospira, it is crucial to develop an integrated strategy for the cultivation, identification, and characterization of these microorganisms. Thus, this review aims to identify some research gaps on Nitrospira and highlight the importance of this genus in the treatment of nitrogen-containing wastewater, as well as the interfering factors associated with niche differentiation and methods currently used to investigate these microorganisms.

Graphical abstract